GEOCHEMISTRY AND BASIN ANALYSIS OF LARAMIDE ROCKY
MOUNTAIN BASINS
by
Majie Fan
_____________________
A Dissertation Submitted to the Faculty of the
DEPARTMENT OF GEOSCIENCES
In Partial Fulfillment of the Requirements
For the Degree of
DOCTOR OF PHILOSOPHY
In the Graduate College
THE UNIVERSITY OF ARIZONA
2009
2
THE UNIVERSITY OF ARIZONA
GRADUATE COLLEGE
As members of the Dissertation Committee, we certify that we have read the dissertation
prepared by Majie Fan
entitled Geochemistry and basin analysis of Laramide Rocky Mountain basins
and recommend that it be accepted as fulfilling the dissertation requirement for the
Degree of Philosophy
_______________________________________________________________________
Date: 4/29/09
Peter DeCelles
_______________________________________________________________________
Date: 4/29/09
David Dettman
_______________________________________________________________________
Date: 4/29/09
Jay Quade
_______________________________________________________________________
Date: 4/29/09
George Gehrels
_______________________________________________________________________
Date: 4/29/09
Kapp Paul
Final approval and acceptance of this dissertation is contingent upon the candidate’s
submission of the final copies of the dissertation to the Graduate College.
I hereby certify that I have read this dissertation prepared under my direction and
recommend that it be accepted as fulfilling the dissertation requirement.
________________________________________________ Date: 4/29/09
Dissertation Director: Peter DeCelles
________________________________________________ Date: 4/29/09
Dissertation Director: David Dettman
3
STATEMENT BY AUTHOR
This dissertation has been submitted in partial fulfillment of requirements for an
advanced degree at the University of Arizona and is deposited in the University Library
to be made available to borrowers under rules of the Library.
Brief quotations from this dissertation are allowable without special permission, provided
that accurate acknowledgment of source is made. Requests for permission for extended
quotation from or reproduction of this manuscript in whole or in part may be grated by
the head of the major department or the Dean of the Graduate College when in his or her
judgment the proposed use of the material is in the interests of scholarship. In all other
instances, however, permission must be obtained from the author.
Signed: Majie Fan
4
ACKNOWLEDGEMENTS
This dissertation would not have been possible without the help of many people. My
husband, Wei, and my daughter, Shunshun, are my backbone, they encourage and
support me for pursuing the research and career I like; my parents and siblings in China
are proud of me and encourage me to be brave in a different country. I am deeply
indebted to my advisors: Drs. Pete DeCelles and David Dettman for the research
opportunities, and their patience, support, advice, encouragement and constructive
criticism. Both of them have spent great amount of time in field and laboratory to teach
me field geology and lab techniques. Dr. Dettman also offered me financial support
throughout time. I am very grateful to Dr. Jay Quade for inspiration, discussion and help.
Dr. Quade deserves to be one of my co-advisors. I would like to thank Dr. George
Gehrels for his help with detrital zircon analyses and Dr. Paul Kapp for helpful
discussion.
Many people have assisted me during my time at the University of Arizona. Lynn
Peyton and Amanda Reynolds have been great support and good friends. I thank Tamara
Goldin and Dan Ross for their assistance with fieldwork in beautiful Wyoming. I
sincerely thank Ailiang Gu, Alex Pullen, Andrew Kowler, Andrew Leier, Antoine
Vernon, Chao Li, Derek Hoffman, Facundo Fuentes, Nathan English, Joel Saylor, John
Volkmer, Shundong He, Soledad Velasco, Timothy Shanahan, Victor Valencia, and
Xiaoyu Zhang for their friendship and help.
This research was supported by grants from the Geological Society of America,
ExxonMobil, Chevron, The Galileo Circle of the U of A, SEPM-RMS Donald L. Smith, and
SEPM Robert J. Weimer Fund.
5
DEDICATION
This dissertation is dedicated to my mom, Caiqin Fan; my dad, Guiwu Ma; and my
husband, Wei Yan.
6
TABLE OF CONTENTS
LIST OF FIGURES………………………………................................………………...8
LIST OF TABLES……………………………............................……....................…...10
ABSTRACT...............................................................................................................…...11
CHAPTER 1: INTRODUCTION.........................................................................…......12
CHAPTER 2: LATE PALEOCENE HIGH LARAMIDE RANGES IN
NORTHEAST WYOMING: OXYGEN ISOTOPE STUDY OF ANCIENT RIVER
WATER............................................................................................................................17
ABSTRACT ..........................................................................…….............................17
INTRODUCTION ...........................................................…….................................18
REGIONAL SETTING.................................................................…........................20
ANALYTICAL METHODS...........................................…......................................21
OXYGEN ISOTOPE RESULTS....................................………………………......22
CALCULATION OF ANCIENT RIVER WATER δ18O VALUES.....................23
CONSTRAINTS, CORRECTIONS, AND APPLICATION TO
PALEOALTIMETRY..........................................................…………………….....24
SEASONAL δ18O VARIATION IN ANCIENT AND MODERN RIVER
WATERS.......................................................…………………………………....….29
DISCUSSION.............................................................……………………………....33
High Canadian Rocky Mountains in Late Cretaceous………………...…..…33
High Surface Elevation of Eastern Laramide Ranges During Paleocene.......35
Lower Surface Elevation of the Western Laramide Province before Early
Eocene...................................................................................................................37
Implications..........................................................................................................38
CONCLUSIONS........................................................................................................40
CHAPTER 3: WIDESPREAD BASEMENT EROSION IN LATE PALEOCENEEARLY EOCENE IN THE LARAMIDE ROCKY MOUNTAINS INFERRED
FROM 87SR/86SR RATIO OF BIVALVE FOSSILS....................................................71
ABSTRACT................................................................................................................71
INTRODUCTION.....................................................................................................72
GEOLOGICAL SETTING AND STRONTIUM SOURCE TERRANES...........74
STUDY AREA AND FIELD SAMPLING..............................................................76
ANALYTICAL METHODS.....................................................................................77
RESULTS...................................................................................................................78
Modern River Water and Shell..........................................................................78
Fossil Shell ......................................................................................................... .80
DISCUSSION.............................................................................................................81
Modern River System..........................................................................................81
7
TABLE OF CONTENTS - continued
Ancient River System and Basement Erosion...................................................83
Powder River Basin ........................................................................................83
Washakie Basin................................................................................................85
Other Basins.....................................................................................................87
The Cause of Positively Correlated 87Sr/86Sr ratios and δ18O values..............88
Implications......................................................................................................90
CONCLUSIONS........................................................................................................92
CHAPTER 4: SEDIMENTOLOGY, DETRITAL ZIRCON GEOCHRONOLOGY,
STABLE ISOTOPE GEOCHEMISTRY OF THE LOWER EOCENE STRATA IN
THE WIND RIVER BASIN, CENTRAL WYOMING..............................................106
ABSTRACT..............................................................................................................106
INTRODUCTION ..................................................................................................107
REGIONAL GEOLOGY .......................................................................................109
Stratigraphy and Age Control..........................................................................110
Tectonic Setting..................................................................................................112
SEDIMENTOLOGY...............................................................................................113
Indian Meadows Formation: Alluvial Fan Association..................................114
Wind River Formation: Braided River Association.......................................115
SANDSTONE PETROGRAPHY AND PROVENANCE ...................................117
Methods and description...................................................................................117
Interpretation.....................................................................................................118
DETRITAL ZIRCON U-Pb GEOCHRONOLOGY............................................119
Samples and Methods............................... ........................................................119
Results.................................................................................................................121
Interpretation.....................................................................................................122
STABLE ISOTOPE GEOCHEMISTRY..............................................................124
Methods...............................................................................................................124
Results.................................................................................................................125
Evaluation of Diagenesis...................................................................................126
Oxygen Isotopes and Paleoaltimetry................................................................127
Carbon Isotopes, Paleoclimate and pCO2........................................................131
REGIONAL PALEOGEOGRAPHY.....................................................................133
IMPLICATIONS FOR TECTONICS....................................................................135
Rapid Late Paleocene-Early Eocene Uplift of Basement-Cored Ranges......135
Post-Early Eocene Regional Uplift...................................................................137
CONCLUSIONS......................................................................................................139
WORKS CITED............................................................................................................178
8
LIST OF FIGURES
Figure 2.1. Shaded relief map of central and Canadian Rocky Mountains.......................42
Figure 2.2. Generalized stratigraphic columns of sedimentary successions......................43
Figure 2.3. Measured and modeled δ18O values of ancient river water............................44
Figure 2.4. Seasonal δ18O variation of representative fossil shells....................................45
Figure 2.5. Seasonal δ18O variation of three kinds of modern river to the east of Rocky
Mountains..........................................................................................................................47
Figure 2.6. Regression for sampling station latitude and the δ18O values of river water in
low-elevation stations within the USA..............................................................................48
Figure 2.7. Estimated paleoelevation of the Canadian and Laramide Rocky Mountains..49
Figure 2.8. Paleodrainage reconstruction of the studied area............................................50
Figure 2.9. Schematic cross-sections showing the mechanism of forming high Laramide
ranges.................................................................................................................................51
Figure 3.1. Simplified geological map of the Laramide Rocky Mountains showing Sr
source terranes. .................................................................................................................94
Figure 3.2. Generalized lithostratigraphic columns of studied sedimentary successions in
studied basins. ...................................................................................................................95
Figure 3.3. Maps of modern river watershed and Geology...............................................96
Figure 3.4. Diagrams of 87Sr/86Sr ratio vs. Sr concentration of river water.......................98
Figure 3.5. Seasonal variation of the δ18O values and 87Sr/86Sr ratios of modern bivalve
Unionids collected in the Tongue River............................................................................99
Figure 3.6. Diagrams of 87Sr/86Sr ratio vs. δ18O value.....................................................100
Figure 3.7. Diagram of 87Sr/86Sr ratio vs. Sr/Ca of modern and ancient rivers...............101
Figure 3.8. Inferred drainage patterns and Precambrian basement exposure in late
Cretaceous-early Paleocene, and late Paleocene-early Eocene....………………...........102
Figure 4.1. General map of the United States, Wyoming and northwestern Wind River
basin............... .................................................................................................................142
Figure 4.2. Chronostratigraphic chart for the northwestern Wind River basin...............143
Figure 4.3. Measured sections.........................................................................................144
Figure 4.4. Photographs of northwestern Wind River basin outcrops.............................147
Figure 4.5. Ternary diagrams showing sandstones compositions....................................148
Figure 4.6. Photos of petrographic thin sections of sandstone .......................................149
Figure 4.7. Photos of the zircon grains............................................................................150
Figure 4.8. U/Pb concordia diagrams..............................................................................151
Figure 4.9. U-Pb age-probability diagrams......................................................................152
Figure 4.10. U/Pb concordia diagrams for a granite pebble............................................154
Figure 4.11. Field photos and images of thin sections of the early Eocene carbonate
nodules.............................................................................................................................155
Figure 4.12. Results of the stable isotope analyses in this study.....................................156
Figure 4.13. Simplified stratigraphy, carbon and oxygen isotope values, percentage of
granite clasts, Achaean zircons, and feldspar through section.........................................157
Figure 4.14. Oxygen isotope data of Early Eocene paleosol carbonate...........................158
9
Figure 4.15. Paleogeographic sketch maps of the northwestern Wind River basin .......159
10
LIST OF TABLES
Table 2.1. Age constraints for the study intervals in each basin........................................52
Table 2.2. Paleomagnetic data and paleolatitude...............................................................53
Table 2.3. δ13C and δ18O values of bulk individual shells and sample locations..............54
Table 2.4. δ13C and δ18O values of micromilled representative shells..............................61
Table 3.1. Element concentration, and corrected strontium isotope ratios for selected
fossil shells.......................................................................................................................103
Table 3.2. Sampling location, isotope ratios, element concentration data for modern
rivers................................................................................................................................104
Table 3.3. Isotope data for modern and fossil shell.........................................................105
Table 4.1. Lithofacies and interpretations used in this study .........................................160
Table 4.2. Modal petrographic point-counting parameters.............................................161
Table 4.3. Modal petrographic data................................................................................162
Table 4.4 U-Pb (zircon) geochronologic analyses by laser-ablation multicollector ICP
mass spectrometer ...........................................................................................................163
Table 4.5 Major age populations of detrital zircons in modern river sand and the early
Eocene Eediment.............................................................................................................175
Table 4.6 Isotope results.................................................................................................176
11
ABSTRACT
The Laramide Rocky Mountains in western U.S.A is an important topographic feature
in the continental interior, yet its formation and evolution are poorly constrained. This
study uses the oxygen and strontium isotope geochemistry of freshwater bivalve fossils
from six Laramide basins in order to reconstruct the spatial evolution of the
paleotopography and Precambrian basement erosion in late Cretaceous-early Eocene. In
addition it uses the sedimentology, detrital zircon U-Pb geochronology, and isotope
paleoaltimetry of early Eocene sedimentary strata to constrain the tectonic setting,
paleogeography and paleoclimate of the Wind River basin. Annual and seasonal variation
in ancient riverwater δ18O reconstructed from shell fossils shows that the Canadian
Rocky Mountains was 4.5±1.0 km high in late Cretaceous-early Paleocene, and the
Laramide ranges in eastern Wyoming reached 4.5±1.3 km high, while the ranges in
western Wyoming were 1-2 km high in late Paleocene. The 87Sr/86Sr ratios of riverwaters
reconstructed from the same fossils show that Proterozoic metamorphic carbonates in the
Belt-Purcell Supergroup were not exposed in the Canadian Rocky Mountains during Late
Cretaceous-early Paleocene, but that Precambrian silicate basement rock was exposed
and eroded in the Laramide ranges during late Paleocene-early Eocene. The sedimentary
environment of the early Eocene Wind River basin changed from gravelly fluvial and/or
stream-dominated alluvial fan to low-sinuosity fluvial systems. Tectonic uplift of the
Washakie and Wind River Range in early Eocene formed the modern paleodrainage
system, although the elevation of the basin floor was only ~500 m high at that time, and
early Eocene paleoclimate is more humid than modern climate.
12
CHAPTER 1: INTRODUCTION
The eastern portion of the Cordilleran orogenic belt in the western interior U.S.A.
consists of the Laramide structural province, a region of Precambrian basement-cored
uplifts and intervening sedimentary basins that developed during late Cretaceous-Eocene
time (e.g., Dickinson and Snyder, 1978; Bird, 1988; Snoke, 1997; DeCelles, 2004). The
deformed region partitioned what had been a continental scale foreland basin that
developed east of the Cordilleran thrust belt ~1,000-1,500 km inland from the subduction
zone. Modern regional elevation of the Laramide province is ~1.5 km with the range
summits at >4 km. By analogy, a similar landscape is present in the Sierras Pampeanas in
South America (e.g., Jordan et al., 1983; Wagner et al., 2005). Shallow subduction of the
Farallon Plate underneath North America is commonly accepted as the tectonic
mechanism for the Laramide deformation (e.g., Coney and Reynolds, 1977; Dickinson
and Snyder, 1978; Bird, 1988; Constenius, 1996; Saleeby, 2003; Sigloch et al., 2008).
However, it remains unclear how shallow subduction would produce the individual
Laramide structures and the extent to which Laramide deformation may be viewed as an
eastward propagation of the greater Cordilleran strain front (Erslev, 1993; DeCelles,
2004).
The timing of individual Laramide uplifts, their paleoelevation at the time of uplift,
and the temporal relationships among Laramide uplifts are essential to the reconstruction
of the regional deformation pattern, tectonic modification after deformation, and the
evaluation of tectonic models. The temporal and spatial patterns of erosional exhumation
of the Precambrian basement cores in Laramide uplifts are critical to understanding the
13
processes leading to the modern landscape. Tectonic models explaining the deformation
mechanism during flat slab subduction include basal shear traction (Bird, 1988), lateral
injection of intracrustal flow from the overthickened Sevier orogenic hinterland
(McQuarrie and Chase, 2001), and lithospheric buckling in response to horizontal
endload of the North American plate (Tikoff and Maxson, 2001). Post-Laramide
modification of the lithosphere in the Laramide region may have played a vital role in
shaping the modern landscape. Mechanisms of modification include thermal uplift caused
by removing the subducted slab or thickened mantle lithosphere in in the western U.S.A.
(Dickinson and Snyder, 1978; Humphreys, 1995; Sonder and Jones, 1999),
subcontinental-scale subsidence by induced asthenospheric counterflow above the
subducted slab (McMillan et al, 2002; Heller et al., 2003; McMillan et al., 2006), and
regional uplift caused by isostatic rebound of lithosphere due to climate driven erosion
and/or thermal upwelling associated with the initiation of Rio Grande Rift (Heller et al.,
2003; McMillan et al, 2006). Therefore, sufficient quantitative data including
paleoelevation, source terrane unroofing, basement exhumation, and paleogeography
within a precise chronological context are required to 1) reconstruct the uplift and
basement erosion pattern during and after Laramide deformation, and 2) evaluate existing
competing hypotheses.
This investigation focuses on oxygen isotope and 87Sr/86Sr ratios of Late Cretaceousearly Eocene river water reconstructed from Unionid shell fossils in six Rocky Mountain
basins and sedimentary strata of the Wind River basin in early Eocene, central Wyoming.
The goals are to: 1) provide the paleoelevation and Precambrian basement erosion history
14
of several Laramide uplifts in Wyoming during late Cretaceous-early Eocene time; and 2)
reconstruct the early Eocene paleogeography and tectonic setting of the Wind River
basin. The data within this dissertation include, but are not limited to, >2000 stable
isotope analyses of carbonate and water; >80
87
Sr/86Sr ratio analyses of carbonate and
water; ~750 m of detailed measured stratigraphic sections; 211 paleocurrent
measurements collected at 18 locations; 1108 clast counts from 11 locations; 16 point
counted petrographic thin sections and >700 U-Pb analyses of zircon grains collected
from six early Eocene sandstones, two modern river sands, and one Precambrian granite
cobble.
The following chapters represent three manuscripts that are in various stages of
publication. Chapter 2, Late Paleocene High Laramide Ranges in Northeast Wyoming:
Oxygen Isotope Study of Ancient River Water, presents the timing and distribution of high
elevation in the Rocky Mountains during Late Cretaceous - early Eocene by tracking the
oxygen isotope ratios of ancient river waters. The oxygen isotope ratios of ancient river
waters are extracted from the δ18O values of well-preserved shell aragonite of the
Unionid family. Both mean annual and seasonal stable isotope record of ancient river
water in the Alberta foreland basin, and five other Laramide basins in Wyoming are
presented. The patterns of low oxygen isotope values in river waters show that the
Canadian Rocky Montanans were at high elevations in late Cretaceous-early Paleocene,
and Laramide ranges reached high elevation in the eastern Laramide province by late
Paleocene. Interestingly the Laramide ranges in the western province seem to achieve
15
high elevation later than the eastern ones. This manuscript is submitted to Earth and
Planetary Science Letters.
Chapter 3, Widespread Basement Erosion in Late Paleocene-early Eocene in the
Laramide Rocky Mountains inferred from
87
Sr/86Sr ratio of bivalve fossil, confirms that
the 87Sr/86Sr ratio of modern river water in the Rocky Mountains are controlled by river
bedrock lithology by examining the modern river water strontium geochemistry in the
Wind River and Powder River tributaries. Weathering of Precambrian silicate rocks in
the cores of Laramide ranges produce high 87Sr/86Sr ratios of highland rivers. Therefore, I
use reconstructions of the
87
Sr/86Sr ratios of late Cretaceous-early Cenozoic river water
from fossil shells in six basins of the Rocky Mountains to trace the erosion of
Precambrian basement cores in the Laramide ranges. The results show that Proterozoic
low-grade metamorphic carbonates in the Belt-Purcell Supergroup were not exposed in
the Canadian Rocky Mountains during late Cretaceous-early Paleocene, and that
Precambrian silicate basement rock was extensively exposed and eroded during late
Paleocene-early Eocene in the Laramide Rocky Mountains. The widespread basement
erosion in late Paleocene-early Eocene is mainly a result of tectonic exhumation of
Laramide ranges, and may have been intensified by the wet and warm global climate.
Chapter 4, Sedimentology, Detrital Zircon Geochronology, Stable Isotope
Geochemistry of the Lower Eocene Strata in the Wind River Basin, Central Wyoming, is
conducted in order to reconstruct basin evolution, source terrane unroofing, and changes
in paleoelevation and paleoclimate. The early Eocene depositional environment changed
from from alluvial fan to low-sinuosity fluvial systems. The paleogeographic
16
reconstruction based on paleocurrent directions, sandstone petrography, and detrital
zircon geochronology shows that rapid unroofing of the Washakie and Wind River
Ranges formed a paleodrainage similar to present in central Wyoming by early Eocene.
Oxygen isotope paleoaltimetry shows that the paleoelevation of the Wind River basin
was ~500 m, and that local relief between the Washakie and Wind River Ranges and the
basin floor was 2.3±0.8 km in early Eocene. Up to 1 km of post-Laramide regional net
uplift is required to form the present landscape in central Wyoming.
17
CHAPTER 2: LATE PALEOCENE HIGH LARAMIDE RANGES IN
NORTHEAST WYOMING: OXYGEN ISOTOPE STUDY OF ANCIENT RIVER
WATER
ABSTRACT
The distribution and initial timing of the establishment of high surface elevations in
the Rocky Mountains during the Early Cenozoic remain controversial despite the
importance of these data in testing tectonic models for this region. We track the timing
and distribution of high elevation in the Rocky Mountains during Late Cretaceous – Early
Eocene by examining the annual and seasonal δ18O values of the ancient river water,
which are extracted from the δ18O values of well-preserved shell aragonite of the Unionid
family. In the Powder River basin of the eastern Laramide province, the δ18O values of
the ancient river water vary between -23.0‰ and -8.0‰SMOW in both seasonal and annual
records in Late Paleocene-Early Eocene. The large variation suggests that the ancient
rivers were fed yearly or seasonally by snowmelt from highland of 4.5±1.3 km. This can
be explained by the existence of the Bighorn Mountains and Black Hills with a drainage
pattern similar to the present in northeast Wyoming. The δ18O values of the ancient river
water along the front of the Sevier thrust belt generally follow a trend from lower values
in north, -14.2±1.4‰ in the Crazy Mountains basin in Early Paleocene, to higher values
in south, ~-11.1±0.8‰ in the Bighorn basin in Late Paleocene, and -7.1±1.6‰ in the
Washakie basin in Early Eocene. The variations within each basin are relatively small.
These rivers most likely rise in the Sevier thrust belt, and may reflect highland elevation
of 1-2 km. The δ18O values in the Alberta foreland and Williston basin are very low (-
18
20.5‰) in Late Cretaceous, indicating the rivers water were fed by snowmelt from the
Canadian Rocky Mountains of 4.5 ±1.0 km high. The attainment of high elevation in the
eastern Laramide province prior to the western province could be explained by
southwestward progression of back-thrusts soled into an earlier east-directed master
detachment, which may be formed by the westward rollback of subducted shallow slab.
Keywords: Rocky Mountains; Paleoelevation; Oxygen isotope ratios; Laramide;
freshwater bivalve
INTRODUCTION
The Laramide orogeny of the Rocky Mountains is a system of basement-cored uplifts
and intervening basins that formed ~80-40 Ma in the foreland basin of the Sevier thrust
belt in the western United States (Dickinson and Snyder, 1978; Bird, 1998; DeCelles,
2004). Analogous to modern flat-slab subduction in western South America (Jordan and
Allmendinger, 1986), Laramide uplifts are the result of the NE-SW compression due to
shallow subduction of the Farallon Plate beneath the North American Plate (e.g.,
Dickinson and Snyder, 1978; Bird, 1998; Saleeby, 2003; DeCelles, 2004). Although this
region is very well studied, some fundamental questions remain unanswered: how does
shallow subduction thicken foreland crust and produce a landscape with intervening
basins and ranges, and how is basement-involved deformation connected to the thinskinned Sevier fold and thrust belt. A range of tectonic models has been proposed to
explain the mechanisms of Laramide deformation: basal traction (Bird 1998), lithospheric
buckling (Tikoff and Maxson, 2001), intracrustal flow (McQuarrie and Chase, 2001), and
19
thrust, back-thrust and crustal detachment (Erslev, 1993; 2005). The timing, magnitude,
and pattern of high surface topography in the Laramide province need to be examined to
help answer these basic questions and to test tectonic models.
Oxygen isotope ratios of precipitation derived from authigenic minerals (e.g.,
paleosol carbonate, biogenic apatite and aragonite) have been applied as paleoaltimeters
in numerous studies (e.g., Dettman and Lohmann, 2000; Garzione et al., 2006; DeCelles
et al., 2007; Quade et al., 2007). This approach is based on the decrease in oxygen
isotope ratios of precipitation as elevation increases, which is controlled by progressive
condensation of atmospheric water vapor due to cooling or adiabatic expansion as the
vapor mass ascends, leading to Rayleigh isotope fractionation (Dansgaard, 1953; Rowley,
2007). At present, there have been only a few studies addressing the paleoelevation of the
Laramide Rocky Mountains (Gregory and Chase 1992; Norris et al., 1996; Wolfe et al.
1998; Dettman and Lohmann, 2000; Fricke 2003; Sewall and Sloan, 2006). Even though
these studies have been mostly focused on Eocene elevations, they have yielded highly
varying results. By using leaf margin analyses, Wolfe et al. (1998), and Gregory and
Chase (1992) suggested that the Eocene southern Rocky Mountains were more than 3 km
high, similar to today’s elevation. This agreed with the δ18O values of lake microbial
carbonates in the Green River basin (Norris et al., 1996), and the δ18O values of unaltered
freshwater bivalves and regional GCM modeling of Early Paleogene Laramide foreland
(Dettman and Lohmann, 2000; Sewall and Sloan, 2006). However, Morrill and Koch
(2002) concluded that diagenesis may have altered the δ18O of lacustrine microbial
carbonates in the Green River basin. Moreover, Fricke (2003) argued that Early Eocene
20
Laramide range elevations were ~500 m based similar δ18O values of mammal teeth from
three Wyoming basins. These conflicting conclusions may arise from a number of
factors: 1). diagenetic overprinting of original isotopic patterns; 2). not accounting for all
the non-altitude factors that can affect the δ18O of surface water (e.g., latitude,
temperature); 3). small sample numbers failing to document a regional pattern in surface
water δ18O values.
In this study we survey the oxygen isotope composition of fossil freshwater bivalves
(Unioniacea superfamily) of Late Cretaceous-Early Eocene age collected from six basins
in the Laramide tectonic province. Unionids have relatively thick growth increments
aiding the study of seasonal isotopic variation. Our study examines both the seasonal and
annual δ18O values of ancient river waters as recorded in fossil shells. We compare these
to δ18O values of modern precipitation and river water in our discussion of the
paleoelevation of ancient river catchments. We then track the timing and spatial patterns
of high elevation regions in Laramide ranges.
REGIONAL SETTING
Fossil shells were collected from the Alberta foreland basin, western Williston basin,
Crazy Mountains basin, northern Bighorn basin, Powder River basin and southern
Washakie basin (Fig. 2.1, 2.2). Prior to Laramide deformation, these regions were a broad
foreland basin of the thin-skinned Sevier fold-thrust belt. Laramide deformation
partitioned the central Rocky Mountain foreland into discrete local basins separated by
basement-cored uplifts with NE-SW to E-W orientations (Dickinson et al., 1988). The
21
uplifts are bounded by moderately dipping to high-angle faults or are broadly anticlinal.
The Crazy Mountains basin, Bighorn basin, Powder River basin and Washakie basin are
of this type. Late Cretaceous through Miocene age sediments derived from the Sevier
thrust belt and Laramide uplifts were deposited in these basins. Fossil shells from the
Washakie basin are from the Luman Tongue Member of the Green River Formation, a
mix of fluvial and lake facies in the early stages of Lake Gosiute (Sklenar and Anderson,
1985). Shell samples in the other three basins are from Paleocene to Early Eocene fluvial
sediments. In the Alberta foreland basin, Laramide age deformation is an eastward
continuation of thin-skinned Sevier fold and thrust, which overthrusted Mesozoic shale
and molasse, but did not generate any basement uplifts (Obsborn et al., 2006). Shells
from the Alberta foreland basin were collected from sediments of Late Campanian and
Maastrichtian age. In the Williston basin, a depression in the Canadian Shield, fossil
shells were collected from Late Cretaceous and Early Paleocene fluvial sediments.
Sample ages are based on radiometric ages, paleomagnetic ages and intrabasin
mammalian biostratigraphic correlation with magnetostratigraphy (Table 1).
ANALYTICAL METHODS
Aragonite shells used in this study are all unaltered as judged by physical appearance,
cathodoluminescence microscopy and X-ray diffraction for a subset of the samples. X-ray
diffraction was performed with a Bruker D8 Advance Diffractometer using Cu Kα
radiation. When possible, ten shells and shell fragments from each stratigraphic horizon
were analyzed for stable isotopes. The bulk shell δ18O values were mostly presented in
Dettman and Lohmann, 2000, with new analyses added (supplementary data). Total of
22
881 individual shell fossil analyses are included in this paper. Shell Aragonites were
collected by drilling through the shell body, integrating isotopic variation and yeilding a
growth amount-weighted average δ18O value. The bulk δ18O value presented in this paper
refers to the average values of all analyzed bulk shell samples in stratigraphic horizon
except the Powder River basin, where some data represent single shell analyses. In
addition, we micro-milled 12 selected samples in order to study the seasonal isotopic
variation of the Early Cenozoic rivers. Shells were sectioned along the axis of maximum
growth, mounted as thick sections (~1 mm). Growth bands in cross-sectioned shells were
subsampled using a computer-controlled micro-mill with a 30 µm sampling resolution
(Dettman and Lohmann, 1995). The δ18O and δ13C values of aragonites were measured
using an automated carbonate preparation device (KIEL-III) coupled to a gas-ratio mass
spectrometer (Finnigan MAT 252). Samples (20 to 150 µg) were reacted with dehydrated
phosphoric acid under vacuum at 70°C. The isotope ratioa are calibrated based on
measurements of NBS-19 and NBS-18; precision is ±0.1‰ for δ18O and ±0.06‰ for δ13C
(1σ).
OXYGEN ISOTOPE RESULTS
The δ18O values of bulk shells from basins along the front of the Sevier thrust belt
follow a trend from lower values in north (-13.7±1.3‰PDB, Crazy Mountains basin) to
higher values in south (-10.7±0.8‰PDB, Bighorn basin, and -7.3±1.5‰PDB, Washakie
basin), and the within-basin variation is small. In the Powder River basin and western
Williston basin, shell δ18O values show large variation between -22.9‰ and -7.9‰ PDB,
and -21.8‰ and -9.3‰PDB, respectively. Our results in the western Williston basin are
23
consistent with values from the eastern Williston basin (Carpenter et al., 2003; Cochran
et al., 2003). The δ18O values of shells in the Alberta foreland basin vary between 19.3‰ and -13.3‰ PDB (Fig. 2.3).
Seasonal isotopic variation of selected shells from each basin are used to compare
ancient and modern river seasonal variability in the Laramide region (Fig. 2.4, 2.5).
Oxygen isotope ratios of modern river water are from Coplen and Kendall (2000),
modern precipitation are from the United States Network for Isotopes in Precipitation
(USNIP)
(www.uaa.alaska.edu/enri/usnip),
Canadian
network
for
Isotopes
in
Precipitation (CNIP) (www.science.uwaterloo.ca/~twdedwar/cnip), and Dutton et al.
(2005).
CALCULATION OF ANCIENT RIVER WATER δ18O VALUES
The oxygen isotope composition of Unionid shell aragonite is controlled by the
temperature and δ18O value of the river water in which it grew (Grossman and Ku, 1986;
Dettman et al., 1999). Here, we use the empirically determined relationship between the
bulk δ18O values of Unionid shell and mean annual river water in temperate climates
from Kohn and Dettman (2007):
δ18O (shell,PDB)=(0.892±0.024) δ18O(riverwater,SMOW)-0.978±0.240 (R2=0.98)
(1)
to calculate the mean annual δ18O values of ancient river water. Because these freshwater
bivalves stop growing below approximately 10-12°C and their growth is heavily biased
to late spring and early summer temperatures, a large majority of shell aragonite is
produced in a limited range of temperatures (20-25°C) (Dettman et al., 1999). This
growth temperature bias leads to a good linear correlation between mean annual river
24
water and bulk shell δ18O values, which can be used to calculate the mean δ18O value of
ancient river water if the climate is temperate and seasonal (Kohn and Dettman, 2007). If
temperatures were not seasonal, but remained at one temperature extreme (e.g. 12° or
30°) throughout the year, then calculated river water δ18O values could be as much as 2‰
too high or too low, but this seems extremely unlikely given prominent growth bands in
the shells, indicating seasonal growth cessation, and the botanical and modeling evidence
for moderate seasonality (Wilf; 2000, Sewall and Sloan, 2006). Our calculated mean
annual δ18O values of ancient river waters range from -23‰ to -5‰SMOW (Fig. 2.3).
Each shell sample represents an average of several years of growth in these river
systems. Although the average river water δ18O values calculated from a single shell
could be affected by a few years of anomalous precipitation patterns, the chances of this
are reduced by averaging ten shells from each stratigraphic level.
CONSTRAINTS,
CORRECTIONS,
AND
APPLICATION
TO
PALEOALTIMETRY
Knowing the δ18O values of ancient river water provides some insight into the
paleoelevation of ancient river catchments, but many other factors can affect the δ18O of
rainfall. Many of these effects (e.g. temperature, continentality) are combined into the
strong relationship between the δ18O of rainfall and latitude (Dutton et al., 2005).
Therefore we will attempt to remove the latitudinal effect on δ18O values by comparing
the ancient river δ18O values to modern low-elevation rivers (representing low-elevation
rainfall δ18O values) across a range of latitudes. We use river water δ18O data because it
is much more abundant than precipitation data and it comes closer to a weighted average
25
of the δ18O of precipitation in the river’s catchment. Accounting for latitudinal
differences is particularly important because North America moved southward, changing
latitude by about 10 degrees, during the time interval under study, and the study region
spans another 10 degrees of latitude. This low-elevation data set will be modified based
on studies of Paleogene meteoric water δ18O values to make the comparison more
appropriate for Late Cretaceous and Cenozoic times. Our data also provides a check on
the latitudinal gradient of δ18O values for low elevation rainfall in late Cretaceous and
Paleogene.
The δ18O value of modern low elevation (<200 m) river water across the USA is
related to the latitude of river stations (Fig. 2.6):
δ18O
2
(river water, SMOW)=(-0.0012±0.0009)|LAT| –(0.3940±0.0816)|LAT|+10.2154±1.7811
(R2=0.91)
(2)
In the dataset of Coplen and Kendall (2000), the elevations of the modern river water
samples in low elevation (<200m) are not necessarily the elevations of river source
catchments. Many rivers have significantly higher source catchments elevation than
sampling site, like Columbia River sampled in Washington, and Missouri River sampled
in South Dakota and North Dakota. Therefore, in our regression we do not include the
rivers that clearly rise at high elevation, and Hawaiian rivers, which are not applicable to
continental interiors, are also excluded. This significantly improves the regression in
Dutton et al., 2005.
The key factors affecting the δ18O values of either modern or ancient river waters
include water vapor source, vapor temperature, source water δ18O values, latitude, and
26
elevation. Note that the effect of evaporation on the δ18O value of river water is usually
quite small, particularly in humid climates, and is ignored in this paper. The modern
climate of the Rocky Mountain region and the western Great Plains is influenced by the
competition of three air masses that originate over the Arctic, the Gulf of Mexico, and the
Pacific Ocean (Bryson and Hare, 1974). Pacific air masses support relatively abundant
winter precipitation in the high Rocky Mountains. The Rocky Mountains, together with
the Basin and Range to the west, form a large high topographic barrier and this rain
shadow largely reduces the contribution of Pacific-sourced moisture to the Laramide
Rocky Mountain province. To the east of the Rocky Mountains, moisture from the Gulf
of Mexico brings relatively abundant summer rainfall. Prior to Latest Cretaceous Paleocene the movement of Sevier fold-and-thrust belt caused significant shortening and
thickening, forming a high-elevation hinterland plateau with rugged topographic front to
the west of the Rocky Mountains (DeCelles, 2004; DeCelles and Coogan, 2006), Given
the topographic similarity to today, we assume that large-scale climate pattern during
Early Cenozoic was similar to present and most of the precipitation is sourced from the
Gulf of Mexico region..
Temperature of the sea surface and middle latitude continental interior in Late
Cretaceous-Early Eocene was higher than present (Zachos et al., 1994; Wilf, 2000;
Zachos et al., 2001). Higher temperature can influence the δ18O values of both source
region water vapor and water condensates (Dansgaard, 1953), which could lead to a
different stable isotope – latitude relationship than that of today. One study of the Early
Eocene latitudinal-isotopic gradient in river water shows that the gradient was similar to
27
today in the middle latitudes, although there is a significant difference in the intercept of
this relationship (Fricke, 2003). The North American Plate has moved southward at least
5°since the Late Cretaceous (Besse and Courtillot, 2002), which could result in a ~2.4‰
difference between the δ18O values of precipitation at present and in the Late Cretaceous
at the location (Fig. 2.6, and Dutton et al., 2005). Neglecting this paleo-latitudinal
correction will lead to overestimates of the paleoaltitude by at least 0.8 km (if a lapse rate
of 2.8‰/km was applied to this difference; Poage and Chamberlain, 2001). The
paleolatitude of our sample localities are derived by using the paleopole locations in
Besse and Courtillot (2002), and the dipole equation in Butler (1992). The lower and
upper limits of paleolatitude are derived from the confidence limits of the paleopole (Α95)
(Table 2).
In order to discuss ancient river water δ18O values in terms of stable isotope patterns
seen on the globe today, we use the regression relationship between the δ18O value of
modern low elevation river water and sampling latitude (Fig. 2.6), incorporate corrections
for 1) higher intercept due to warmer temperature in Late Cretaceous- Early Eocene
(+4±2.8‰, Fricke, 2003); 2) changes in the δ18O value of seawater due to smaller global
ice volume (-1‰, Zachos et al., 1994); and 3) latitude change due to continental drift of
North America since Late Cretaceous-Early Eocene (Besse and Courtillot, 2002), to
model the low elevation river water
18
O values. Errors propagated from the three
corrections yield a δ18O range for low elevation river water (Fig. 2.3). If an ancient river
catchment was at low elevation, the determined δ18O values of ancient river water should
be in the range of modeled δ18O values for low-elevation river water. Note in Figure 3
28
that our most positive δ18O values, probably sampling the lowest elevation catchments,
are within the ancient low-elevation river water field, suggesting that the corrections
approximate low-elevation precipitation relatively well. If the ancient river rises from a
high elevation catchment, the determined δ18O values should be lower than the area of
modeled δ18O values. The elevation of the river source terrane can then be calculated
from the difference in the δ18O value between the ancient river water and the lower limit
of the modeled low elevation river water, and a lapse rate of -2.8(±0.6)‰/km. This leads
to a conservative estimate of elevation as we use the lower limit of the modeled low
elevation river water. This lapse rate is derived from global precipitation δ18O values
(Poage and Chamberlain, 2001), and is similar to the lapse rate derived from North
America precipitation (-2.9‰/km Dutton et al. 2005). Note that, although our bivalvebased data reconstructs river water δ18O values, we use an isotopic lapse rate based on
precipitation instead of one based on river water. This is because we will discuss the
elevation of the catchments of these ancient river systems rather than the elevation of the
point in the river system sampled by the bivalves. In general river sample isotopic lapse
rates are much higher than precipitation-based ones because the former reflect rainfall in
the river catchment at higher elevations than that of the sampling point (e.g. Dutton et al.
2005). If a river has a high elevation catchment the δ18O values of the river water will
tend to be lower, even if the sample of river water is collected near sea level. The biggest
problem with using the river water lapse rate is the lack of information on the elevation
difference in a river’s catchment and that the elevation of a single sampling point in a
river system has little to do with the overall elevation of its catchment (Kohn and
29
Dettman, 2007). The shells in this study are limited to the basin floors, where sediment
accumulates and preserves these fossils. In some basins there is a very large range in the
δ18O of river waters, a range that clearly represents variation in the elevation of the
different river catchments, and not dramatic changes in the elevation of the basin floor
(Dettman and Lohmann, 2000).
The Western Interior Seaway covered a large area of North America in Late
Cretaceous (Roberts and Kirschbaum, 1995), and this water body probably dominated the
water vapor cycle of the Campanian and Maastrichtian Alberta foreland and Williston
basins. Because this was basically a coastal system we will not use the low elevation
latitude – rainfall δ18O relationship of Figure 3, which is more appropriate for a
continental interior region, to interpret the Alberta and Williston basin data. In this case,
we will use a modern empirically-tested model of the ∆δ18O-elevation relationship to
reconstruct river catchment elevations (Rowley et al., 2001; Rowley, 2007). The ∆δ18O
value is the δ18O difference between highland precipitation and lowland precipitation.
The modeled ∆δ18O-elevation relationship, which tracks a single rising package of water
vapor cannot be applied to the Early Cenozoic samples because of the retreat of the
interior seaway and the possibility that water vapor came into the Laramide region from
different sources. The uncertainties reported in this paper, encompassing the model,
corrections, and calculations of paleoelvation all are one standard deviation (1σ).
SEASONAL δ18O VARIATION IN ANCIENT AND MODERN RIVER WATERS
The δ18O values of river waters are controlled by surface runoff and groundwater in
river catchments. Rivers with low elevation catchments tend to have higher δ18O values
30
in contrast to high elevation catchments. High-elevation snowmelt can feed lowland
rivers as surface runoff during the spring and early summer or year-round as
groundwater. The δ18O values of this type of river water is often very low in spring and
early summer, equivalent to the δ18O values of high-elevation snowmelt (Horton et al.,
1999). At present, in the Laramide region, summer precipitation amount is about two
times that of winter precipitation amount (Dutton et al., 2005), and the highest river
discharge
is
generally
in
March-June
(SAGE
River
Discharge
Database,
www.sage.wisc.edu/riverdata). We group the isotopic patterns of rivers in this region into
three types.
1. Rivers originating at high elevation with different sources of water seasonally.
The Milk River flows east from Glacier National Park, Montana, with
catchment elevations between 1.0 and 2.8 km. Precipitation at the closest rain
monitoring station (MT-05, Glacial National Park, 968m) averages 18.3‰SMOW with a range of 15.6‰ (Dutton et al., 2005; USNIP). The large
seasonal δ18O variation in the Milk River at the Nashua station (48.13°N,
106.36°W, 696m) shows that the river is fed by snow melt from elevations
higher than station MT-05 in spring with δ18O values as low as -23‰. In the
summer, local and lower elevation rain seems to dominate, with δ18O value as
high as -10‰. During the winter, when surface runoff is frozen, groundwater
supports the river with intermediate δ18O values (Fig. 2.5A).
2. Rivers with year-round high-elevation sources of precipitation. Halfmoon
Creek rises in the Sawatch Range, central Colorado, which contains several of
31
the
highest
peaks
(>4
km)
in
the
Rockies.
At
station
Malta
(39.17°N，106.39°W, 2996m), the δ18O value is low and very stable
throughout the year, -17.0±1.2‰. There is a small increase in the δ18O value
of river water in the late summer (Fig. 2.5B). Precipitation at the closest
station (CO-02, Niwot Saddle, 3520m) has an annual average δ18O value of 14.3‰ (USNIP). This suggests that the river is primarily fed by groundwater
that integrates annual precipitation, perhaps derived from higher elevations.
Summer local precipitation seems to increase river water δ18O values only
slightly.
3. Rivers originating at low elevation. The Big Sioux River catchment begins in
Roberts County, South Dakota, with an elevation less than 500 m. At station
Akron (42.83°N，96.56°W, 341m), the seasonal δ18O variation of the river
water is very small, -8.6±1.0‰ (Fig. 2.5C). The annual average δ18O value of
precipitation at the closest station (MN-27, Lamberton, 343m) is -8.6‰
(USNIP). The small seasonal isotopic cycle and similarity in δ18O value to
precipitation suggests that the river is fed by ground water, which is recharged
by local precipitation.
Micromilled shells from the different areas surveyed show a variety of seasonal
oxygen isotopic patterns: three types in the Powder River and Williston basins, two
patterns in the Alberta foreland basin and only one pattern in the Crazy Mountains,
Bighorn and Washakie basins (Fig. 2.4). Although the amplitude of seasonal oxygen
isotope cycles in shells are not directly comparable to river water δ18O cycles due to the
32
seasonal temperature variation, large changes in river water δ18O values (greater than 4‰
in many cases) must be reflected in the δ18O cycles in shells. This is because the limited
range of shell growth temperatures can only cause ~4‰ variation in shell δ18O values
(Dettman et al., 1999). In the Powder River basin, shell PR10-86A has a large amplitude
δ18O cycle (-17.9‰ to -7.0‰), similar to that of the Milk River. This high-amplitude
shell must have lived in a river with large seasonal δ18O amplitude, suggesting that the
river was seasonally fed by snowmelt from high elevation either as groundwater or as
surface runoff. Powder River basin shell PR2-85 has an isotopic cycle similar to the Big
Sioux River. It has small δ18O amplitude (between -11.8‰ and -7.0‰) and the mean
δ18O value is relatively high. This kind of river is found today at low elevations, fed by
local precipitation. PR3-83 is similar to Halfmoon Creek, with a small δ18O amplitude,
but with a very low mean δ18O value (-24.3±2.6‰). This kind of river usually originates
in high elevations and is fed by a groundwater supply that is recharged at high elevation
(Fig. 2.4A). In the western Williston basin, shells with these three types of seasonal δ18O
patterns are present (Fig. 2.4B). In the Alberta foreland basin, seasonal δ18O variation in
ancient river water recorded in samples 93-13 and Tyrell, is very similar to Big Sioux
River, with a small amplitude and higher δ18O values (-13.6±1.0‰). In contrast, one
shell, sample 93-11, is similar to Halfmoon Creek, also low amplitude, but with very low
δ18O values (-18.9±0.8‰) (Fig. 2.4C). In the Crazy Mountains basin, Bighorn basin, and
Washakie basin, the seasonal δ18O variation in shells have relatively small amplitudes
and are intermediate in average δ18O value. These rivers are of Big Sioux River type, and
33
fed by local precipitation (Fig. 2.4D, E, F). Our Washakie basin shell data are similar to
seasonal records from other well-preserved shells from the Green River basin (Morrill
and Koch, 2002).
DISCUSSION
High Canadian Rocky Mountains in Late Cretaceous
The δ18O value of paleosol carbonate in the Late Maastrichtian lower Willow Creek
Formation in southern Alberta is -12.1±0.9‰PDB (n=7) (Mack and Cole, 2005). From this
we calculate the δ18O value of lowland mean annual precipitation as -10.3±2.5‰ using
the calcite oxygen isotope fractionation relationship (Kim and O’Neil, 1997) and a
temperature of 12-30°C, assumed to be the formation temperature of soil carbonate
during warm growing season (Cerling and Quade 1993). Although evaporation can
increase the δ18O values of soil water relative to mean annual precipitation, this effect is
minimal in wet climates (Quade et al., 2007). Given the proximity of the interior seaway
and wet climate in Late Cretaceous (Roberts and Kirschbaum, 1995; Golovneva, 2000),
strong evaporation is very unlikely. The similar δ18O values between the lowland
precipitation and the highest river water suggests that the shells with the relatively
positive oxygen isotope cycle in Fig. 2.4C lived in river water fed mainly by local
precipitation. The occurrence of much lower values can therefore be attributed to the low
δ18O values of distal highland precipitation. This can be seen in the shell 93-11 in Fig.
2.4C, which grew in water that had low δ18O values all year long. Numerous other shells
with bulk δ18O values in the -18‰ to -20‰ range have similar cycles and these low
values cannot be the result of seasonal low-elevation snowmelt events. Our estimated
34
highland elevation is 4.3±1.0 km during Late Cretaceous (Fig. 2.7A). In the Alberta
foreland basin, paleocurrent directions are generally east to southeast (Mack and Cole,
2005), suggesting that high elevation snowmelt came from the Canadian Rocky
Mountains to the west of the basin. This is consistent with tectonic reconstructions of this
region, which argue that thrusting was active during Late Cretaceous, and that a high
orogenic plateau sat to the west of the basin (Van der Pluijm et al., 2006).
The δ18O range of river water in the Williston basin is -18.3 to -21.5‰SMOW. This is
8.5 to 11.7‰ lower than the δ18O value of the low elevation river water (Fig. 2.3) and is
similar to that of the Alberta foreland basin. This suggests mountains with similar
elevations, in this case 4.5±1.0 km, were present (Fig. 2.7A). Oxygen isotope cycles in
ancient river water further suggest that highland snowmelt fed some rivers seasonally or
yearly (Fig. 2.4B). Rivers rising in the lowlands of the basin have much higher δ18O
values that fall within the range of modeled low elevation river water (Fig. 2.3) and
seasonal records of shell δ18O values reflect both high and low elevation catchments. The
upper Cretaceous and lowest Cenozoic strata in southeastern Montana contains high
amounts of volcanic lithics and andesitic conglomerate, and paleoflow directions are
from the southwest to west in the region; both suggest that the sediment source terrane
was the Sevier thrust belt in Idaho and southwest Montana (Cherven and Jacob, 1985;
Fastovsky, 1987). Therefore, the high elevation catchments for rivers in the western
Williston basin were most likely in the Rocky Mountains. Large rivers frequently carry
high elevation snowmelt >500 km without any significant change in the water δ18O value
and this is the most plausible explanation for the low δ18O values in Williston basin (Fig.
35
2.8A). Examples of rivers carrying water with very negative δ18O values over long
distances are the Colorado and Missouri Rivers, which have significantly lower δ18O
values in Arizona and South Dakota than the local precipitation (Coplen and Kendall,
2000).
High Surface Elevation of Eastern Laramide Ranges during Paleocene
In the Powder River basin, the lowest δ18O value of the river water is -22‰SMOW,
which is ~11‰ below the minimum δ18O value modeled for low-elevation ancient river
water (Fig. 2.3). The negative offset reflects high elevation in the river catchments.
Seasonal oxygen isotope variation in ancient shells further suggest the presence of both
highland and low elevation precipitation in local rivers (Fig. 2.4A). The estimated
elevation of the mountain ranges that provide runoff to the Powder River basin is 4.5
±1.3 km in Late Paleocene (Fig. 2.7B). The simplest scenario for the paleography in the
Powder River basin based on these three different types of river isotopic records would
be a variety of river catchments that carried distal high elevation waters and/or basinal
lowland precipitation (Fig. 2.8B).
The high elevation region in the eastern Laramide province was most likely the
Bighorn Mountains in northern Wyoming and Black Hills in South Dakota. Today the
rivers of this region flow east and northeast from the high Laramide ranges in northern
Wyoming and southwest Montana. These rivers have low δ18O values due to high
elevation snowmelt input. For example, the Tongue River which flows northward from
the northern Bighorn Mountains has a δ18O value of -16.6±2.0‰SMOW; tributaries of the
Powder River with δ18O values of ~ -17‰ flow from the eastern Bighorn Mountains and
36
western Black Hills toward the center of the basin merging as the Powder River (Coplen
and Kendall, 2000). The Powder River and Tongue River then join the Yellowstone
River in southwestern Montana, and form a large tributary of Missouri River. A Late
Paleocene scenario similar to the modern drainage pattern could explain the very low
δ18O values of the river waters in the Powder River basin. Such a paleodrainage scenario
is supported by the paleogeographical reconstruction of the Powder River basin, which is
very similar to the pattern of the modern drainage system just described (Flores and
Ethridge, 1985). Low-temperature thermochronology studies also support this
paleogeography, suggesting major exhumation of the Bighorn Mountains at 65±5Ma and
Early Paleocene cooling of the Black Hills (Strecker, 1996; Crowley et al., 2002). In
addition, Late Paleocene-Early Eocene synorogenic conglomerates with a high proportion
of Precambrian basement clasts are found along the eastern flank of the Bighorn
Mountains (Hoy and Ridgeway, 1997).
Fricke (2003) pointed out that seasonal or episodic Arctic air mass incursions could
result in very low δ18O values in the Powder River basin. Although this phenomenon can
explain very negative δ18O values in seasonal precipitation (snow) at low elevations
today, it is very unlikely to affect the average annual or warm season δ18O value of river
waters. In southern Saskatchewan, where the present latitude is equivalent to the
paleolatitude of the Williston basin and Powder River basin, winter snow δ18O values are
often less than -25‰ (CNIP), but the modeled δ18O value of low-elevation river water is 16±2‰, which is the same as the δ18O value of the local mean annual precipitation
(CNIP). In this case the low-elevation rivers are not biased in favor of winter
37
precipitation, rather they are supported by local groundwater. This argument is also
supported by the fact that low elevation rivers in Minnesota and Michigan have δ18O
values similar to that of the local mean annual precipitation, which is relatively high (-8
to -10‰), even though these areas are equally subject to significant water input from
arctic air masses (Coplen and Kendall, 2000; USNIP).
Lower Surface Elevation of the Western Laramide Province before Early Eocene
The δ18O values of Paleocene and Early Eocene river water in the Crazy Mountains
basin, Bighorn basin, and Washakie basin fall within or close to the range of modeled
low elevation river water (Fig. 2.3), which suggests that the catchments of these ancient
rivers were at relatively low elevation. Seasonal oxygen isotopic variation in shells from
the three basins further shows that river water did not have extremely low δ18O values (<15‰) seasonally or annually (Fig. 2.4D, E, F). Although we suggest that this indicates
low elevation catchments for the sampled rivers in these localities, we can not completely
rule out some effect of local relief on these samples for two reasons: 1) both modeled and
measured low elevation river water δ18O values have a range of ~4.5‰, which could
mask ~2 km of elevation variability; 2) the δ18O values of ancient mean annual
precipitation recorded in the paleosol carbonate nodules of Paleocene-Early Eocene age
in this area are higher than our calculated river water δ18O values, which suggests an
elevation difference between local and distal precipitation sources. The δ18O values of
paleosol carbonates in the Wind River basin are -10.0‰ to -8.0‰PDB in Early Eocene
(our unpublished data), and are -10.0‰ to -7.5‰PDB in the Bighorn basin in Late
Paleocene-Early Eocene (Koch et al., 1995). Using a broad temperature range (12 - 30°C)
38
we can estimate the δ18O values of rainfall in these basins as between -4.5 and 11‰SMOW. Unionid shells in Bighorn basin (-12.6‰ to -8.6‰PDB) imply that water δ18O
values are in the -8.5 to -13‰SMOW range (using eq. 1, above). In the Sage Creek basin,
southwest Montana, the δ18O values of paleosol carbonates varies between -9.0‰ and 5.0‰PDB during Early Eocene Climatic Optimum, while the δ18O values of Paleocene
fluvial calcite cements are -11.0‰ to -9.0‰PDB (Kent-Corson et al., 2006), again this
suggests that river water δ18O values are lower than local precipitation. This difference is
increased if the Eocene soils were warmer than the Paleocene rivers. The differences
between the δ18O values of ancient river carbonates and soil carbonate in these basins
suggest a maximum local relief of 1-2 km. Such relief is tectonically very plausible
because crustal shortening and thickening of the Sevier fold-thrust belt during Late
Cretaceous-Paleocene formed a high-elevation hinterland plateau to the west of the
Rocky Mountains (DeCelles, 2004; DeCelles and Coogan, 2006). Paleocene paleocurrent
directions in the studied strata of the Bighorn and Crazy Mountains basins are generally
eastward, which supports the scenario that rivers sourced in the Sevier thrust belt
delivered water with lower δ18O values to the basins (Dickinson et al, 1988; DeCelles et
al., 1991; Borrell and Hendrix, 2000). There are no robust paleocurrent direction
measurements in the Luman Tongue Member in the Washakie basin. Our data therefore
suggest there was no Laramide range in the western Laramide province as high as those
in the eastern region in Late Paleocene.
Implications
39
This study adds to a growing body of knowledge regarding the topographic
development of the Rocky Mountains. High elevation, 4.5±1.3 km, developed in the
eastern Laramide province, and a catchment draining the high regions of the Bighorn
Mountains and the Black Hills formed in the Powder River basin by the Late Paleocene.
Our data from the western Laramide province (Crazy Mountains, Bighorn, and Washakie
basins) suggest that a maximum of 1-2 km of local relief existed between the Sevier
thrust belt or Laramide ranges and basins in Paleocene-Early Eocene. Therefore, ranges
in eastern Laramide province reached high surface elevation earlier than ones in west.
This pattern is analogous to the westward migration of the exhumation front in the Sierras
Pampeanas and the high surface elevation of the Sierra Grande in the eastern Sierras
Pampeanas (Coughlin et al., 1998). Significant elevation increase of Laramide ranges
after the Late Paleocene in the western Laramide province is required to form the present
landscape of the Rocky Mountains.
Sedimentological and structural evidence have shown that Laramide deformation was
initiated in Late Cretaceous (e.g., Gries, 1983 and ref. therein, Dickinson et al., 1988;
Bird, 1998; DeCelles, 2004). However, this study shows that Laramide ranges with
elevations comparable to today’s were not formed until Late Paleocene in the eastern
Laramide province, and that ranges in eastern province attained high topography prior to
the western province. Erslev (1993) suggested that the Laramide uplifts are a system of
thrusts and back-thrusts which were connected to a detachment in the lower curst. We
therefore propose that the pattern we observe could be explained by southwestward
progression of back-thrusts soled into an east-directed master detachment that formed
40
earlier (Fig. 2.9) (Erslev, 1993; 2005). The shallow subduction of the Farallon Plate
beneath North America buckled the lithosphere in the Sevier foreland by basal traction or
horizontal endloading of highlands in the Sevier hinterland during Late Cretaceous to mid
Paleocene time (Bird, 1998; Tikoff and Maxson, 2001). This buckling could have led to
high Laramide ranges relative to the basins. The subsequent development of an eastdirected crustal detachment may have formed the Black Hills and Bighorn Mountain
uplifts in Late Paleocene at the detachment tips. Following this, back-thrusts could
develop in the folded area and lead to high ranges in the western Laramide province
(Erslev, 1993; 2005). The development of the detachment thrust and back-thrusts may
follow the magmatic sweep caused by eastward shallow subduction and westward
rollback of the subducted slab (Constenius, 1996).
Although our research is based on what is by far the largest paleo-surface water δ18O
data set collected to date, with good age control and multiple basin distribution, it is clear
that a much more detailed temporal and spatial data set is needed to reconstruct the
elevation history of the Laramide ranges and test our proposed kinematic model. In
addition, more work is needed on the post-Laramide basins to document later erosional
exhumation, uplift, or subsidence that led to the topographic patterns we see today.
CONCLUSIONS
After removing the latitudinal δ18O effects on the δ18O of ancient river water, we can
discuss the patterns of elevation change across the Late Cretaceous-Early Eocene
foreland basin of Canadian Rocky Mountains and the intermontane basins of the central
Laramide Rocky Mountains. The Canadian Rocky Mountains were 4.3±1.0 km high
41
during Late Cretaceous, and snowmelt from Rocky Mountains recharged the river water
in the Alberta foreland basin, and western Williston basin both annually and seasonally.
Laramide uplifts attained elevations up to 4.5±1.3 km in northeast Wyoming in the Late
Paleocene, the most likely locus of this high elevation was the ancestral Bighorn
Mountains and the Black Hills. Paleodrainage patterns similar to the present developed in
the Powder River basin in the Late Paleocene; rivers in the basin had catchments at a
variety of elevations, some carrying high elevation precipitation, others sourced at low
elevations. No comparably high topography developed in the western Laramide province
before the Early Eocene. This east-west difference in timing of high elevation
development for the Laramide ranges can be explained by southwestward progression of
back-thrusts soled into an earlier northeast-directed master detachment, which may be
formed by the westward rollback of a subducted shallow slab.
42
Figure 2.1. Shaded relief map of central and Canadian Rocky Mountains. Symbols denote
sampling locations and mean δ18O values of fossil shells. Basins discussed in text are
bordered by dotted line. AB: Alberta foreland basin; BH: Bighorn basin; BlH; Black
Hills; BM: Bighorn Mountains; BT: Beartooth Mountains; CM: Crazy Mountains basin;
GR: Green River basin; PD: Powder River basin; SC: Sage Creek basin; WR: Wind River
basin; WRR: Wind River Range; WaB: Washakie basin; WiB: Williston basin. Arrows
are paleocurrent directions (Flores and Ethridge, 1985; Dickinson et al., 1988; DeCelles
et al., 1991; Borrell and Hendrix, 2000; Mack and Cole, 2005).
43
Age
(Ma) Epoch
POWDER
RIVER
BIGHORN WASHAKIE
WILLISTON
51
53
CRAZY
MTNS.
55
57
59
61
63
ALBERTA
2
65
67
ALBERTA
1
69
71
Strata with sampled fossil unionids
73
Conglomerate deposits of alluvial fans and coarse,
braided fluvial systems
75
Sandy deposits of meandering or braided fluvial systems
77
Shaly deposits of lacustrine and/or paludal and fine-grained
meandering fluvial systems
Figure 2.2 Generalized stratigraphic columns of sedimentary successions involved in
each studied basin (age determinations of strata with sampled fossil unionid are listed in
Table 1). Key references: Cherven and Jacob, 1985; Flores and Ethridge, 1985;
Lerbekmo and Coulter, 1985; Robinson and Honey, 1987; Dickinson et al., 1988; Eberth
and Hamblin, 1993; DeCelles et al., 1991; Buckley, 1994.
44
-2
-6
δ 18O (SMOW)
-10
-14
Powder River basin (58-54Ma)
-18
Williston basin (68-62Ma)
Crazy Mountains basin (61-65Ma)
Bighorn basin (59-54Ma)
-22
Washakie basin (54-53Ma)
Modeled low elevation river water with uncertainties
-26
42
44
46
48
50
52
54
56
58
Paleo-Latitude °N
Figure 2.3. Measured and modeled δ18O values of ancient river water for western interior
of North America plotted against paleo-latitude of sampling location. Dotted lines are the
1σ uncertainties of modeled low elevation δ18O values based on paleolatitude data in
Table 2 and corrections discussed in text. See text for details of calculations and
modeling.
45
-5
A:
18
δ O (PDB)
-9
-13
PR2-85
PR3-83
PR10-86A
-17
-21
-25
0
0.5
1
1.5
2
Distance (mm)
B:
-8
18
δ O (PDB)
-10
-12
-14
92-31
92-20
92-32
-16
-18
-20
-22
0
0.5
1
1.5
2
Distance (mm)
C:
-11
93-16
Tyrell
93-11
-15
18
δ O (PDB)
-13
-17
-19
0
0.5
1
Distance (mm)
1.5
2
46
D:
-10
18
δ O (PDB)
-11
-12
93-27
93-30
-13
-14
-15
0
0.5
1
1.5
2
2.5
Distance (mm)
E:
-7
91-29
91-11
18
δ O (PDB)
-8
-9
-10
-11
-12
-13
0
0.5
1
1.5
2
2.5
Distance (mm)
F:
-4
93-3
93-5
18
δ O (PDB)
-5
-6
-7
-8
-9
0
0.5
1
1.5
Distance (mm)
2
2.5
47
-10
25
-12
20
10
-16
5
-18
0
-20
-5
18
δ O
Temperature
-22
-24
10/31/1984
5/19/1985
12/5/1985
6/23/1986
1/9/1987
-10
-15
7/28/1987
18
δ O (SMOW)
-10
20
-12
15
-14
10
-16
5
-18
0
-20
-5
-22
-24
1/3/1985
Temperature (℃
℃)
Sampling date
A:
7/22/1985
2/7/1986
8/26/1986
3/14/1987
-10
9/30/1987
-6
25
-8
20
15
18
δ O (SMOW)
-10
10
-12
5
-14
0
-16
-5
-18
-10
-20
-22
11/15/1984
Temperature (℃
℃)
Sampling date
B:
C:
Temperature (℃
℃)
15
-14
18
δ O (SMOW)
Figure 2.4. Seasonal δ18O variation of representative fossil shells in the studied basins. A:
Powder River basin; B: western Williston basin; C: Alberta foreland basin; D: Crazy
Mountains basin; E: Bighorn basin; F: southern Washakie basin.
-15
-20
6/3/1985
12/20/1985
7/8/1986
1/24/1987
8/12/1987
Sampling date
Figure 2.5. Seasonal δ18O variation (black circles) of three kinds of river to the east of
Rocky Mountains. A: Milk River; B: Halfmoon Creek; C: Big Sioux River. River water
δ18O data are from Coplen and Kendall, 2000. Temperature (gray circles) is the average
temperature for the day of sampling from a nearby climate station (NCDC:
http://www.ncdc.noaa.gov/oa/ncdc.html).
48
Figure 2.6. Regression for sampling station latitude and the δ18O values of river water in
low-elevation stations (<200m) within the USA (data from Coplen and Kendall (2000)).
Open circles are rivers in Hawaii (<23° latitude) or rivers that are sourced in high
elevation catchments with sampling stations at low-elevation, which are not included in
the regression.
49
6
A
Paleoelevation (km)
5
4.5±1.3 km
4
3
2
+1 Sigma
1
-1 Sigma
Alberta foreland basin
0
-14
-12
-10
-8
-6
18
∆δ
δ O (SMOW)
-4
-2
0
6
Crazy Mountain basin, Bighorn
basin, and Washakie basin
Powder River basin
Paleoelevation (km)
5
Williston basin
B
4.5±1.5 km
4
3.3±1.1 km
3
2
1
0
40
42
44
46
48
Latitude °N
Figure 2.7. A): Estimated paleoelevation of the Late Cretaceous and Early Paloecene
Canadian Rocky Mountains by using thermodynamic based lapse rate in Rowley, 2007;
B): Estimated paleoelevation of mid Paleocene-Early Eocene river source region by using
50
lapse rate against present latitude of sampling sites in Laramide Rocky Mountain basins.
Elevation of river catchment with measured δ18O values higher than modeled lowelevation values are arbitrarily assigned as zero.
Figure 2.8. Paleodrainage reconstruction of the studied area based on the presented data,
and the inferred elevation of Rocky Moutnains. Lines with arrows stand for the
paleorivers with the δ18O value shown. See Fig.2.1 for names of major structures and
basins, and references of paleoflow directions.
51
Figure 2.9. Schematic cross-sections showing the mechanism of forming high ranges in
eastern Laramide province earlier than the western province. Not to scale.
52
Table 2.1. Age constraints for the study intervals in each basin
Sample Location
Formation
Age (Ma)
Constraint
Dating Method
Reference
Alberta foreland
basin 1
Oldman and Dinosaur Park
Formations
74-76
Bentonite bed above the Dinosaur Park-Oldman
Formation contact
K-Ar, Ar-Ar
Eberth and Hamblin, 1993
Alberta foreland
basin 2*
Horseshoe Canyon Formation
68-73
C31r.1r-C32r.1r
Magnetostratigraphy
Lerbekmo and Coulter, 1985
Williston basin
Hell Creek Formation and Tullock
Member of Fort Union Formation
62.3-68
K-T boundary, bentotite beds
Ar-Ar, Magnetostratigraphy,
NALMA
Swisher et al., 1993; Lund et al., 2002
Crazy Mountain
basin
Bear, Lebo, and Melville Member
of Fort Union Formation
61-65
Interval of C26r-C29r,
Magnetostratigraphy
Buckley, 1994; Butler et al., 1987
Bighorn basin
Fort Union and Willwood
Formations
53.6-59
Interval of C24n-C26r, carbon isotope excursion
Ar-Ar and
Magnetostratigraphy
Koch et al., 1995; Secord et al., 2006
54-58
Coal stratigraphy, occurrence of Platycarya
pollen , and correlation with Bighorn Basin
NALMA, Biostratigraphy
Wolberg, 1979; Robinson and Honey,
1987; Wing et al., 1991
53-54
Volcanic tuff above the Member, top of C24n
Ar-Ar and
Magnetostratigraphy
Smith et al., 2003
Tongue River Member of Fort
Powder River basin
Union and Wasatch Formations
Washakie basin
Luman Tongue Member of Green
River Formation
Note: * only one shell bed in the locality.
53
Table 2.2. Summary of paleomagnetic data for paleolatitude reconstruction
Present Latitude
Present
(Nº)
Longitude (Wº) Pole (Nº) Pole (Eº)
Sample Location
Age (Ma)
Alberta foreland basin 1
74-76
49.16
110.41
74.70
Alberta foreland basin 2
71
50.95
112.09
74.20
A 95
P
Paleolatitude
(Nº)
Southward
transport (º)
204.70
5.90
0.55
58.43
9.3±5.9
204.80
3.20
0.51
60.75
9.8±3.2
Williston basin
65-66
47.55
107.01
74.20
204.80
3.20
0.59
56.36
8.8±3.2
Crazy Mountains basin
60-65
46.21
109.73
75.90
196.80
2.90
0.64
53.18
7.0±2.9
Bighorn basin
55-59
44.84
108.81
75.90
196.80
2.90
0.67
51.67
6.8±2.9
Powder River basin
54-57
44.8
106.08
75.90
196.80
2.90
0.68
51.01
6.2±2.9
Washakie basin
51.8-52
40.89
108.66
77.90
179.30
3.40
0.81
43.55
2.7±3.4
Note: Pre. Lat. is present latitude. Pre. Lon. is present longitude. Pole is paleomagnetic reference pole (Besse and Courtillot, 2002). A 95 is 95% confidence limits. P is the angular
distance between sample site and reference pole (Eq.A20 in Butler, 1992). Paleolat. is the calculated paleolatitude (Eq.A26 in Butler, 1992). Southward transport is the latitude
difference (and 95% confidence limits) between present latitude and paleolatitude.
54
Table 2.3. δ13C and δ18O values of bulk individual shells and sample locations
Ave. δ18O Max. δ18O Min.δ18O
Sample Age (Ma) δ13C (PDB) δ18O (PDB)
Location
(PDB)
(PDB)
(PDB)
*only new analysis are presented, other data are from Dettman and Lohmann, 2000
Washakie Basin
193.11*
51.79
0.39
-6.24
-5.92
-4.98
-7.19 N40°53'26",
193.12*
51.79
0.34
-4.98
W108°39'27"
193.13*
51.79
-0.36
-6.29
193.14*
51.79
-0.73
-6.38
193.15*
51.79
-1.08
-5.90
193.16*
51.79
-0.54
-5.88
193.17*
51.79
-1.16
-6.65
193.18*
51.79
-0.86
-5.14
193.19*
51.79
-1.01
-5.80
193.2*
51.79
0.44
-4.99
293.11*
51.82
-1.44
-7.86
-7.26
-5.81
-9.79 N40°53'26",
293.12*
51.82
-0.49
-7.15
W108°39'30"
293.13*
51.82
-1.79
-5.81
293.14*
51.82
-0.93
-7.39
293.15*
51.82
-0.61
-6.72
293.16*
51.82
-0.93
-7.64
293.17*
51.82
-1.40
-6.56
293.18*
51.82
-2.49
-6.66
293.19*
51.82
-1.83
-6.26
293.20*
51.82
-1.98
-6.51
393.11*
51.91
-3.02
-4.77
-5.30
-4.46
-7.13 N40°53'27",
393.12*
51.91
-1.80
-4.74
W108°39'31"
393.13*
51.91
-2.11
-4.76
393.14*
51.91
-2.17
-4.84
393.15*
51.91
-1.35
-5.84
393.16*
51.91
-1.46
-5.62
393.17*
51.91
-2.15
-5.06
393.18*
51.91
-2.72
-4.46
393.19*
51.91
-2.95
-4.57
393.20*
51.91
-2.87
-4.71
493.11*
51.95
-0.78
-8.05
-7.97
-7.19
-9.06 N40°53'28",
493.12*
51.95
-0.57
-7.25
W108°39'33"
493.13*
51.95
-1.41
-7.81
493.14*
51.95
-1.50
-7.76
493.15*
51.95
-1.68
-7.35
493.16*
51.95
-0.58
-7.76
493.17*
51.95
-1.01
-7.19
493.18*
51.95
-0.54
-7.47
493.19*
51.95
-1.56
-8.36
493.20*
51.95
-1.57
-7.42
693.12*
51.99
-2.77
-7.32
-7.94
-6.41
-11.14 N40°53'29",
693.13*
51.99
-3.76
-8.57
W108°39'34"
693.14*
51.99
-2.88
-6.73
55
Sample
13
Age (Ma) δ C (PDB)
693.15*
693.16*
693.17*
693.18*
Bighorn Basin
9134.11*
9134.12*
9134.13*
9134.14*
9134.15*
9134.16*
9134.17*
9134.18*
9134.19*
9111.10*
9111.11*
9111.12*
9111.13*
9111.14*
9111.15*
9111.16*
9111.17*
9117.09*
9117.10*
9117.11*
9117.12*
9117.13*
9117.14*
9117.15*
9117.16*
9117.17*
9117.18*
9118.09*
9118.10*
9118.11*
9118.12*
9118.13*
9118.14*
9118.15*
9118.16*
9113.08*
9113.09*
9113.10*
9113.11*
9113.12*
51.99
51.99
51.99
51.99
-3.31
-2.96
-2.87
-2.34
56.37
56.37
56.37
56.37
56.37
56.37
56.37
56.37
56.37
55.96
55.96
55.96
55.96
55.96
55.96
55.96
55.96
55.77
55.77
55.77
55.77
55.77
55.77
55.77
55.77
55.77
55.77
55.48
55.48
55.48
55.48
55.48
55.48
55.48
55.48
55.30
55.30
55.30
55.30
55.30
-2.73
-4.32
-3.59
-3.06
-4.41
-4.79
-4.46
-3.48
-4.45
-5.14
-5.97
-5.45
-5.50
-5.66
-5.28
-6.26
-5.06
-4.25
-5.24
-5.40
-4.44
-4.18
-4.53
-5.37
-5.41
-4.81
-4.85
-4.13
-4.26
-4.78
-4.12
-4.07
-4.71
-4.18
-3.96
-5.72
-6.43
-4.29
-4.82
-5.41
Table 2.3. (Cont'd)
Ave. δ18O
δ18O (PDB)
(PDB)
-6.44
-8.25
-7.99
-7.03
-11.69
-11.26
-11.03
-11.44
-11.41
-12.15
-10.61
-10.81
-11.79
-10.28
-10.60
-10.45
-10.30
-10.65
-10.82
-10.50
-10.64
-10.82
-10.95
-11.45
-10.69
-11.07
-10.78
-10.78
-11.81
-10.95
-11.00
-10.98
-11.29
-12.15
-11.51
-11.39
-11.89
-11.20
-11.08
-11.57
-13.03
-10.88
-10.67
-10.90
Max.
δ18O
Min.δ18O
(PDB)
Location
-11.65 -10.61
-12.82 N44°50'19",
W108°48'34"
-10.55
-9.47
-11.54 N44°50'45",
W108°53'06"
-10.91
-9.98
-11.81 N44°53'01",
W109°04'09"
-11.50 -10.73
-12.22 N44°51'21",
W109°04'54"
-11.42 -10.12
-12.86 N44°48'34",
W108°54'50"
56
Sample
9121.09*
9121.10*
9121.11*
9121.12*
9121.13*
9121.14*
9121.15*
9121.16*
9121.17*
9122.10*
9122.11*
9122.12*
9122.13*
9122.14*
9122.15*
9122.16*
9122.17*
9122.18*
9122.19*
9135.11*
9135.12*
9135.13*
9135.14*
9135.15*
9135.16*
9135.17*
9135.18*
9120.10*
9120.11*
9120.12*
9120.13*
9120.14*
9120.15*
9120.16*
9120.17*
9120.18*
9127.10*
9127.11*
9127.12*
9127.13*
9125.10*
9125.11*
9125.12*
9125.13*
9125.14*
Table 2.3. (Cont'd)
Ave. δ18O Max. δ18O Min.δ18O
Age (Ma) δ C (PDB) δ O (PDB)
(PDB)
(PDB)
(PDB)
55.30
-4.90
-10.75
-10.88
-9.92
-12.38
55.30
-4.89
-10.64
55.30
-6.05
-10.49
55.30
-5.40
-10.81
55.30
-5.25
-10.69
55.30
-4.84
-10.64
55.30
-4.88
-10.57
55.30
-4.89
-10.57
55.30
-6.22
-11.53
55.30
-4.14
-10.11
-10.27
-9.04
-11.23
55.30
-5.77
-10.35
55.30
-3.56
-9.43
55.30
-4.84
-10.46
55.30
-4.39
-10.27
55.30
-4.01
-10.13
55.30
-5.19
-10.43
55.30
-5.69
-11.21
55.30
-4.51
-10.19
55.30
-4.01
-10.05
55.26
-4.47
-10.19
-10.73
-9.97
-12.38
55.26
-4.18
-10.14
55.26
-4.45
-9.97
55.26
-4.83
-10.64
55.26
-4.90
-10.66
55.26
-3.90
-10.30
55.26
-3.95
-11.78
55.26
-4.10
-10.24
55.24
-5.33
-11.06
-10.62
-9.86
-11.45
55.24
-6.43
-10.40
55.24
-5.06
-10.80
55.24
-5.74
-9.92
55.24
-6.98
-10.19
55.24
-4.90
-10.35
55.24
-5.53
-9.86
55.24
-5.41
-10.16
55.24
-5.03
-10.29
55.21
-4.64
-11.11
-11.09
-10.40
-11.59
55.21
-5.05
-11.04
55.21
-4.43
-11.10
55.21
-6.24
-10.70
55.03
-4.17
-10.28
-10.86
-9.82
-11.54
55.03
-3.79
-10.87
55.03
-4.55
-11.03
55.03
-4.42
-10.44
55.03
-3.58
-10.66
13
18
Location
N44°50'37",
W109°03'30"
N44°50'44",
W109°03'30"
N44°49'59",
W109°00'39"
N44°50'32",
W109°03'26"
N44°49'59",
W109°01'15"
N44°49'20",
W109°02'40"
57
Sample
9125.15*
9125.16*
9125.17*
9132.10*
9132.11*
9132.12*
9132.13*
9132.14*
9132.15*
9132.16*
9126.13*
9126.14*
9126.15*
9126.16*
9126.17*
9126.18*
9126.19*
9128.12*
9128.13*
9128.14*
9128.15*
9129.16*
9129.17*
9129.18*
9129.19*
9129.20*
9129.21*
9129.22*
9129.23*
9129.24*
9124.11*
9124.12*
9124.13*
9124.14*
9124.15*
9124.16*
9124.17*
9124.18*
9124.19*
9124.20*
9123.13*
9123.14*
9123.15*
9123.16*
9123.17*
13
Age (Ma) δ C (PDB)
55.03
55.03
55.03
55.03
55.03
55.03
55.03
55.03
55.03
55.03
54.95
54.95
54.95
54.95
54.95
54.95
54.95
54.89
54.89
54.89
54.89
54.88
54.88
54.88
54.88
54.88
54.88
54.88
54.88
54.88
54.86
54.86
54.86
54.86
54.86
54.86
54.86
54.86
54.86
54.86
54.63
54.63
54.63
54.63
54.63
-4.71
-4.35
-4.16
-7.57
-7.26
-5.73
-7.21
-6.89
-7.08
-5.50
-5.50
-6.54
-5.69
-3.91
-5.29
-4.30
-5.34
-4.14
-4.20
-4.69
-3.86
-6.02
-4.59
-4.94
-5.21
-4.70
-4.87
-4.94
-4.15
-5.32
-4.49
-5.43
-4.92
-4.80
-3.86
-5.35
-4.76
-3.95
-4.96
-5.04
-4.94
-4.36
-5.34
-4.41
-3.81
Table 2.3. (Cont'd)
Ave. δ18O Max. Min.δ18O
δ18O (PDB)
(PDB)
(PDB)
δ18O
-9.82
-10.90
-10.85
-10.30
-10.50 -9.83
-11.72
-10.13
-10.37
-10.75
-9.83
-10.97
-10.09
-10.60
-10.71 -9.82
-12.19
-11.19
-11.24
-10.51
-10.78
-9.82
-10.45
-10.59
-10.96 -10.18
-11.44
-10.73
-10.67
-10.72
-10.80
-10.45 -7.86
-11.89
-10.26
-10.02
-11.31
-10.04
-9.53
-9.99
-10.27
-10.65
-9.68
-9.97 -9.26
-10.91
-10.02
-9.56
-9.60
-9.26
-10.14
-10.00
-10.07
-10.27
-10.91
-10.27
-10.15 -9.33
-10.91
-10.08
-10.23
-9.79
-10.14
Location
N44°49'08",
W109°02'3
5"
N44°49'28",
W109°02'4
N44°47'04",
W109°00'5
N44°47'24",
W109°00'3
N44°48'59",
W109°04'0
N44°48'37",
W109°05'2
58
Sample
9123.18*
9123.19*
9123.20*
9123.21*
9123.22*
9108.09*
9108.10*
9108.11*
9108.12*
9108.13*
9108.14*
9108.15*
9108.16*
9114.16*
9114.17*
9114.18*
9114.19*
9114.20*
9114.21*
9114.22*
9114.23*
9131.11*
9131.12*
9131.13*
9131.14*
9131.15*
9131.16*
9131.17*
9131.18*
9115.09*
9115.10*
9115.11*
9115.12*
9115.13*
9115.14*
9115.15*
9115.16*
9115.17*
9116.08*
9116.09*
9116.10*
9116.11*
9116.12*
9116.13*
13
Age (Ma) δ C (PDB)
54.63
54.63
54.63
54.63
54.63
54.34
54.34
54.34
54.34
54.34
54.34
54.34
54.34
54.32
54.32
54.32
54.32
54.32
54.32
54.32
54.32
54.32
54.32
54.32
54.32
54.32
54.32
54.32
54.32
53.99
53.99
53.99
53.99
53.99
53.99
53.99
53.99
53.99
53.99
53.99
53.99
53.99
53.99
53.99
-4.69
-4.07
-5.46
-4.22
-4.96
-4.82
-3.01
-4.02
-3.98
-3.89
-4.80
-4.90
-4.26
-3.85
-4.29
-2.62
-8.43
-5.19
-5.03
-5.14
-5.89
-4.01
-3.97
-3.37
-4.32
-4.00
-3.90
-3.92
-3.80
-2.81
-4.66
-3.40
-4.70
-3.46
-3.06
-4.60
-3.14
-3.15
-7.33
-7.12
-4.38
-5.78
-4.62
-7.95
Table 2.3. (Cont'd)
Ave. δ18O Max. δ18O Min.δ18O
δ O (PDB)
(PDB)
(PDB)
(PDB)
-10.13
-10.17
-10.91
-10.07
-10.39
-10.99
-11.08
-10.38
-12.30
-11.35
-11.03
-10.74
-11.29
-10.59
-11.78
-11.13
-10.76
-11.16
-10.60
-11.90
-11.01
-10.80
-10.81
-11.05
-11.20
-11.29
-11.12
-10.56
-10.80
-10.08 -11.759
-10.64
-10.56
-10.83
-10.93
-10.50
-10.79
-10.65
-10.63
-10.92
-10.51
-11.89
-10.92
-10.76
-11.24
-10.64
-10.67
-10.97
-11.05
-10.57
-9.28
-10.25
-9.28
-11.07
-9.81
-10.68
-10.01
-10.91
-9.46
18
Location
N44°46'51"
,W109°05'0
N44°47'10"
,W109°06'3
N44°48'21"
,W109°06'4
N44°45'40"
,W109°06'4
N44°45'46"
,W109°06'5
59
Sample
13
Age (Ma) δ C (PDB)
9133.02*
53.58
9133.03*
53.58
9133.04*
53.58
9133.05*
53.58
9133.06*
53.58
9133.07*
53.58
9133.08*
53.58
Powder River Basin
916.11*
53.70
916.12*
53.70
916.13*
53.70
916.14*
53.70
916.15*
53.70
916.16*
53.70
916.17*
53.70
916.18*
53.70
917.10*
55.46
917.11*
55.46
917.12*
55.46
917.13*
55.46
917.14*
55.46
917.15*
55.46
917.16*
55.46
917.17*
55.46
915.17*
56.89
915.18*
56.89
915.19*
56.89
915.2*
56.89
915.21*
56.91
915.22*
56.91
915.23*
56.91
915.24*
56.91
915.25*
56.91
914.13*
57.02
914.14*
57.02
914.15*
57.02
914.16*
57.02
914.17*
57.02
914.18*
57.02
914.19*
57.02
914.20*
57.02
914.21*
57.02
914.22*
57.02
911.10*
57.13
911.11*
57.13
-4.67
-4.99
-5.20
-5.35
-4.83
-4.48
-4.66
-6.10
-5.91
-5.45
-5.42
-6.03
-5.52
-5.23
-6.53
-4.97
-4.61
-4.87
-6.93
-5.24
-5.17
-6.01
-5.14
-3.53
-3.49
-2.75
-2.98
-3.25
-2.73
-3.30
-3.02
-3.19
-1.73
-2.87
-2.43
-2.63
-2.10
-0.55
-2.22
-4.10
-3.98
-1.95
-4.57
-5.22
Table 2.3. (Cont'd)
Ave. δ18O Max. δ18O Min.δ18O
Location
δ18O (PDB)
(PDB)
(PDB)
(PDB)
-10.46
-10.90
-10.90
-10.90 N44°46'45",
-11.38
W109°10'12"
-11.88
-11.34
-11.52
-11.48
-11.41
-11.48
-11.11
-11.18
-10.47
-11.65
-11.59
-11.63
-11.53
-12.55
-15.64
-12.41
-16.16
-14.70
-13.24
-15.21
-15.45
-10.18
-9.96
-11.86
-8.45
-16.70
-19.65
-17.81
-18.96
-17.89
-9.61
-9.57
-8.96
-9.55
-8.81
-8.90
-9.14
-9.36
-10.00
-8.95
-15.38
-14.97
-11.48
-9.32
-15.91 N44°39'00",
W105°58'48"
-14.44
-11.97
-19.36 N44°37'12",
W106°27'00"
-9.97
-8.41
-13.68 N45°35'38",
W105°40'54"
-17.74
-15.48
-20.47 N45°35'38",
W105°40'54"
-9.20
-7.89
-10.00 N45°34'01",
W105°42'48"
-15.67
-14.06
-17.85 N45°30'56",
W106°05'31"
60
Table 2.3. (Cont'd)
Ave. δ18O Max. δ18O Min.δ18O
Sample Age (Ma) δ C (PDB) δ O (PDB)
(PDB)
(PDB)
(PDB)
911.12*
57.13
-4.93
-15.19
911.13*
57.13
-4.73
-15.17
911.14*
57.13
-5.41
-15.10
911.15*
57.13
-5.35
-15.24
911.16*
57.13
-4.21
-16.86
911.17*
57.13
-4.60
-14.06
911.18*
57.13
-5.27
-15.69
913.09*
57.27
-3.61
-18.20
-18.23
-16.68
-20.77
913.10*
57.27
-4.23
-17.83
913.11*
57.27
-3.16
-18.80
913.12*
57.27
-3.86
-17.24
913.13*
57.27
-3.60
-16.68
913.14*
57.27
-3.31
-17.91
913.15*
57.27
-3.62
-17.98
913.16*
57.27
-3.64
-17.70
912.10*
57.28
-5.85
-20.53
-21.24
-19.89
-22.93
912.11*
57.28
-3.95
-21.40
912.12*
57.28
-4.19
-20.89
912.13*
57.28
-4.13
-20.82
912.14*
57.28
-4.04
-20.07
912.15*
57.28
-4.98
-21.25
912.16*
57.28
-4.94
-21.33
912.17*
57.28
-4.36
-21.72
912.18*
57.28
-3.62
-21.41
912.19*
57.28
-3.00
-20.04
Alberta Foreland Basin
uncat Tyr 02* 70.60
-0.21
-13.33
-13.33
13
1593.11*
1593.12*
1593.13*
1593.14*
1593.15*
1593.16*
1593.17*
1593.18*
1593.19*
1593.2*
1693.11*
1693.12*
1693.13*
1693.14*
1693.15*
1693.16*
74.71
74.71
74.71
74.71
74.71
74.71
74.71
74.71
74.71
74.71
74.71
74.71
74.71
74.71
74.71
74.71
18
-3.31
-3.45
-3.38
-3.56
-4.67
-0.89
-3.06
-3.90
-5.15
-4.22
-4.28
-2.46
-2.03
-2.88
-2.66
-4.06
-14.19
-14.28
-14.12
-14.13
-14.22
-14.17
-14.41
-14.61
-14.21
-14.00
-13.91
-14.48
-14.62
-14.51
-14.26
-14.49
-14.74
-14.00
-14.92
-14.33
Location
N45°43'30",W
105°48'00"
N45°45'00",W
105°51'00"
N50°57'00",W
112°54'00"
-17.21 N49°58'21",W
110°25'30"
-15.75 N49°58'21",W
110°25'26"
61
13
18
Table 2.4. δ C and δ O values of micromilled representative shells
Powder River basin
PR2-85
PR3-83
18
Distance
δ13C
Distance δ13C
δ O
(mm)
(PDB) (PDB) (mm)
(PDB)
0.025
-4.28
-10.28
0.025
-4.06
0.050
-4.50
-10.10
0.050
-3.86
0.075
-4.34
-10.08
0.075
-3.73
0.100
-4.63
-10.24
0.100
-3.31
0.125
-4.62
-10.13
0.125
-3.41
0.150
-3.95
-9.40
0.150
-3.63
0.175
-3.39
-8.87
0.175
-3.30
0.200
-2.36
-8.18
0.200
-2.81
0.225
0.15
-7.04
0.225
-2.07
0.250
1.35
-7.23
0.250
-1.57
0.275
1.75
-8.12
0.275
-1.88
0.300
1.41
-8.38
0.300
-2.09
0.350
1.34
-8.78
0.325
-2.23
0.375
1.37
-8.85
0.350
-2.61
0.400
1.23
-8.98
0.375
-3.09
0.425
1.20
-9.11
0.400
-3.38
0.450
1.29
-8.67
0.425
-3.95
0.475
1.31
-8.40
0.450
-4.50
0.500
0.52
-9.59
0.475
-4.45
0.525
0.39
-9.41
0.500
-4.23
0.550
-0.14
-10.10
0.525
-4.57
0.575
-0.13
-10.14
0.550
-4.70
0.600
-0.19
-10.19
0.575
-4.11
0.625
-0.66
-10.33
0.600
-3.60
0.650
-1.03
-10.52
0.625
-3.27
0.675
-1.00
-10.51
0.675
-3.55
0.700
-1.18
-10.32
0.700
-3.67
0.725
-1.46
-10.71
0.725
-3.95
0.750
-1.83
-10.91
0.750
-4.36
0.775
-2.13
-10.89
0.775
-5.12
0.800
-3.08
-11.00
0.825
-5.13
0.825
-3.60
-11.12
0.850
-5.19
0.850
-3.37
-11.52
0.875
-5.85
0.875
-3.07
-11.00
0.900
-3.87
0.900
-3.54
-11.22
0.925
-4.47
0.925
-3.68
-11.04
0.950
-4.58
0.950
-3.65
-10.97
0.975
-4.83
0.975
-3.55
-10.76
1.000
-4.79
1.000
-3.67
-10.60
1.025
-4.65
1.025
-3.15
-10.65
1.050
-4.69
1.050
-2.08
-8.91
1.075
-4.33
1.075
-0.52
-7.67
1.125
-3.86
1.100
0.48
-7.55
1.150
-4.32
δ18O
(PDB)
-22.47
-21.92
-21.17
-20.56
-20.30
-20.93
-20.55
-19.85
-18.61
-18.61
-19.74
-20.36
-21.59
-22.26
-22.57
-22.84
-23.07
-23.24
-22.80
-22.27
-22.27
-22.04
-20.91
-19.16
-18.56
-19.28
-20.70
-21.25
-20.91
-21.02
-20.12
-20.66
-21.43
-19.38
-20.03
-20.42
-21.18
-21.41
-20.65
-20.30
-18.62
-19.57
-19.81
PR10-86A
Distance δ13C
(mm)
(PDB)
0.027
-5.83
0.137
-6.00
0.245
-5.76
0.323
-6.36
0.402
-6.29
0.481
-6.22
0.508
-5.73
0.534
-5.69
0.562
-5.66
0.590
-5.37
0.618
-5.64
0.646
-5.00
0.702
-4.30
0.731
-3.61
0.760
-3.12
0.789
-2.11
0.818
-2.57
0.847
-3.19
0.874
-3.71
0.902
-3.84
0.929
-4.37
0.956
-4.63
0.983
-5.43
1.010
-5.34
1.037
-5.36
1.065
-5.56
1.092
-5.80
1.119
-5.82
1.148
-5.70
1.178
-5.67
1.207
-5.97
1.236
-6.55
1.265
-6.71
1.295
-6.46
1.354
-6.32
1.385
-5.97
1.416
-6.32
1.446
-6.19
1.475
-5.33
1.504
-4.33
1.533
-3.89
1.562
-4.11
1.591
-4.43
δ18O
(PDB)
-13.50
-15.09
-16.17
-16.96
-16.82
-15.70
-14.43
-12.68
-10.95
-9.82
-9.48
-9.52
-9.60
-9.06
-8.69
-7.18
-8.06
-8.95
-9.04
-9.22
-9.72
-10.01
-10.74
-11.12
-11.26
-11.82
-12.45
-13.15
-14.23
-15.02
-14.66
-14.97
-14.86
-13.82
-11.83
-10.43
-9.04
-8.10
-7.44
-7.23
-7.94
-8.42
-8.99
62
Table 2.4. (Cont'd)
PR2-85
PR3-83
18
Distance δ13C
Distance δ13C
δ O
(mm)
(PDB) (PDB) (mm)
(PDB)
1.125
0.92
-7.83
1.175
-4.45
1.150
0.97
-8.23
1.225
-4.47
1.175
0.84
-8.64
1.200
0.80
-8.99
1.225
0.90
-9.08
1.250
0.72
-8.81
1.275
0.24
-8.83
1.300
-0.57
-9.70
1.325
-1.62
-9.85
1.350
-1.96
-9.87
1.375
-2.45
-9.57
1.400
-3.52
-9.76
1.425
-4.07
-9.90
1.450
-3.80
-9.70
1.475
-3.36
-9.58
1.500
-3.56
-9.80
1.525
-4.15 -10.23
1.550
-4.52 -10.26
1.575
-4.83 -10.64
1.600
-4.84 -10.88
1.625
-4.13 -10.10
1.675
-2.87
-9.13
1.700
-2.52
-9.04
1.725
-2.15
-8.36
1.750
-2.14
-8.14
1.775
-1.82
-7.28
1.800
-0.77
-7.04
1.825
-0.25
-7.74
1.850
-0.15
-8.22
1.875
-0.16
-8.69
1.900
0.05
-8.95
1.925
0.20
-8.93
1.950
0.03
-9.13
Williston basin
92-31
0
-8.81
0.044
-8.93
0.088
-9.07
0.132
-9.25
0.176
-9.23
0.22
-9.37
0.264
-9.31
0.308
-9.39
-8.73
-8.78
-9.28
-9.66
-9.65
-9.86
-9.71
-9.73
92-20
0
0.046
0.092
0.138
0.184
0.23
0.276
0.316
-5.25
-5.45
-5.51
-5.32
-5.25
-5.72
-5.44
-5.20
PR10-86A
δ18O
Distance
(PDB) (mm)
-19.64
1.620
-20.10
1.649
1.678
1.708
1.766
1.795
-17.02
-17.10
-16.88
-17.28
-17.04
-16.91
-16.79
-15.92
92-32
0.000
0.042
0.084
0.126
0.168
0.210
0.252
0.294
δ13C
(PDB)
-4.40
-4.54
-4.79
-5.19
-5.91
-6.32
δ18O
(PDB)
-9.46
-9.79
-10.23
-11.12
-10.72
-10.82
-4.89
-5.16
-5.19
-5.38
-5.26
-4.95
-5.14
-5.30
-15.34
-15.40
-15.53
-15.65
-15.65
-15.26
-15.70
-16.08
63
Table 2.4. (Cont'd)
Distance δ13C
(mm)
(PDB)
0.352
-9.44
0.396
-9.55
0.44
-9.42
0.484
-9.43
0.528
-9.45
0.572
-9.41
0.616
-9.34
0.66
-9.30
0.704
-9.23
0.748
-9.20
0.792
-9.13
0.836
-9.20
0.885
-9.19
0.934
-9.53
0.983
-9.39
1.032
-9.52
1.081
-9.77
1.13
-9.52
1.179
-9.60
1.228
-9.47
1.277
-9.59
1.326
-9.53
1.375
-9.29
1.424
-9.24
1.473
-9.25
1.522
-8.97
1.571
-9.03
1.62
-9.20
1.669
-9.37
1.718
-9.77
1.767
-9.87
1.796
-9.71
1.825
-9.63
1.854
-9.71
1.883
-9.77
1.912
-9.71
δ18O
(PDB)
-10.00
-10.22
-10.01
-9.97
-9.99
-9.84
-9.78
-9.64
-9.57
-9.56
-9.30
-9.39
-9.71
-9.86
-9.53
-9.73
-10.08
-9.97
-10.04
-9.88
-10.04
-10.15
-9.76
-9.71
-9.52
-9.51
-9.38
-9.31
-9.11
-8.64
-8.57
-8.54
-8.53
-8.56
-8.26
-8.15
Alberta foreland basin
Tyrell
0.033
-0.39
0.066
0.55
0.099
0.16
0.132
0.18
0.165
-0.22
-13.71
-13.72
-13.57
-13.47
-12.85
Distance δ13C
δ18O
Distance δ13C
(mm)
(PDB) (PDB)
(mm)
(PDB)
0.356
-5.40
-16.46
0.378
-5.23
0.396
-5.15
-17.39
0.504
-5.46
0.436
-5.03
-21.32
0.546
-5.54
0.476
-4.52
-21.65
0.588
-5.74
0.516
-4.15
-20.90
0.630
-5.47
0.556
-4.00
-20.29
0.672
-5.47
0.596
-3.66
-20.28
0.714
-5.71
0.636
-3.60
-20.27
0.756
-5.34
0.676
-3.20
-20.03
0.798
-5.83
0.716
-3.02
-19.58
0.840
-5.35
0.756
-3.73
-17.76
0.882
-5.41
0.796
-3.82
-17.29
0.924
-5.60
0.836
-3.78
-16.78
0.966
-5.34
0.876
-4.16
-16.13
1.050
-5.04
0.916
-4.03
-16.27
1.092
-5.06
0.956
-4.16
-16.32
1.134
-5.00
0.996
-4.62
-16.44
1.176
-5.46
1.036
-4.85
-16.79
1.218
-5.59
1.076
-5.08
-16.82
1.260
-5.31
1.116
-5.36
-17.62
1.302
-5.54
1.156
-5.50
-18.43
1.344
-5.73
1.196
-5.45
-18.68
1.386
-5.83
1.236
-5.58
-19.06
1.428
-6.11
1.276
-5.62
-18.86
1.470
-6.24
1.316
-5.65
-19.11
1.512
-6.22
1.356
-5.64
-19.20
1.554
-6.27
1.396
-5.67
-19.24
1.596
-6.19
1.436
-5.77
-19.30
1.638
-6.10
1.476
-5.73
-19.20
1.680
-5.65
1.516
-5.57
-19.14
1.722
-5.30
1.556
-5.64
-19.22
1.764
-4.84
1.596
-5.61
-19.19
1.806
-4.69
1.636
-5.53
-19.42
1.848
-4.58
1.676
-5.44
-19.48
1.890
-4.58
1.716
-5.42
-19.57
1.932
-4.54
1.756
-5.21
-20.04
1.974
-4.52
1.796
-5.08
-20.10
93-16
0.050
0.100
0.150
0.200
0.250
0.80
-0.26
-1.45
-2.58
-3.01
-14.05
-13.58
-13.67
-13.56
-13.16
93-11
0.000
0.038
0.076
0.114
0.152
-2.61
-3.14
-3.42
-4.31
-3.56
δ18O
(PDB)
-15.86
-16.00
-15.71
-16.24
-15.61
-16.09
-16.38
-16.17
-16.91
-15.80
-15.62
-15.92
-14.92
-14.78
-14.35
-12.52
-10.98
-10.11
-9.30
-9.57
-9.87
-9.91
-9.93
-10.15
-10.41
-10.36
-10.57
-10.81
-11.42
-12.37
-13.62
-14.83
-16.02
-16.74
-16.67
-16.09
-18.22
-18.47
-18.51
-19.25
-18.60
64
Table 2.4. (Cont'd)
Distance δ13C
(mm)
(PDB)
0.198
-0.52
0.231
-0.42
0.264
-0.76
0.297
0.16
0.33
-0.52
0.363
-0.93
0.396
-0.76
0.429
-0.38
0.462
0.42
0.495
1.03
0.528
0.42
0.561
-0.15
0.594
-0.59
0.627
-0.31
0.66
0.34
0.693
0.09
0.726
-0.16
0.759
-0.14
0.792
-0.37
0.824
-0.70
0.856
0.41
0.888
0.32
0.92
-0.12
0.952
0.04
0.984
0.21
1.016
-0.08
1.048
-0.20
1.08
-0.42
1.112
-0.69
1.144
-0.38
1.176
-0.14
1.208
-0.28
1.24
-0.36
1.271
-0.55
1.302
-0.42
1.333
-0.64
1.364
-0.67
1.395
-0.65
1.426
-0.62
1.457
-0.21
δ18O
Distance δ13C
(PDB)
(mm)
(PDB)
-12.70
0.300
-3.63
-12.69
0.350
-3.57
-12.40
0.400
-3.75
-13.37
0.450
-4.00
-12.16
0.500
-3.96
-12.35
0.550
-4.14
-12.36
0.600
-4.37
-12.24
0.650
-4.30
-12.16
0.700
-4.87
-12.85
0.750
-4.90
-13.96
0.800
-4.96
-14.03
0.850
-5.00
-13.08
0.900
-5.18
-13.09
0.950
-5.35
-12.85
1.000
-5.23
-12.99
1.050
-5.49
-13.29
1.100
-5.37
-13.73
1.150
-5.27
-13.75
1.200
-5.15
-13.04
1.250
-5.02
-12.83
1.300
-4.73
-13.62
1.350
-2.14
-13.53
1.400
-1.95
-13.26
1.450
-3.65
-13.25
1.500
-4.74
-13.61
1.550
-4.82
-13.54
1.600
-5.44
-13.72
1.650
-5.56
-13.74
1.700
-5.53
-13.40
1.750
-4.65
-13.45
1.800
-4.45
-13.54
1.850
-3.82
-13.98
1.900
-2.60
-13.99
1.950
-3.57
-14.15
2.000
-4.08
-13.85
2.050
-5.08
-13.98
2.100
-5.48
-13.97
2.150
-5.42
-13.99
2.200
-4.53
-13.97
2.250
-4.74
2.300
-4.52
Crazy Mountains basin
93-27
93-30
0.033
-5.59
-14.52
0.040
-5.92
δ18O
Distance δ13C
(PDB) (mm)
(PDB)
-12.96
0.190
-3.23
-13.42
0.228
-2.69
-13.25
0.266
-2.44
-13.40
0.304
-1.79
-13.35
0.342
-2.10
-13.60
0.380
-1.72
-13.65
0.418
-2.80
-13.61
0.456
-2.70
-13.74
0.494
-2.87
-13.75
0.532
-2.86
-13.28
0.570
-3.09
-13.39
0.608
-3.32
-13.04
0.648
-3.69
-13.16
0.688
-2.91
-13.43
0.728
-3.37
-13.07
0.768
-2.97
-13.01
0.808
-3.24
-12.72
0.848
-2.67
-12.90
0.888
-2.74
-12.54
0.928
-2.47
-12.57
0.968
-1.70
-12.46
1.008
-1.37
-13.33
1.048
-1.51
-13.86
1.088
-2.54
-13.91
1.128
-2.90
-13.58
1.168
-3.57
-13.66
1.208
-3.74
-13.25
1.248
-3.63
-13.66
1.288
-4.45
-13.45
1.328
-3.97
-13.21
1.368
-3.49
-12.94
1.408
-3.42
-13.82
1.448
-3.10
-14.06
1.488
-2.56
-13.94
1.528
-2.02
-14.05
1.568
-1.77
-13.91
1.608
-2.16
-13.70
1.648
-2.58
-14.13
1.688
-2.89
-13.63
1.728
-3.30
-14.45
1.768
-3.53
1.808
-3.34
-12.52
δ18O
(PDB)
-18.60
-18.42
-18.20
-18.00
-18.03
-18.04
-18.36
-18.15
-18.38
-18.65
-18.47
-18.75
-18.78
-18.65
-18.65
-18.66
-18.83
-18.49
-18.67
-18.68
-18.37
-18.05
-18.15
-18.21
-18.42
-18.36
-18.11
-18.24
-18.18
-18.13
-17.87
-17.59
-17.73
-17.48
-17.57
-17.22
-17.78
-17.83
-17.82
-17.94
-18.60
-18.55
65
Table 2.4. (Cont'd)
Distance
(mm)
0.066
0.099
0.132
0.165
0.198
0.231
0.264
0.297
0.330
0.363
0.396
0.429
0.462
0.495
0.528
0.561
0.594
0.627
0.660
0.693
0.726
0.759
0.792
0.825
0.858
0.891
0.924
0.957
0.990
1.023
1.056
1.089
1.122
1.155
1.188
1.221
1.254
1.287
1.320
1.361
1.402
1.443
1.484
1.525
1.566
δ13C
(PDB)
-6.25
-5.38
-6.42
-5.43
-5.45
-5.44
-5.39
-5.34
-6.16
-6.68
-6.64
-5.93
-6.34
-5.84
-6.23
-5.85
-5.38
-5.19
-5.70
-6.50
-6.94
-7.38
-7.50
-6.82
-5.98
-5.51
-5.66
-5.32
-5.02
-4.65
-4.37
-4.39
-4.62
-4.57
-4.60
-4.56
-4.27
-4.95
-6.29
-7.88
-7.50
-7.20
-7.16
-6.87
-6.80
δ18O
Distance δ13C
(PDB) (mm)
(PDB)
-14.46
0.080
-5.71
-14.33
0.120
-5.88
-14.51
0.160
-5.82
-13.89
0.200
-5.86
-14.15
0.240
-5.83
-14.39
0.280
-5.74
-13.59
0.320
-5.71
-13.82
0.360
-5.53
-13.84
0.400
-5.74
-14.07
0.440
-5.88
-13.84
0.480
-5.93
-13.51
0.520
-5.85
-13.48
0.560
-5.82
-14.59
0.600
-5.78
-15.00
0.640
-6.29
-14.85
0.680
-5.96
-14.13
0.720
-6.22
-13.01
0.760
-6.56
-12.87
0.800
-6.82
-12.73
0.840
-6.55
-13.54
0.880
-6.14
-13.88
0.920
-5.84
-13.73
0.960
-5.94
-13.75
1.000
-6.04
-13.73
1.040
-6.19
-14.00
1.080
-6.19
-14.42
1.120
-6.05
-14.55
1.160
-5.56
-14.48
1.200
-5.41
-14.18
1.240
-5.18
-13.99
1.280
-5.21
-13.72
1.320
-5.23
-13.73
1.360
-5.30
-13.48
1.400
-5.37
-13.45
1.440
-5.58
-12.98
1.480
-5.69
-12.81
1.520
-5.69
-12.33
1.560
-5.59
-12.31
1.600
-5.54
-13.04
1.640
-5.66
-13.35
1.680
-5.84
-13.28
1.720
-6.02
-13.40
1.760
-6.46
-13.40
1.800
-6.37
-13.53
1.840
-6.42
δ18O
Distance δ13C
(PDB)
(mm)
(PDB)
-12.26
-12.51
-12.29
-12.25
-12.23
-11.98
-12.09
-11.93
-12.04
-12.05
-11.98
-11.83
-11.98
-12.07
-12.34
-12.08
-12.20
-12.91
-12.98
-12.63
-12.25
-11.79
-11.87
-11.73
-11.59
-11.63
-11.52
-11.55
-11.66
-11.38
-11.41
-11.28
-11.31
-11.32
-11.57
-11.50
-11.50
-11.72
-11.86
-11.80
-11.81
-11.70
-11.69
-11.42
-11.22
δ18O
(PDB)
66
Table 2.4. (Cont'd)
Distance
(mm)
0.066
0.099
0.132
0.165
0.198
0.231
0.264
0.297
0.330
0.363
0.396
0.429
0.462
0.495
0.528
0.561
0.594
0.627
0.660
0.693
0.726
0.759
0.792
0.825
0.858
0.891
0.924
0.957
0.990
1.023
1.056
1.089
1.122
1.155
1.188
1.221
1.254
1.287
1.320
1.361
1.402
1.443
1.484
1.525
1.566
δ13C
(PDB)
-6.25
-5.38
-6.42
-5.43
-5.45
-5.44
-5.39
-5.34
-6.16
-6.68
-6.64
-5.93
-6.34
-5.84
-6.23
-5.85
-5.38
-5.19
-5.70
-6.50
-6.94
-7.38
-7.50
-6.82
-5.98
-5.51
-5.66
-5.32
-5.02
-4.65
-4.37
-4.39
-4.62
-4.57
-4.60
-4.56
-4.27
-4.95
-6.29
-7.88
-7.50
-7.20
-7.16
-6.87
-6.80
δ18O
Distance δ13C
(PDB) (mm)
(PDB)
-14.46
0.080
-5.71
-14.33
0.120
-5.88
-14.51
0.160
-5.82
-13.89
0.200
-5.86
-14.15
0.240
-5.83
-14.39
0.280
-5.74
-13.59
0.320
-5.71
-13.82
0.360
-5.53
-13.84
0.400
-5.74
-14.07
0.440
-5.88
-13.84
0.480
-5.93
-13.51
0.520
-5.85
-13.48
0.560
-5.82
-14.59
0.600
-5.78
-15.00
0.640
-6.29
-14.85
0.680
-5.96
-14.13
0.720
-6.22
-13.01
0.760
-6.56
-12.87
0.800
-6.82
-12.73
0.840
-6.55
-13.54
0.880
-6.14
-13.88
0.920
-5.84
-13.73
0.960
-5.94
-13.75
1.000
-6.04
-13.73
1.040
-6.19
-14.00
1.080
-6.19
-14.42
1.120
-6.05
-14.55
1.160
-5.56
-14.48
1.200
-5.41
-14.18
1.240
-5.18
-13.99
1.280
-5.21
-13.72
1.320
-5.23
-13.73
1.360
-5.30
-13.48
1.400
-5.37
-13.45
1.440
-5.58
-12.98
1.480
-5.69
-12.81
1.520
-5.69
-12.33
1.560
-5.59
-12.31
1.600
-5.54
-13.04
1.640
-5.66
-13.35
1.680
-5.84
-13.28
1.720
-6.02
-13.40
1.760
-6.46
-13.40
1.800
-6.37
-13.53
1.840
-6.42
δ18O
Distance δ13C
(PDB)
(mm)
(PDB)
-12.26
-12.51
-12.29
-12.25
-12.23
-11.98
-12.09
-11.93
-12.04
-12.05
-11.98
-11.83
-11.98
-12.07
-12.34
-12.08
-12.20
-12.91
-12.98
-12.63
-12.25
-11.79
-11.87
-11.73
-11.59
-11.63
-11.52
-11.55
-11.66
-11.38
-11.41
-11.28
-11.31
-11.32
-11.57
-11.50
-11.50
-11.72
-11.86
-11.80
-11.81
-11.70
-11.69
-11.42
-11.22
δ18O
(PDB)
67
Table 2.4. (Cont'd)
Distance δ13C
(mm)
(PDB)
1.607
-6.80
1.648
-6.87
1.689
-6.75
1.730
-6.33
1.771
-6.08
1.812
-5.95
1.853
-5.78
1.894
-6.14
1.935
-5.80
1.976
-5.75
2.017
-5.76
2.058
-6.31
2.099
-6.04
2.140
-6.20
δ18O
(PDB)
-13.69
-13.89
-14.06
-14.23
-14.00
-13.32
-12.99
-13.24
-13.76
-13.84
-13.84
-13.79
-13.64
-13.63
Bighorn basin
93-11
Distance δ13C
(mm)
(PDB)
0.023
-6.00
0.068
-5.63
0.091
-5.93
0.113
-5.91
0.136
-5.81
0.159
-5.86
0.181
-5.42
0.204
-5.25
0.227
-4.73
0.249
-3.90
0.272
-3.00
0.294
-3.20
0.317
-3.57
0.339
-4.05
0.362
-4.78
0.407
-5.60
0.429
-6.35
0.452
-6.60
0.473
-6.47
0.495
-6.49
0.517
-6.33
0.538
-6.12
0.560
-5.99
0.581
-5.91
δ18O
(PDB)
-11.22
-10.43
-10.67
-10.81
-10.85
-10.77
-10.35
-10.17
-9.87
-9.28
-9.07
-9.14
-9.30
-9.46
-9.65
-10.07
-10.51
-10.72
-10.93
-11.10
-11.22
-11.24
-11.44
-11.43
Distance δ13C
(mm)
(PDB)
1.880
-7.27
1.920
-7.84
1.960
-7.51
2.000
-6.80
2.040
-6.35
2.080
-6.01
2.120
-5.78
2.160
-5.95
2.200
-6.26
2.240
-6.92
2.280
-6.68
2.321
-6.42
2.362
-6.22
2.403
-6.17
2.444
-6.00
2.485
-6.22
δ18O
Distance δ13C
(PDB)
(mm)
(PDB)
-11.09
-11.08
-11.11
-11.11
-11.20
-11.20
-10.99
-10.92
-11.17
-11.77
-11.31
-11.06
-11.02
-11.32
-11.38
-11.41
93-30
Distance δ13C
(mm)
(PDB)
0.022
-4.52
0.044
-4.26
0.067
-3.95
0.092
-3.25
0.118
-4.24
0.194
-4.99
0.245
-4.75
0.271
-4.24
0.323
-3.72
0.349
-3.98
0.428
-4.62
0.506
-5.33
0.581
-5.53
0.631
-5.95
0.655
-6.28
0.730
-6.14
0.780
-6.04
0.805
-5.60
0.879
-5.46
0.954
-5.43
1.029
-5.49
1.055
-5.93
1.080
-6.29
1.106
-6.00
δ18O
(PDB)
-9.73
-9.43
-9.28
-8.11
-8.01
-8.22
-9.10
-9.53
-9.61
-10.10
-10.17
-10.30
-10.56
-10.70
-10.77
-10.92
-10.89
-10.91
-11.28
-11.33
-10.91
-10.23
-8.76
-7.96
δ18O
(PDB)
68
Table 2.4. (Cont'd)
Distance δ13C
(mm)
(PDB)
0.603
-6.02
0.624
-6.21
0.646
-6.66
0.667
-6.91
0.687
-7.31
0.708
-6.43
0.729
-7.30
0.750
-7.55
0.793
-7.48
0.814
-7.20
0.835
-7.38
0.857
-7.23
0.878
-7.27
0.899
-7.14
0.921
-7.08
0.942
-6.95
0.964
-6.44
0.985
-6.05
1.006
-5.50
1.029
-4.59
1.053
-4.65
1.076
-4.98
1.099
-5.70
1.122
-5.75
1.145
-5.85
1.169
-5.86
1.192
-5.86
1.215
-5.96
1.238
-5.92
1.260
-5.78
1.283
-5.85
1.328
-6.12
1.351
-6.05
1.396
-6.41
1.419
-6.24
1.485
-6.14
1.550
-6.20
1.572
-5.95
1.594
-5.80
1.615
-5.15
1.637
-4.80
1.659
-4.15
1.680
-4.03
1.702
-3.41
1.724
-3.76
δ18O
(PDB)
-11.53
-11.33
-11.09
-11.22
-11.31
-11.14
-10.95
-11.07
-11.30
-11.09
-11.27
-11.03
-10.89
-10.45
-10.51
-10.55
-10.30
-10.08
-9.74
-9.59
-9.51
-9.67
-9.91
-10.36
-10.47
-10.63
-10.90
-11.15
-11.51
-11.55
-11.63
-12.08
-11.91
-12.07
-11.59
-11.40
-11.29
-11.12
-10.93
-10.69
-10.54
-10.12
-10.08
-9.39
-9.88
Distance δ13C
(mm)
(PDB)
1.131
-5.55
1.156
-5.24
1.182
-4.92
1.207
-4.84
1.233
-5.17
1.259
-5.82
1.285
-6.00
1.312
-6.17
1.338
-6.06
1.365
-5.84
1.391
-5.56
1.417
-5.67
1.442
-5.66
1.466
-5.44
1.490
-5.39
1.514
-6.51
1.538
-7.25
1.562
-7.53
1.587
-7.32
1.611
-6.44
1.659
-6.22
1.707
-6.39
1.732
-6.69
1.758
-6.68
1.784
-6.46
1.811
-6.63
1.837
-8.01
1.864
-8.40
1.888
-8.23
1.912
-8.05
1.936
-7.62
1.960
-7.24
1.984
-6.78
2.008
-6.29
2.057
-6.18
2.081
-6.28
δ18O
(PDB)
-7.64
-7.68
-7.83
-8.19
-8.85
-9.32
-9.53
-9.63
-10.10
-10.16
-10.42
-10.56
-10.71
-10.70
-10.43
-10.74
-10.86
-10.87
-11.14
-11.56
-11.68
-11.37
-11.21
-11.06
-10.65
-9.55
-9.38
-9.27
-9.76
-9.96
-10.84
-10.77
-11.56
-11.44
-11.40
-11.22
18
Distance δ13C
δ O
(mm)
(PDB) (PDB)
69
Table 2.4. (Cont'd)
Distance δ13C
(mm)
(PDB)
1.747
-4.52
1.792
-5.42
1.815
-5.66
1.838
-6.00
1.861
-5.88
1.883
-5.96
1.906
-5.88
1.929
-5.61
1.952
-5.19
1.976
-5.04
1.999
-5.17
2.023
-5.02
2.047
-5.14
2.069
-5.46
2.091
-6.10
2.114
-6.57
2.136
-6.81
2.158
-6.87
2.202
-6.77
2.224
-6.29
2.246
-5.41
2.268
-4.90
2.290
-4.85
2.313
-4.89
2.335
-5.52
2.357
-5.47
2.379
-5.65
δ18O
(PDB)
-10.16
-10.33
-10.64
-11.05
-11.24
-11.28
-11.40
-11.39
-11.09
-10.76
-10.86
-10.68
-10.89
-11.06
-11.64
-11.84
-11.79
-11.49
-11.23
-11.01
-10.56
-10.31
-10.50
-10.62
-11.14
-10.92
-10.71
Washakie basin
93-3
Distance δ13C
(mm)
(PDB)
0.000
-2.84
0.041
-2.58
0.082
-2.55
0.123
-2.56
0.164
-2.71
0.205
-2.81
0.246
-3.03
0.287
-3.03
0.328
-3.00
0.369
-3.21
0.410
-3.45
0.451
-3.20
0.492
-3.15
δ18O
(PDB)
-5.55
-5.70
-5.81
-5.45
-5.75
-5.70
-5.55
-5.45
-5.26
-4.80
-4.40
-4.34
-4.38
Distance δ13C
(mm)
(PDB)
δ18O
(PDB)
93-5
Distance δ13C
(mm)
(PDB)
0.037 -7.61
0.074 -7.87
0.111 -7.93
0.148 -7.97
0.185 -7.96
0.222 -7.93
0.259 -8.14
0.296 -8.18
0.333 -8.03
0.370 -7.71
0.407 -7.60
0.444 -7.64
0.481 -7.74
δ18O
(PDB)
1.26
1.16
1.40
1.36
1.73
1.30
1.62
1.87
1.08
1.65
1.14
1.82
1.87
Distance δ13C
(mm)
(PDB)
δ18O
(PDB)
70
Table 2.4. (Cont'd)
Distance δ13C
(mm)
(PDB)
0.533
-3.07
0.574
-3.02
0.615
-3.12
0.656
-3.23
0.697
-2.58
0.738
-2.39
0.779
-2.45
0.820
-2.58
0.861
-2.59
0.902
-2.85
0.943
-3.25
0.984
-3.35
1.025
-3.60
1.066
-3.58
1.107
-3.46
1.148
-3.30
1.189
-3.25
1.230
-3.16
1.271
-2.92
1.312
-3.03
1.353
-2.67
1.394
-2.74
1.435
-2.65
1.476
-2.74
1.517
-2.73
1.558
-3.15
1.599
-2.99
1.640
-3.05
1.681
-3.04
1.722
-3.03
1.763
-3.00
1.804
-3.29
1.845
-3.41
1.886
-3.64
1.927
-3.69
1.968
-3.69
2.009
-3.97
2.050
-3.43
2.091
-3.24
2.132
-3.33
δ18O
(PDB)
-4.68
-5.09
-5.65
-6.27
-6.03
-6.12
-5.98
-5.82
-5.60
-5.51
-5.22
-4.96
-4.62
-4.34
-4.11
-4.27
-4.09
-4.22
-4.89
-4.91
-5.35
-5.39
-5.69
-5.99
-5.95
-6.69
-6.42
-6.63
-6.70
-6.74
-6.60
-6.89
-7.07
-6.98
-6.86
-6.69
-6.37
-6.38
-6.25
-6.39
Distance δ13C
(mm)
(PDB)
0.518 -7.99
0.554 -8.09
0.590 -8.28
0.626 -8.58
0.662 -8.55
0.698 -8.13
0.734 -7.72
0.770 -7.48
0.806 -7.24
0.842 -7.14
0.878 -6.93
0.950 -7.06
0.990 -6.31
1.030 -6.43
1.070 -6.28
1.110 -6.41
1.150 -6.67
1.190 -6.94
1.230 -7.65
1.270 -7.86
1.310 -8.29
1.350 -8.53
1.390 -8.72
1.430 -8.65
1.470 -8.57
1.510 -8.61
1.550 -8.38
1.590 -8.05
1.630 -7.82
1.670 -7.42
1.710 -6.84
1.750 -6.33
1.790 -6.35
1.830 -6.44
1.870 -6.68
1.910 -7.12
1.950 -7.54
1.990 -7.76
2.030 -8.26
2.070 -8.48
δ18O
(PDB)
1.68
1.39
1.97
1.18
1.08
1.24
1.19
1.07
1.62
1.80
1.34
1.37
2.39
2.84
1.62
2.38
1.69
1.65
2.03
0.83
1.80
2.00
1.91
1.38
2.59
2.44
1.79
1.34
2.18
1.16
1.85
1.46
2.56
1.32
2.35
2.04
1.71
1.78
1.42
1.24
Distance δ13C
(mm)
(PDB)
δ18O
(PDB)
71
CHAPTER 3: WIDESPREAD BASEMENT EROSION IN LATE PALEOCENEEARLY EOCENE IN THE LARAMIDE ROCKY MOUNTAINS INFERRED
FROM 87SR/86SR RATIO OF BIVALVE FOSSILS
ABSTRACT
We use reconstructions of the 87Sr/86Sr ratios of late Cretaceous-early Cenozoic river
water from fossil shells in six basins of the Rocky Mountains to trace the erosion of
Precambrian basement cores in the Laramide ranges. The
87
Sr/86Sr ratios and Sr
concentration of modern river water in the Rocky Mountains are controlled by river
bedrock lithology. Weathering of Precambrian silicate rocks in the cores of Laramide
ranges produce high
87
Sr/86Sr ratios of highland rivers. Weathering of Paleozoic and
Mesozoic carbonates along the basin margins reduces the 87Sr/86Sr ratios and increases Sr
concentration of rivers as they flow basinward. Lowland rivers that head in Precambrian
basement mostly have
87
Sr/86Sr ratios > 0.711, whereas rivers confined to or with very
long reaches in basins have
87
Sr/86Sr ratios between 0.709 and 0.711. River water δ18O
values do not change in response to changes in catchment elevation.
Our results from fossil shell contextualized by our modern studies show that
Proterozoic low-grade metamorphic carbonates in the Belt-Purcell Supergroup were not
exposed in the Canadian Rocky Mountains during late Cretaceous-early Paleocene, and
that Precambrian silicate basement rock was extensively exposed and eroded during late
Paleocene-early Eocene in the Laramide Rocky Mountains. The widespread basement
72
erosion in late Paleocene-early Eocene is mainly a result of tectonic exhumation of
Laramide ranges, and may have been intensified by the wet and warm global climate.
INTRODUCTION
The North American Cordilleran orogenic belt stretches more than 5,000 km from
northern British Columbia to New Mexico in western North America (Burchfiel et al.,
1992; Dickinson, 2004). The orogenic belt comprises a mainly Cretaceous magmatic belt
in the west and the eastward verging Sevier fold-thrust belt in the western U.S.A.
(Armstrong, 1968). East of the Sevier belt in southwestern Montana, Wyoming,
Colorado, Utah, Arizona, and western New Mexico lies the Laramide province, a region
of Precambrian basement-involved uplifts that are bounded by moderately dipping thrust
faults and intervening sedimentary basins (Dickinson et al., 1988; Erslev, 1993).
Although the Sevier belt contains local basement-involved structures (e.g., Camilleri et
al., 1997; DeCelles, 2004), the main locus of widespread Precambrian basement
exposures during Late Cretaceous and early Cenozoic time was in the Laramide province.
Formation of the Laramide uplifts by the northeast-southwest compression related to
flat subduction of the Farallon plate underneath North America between ~80 and 40 Ma
(Dickinson and Snyder, 1978; Bird, 1998; Saleeby, 2003) is consistent with patterns of
magmatism (Coney and Reynolds, 1977; Constenius, 1996) and, by analogy, with
modern flat-slab subduction in western South America (Jordan et al., 1983; Wagner et al.,
2005). However, the exact mechanisms of crustal shortening and thickening in the region
remain poorly understood, partly because of a lack of regionally integrated ages for the
exhumation of Laramide uplifts.
73
One approach to examining the regional time-space pattern of deformation in the
Laramide region is documentation of regional scale patterns of erosional exhumation of
the Laramide uplifts. Data from thermochronologic studies of the Laramide region and
sedimentary records in the intervening basins have been used to estimate the timing of
exhumation of several Laramide uplifts. The apatite fission track cooling history of the
Beartooth uplift shows that 4-8 km of exhumation occurred during the Laramide event,
and ~4 km of exhumation occurred since late Miocene-Pliocene (Omar et al., 1994). The
two stages of exhumation are also found in apatite fission track and (U-Th)/He
thermochronology studies of the Bighorn Mountains, Wind River Range, and Black Hills
(Cerveny and Steidtmann, 1993; Strecker, 1996; Crowley et al., 2001; Peyton et al.,
2007; Carrapa and DeCelles, unpublished data). Local exhumation during the Laramide
event revealed from thermochronologic data is consistent with unroofing sequences
recorded in syntectonic deposits in the sedimentary basins (e.g. Graham et al., 1986;
DeCelles et al., 1987; Dickinson et al., 1988; DeCelles et al., 1991; Steidmann and
Middleton, 1991; Seeland, 1992; Hoy and Ridgway, 1997). Although these studies reveal
a reasonably consistent pattern of Laramide uplift, the temporal resolution is poor and the
thermochronologic approach does not directly measure the timing of basement exposure
insofar as local geothermal and rock cover conditions may be quite variable at the spatial
scale of the Laramide region.
Geochemical tracers, especially strontium isotope ratios (87Sr/86Sr), have been widely
applied to provenance studies in sedimentary basins (e.g. Basu et al., 1990; McLennan et
al., 1993; Quade et al., 1997; Rhodes et al., 2002; Carroll et al., 2008; Davis et al., 2008;
74
Gierlowski-Kordesch et al., 2008). This approach requires that sediment source terranes
have distinct
87
Sr/86Sr ratios and Sr concentrations, as they are the first-order control of
the 87Sr/86Sr ratios of river water (Palmer and Edmond, 1992; Galy et al., 1999; Bickle et
al., 2003; English et al., 2003; Tipper et al., 2006). Mineral weatherability also plays an
important role in river water Sr geochemistry. The Precambrian basement in the
Laramide region has high
87
Sr/86Sr ratios because of its high Rb content and great
antiquity, whereas ratios of Phanerozoic marine carbonate and siliclastic sediments are
much lower. Similarly, streams flowing through Precambrian basement rock should have
high
87
Sr/86Sr ratios. If these streams or rivers reach the lowlands, their high
87
Sr/86Sr
ratios should be archived in carbonate phases that once grew in the rivers. The sister
study of this paper has addressed the paleo-elevation of Laramide ranges during Late
Cretaceous and early Eocene time by studying the δ18O values of fossil Unionid bivalves
(Fan and Dettman, submitted). In this paper, we reconstruct the 87Sr/86Sr ratios of ancient
river water during late Cretaceous-early Eocene time from analysis of 87Sr/86Sr ratios of
the same fossil bivalves collected in six Laramide basins. By comparing the
87
Sr/86Sr
ratios of ancient river water with those of the modern river system in the region, we
reconstruct the pattern of the basement exhumation during the development of the
Laramide basement-involved uplifts.
GEOLOGICAL SETTING AND STRONTIUM SOURCE TERRANES
The cores of the basement uplifts in southwestern Montana and Wyoming are mostly
composed of Achaean gneisses of the Wyoming craton, which includes mainly
orthogneisses and minor metavolcanic-metasedimentary rocks older than 2.6-2.7 Ga
75
(Frost and Frost, 1993) (Fig. 3.1). In southwestern Wyoming and northern Colorado, the
cores of the basement uplifts are assemblages of highly deformed early Proterozoic
metavolcanic and metasedimentary supracrustal rocks intruded by numerous plutons,
which were accreted onto the Wyoming craton along the Cheyenne belt at ~1.86 Ga
(Frost and Frost, 1993; Foster, 1999). Thick middle Proterozoic lower greenschist-grade
siliclastic and minor carbonate strata of the Belt-Purcell Supergroup are widely exposed
in eastern Idaho, western Montana and Southern Alberta; these rocks were deposited
along the northwestern margin of the North American craton in the Belt basin (Cressman,
1989). In Nevada and Utah middle to early late Proterozoic strata of the Uinta Mountain
Group and the Big Cottonwood Formation accumulated along the rifted western margin
of Laurentia and in failed rift arms that extend eastward into the North American craton
(Sears et al., 1982; Dehler et al., 2005). The 87Sr/86Sr ratios of the Precambrian crystalline
basement rocks and metamorphic carbonate rocks fall in the range of 0.710-1.000 (Hills
et al., 1968; Naylor et al., 1970; Crittenden and Peterman1975; Nelson and DePaolo,
1984; Walker et al, 1986; Koesterer et al., 1987; Wooden and Mueller, 1988; Geist et al.,
1990; Hall and Veizer, 1999).
During Paleozoic and early Mesozoic, a succession of ~1.5 km thick marine
carbonate rocks interlayerd with thin clastic sedimentary rocks accumulated in the
western interior of North America (Keefer, 1970). From the Triassic onwards,
depositional environments changed from dominantly shallow marine to nonmarine.
During Late Jurassic and mid- to Late Cretaceous, a broad foreland basin developed east
of the Sevier fold-thrust belt and filled with up to ~6 km of mainly clastic marine and
76
nonmarine strata (DeCelles, 2004). These Paleozoic and Mesozoic marine rocks–largely
carbonates–are now exposed along the margins of the Laramide basins. Globally,
unaltered
87
Sr/86Sr ratios of marine carbonate range from 0.706 to 0.7095 (Veizer et al.,
1999). Early Cenozoic volcanic rocks are locally distributed in northwest Wyoming,
southwest Montana and Idaho, and the 87Sr/86Sr ratios of volcanic rocks in the Absaroka
Volcanic Field and Challis Volcanic Field are 0.7051-0.7062 (Hiza, 1999; Dostal et al.,
2003).
STUDY AREA AND FIELD SAMPLING
In this study fossil bivalves were collected from Cretaceous and lower Cenozoic
strata in the foreland basin of Alberta, and the western Williston basin, Crazy Mountains
basin, northern Bighorn basin, Powder River basin and southwestern Washakie basin
(Fig. 3.1; Fig. 3.2). The Crazy Mountains, Bighorn, Powder River and Washakie basins
are bounded by Laramide-age basement-cored uplifts. We collected fossil shells from the
paleo-floodplain deposits in the Bear, Lebo, and Melville Formations in the Crazy
Mountains basin; Fort Union and Willwood Formations in the Bighorn basin; and Tongue
River Member of Fort Union and Wasatch Formations in the Powder River basin. Fossil
samples in the Washakie basin were collected from the Luman Tongue Member in the
Vermillion Creek area, which accumulated during the depositional transition from fluvial
system to the early stages of Lake Gosiute (Sklenar and Anderson, 1985). In the Alberta
foreland basin, fossil samples were collected from floodplain deposits of late Campanian
and Maastrichtian age. In the Williston basin fossil shell samples were collected from
fluvial sediments in the Hell Creek and Tullock Formations of Late Cretaceous and early
77
Paleocene age. Sample ages were assigned on the basis of radiometric ages,
paleomagnetic ages and intrabasin mammalian biostratigraphic correlation with
paleomagnetic stratigraphy (Fan and Dettman, submitted).
We collected a total of 38 modern river water samples for analysis of δ18O and δD
values, 87Sr/86Sr ratios, and Ca, Rb, and Sr concentrations. We targeted tributaries to the
Wind River and Powder River for modern river water sampling. Paired samples were
collected in streams and rivers draining highland Precambrian silicate rocks and in
basinal lowland areas draining Paleozoic-Mesozoic marine carbonates (Fig. 3.3). Otter
Creek is the only stream in our collection that rises in basinal lowlands; it drains early
Cenozoic sedimentary rocks only, and is probably fed by local precipitation and
groundwater. Water samples were passed through a disposable 0.2 µm filter, and
collected in acid-washed polyethylene bottles. We also collected two modern Unionid
bivalves from Tongue River to examine seasonal variation of
87
Sr/86Sr ratios and δ18O
values.
ANALYTICAL METHODS
The δ18O values of water samples were analyzed by a H2O-CO2 equilibrator attached
to a dual inlet mass spectrometer (Delta-S). The δD values of water were analyzed by an
automated chromium reduction device (H-Device) attached to the same mass
spectrometer. The values were corrected based on internal lab standards, which are
calibrated through SMOW and SLAP. The analytical precision is 0.08‰ and 0.1‰,
respectively (1σ). The sampling and analytical methods for obtaining δ18O values of
bivalve samples are described in Fan and Dettman (submitted).
78
Aragonite shells used in this study are all unaltered based on physical appearance,
verified by cathodoluminescence microscopy and X-ray diffraction for a subset of the
samples. X-ray diffraction was performed with a Bruker D8 Advance Diffractometer
using Cu Kα radiation.
For
87
Sr/86Sr ratio analysis, shell fragments (~50 mg) were separated from hand
samples and cleaned of adhering detritus and any calcite overgrowths by scraping under a
microscope, and 15-30 ml of water samples were dried in Teflon beaker on hotplate.
Water sample evaporates and shell fragments were then dissolved in 3.5 M ultrapure
HNO3. The resulting solution is passed through ion-specific resin to separate strontium.
The
87
Sr/86Sr ratios were measured on a Micromass Sector 54 thermal ionization mass
spectrometer by loading strontium onto single Ta filaments with phosphoric acid. Thirtyone analyses of NBS 987 standard in the period of sample analyses produced an average
87
Sr/86Sr ratio of 0.71023±0.00002 (1σ). Element concentration was analyzed with 5%
uncertainty by inductively coupled plasma mass spectrometry (ICP-MS). Using the
measured
87
Sr/86Sr ratio, Sr and Rb concentrations of the seven representative shell
samples, we recalculated the initial 87Sr/86Sr ratio with the radioactive decay equation to
the depositional ages (Table 1). Such adjustment is negligible because of the high
strontium and low rubidium concentrations in shell aragonite.
RESULTS
Modern River Water and Shell
The δ18O values of stream water in the Wind River and Powder River tributaries
varies between -18.7‰ and -10.5‰. The rivers draining highland silicate rocks have the
79
lowest δ18O values, and the values remain unchanged after these rivers flow into the
basins (Table. 2).
The
87
Sr/86Sr ratio of stream water varies between 0.70842 and 0.73996. Water
samples draining silicate basement have high
87
Sr/86Sr ratios, and these ratios decrease
once the river flows through Phanerozoic carbonates (Fig. 3.3, Table. 2). The
87
Sr/86Sr
ratio of Otter Creek, which drains only lower Cenozoic sedimentary rocks, is 0.70929.
This
87
Sr/86Sr ratio is slightly higher than the upper limit of the ratio for all marine
limestone (Veizer et al., 1997) of about 0.7095. Large rivers, such as Wind River, Powder
River and its large tributaries, the North Fork, South Fork, Middle Fork and Tongue
Rivers, have relatively low and uniform 87Sr/86Sr ratios of 0.7111±0.0008.
The Ca, Sr, Rb concentrations of stream waters vary between 0.06 and 4.71 mmol/L,
0.06 and 32.2 µmol/L, 0.01 and 123.57 nmol/L respectively. As expected, the Sr
concentration of rivers draining only silicate rocks is low compared to the rivers with
carbonates in the drainage. Downstream, the
87
Sr/86Sr ratio of the Wind River and
Powder River tributaries decreases as the Sr concentration increases , which coincides
with the change from crystalline silicates to carbonates in the watershed (Fig. 3.3, Table
2). No correlation exists between the river water δ18O values and 87Sr/86Sr ratios, whereas
the correlation between Sr concentration and 87Sr/86Sr ratios generally follows a two endmember mixing line between silicate-dominated and carbonate-dominanted weathering
(Table 2; Fig. 3.4).
The δ18O value of the modern shell collected in the Tongue River varies between 15.4‰ and -17.5‰ (PDB) seasonally, which is consistent with the δ18O value (-16.4‰,
80
SMOW) of Tongue River water and rapid shell-growth temperature in the late spring and
early summer (20-25℃) (Grossman and Ku, 1986; Kohn and Dettman, 2007). The
87
Sr/86Sr ratio of the modern shell varies between 0.70965 and 0.71017 seasonally (Fig.
3.4), very similar
87
Sr/86Sr ratios as Tongue River water (0.70987).This suggests that
there is no significant strontium isotope fractionation between shell aragonite and habitat
water.
Fossil Shell
The
87
Sr/86Sr ratios of shell fossils are in the range of 0.70656-0.71434. The lowest
ratios come from the Alberta foreland Crazy Mountains basins. Shell fossils from the
Bighorn and Williston basins have intermediate 87Sr/86Sr ratios (0.709-0.711); shells from
the Powder River basin show a large range of
87
Sr/86Sr ratios (0.709-0.714); and shells
from the Washakie basin have high and relatively uniform 87Sr/86Sr ratios (0.713-0.714).
The Ca, Sr, and Rb concentrations of shell aragonite vary between 9.48 and 11.74
mmol/g, 0.02 and 3.26 µmol/g, 2.93 and 8.80 nmol/g respectively. Ancient river Sr/Ca
ratios can be estimated by using the Sr/Ca ratio of the fossil shell and a distribution
coefficient that relates the Sr/Ca ratios between shell aragonite and habitat water. This
distribution coefficient is influenced by mineralogy, physiology, temperature, and shell
growth rate. The distribution coefficient is generally in the range 0.24±0.07 for shell
aragonite based on the literature review in Holmden and Hudson (2003).
The δ18O values of ancient river water are calculated from the δ18O values of shell by
using an empirically determined relationship between the δ18O values of modern shell
81
and river water in temperate climates, and corrected for changes in paleolatitude and in
sea water δ18O values (Kohn and Dettman, 2007; Fan and Dettman, submitted).
DISCUSSION
Modern River System
The
87
Sr/86Sr ratio of river water is controlled mainly by the
87
Sr/86Sr ratio of the
rocks that interact with water at or near surface and the relative contribution of Sr from
each type of rock (Palmer and Edmond, 1992; Galy et al., 1999; Bickle et al., 2003;
English et al., 2003). Three main types of source rock, Precambrian basement,
Phanerozoic carbonates, and Eocene volcanic rocks, are exposed in the river water
sampling area. The modern rivers that we sampled do not flow through Eocene volcanic
rocks, and Sr produced by weathering of windblown Eocene volcanic material in the river
catchments should be negligible. Therefore, Precambrian crystalline rocks and
Phanerozoic carbonates are the two major sources that control the 87Sr/86Sr ratios and Sr
concentration of modern river water.
The Wind River and Powder River tributaries display no downstream change in δ18O
values, suggesting basinal rivers with low δ18O values are dominated by precipitation
from the surrounding highlands. The seasonal δ18O value variation of modern shell from
the Tongue River mimics that of the river water, with the lowest δ18O values reflecting
dominant surface runoff of late spring snowmelt from the Bighorn Mountains, and the
highest values associated with addition of basinal summer precipitation (Coplen and
Kendall, 2000) (Fig.3.5).
82
The seasonal variation of the modern shell
δ18O values (Fig. 3.5). Three
87
87
Sr/86Sr ratios follows the variations of
Sr/86Sr ratios representing late spring, summer, fall-early
spring run-off, show seasonal decreases of up to 0.0003, with the highest
87
Sr/86Sr ratio
associated with the lowest δ18O values. During late spring, the basinal river water is
largely fed by snowmelt from surrounding highlands where silicate rocks dominate river
catchments. Such snowmelt has the lowest δ18O values and highest
87
Sr/86Sr ratios. In
summer, the basinal precipitation (summer monsoon) contributes to the river water,
which increases the δ18O values of the river water, and decreases the
87
Sr/86Sr ratios as
carbonate has faster dissolution kinetics. In fall and early spring, both the δ18O values and
87
Sr/86Sr ratios are intermediate as the water is a mixture of highland snowmelt and
basinal precipitation in the form of surface runoff and/or groundwater. These
relationships are also seen in seasonal isotopic variation of the Clarks Fork of the
Yellowstone River (Horton et al., 1999).
Sr isotope water chemistry of rivers draining the two main rock types–carbonates and
crystalline basement rocks– in our study area fits a mixing model. In the model, we use
the Sr water chemistry of Otter Creek to represent waters draining carbonates only, and
Torrey Creek to represent drainage of silicates only (Fig. 3.4). We chose a range of
87
Sr/86Sr ratios as the end member ratio of waters draining only Precambrian basement
rocks varies considerably. The mixing model using these end-members suggests the Sr
flux of most Wind River and Powder River tributaries in the highlands is mainly from
silicate weathering (>95%) with the 87Sr/86Sr ratio between 0.76 and 0.90, and Sr flux in
lowland rivers is dominated by carbonate weathering (Fig. 3.5). The
87
Sr/86Sr ratios
83
(0.710±0.01) of rivers confined to basins and large rivers originating in highland silicate
rocks with long residence times in Tertiary deposits are dominated by weathering of
carbonate rocks in catchments. These ratios are consistent with those of the modern
streams that drain Paleozoic and Mesozoic carbonate rocks in the front of the Sevier
thrust belt in Utah (Hart et al., 2004; Gierlowski-Kordesch et al., 2008).
Our study of modern rivers shows that weathering of silicate rocks is only clearly
indicated where the
87
Sr/86Sr ratio of rivers in the Laramide basins is higher than 0.711.
This cut-off is higher than the average
87
Sr/86Sr ratios of Phanerozoic carbonates,
probably because basement rocks buried near surface in the source terrane can raise the
87
Sr/86Sr ratio of groundwater that will flow into local rivers, and because Sr can be
recycled from Proterozoic sediment with high
87
Sr/86Sr ratios. Proterozoic sedimentary
rocks are not exposed in Wyoming, but they are abundant in parts of the Sevier thrust
belt. Moreover, Proterozoic sedimentary rocks were recycled into the foreland basin.
Ancient River System and Basement Erosion
Powder River Basin
The seasonal variation deduced from shell transect sampling of the δ18O values of the
ancient rivers in the Powder River basin in late Paleocene-early Eocene shows that there
are three types of rivers: 1) Type I rivers with high δ18O values and low seasonal
amplitude that originated at low elevation with a constant water source throughout the
year; 2) Type II rivers with relatively low δ18O values and high seasonal amplitude that
originated at high elevation with different sources of water seasonally; and 3) Type III
rivers with low δ18O values and low seasonal amplitude are originated at high elevation
84
with a constant source throughout the year. The average paleoelevation of the highlands
surrounding the Powder River basin in late Paleocene-early Eocene is thought to have
been ~4.5 km and the highlands are most likely the Bighorn Mountains and/or Black
Hills (Fan and Dettman, submitted).
The variation of the
87
Sr/86Sr ratios of ancient river water defines the bedrock types
present in river catchments (Fig. 3.6A, B). The occurrence of high 87Sr/86Sr ratios of late
Paleocene-early Eocene river water in the Powder River basin suggests that Precambrian
basement rocks were exposed in the river catchments. This is consistent with the high
feldspar content in late Paleocene channel-fill sandstones in the Powder River basin, and
the high basement clast content in early Eocene Kingsbury Conglomerates in the eastern
flank of the Bighorn Mountains (Whipkey et al., 1991; Hoy and Ridgeway, 1997) (Fig.
3.2). The 87Sr/86Sr ratios of Type I rivers in the Powder River basin are lower than 0.711.
Based on the modern relationships previously discussed, we suggest that these
watersheds did not contain Precambrian silicate rocks, and carbonate weathering
dominated the river water 87Sr/86Sr ratios. The 87Sr/86Sr ratios of Type II rivers are higher
than 0.711, suggesting that these rivers drained silicate rocks in the highlands. Such
paleorivers are most similar to small modern rivers in our dataset with highland sources.
The
87
Sr/86Sr ratios of Type III rivers are ~0.711, suggesting silicate weathering
overprinted by carbonate weathering. These rivers are most likely large rivers similar to
the modern Wind River, Tongue River, and Middle Fork of the Powder River, which rise
in the highlands, merge with several more locally drained tributaries en route to the basin,
and then flow over long distances in basin sediment.
85
Washakie Basin
The high and large range of δ18O values of the fresh water lake in the Washakie basin
during early Eocene suggests that the regional relief was at most 1-2 km (Fan and
Dettman, submitted). Such relief very likely existed during early Eocene time between
the hinterland of the Sevier thrust belt and its foreland basin in Wyoming (DeCelles,
1994; 2004). However, we cannot rule out the possibility that local relief of 1-2 km
between the Laramide ranges and Washakie basin.
The high 87Sr/86Sr ratios of the lake water in the Washakie basin (0.713-0.714) define
the water drainage lithology, and therefore can help to distinguish the area of high
elevation. Lake water with high δ18O values and high 87Sr/86Sr ratios is also observed in
the Uinta basin and Green River basin in early Eocene (Rhodes et al., 2002; Carroll et al.,
2008; Davis et al., 2008). The indistinguishable water isotope chemistry in the three
basins is explained by a hydrological connection between the Lake Gosiute in the Green
River basin and Washakie basin, and Lake Uinta in the Uinta basin (Davis et al., 2008).
Such high
87
Sr/86Sr ratios during the early Eocene can only be explained by lake water
that was fed by surface runoff draining Precambrian basement rock (Fig. 3.6A, C).
Weathering of Precambrian basement rocks in the western hinterland of the Sevier
thrust belt seems unlikely as an dominant strontium source in Lake Goshuite and Unita.
The Precambrian rocks that would potentially influence the
87
Sr/86Sr ratios of Lake
Gosiute and Uinta are exposed in the Wasatch culmination in northeastern Utah (Yonkee
et al., 1992; DeCelles, 2004). Modern rivers draining the Wasatch Range have
87
Sr/86Sr
ratios up to 0.714 (Hart et al., 2004). However, it is very unlikely that the strontium from
86
Wasatch culmination dominates the water chemistry of both Lake Gosiute and Uinta in
early Eocene because: 1) the area of Precambrian crystalline basement exposed in the
culmination is small (Yonkee et al., 1992); 2) Proterozoic sediment exposed in Utah is
mostly quartzite, which is low in Sr concentration (Yonkee et al., 1992; Condie et al.,
2001); 3) during the eastward propagation of the Sevier thrust system, thick Phanerozoic
carbonates were stacked in the Wasatch culmination and exhumed in the thrust front,
which could have overprinted the high
87
Sr/86Sr ratios produced by silicate weathering
(DeCelles, 1994; 2004); and 4) Precambrian crystalline basement had been exhumed in
the Sevier hinterland before late Paleocene (DeCelles, 1994), but it did not influence the
strontium geochemistry of foreland river water as the late Paleocene fluvial sediments in
the Uinta basin have low 87Sr/86Sr ratios (0.7095-0.7100) (Davis et al., 2008).
Therefore, we favor the basement cores of the Laramide ranges as the source for the
high
87
Sr/86Sr ratios in Lake Gosiute and Uinta during early Eocene time. Precambrian
basement rocks are currently distributed in the Uinta Mountains, Wind River Range,
Granite Mountains, Sierra Madre Uplift and Front Range surrounding the Green River,
Washakie and Uinta basins. Unfortunately, there are no robust paleocurrent data available
pointing to the source of the lake water during the deposition of the Luman Tongue
Member. The basement erosion in early Eocene in southwestern Wyoming is consistent
with the high Precambrian basement clast content in conglomerates Richards Mountains
Conglomerates in southern Green River basin, which is derived from the Uinta
Mountains (Crews and Ethridge, 1993), and the Wind River Formation in northwestern
87
Wind River basin, which is from the Wind River Range (Winterfeld and Conard, 1983
and our unpublished data) (Fig.3.2).
Other Basins
Rivers draining the Canadian Rocky Mountains at present have high
87
Sr/86Sr ratios
(0.711-0.758) and low Sr/Ca ratios (0.19-2.18 µmol/mol) (Millot et al., 2003). The
elevated 87Sr/86Sr ratios are controlled by weathering Proterozoic low-grade metamorphic
carbonates in the Belt-Purcell Supergroup in the Rocky Mountains, a situation very
similar to influence of old carbonate rock weathering in the Lesser Himalayan terranes of
India and Nepal (Galy et al., 1999; English et al., 2003; Millot et al., 2003). The
paleoflow directions in the late Cretaceous Alberta foreland basin, late Cretaceous-early
Paleocene Williston basin, and early Paleocene Crazy Mountains basin are east to
southeast (Cherven and Jacob, 1985; Eberth and Hamblin, 1993; Borrell and Hendrix,
2000). The low 87Sr/86Sr ratios (<0.709) and low Sr/Ca ratio of the ancient river water in
these basins suggests that carbonate weathering dominates the river water Sr chemistry,
and that the thick middle Proterozoic Belt-Purcell Supergroup was not widely exposed in
eastern Idaho and Alberta during late Cretaceous-early Paleocene (Fig. 3.6A. 7). This is
consistent with the sedimentary record in the foreland of Lewis-Eldorado-Hoadley thrust
slab in which denudation products of the Belt-Pucell Supergroup were absent in 74-60
Ma (Sears, 2001).
Our fossil shell samples in the Bighorn basin were collected close to the southern
portion of the Beartooth Mountains, where basement silicate rocks are widely exposed at
present. The upper Beartooth Conglomerate in its northern exposure contains up to 90%
88
of Precambrian crystalline basement clasts, suggesting the basement rocks were
extensively exposed, at least in the northern portion, in late Paleocene (Fig. 3.2)
(DeCelles et al., 1991; Secord et al., 2006 and references therein). However, the low
87
Sr/86Sr ratios (0.709-0.711) suggest the ancient rivers mainly drained carbonate source
terrane. The δ18O values of the modern rivers (~-18.0‰, Clarks Fork River and Little
Rock Creek in Table 2) that drain the Beartooth Mountains are much lower than the
values of ancient river water (-6.9±1.7‰), consistent with paleocatchments confined to
low elevations during the late Paleocene (Fan and Dettman, submitted). Apparently,
rivers draining the Beartooth Range uplands simply did not flow into the portion of the
Bighorn basin and time slice that we sampled.
The Cause of Positively Correlated 87Sr/86Sr ratios and δ18O values
The
87
Sr/86Sr ratios and δ18O values of the bivalve fossils in the Washakie basin are
positively correlated (Fig. 3.6C), the opposite of the modern pattern. This is intriguing
and we want to examine the possible causes. The correlation could be explained by
mixing of two ancient source water end members. If the ancient river water chemistry is
controlled mainly by the relative contribution of highland surface runoff and basinal
precipitation, as with the Tongue River today (Fig. 3.5), we would expect to see a
negative correlation between the
87
Sr/86Sr ratios and δ18O values of the bivalve fossils.
Since we instead see a positive correlation in our fossil shells, mixing of paleowater from
other source terranes in lake catchments is required.
Another possible scenario to explain the positive correlation is mixing water from
Laramide ranges and Sevier hinterland. In this case, lake water in the Washakie basin
89
represents a mixture of runoff from local basement-cored Laramide highlands with
relatively high δ18O values and
87
Sr/86Sr ratios, and runoff from the hinterland of the
Sevier thrust belt with low δ18O values and low
87
Sr/86Sr ratios. However, our fossil
samples in the Washakie basin only cover ~200 ky, and the variation of isotope ratios is
not systematic over that period. Frequent alternation of water sources over such a short
span between Sevier hinterland and Laramide highlands seems unlikely. Moreover, it is
unlikely to have the δ18O values (~-5‰) of surface runoff from the Laramide highlands
during the Eocene significantly higher than the annual average δ18O values of
precipitation along the south flank of the Wind River Range today (Pinedale, at elevation
of 2.4 km, -14.7‰) (http://www.uaa.alaska.edu/enri/usnip).
High
87
Sr/86Sr ratios associated with high δ18O values are also observed in ancient
and modern evaporated lakes (Hart et al., 2004; Rhodes et al., 2002). However, no
evaporates are associated with the freshwater bivalves in the Washakie basin, and the
Sr/Ca ratios of the ancient water recorded in seven representative shell fossils are
consistent with the lower end of the Sr/Ca ratios of modern rivers both rising at lowland
and highland elevations, suggesting the ancient river and lake waters were not
evaporative (Fig. 3.7).
The seasonal isotopic pattern associated with the modern South Asian Monsoon
offers another possible explanation. Seasonally the
87
Sr/86Sr and δ18O values of large
Himalayan rivers are positively correlated (e.g. Bickle et al., 2003; Galy et al., 1999;
Palmer and Edmond, 1992; Tipper et al., 2006), as in the case of our Eocene paleowaters.
Intense monsoonal rainout depresses δ18O values (the Amount Effect) in the wet season,
90
at the same time as rapid dissolution favors carbonate dissolution with low 87Sr/86Sr ratios
over much slower silicate dissolution (Bickle et al., 2003; Tipper et al., 2006).
Paleobotanical analysis in southwest Wyoming suggests the climate was warm and wet
during 52-53 Ma (Wilf, 2000). Therefore, the positive correlation between the
87
Sr/86Sr
ratios and δ18O values in the Lake Gosiute could be explained by the rapid weathering of
carbonate under a wet climate. Seasonal variation of 87Sr/86Sr ratios by the factor of 10-3
is also observed in the rivers that drain the Himalaya (Tipper et al., 2006).
Implications
Our previous study based on the δ18O values of fossil shells has shown that the
Laramide ranges in northeast Wyoming (Bighorn Mountains and/or Black Hills) reached
elevation of ~4.5 km high in late Paleocene-early Eocene time (Fan and Dettman,
submitted). The
87
Sr/86Sr ratios of ancient river water extracted from the same fossil
shells in this study further show that Precambrian basement cores were widely exposed in
these ranges in late Paleocene-early Eocene. Previous study of fossil shell δ18O values in
the Washakie basin shows that the local relief was at most 1-2 km in early Eocene time.
This study further suggests that Laramide ranges were exhumed and basement rocks were
also widely exposed in southwest Wyoming and northern Colorado in early Eocene.
Rivers draining the highland of the Sevier thrust belt dominate the river chemistry of
late Cretaceous-early Paleocene Alberta foreland basin, Crazy Mountains basin and
western Williston basin. There is no robust evidence for high elevation of Laramide
ranges and basement erosion in front of the Sevier thrust belt until early Eocene (Davis et
al., 2008; Fan and Dettman, submitted, and this study). By combining clast composition
91
of conglomerates, paleocurrent directions, the δ18O values in previous studies, and Sr
water chemistry in this paper, we have reconstructed the regional drainage pattern in late
Cretaceous-early Eocene (Fig. 3.8).
The widespread erosion of the Precambrian silicate basement first requires significant
tectonic exhumation to displace the Precambrian rocks on the top of the Laramide ranges.
Many previous studies have shown that deformation of the Laramide Rocky Mountains
was related to flat subduction of the Farallon plate underneath North America, and
consistent with the patterns of magmatism in the western U.S.A started in late Cretaceous
(Coney and Reynolds, 1977; Dickinson and Snyder, 1978; Constenius, 1996; Bird, 1998;
Saleeby, 2003). However, the widespread erosion of the Precambrian silicate basement
only began in late Paleocene-early Eocene. The Precambrian basement rocks were not
exposed in northeastern Wyoming before late Paleocene, but are denudated from ranges
of ~4.5 km high in late Paleocene and early Eocene. The Pharnerozoic sedimentary cover
in the region is up to ~2 km thick (Keefer, 1970). Therefore, up to 6.5 km of tectonic
exhumation occurred in late Paleocene and early Eocene in the Laramide ranges in
northeast Wyoming. The fast tectonic exhumation documented by using geochemical
approach in the Laramide province is consistent with the result of many
thermochronology and syntectonic deposit studies (Graham et al., 1986; DeCelles et al.,
1987; Dickinson et al., 1988; DeCelles et al., 1991; Steidmann and Middleton, 1991;
Seeland, 1992; Cerveny and Steidtmann, 1993; Omar et al., 1994; Strecker, 1996; Hoy
and Ridgway, 1997; Crowley et al., 2001; Peyton et al., 2007; Carrapa and DeCelles,
unpublished data).
92
Warm and wet climate in late Paleocene-early Eocene may have promoted
widespread erosion of basement silicates. The paleoclimate in Wyoming during the late
Paleocene-early Eocene was warm and wet based on the abundant plant leaf fossils of
mixed deciduous and evergreen (Hickey and Hodges, 1975; Wilf et al., 1998; Wilf,
2000). Studies in the Himalaya fronts and Washington Cascades have shown that high
precipitation is coupled with high erosion and sediment denudation rates (Reiners et al.,
2003; Thiede et al., 2005). The denudation and chemical weathering rates in the Rocky
Mountains during the Early Eocene Climatic Optimum was also elevated (Smith et al.,
2008).
CONCLUSIONS
87
Sr/86Sr ratios and Sr concentrations of modern river water in the Laramide Rocky
Mountains are strongly influenced by bedrock composition and age. Weathering of
Precambrian silicate rocks in the cores of Laramide ranges dominates the Sr
geochemistry of highland rivers. Weathering of Paleozoic and Mesozoic carbonates along
the basin margins reduces the 87Sr/86Sr ratios and increases Sr concentration of rivers as
they flow basinward. Lowland rivers that head in Precambrian basement mostly have
87
Sr/86Sr ratios > 0.711, whereas rivers confined to or with very long reaches in basins
have 87Sr/86Sr ratios between 0.709 and 0.711. The δ18O values of modern river water are
rather conservative, in that high-elevation recharge into rivers dominates δ18O values
along the entire reach of the river and into the basins.
Using these observations from modern rivers, the 87Sr/86Sr ratio in river water can be
used as a tool for tracking the erosion of Precambrian basement rock by analyzing the
93
87
Sr/86Sr ratio of fossil shells in fluvial basin deposits. Proterozoic low-grade
metamorphic carbonates of the Belt-Purcell Supergroup were not exposed in the
Canadian Rocky Mountains during late Cretaceous-early Paleocene when the mountains
were ~4.5 km high. Up to ~6 km of tectonic exhumation in the Laramide ranges in
northeastern Wyoming displaced the Precambrian silicate basement rock on the top of
high Bighorn Mountains and/or Black Hills in late Paleocene. Although the widespread
basement erosion in Laramide province during late Paleocene-early Eocene is controlled
by tectonic exhumation, the wet and warm greenhouse conditions of the time may have
intensified the basement erosion.
94
Figure 3.1. Simplified geological map of the Laramide Rocky Mountains showing Sr
source terranes.
95
Figure 3.2. Generalized lithostratigraphic columns of studied sedimentary successions in
studied basins (age determinations of strata with sampled fossil unionid are listed in
Table 1 in Fan and Dettman, in review) and conglomerates discussed in paper (based on
Dickinson et al., 1988). Key basin references: Lerbekmo and Coulter, 1985, Eberth and
Hamblin, 1993 for Alberta foreland basin; Cherven and Jacob, 1985, Swisher et al., 1993
for Williston basin; Buckley, 1994 for Crazy Mountains basin; Gingerich, 1983, Secord
et al., 2006 for Bighorn basin; Robinson and Honey, 1987, Flores and Ethridge, 1985 for
Powder River basin; Sklenar and Anderson, 1985; Smith et al., 2003 for Washakie Basin;
DeCelles et al., 1991, Secord et al., 2006 for Beartooth Conglomerate in western Bighorn
basin; Hoy and Ridgway, 1997 for Kingsbury Conglomerate in western Powder River
basin; Crews and Ethridge, 1993 for Richard Mountain Conglomerate in southern Green
River basin; Winterfeld and Conard (1983) and our unpublished data for Indian Meadows
Formation in northwestern Wind River basin.
96
(A)
97
(B)
Figure 3.3. Maps of modern river watershed and geology. A. Wind River, B. Powder
River. Both rivers are not shown entirely. Black dots represent sampling sites. Data are
presented in Table.3.2.
98
(0.06, 0.80)
(0.06, 0.76)
(0.06, 0.90)
0.745
0.740
(0.06, 0.74)
87
Sr/86Sr
0.735
0.730
Highand
0.725
0.720
0.715
Lowland
0.710
0.705
0.01
(18.10, 0.709)
0.1
1
10
100
Sr mmol/L
Figure 3.4. Diagrams of 87Sr/86Sr ratio vs. Sr concentration of river water. Solid lines are
modeled mixing between two end members. Otter Creek represents the end member of
the lowland river (solid open star), and four highland end members (open stars) are
assigned with fixed Sr concentration of 0.06 mmol/L, and 87Sr/86Sr ratio of 0.74, 0.76,
0.80, 0.90.
99
-15.0
one growth year
summer
δ 1 8 Ο (PDB)
-15.5
-16.0
0.70965
fall-early spring
-16.5
-17.0
0.70997
late spring
-17.5
late spring
0.71012
-18.0
1
2
3
4
5
6
7
8
9
10
11
Samples from umbo
Figure 3.5. Seasonal variation of the δ18O values and 87Sr/86Sr ratios of modern bivalve
Unionids collected in the Tongue River (N45º16.127', W106º37.492', 978m).
100
A
-4
-6
-8
modern stream
Powder River basin (58-54 Ma)
low
catchment
elevation
Williston basin (68-62.3 Ma)
Crazy Mountains basin (65-61 Ma)
18
δ O (SMOW)
Bighorn basin (59-53.6 Ma)
-10
Washakie basin (54-53 Ma)
Alberta foreland basin (76-68 Ma)
-12
-14
-16
highland
-18
lowland
-20
silicate rocks dominate
-22
0.700
0.705
0.710
0.715
0.720
87
0.725
0.730
0.735
0.740
86
Sr/ Sr
18
lowland yearly
I
-12
-14
II
-16
highland seasonaly
-18
-20
-22
0.708
18
-10
δ O (SMOW)
C
-8
δ O (SMOW)
B
-4
R2 = 0.47
-6
-8
highland yearly
III
0.710
0.712
87
86
Sr/ Sr
0.714
0.716
-10
0.7130
0.7135
87
0.7140
0.7145
86
Sr/ Sr
Figure 3.6. Diagrams of 87Sr/86Sr ratio vs. δ18O value of (A) all modern water samples
and ancient river water recorded in fossil shell; (B) ancient river water in late Paleocene
Powder River basin; and (C) ancient river water in early Eocene Washakie basin. The
δ18O values are present in Fan and Dettman, submitted. Gray band in (A) represents the
cut off of the 87Sr/86Sr ratios of silicate weathering dominated modern rivers and
carbonate weathering dominated modern rivers.
101
0.740
0.735
modern river
ancient river
highland
87
86
Sr/ Sr
0.730
0.725
0.720
lowland
0.715
0.710
0.705
0
1
2
3
4
5
6
7
8
Sr/Ca (mmol/mol)
Figure 3.7. Diagram of 87Sr/86Sr ratio vs. Sr/Ca of modern and ancient rivers with modern
highland and lowland waters enclosed in boxes.
102
Figure 3.8. Inferred drainage patterns and Precambrian basement exposure in late
Cretaceous-early Paleocene, and late Paleocene-early Eocene (refer to Fig.1 for names of
major structures and basins). Line with arrows stand for the paleorivers with the 87Sr/86Sr
ratio and δ18O value shown. See discussion for references of paleoflow directions.
103
Table 3.1. Element concentration, and corrected strontium isotope ratios for selected fossil shells
Sample
93-11.10
93-17.3
93-26.3
92-20#1
92-27
91-7#1
91-5.7
93-5#2
87
Sr/
86
µmol/g) Rb (nmol/g) Sr/Ca (mmol/mol)
Age (Ma) Ca (mmol/g) Sr (µ
71
9.63
6.09
1.35
0.63
75
9.89
3.76
3.26
0.38
64
11.74
8.80
1.14
0.75
66
11.33
4.34
0.02
0.38
66
10.30
2.93
0.27
0.28
55
10.39
6.44
0.16
0.62
55
9.95
6.99
0.68
0.70
5.19
0.06
52
Sr * is the corrected
9.48
87
Sr/
86
Sr ratio for
87
Rb decay and depositional age,
0.55
87
Rb=0.278Rb,
86
Sr=0.0986Sr
87
Sr/86Sr
0.70688
0.70765
0.70656
0.70932
0.71034
0.71164
0.70981
0.71319
87
Sr/86Sr *
0.70688
0.70765
0.70656
0.70932
0.71034
0.71164
0.70981
0.71319
104
Table 3.2. Sampling location, isotope ratios, element concentration data for modern rivers
Elev.
87
86
σ*10-5
Sr/ Sr 2σ
(m)
Sample
Latitude
Longitude
Wind River tributary
1. Little Popo River 1
N42º37.873' W108º46.131' 2213
2. Little Popo River 2
N42º36.561' W108º51.336' 2687
0.72938
8
3. Little Popo River 3
N42º42.897' W108º38.600' 1665
0.70953
2
4. Middle Popo River
N42º43.223' W108º53.031' 2388
0.72700
9
5. Middle Popo River 2
N42º46.896' W108º46.454' 1764
0.70869
3
6. Torrey Creek
N43º25.379' W109º34.397' 2331
0.73996
4
7. Torrey Creek 2
N43º30.173' W109º33.415' 2070
0.72101
3
8. South Form of Sawmill Creek
N42º41.044' W108º53.083' 2674
0.72194
3
8. South Fork of Sawmill Creek-dup.
0.72192
4
9. Sawmill Creek
N42º42.433' W108º50.496' 2372
0.70950
3
10. Wind River
N43º26.508' W109º27.838' 2018
0.71188
3
11. Townsend Creek
N42º42.560' W108º52.116' 2586
0.72730
9
12. Willow Creek
N42º43.083' W108º42.727' 1792
0.72261
3
13. Canyon Creek
N42º39.646' W108º48.827' 2432
0.72163
4
14. Pass Creek
N42º37.876' W108º46.037' 2214
15. Luis Creek
N42º35.232' W108º51.239' 2623
16. Little Wind River
N43º00.706' W108º52.925' 1694
17. Bear Creek
N43º37.473' W109º28.956' 2218
Powder River tributary
18. South Fork of Clean Creek
N44º16.633' W106º56.889' 2362
0.72983
9
19. Middle Fork of Clean Creek
N44º18.123' W106º56.835' 2265
0.72781
2
20. Clean Creek
N44º19.837' W106º47.881' 1688
0.72470
3
21. Crazy Woman Creek
N44º10.031' W106º55.186' 2364
0.72973
5
22. Crazy Woman Creek 2
N44º11.256' W106º49.978' 1806
0.72460
2
23. Crazy Woman Creek 3
N44º10.651' W106º43.946' 1559
0.71462
3
24. Muddy Creek 1
N44º09.023' W106º55.987' 2436
0.73138
3
25. Muddy Creek 2
N44º07.932' W106º42.630' 1480
0.70842
3
26. South Fork of Billy Creek
N44º08.362' W106º54.244' 2370
0.72258
3
27. Billy Creek 2
N44º07.643' W106º42.683' 1485
0.71083
3
28. Sourdough Creek
N44º15.262' W106º57.006' 2387
0.71661
3
29. Pole Creek
N44º11.680' W106º55.667' 2487
0.72608
3
30. Tongue River
N45º16.127' W106º37.492' 978
0.70987
2
31. Powder River
N45º25.641' W105º24.243' 924
0.71117
3
32. South Fork of Powder River
N43º37.352' W106º34.585' 1405
0.71145
3
33. Middle Fork of Powder River
N43º42.530' W106º38.352' 1423
0.71100
3
34. North Fork of Powder River
N43º46.066' W106º36.625' 1435
35. Otter Creek
N45º35.289' W106º15.299' 896
0.70924
3
35. Otter Creek -dup.
0.70929
2
36. Seven Brothers
N44º19.140' W106º56.538' 2225
Others
Clarks Fork River
N44°50.503' W109°19.034' 1360
Little Rock Creek
N44°53.777' W109°12.182' 1341
*Drainage 1 is Precambrain silicates only, drainage 2 includes Paleozoic-Mesozoic carbonates
18
δ O
(SMOW)
Sr
δD
Ca
Rb
µmol/L) (nmol/L)
(SMOW) Drainage* (mmol/L) (µ
-15.8
-15.6
-16.9
-15.9
-15.5
-16.3
-15.7
-18.2
-122
-120
-129
-120
-123
-123
-120
-136
1
1
2
1
2
1
2
1
0.06
0.98
0.07
0.35
3.25
0.12
0.15
0.24
3.74
0.23
0.69
0.06
0.17
0.32
2.67
6.69
5.33
2.67
2.71
4.01
1.34
-16.7
-17.2
-13.8
-18.7
-18.4
-15.8
-17.6
-15.7
-17.6
-128
-131
-113
-141
-139
-122
-130
-121
-134
2
2
1
1
1
1
1
2
2
0.15
0.83
0.06
1.08
0.21
-
0.32
1.72
0.22
5.60
0.38
-
1.34
32.10
5.35
4.01
0.01
-
-15.7
-16.0
-15.6
-17.2
-16.4
-15.7
-16.0
-14.4
-16.5
-14.6
-16.6
-16.1
-16.4
-10.5
-11.4
-17.7
-16.7
-14.1
-120
-122
-119
-129
-123
-120
-121
-115
-124
-115
-124
-122
-130
-98
-101
-137
-131
-122
1
1
2
1
1
2
1
2
1
2
1
1
2
2
2
2
2
2
0.06
0.08
0.08
0.22
0.39
0.21
4.71
0.28
0.70
0.15
0.21
0.91
0.75
2.40
0.20
0.30
0.27
0.45
1.04
0.69
32.32
0.48
3.12
0.40
0.54
3.87
12.58
18.10
2.67
2.66
0.01
2.66
10.63
4.00
15.90
3.98
4.00
0.01
1.34
18.62
123.57
39.86
-16.1
-123
1
-
-
-
-17.9
-18.6
-133
-136
-
-
-
-
105
Table 3.3. Isotope data for fossil and modern shell
87
86
−5
18
Sr / Sr
2σ∗10
σ∗10
δ O (PDB)
Sample
18
δ O* (SMOW)
Alberta foreland basin
93-11.10
0.70688
2
-17.8
93-11 #12
0.70696
2
-19.1
-18.9
-20.2
93-15#1
0.70723
2
-14.3
-14.9
93-16.8
0.70731
4
-15.8
-16.5
93-17.3
0.70765
2
-14.9
-15.7
93-25.4
0.70991
2
-16.5
-17.3
Tyrell 5
0.70817
2
-19.3
-20.5
93-12.6
0.71020
2
-18.1
-19.1
93-26.3
0.70656
2
-15.1
-15.9
93-27.2
0.70677
2
-15.2
-16.0
93-27.9
0.70702
2
-15.3
-16.1
93-28 #3
0.70769
2
-14.0
-14.6
Crazy Mountains basin
93-29.7
0.70707
2
-13.3
-13.8
93-30 #1
0.70697
3
-11.9
-12.2
93-30.3
0.70712
2
-11.8
-12.1
92-20 #1
0.70932
2
-20.0
-21.2
92-21.1
0.70923
2
-19.7
-20.9
92-21.10
0.70839
2
-17.7
-18.7
92-27 #2
0.71077
3
-19.3
-20.5
92-31
0.70945
2
-9.7
-9.8
92-32 #1
0.71060
2
-19.0
-20.2
92-32.1
0.71048
2
-19.0
-20.2
Willistone basin
Bighorn basin
92-2
0.70944
4
-11.6
-11.9
91-15
0.71012
3
-11.0
-11.3
91-11 # 5
0.71020
2
-10.7
-10.9
92-27
0.71034
2
-11.1
-11.4
-13.0
92-33
0.71091
2
-12.6
92-3.7
0.71118
2
-9.5
-9.6
91-24.8
a
91-8 #7
0.71056
2
-10.2
-10.4
0.71015
2
-15.2
-15.9
-21.3
Powder River Basin
91-2 #5
0.71014
2
-20.1
91-4
0.70883
4
-9.0
-9.0
91-7.8
0.71405
2
-14.7
-15.4
91-6#1
0.71274
2
-11.5
-11.8
91-1#1
0.70946
2
-15.4
-16.1
91-5#2
0.70975
2
-10.2
-10.4
91-7 #1
0.71164
2
-12.6
-13.0
91-7 #1 repeat
0.71177
2
-12.6
-13.0
91-5.7
0.70981
2
-18.2
-19.3
91-3.6
0.70995
2
-19.4
-20.6
PR1-80
0.70868
2
-9.8
-10.0
PR23-76
0.71005
2
-9.0
-9.0
PR38-78
0.71328
2
-15.5
-16.3
PR12-84
0.71065
2
-8.6
-8.5
93-1 #9
0.71428
2
-5.8
-5.5
93-2.3
0.71360
2
-6.4
-6.1
93-3.9
0.71434
2
-5.4
-5.0
93-6.6
0.71396
2
-9.2
-9.3
93-6.9
0.71323
3
-9.3
-9.4
93-5 #2
0.71319
2
-8.4
-8.4
Washakie basin
Modern shell in Tongue River
a
Tongue River large shell
0.70978
2
-17.5
-18.5
Tongue River small shell
0.70972
3
-17.0
-17.9
Tongue River shell 2-4
0.70997
4
-16.4
-17.3
Tongue River shell 7-8
0.70965
3
-17.6
-18.6
Tongue River shell 10
0.71012
3
-18.5
-19.6
18
18
Aragonite altered into calcite, δ O* is the calculated δ O value of ancient river water in Fan and Dettman (Accepted).
106
CHAPTET 4: SEDIMENTOLOGY, DETRITAL ZIRCON GEOCHRONOLOGY,
STABLE ISOTOPE GEOCHEMISTRY OF THE LOWER EOCENE STRATA IN
THE WIND RIVER BASIN, WYOMING
ABSTRACT
Understanding the construction and modification processes of the Laramide Rocky
Mountains in Wyoming partly relies on knowledge of the regional tectonics and
topographic conditions during Laramide deformation (~80-40 Ma). The Wind River
basin in central Wyoming is filled with sedimentary strata that record changes of
paleogeography and paleoelevation during Laramide deformation. We conducted a
multidisciplinary study of the sedimentology, detrital zircon geochronology, and stable
isotopic geochemistry of the lower Eocene Indian Meadows and Wind River Formations
in the northwestern corner of the Wind River basin in order to reconstruct basin
evolution, source terrane unroofing, and changes in paleoelevation and paleoclimate.
Depositional environments changed from alluvial fan during deposition of the Indian
Meadows Formation to low-sinuosity fluvial systems during deposition of the Wind
River Formation. Paleocurrent directions changed from southwestward to mainly
eastward through time. Conglomerate compositions suggest that the Washakie and/or
western Owl Creek Ranges to the north of the basin experienced rapid unroofing ca. 55.554.5 Ma, producing a trend of predominantly Mesozoic clasts giving way to Precambrian
basement clasts up-section. The rapid source terrane unroofing is also supported by the
evolution of the detrital zircon U-Pb ages. Zircons with Archean U-Pb ages were derived
from the Wind River Range, indicating that the range was largely denuded by ~53-51
107
Ma. Detrital zircons in the upper Wind River Formation show age distributions similar to
those of modern sands derived from the Wind River Range, suggesting that the modern
paleodrainage system was essentially set up by Eocene time.
Carbon isotope data from paleosols and modern soil carbonate show that the soil CO2
respiration rate during the early Eocene was higher than present, from which a more
humid Eocene paleoclimate is inferred. Atmosphere pCO2 estimated from paleosol
carbon isotope ratios decreased from 2050±450 ppmV to 900±450 ppmV in early
Eocene, consistent with previous studies. Oxygen isotope data from paleosol and fluvial
cement carbonates show that the paleoelevation of the Wind River basin was comparable
to that of the modern Great Plains (~500 m), and that local relief between the Washakie
and Wind River Ranges and the basin floor was 2.3±0.8 km. Up to 1 km of postLaramide regional net uplift is required to form the present landscape in central
Wyoming.
Keywords: Laramide, Wind River basin, early Eocene, paleogeography, humid
paleoclimate, paleoaltimetry
INTRODUCTION
The eastern portion of the Cordilleran orogenic belt in the western interior U.S.A.
consists of the Laramide structural province, a region of Precambrian basement-cored
uplifts and intervening sedimentary basins that developed during late Cretaceous-Eocene
time (Dickinson and Snyder, 1978; Bird, 1988; Snoke, 1997; DeCelles, 2004). The
108
deformed region partitioned what had been a continental-scale foreland basin that
developed east of the Cordilleran thrust belt ~1,000-1,500 km inland from the subduction
zone. Modern regional elevation is ~1.5 km with the range summits at >4 km. Similar
basement-involved uplifts in the foreland of a major Cordilleran style orogenic system
are present in the Sierras Pampeanas in South America, where flat-slab subduction is
intimately associated with the region of intraforeland basement deformation (Jordan et
al., 1983). Although shallow subduction of the Farallon Plate underneath North America
is the commonly accepted tectonic mechanism for the Laramide deformation (e.g.
Dickinson and Snyder, 1978; Bird, 1988; Saleeby, 2003; Sigloch et al., 2008), it remains
unclear how shallow subduction would produce the individual Laramide structures and
the extent to which Laramide deformation may be viewed as an eastward propagation of
the greater Cordilleran strain front (Erslev, 1993; DeCelles, 2004). Critical information
about the timing of individual Laramide uplifts, their paleoelevations at the time of uplift,
and the temporal relationships among Laramide uplifts have yet to be documented at
regional scale.
Many previous structural, sedimentological, thermochronological, and paleoelevation
studies have shown that deformation and uplift in the Laramide region is highly variable
in time and space (e.g. Love, 1939; Keefer, 1957; Soister, 1968; Seeland, 1978; Gries,
1983; Winterfeld and Conard, 1983; Flemings, 1987; Dickinson et al., 1988; DeCelles,
1991; Gregory and Chase 1992; Cerveny and Steidtmann, 1993; Crews and Ethridge,
1993; Omar et al., 1994; Strecker, 1996; Hoy and Ridgway, 1997; Dettman and
Lohmann, 2000; Wolfe et al., 1998; Crowley et al., 2001; Fricke, 2003; Peyton and
109
Reiners, 2007; Fan and Dettman, submitted). Tectonic models explaining deformation
during flat slab subduction include basal shear traction (Bird, 1988), lateral injection of
intracrustal flow from the overthickened Sevier orogenic hinterland (McQuarrie and
Chase, 2001), and lithospheric buckling in response to horizontal endload of the North
American plate (Tikoff and Maxson, 2001). Post-Laramide modification of the
lithosphere in the Laramide region may have played a vital role in shaping the modern
landscape. Mechanisms of modification include: (1) thermal uplift due to asthenospheric
upwelling by removing the subducted slab or thickened mantle lithosphere beneath the
western U.S. (Dickinson and Snyder, 1978; Humphreys, 1995; Sonder and Jones, 1999);
(2) subcontinental-scale subsidence by induced asthenospheric counterflow above the
subducted slab (McMillan et al, 2002; Heller et al., 2003; McMillan et al., 2006); (3)
regional uplift caused by isostatic rebound of lithosphere due to climate-driven erosion;
and/or (4) thermal upwelling associated with the initiation of Rio Grande Rift (Heller et
al., 2003; McMillan et al, 2006). Quantitative data on paleoelevation, source-terrane
unroofing and exhumation, climate, and paleogeography within a precise chronological
context are required to evaluate these competing hypotheses. In this paper we report
results of a multidisciplinary study of the sedimentology, petrology, detrital
geochronology, and stable isotope geochemistry of the early Eocene basin fill in the
Wind River Basin, central Wyoming. From these data we reconstruct paleogeography,
paleoclimate, source-terrane exhumation, tectonic setting, and the basin evolution.
REGIONAL GEOLOGY
110
Stratigraphy and Age Control
The Wind River basin in central Wyoming is one of many Laramide intermontane
basins formed to the east of the Sevier thrust belt. The basin is surrounded by moderate to
high angle fault-bounded, basement-cored uplifts, including the Wind River Range on the
southwest, the Washakie Range, Owl Creek Mountains, and Bighorn Mountains on the
north, the Casper arch on the east, and the Granite Mountains on the south (Fig. 4.1).
Deposits of late Cretaceous-Eocene age are well exposed along the basin margin, and
have been studied extensively in the last century (Keefer, 1965; Soister, 1968; Courdin
and Hubert, 1969; Seeland, 1978; Phillips, 1983; Winterfeld and Conard, 1983; Love and
Christiansen, 1985; Flemings, 1987). Among them, only Courdin and Hubert (1969) and
Flemings (1987) presented petrologic analysis of late Cretaceous and Paleocene strata in
the western and southern basin. Flat-lying lower Eocene Wind River Formation fills the
center of the basin, with its greatest thickness along the east-northeastern basin margin
(Keefer, 1965). In the northwestern corner of the basin, the Indian Meadows Formation,
slightly older than the Wind River Formation, crops out locally along the basin margin
(Love, 1939; Keefer, 1957; Seeland, 1978; Soister, 1968; Winterfeld and Conard, 1983;
Flemings, 1987). The Indian Meadows Formation is tilted and displaced on the top of the
Wind River Formation by several northwest-striking thrust faults. Surface mapping and
subsurface data suggest that these faults flatten at depth in Triassic shales or upper
Paleozoic rocks (Winterfeld and Conard, 1983). A moderate angular unconformity
between the Indian Meadows Formation and underlying Mesozoic rocks has been
observed along the southwestern flank of the Washakie Range (Winterfeld and Conard,
111
1983; this study). Our study focuses on the northwestern corner of the Wind River Basin
(Dubois-East Fork area, Fremont County), where down-cutting by the Wind River
exposed ~700 m of the Indian Meadows Formation and the Wind River Formation along
the north bank, which is the thickest outcrop of the lower Eocene strata in the basin.
The ages of the Wind River and Indian Meadows Formations are constrained by
North America Land Mammal Ages (Love, 1939; Keefer and Troyer, 1956; Keefer,
1957; Winterfeld and Conard, 1983), whose boundaries in the early Eocene have been
revised
based
on
correlation
and
calibration
with
radioisotope
ages
and
magnetostratigraphy in the Green River Basin (Fig.4.2) (Clyde et al., 1997; Robinson et
al., 2004, Smith et al., 2008). The Indian Meadows Formation consists of banded brickred, gray, white, brown conglomerate, sandstone, and siltstone. The presence of Canitius,
Hyopsodus, and Diacodexis places the Formation in the early Wasatchian (Wa1-Wa3,
55.5-54.5 Ma) (Clyde et al., 1997; Robinson et al., 2004, Smith et al., 2008). The Wind
River Formation consists of banded purple, gray, and brown conglomerate, sandstone,
and siltstone. Siltstone beds have darker color and abundant paleosol nodules compared
to the Indian Meadows Formation. The presence of Heptodon and Lambdotherium places
the Indian Meadows Formation in the late Wasatchian (Wa6 - Wa7, ~53-51 Ma) (Clyde
et al., 1997; Robinson et al., 2004, Smith et al., 2008). The youngest U-Pb ages of detrital
zircons collected from fluvial sandstones in this study cluster at 62.3±1.3 Ma, which is
older than the mammalian age and thus provides no additional constraints on depositional
ages. The contact between the Indian Meadows Formation and the Wind River Formation
112
is complex, but appears conformable in the East Fork area (Winterfeld and Conard, 1983;
this study).
Tectonic Setting
Wyoming crust consists of mainly Achaean craton, which includes granite gneisses
and minor amounts of metavolcanic-metasedimentary rocks older than 2.6-2.7 Ga (Frost
and Frost, 1993; Frost et al., 2000). Early Proterozoic metavolcanic and metasedimentary
rocks intruded by numerous plutons were accreted onto the Wyoming craton along the
Cheyenne belt at ~1.86 Ga (Frost and Frost, 1993). Rifting of the western margin of
Laurentia during Neoproterozoic-early Paleozoic time accommodated the siliciclastic
sedimentary and metasedimentary rocks deposited under predominantly marine
environments (Levy and Christie-Blick, 1991). During Paleozoic-early Mesozoic time,
the western United States was in the Cordilleran miogeocline, and a thick of succession
of carbonate rocks and subordinate siliciclastic rocks was deposited in a passive margin
setting (Devlin and Bond, 1987). From late Jurassic to late Cretaceous, the area of Wind
River basin was in the foreland of the Sevier thrust belt, and a thick succession of marine
sediments was deposited when the Western Interior Seaway inundated Wyoming. During
~80-40 Ma, Laramide deformation tectonically partitioned the foreland basin in
Wyoming, Montana, and Colorado, and produced the basement-cored uplifts and
intervening basins such as the Wind River basin.
Two schools of thought exist on the tectonic history of the Wind River Basin during
Laramide deformation. Keefer (1965) suggested that the basin experienced three stages of
113
subsidence in response to the three uplift events in surrounding mountains, with the
climax of deformation during the early Eocene. These three uplifts include the: (1)
Washakie Range and Granite Mountains uplift during Maastrichtian time; (2) Wind River
Range and Owl Creek Mountains during the earliest Paleocene, with exhumation of
Precambrian cores by late Paleocene; and (3) Casper Arch, southern Bighorn Mountains,
and Owl Creek Mountains at a rapid rate during earliest Eocene time. In contrast,
Flemings (1987) concluded that the maximum rate of uplift and deformation was during
Maastrichtian time, and the structural shortening at that time resulted from thrusting
localized in the Wind River Range and Granite Mountains.
SEDIMENTOLOGY
Environments of deposition are interpreted on the basis of four measured sections,
totaling ~750 m in thickness, in the northwestern Wind River Basin (Fig. 4.3). Measured
sections 3DB and 4DB are close, as each is tilted on the hanging wall of small thrust
faults. Sections 1DB, 2DB, 4DB are separated by >5 km distance (Fig. 4.1C). The minor
faulting precludes precise correlation between sections. Paleocurrent directions are based
on 211 measurements of imbricated clasts (10 per station) and limbs of trough crossstrata (method I of DeCelles et al., 1983) The Eocene sedimentary rocks in the basin are
described in previous literature (Love, 1939; Keefer, 1957; Seeland, 1978; Soister, 1968;
Winterfeld and Conard, 1983; Flemings, 1987), but detailed lithofacies data have not
been reported. Lithofacies that we documented in the field are typical of fluvial deposits
and are well understood in terms of depositional processes (summaries in Miall, 1978;
1996). Therefore, we provide a summary table of the most common lithofacies and
114
physical process in this study, and focus on interpreting lithofacies assemblages and the
corresponding depositional systems (Table 1).
Indian Meadows Formation: Alluvial Fan Association
The Indian Meadows Formation consists of interlayered grey/yellow conglomerate,
sandstone, and brick-red siltstone with paleosols, totaling 315 m in thickness (Fig. 4.3B).
The Formation includes: (1) a fining-upward package of conglomerate (Gch, Gct),
sandstone (Sh, Sm), siltstone (Fm) and paleosol (P) (11-25 m of section 3DB), which rest
on an erosional unconformity on upper Cretaceous Cody Shale; (2) a sequence of
intercalated conglomerate (Gmm, Gcm), sandstone (Sm), siltstone (Fm) (25-80 m of
3DB); (3) a fining-upward package of stacked tabular conglomerate (Gch, Gct),
sandstone (Sh, Sr), siltstone (Fm) and paleosol (P) (80-100 m of 3DB); (4) a thick
conglomerate sequence (Gcm, Gcmi, Gct, and Gcp) (0-110 m of 4DB, top of 2DB); and
(5) and a thick package of intercalated cobble-conglomerates (Gcm, Gcmi, Gcp, Gct),
sandstone (Sm), siltstone (Fm), and paleosols (P) (110-210 m of 4DB). The paleosols
have distinct massive pedogenic nodular carbonate intervals, and are classified as
Calcisols (Mack et al., 1993). Clasts in Gcm, Gmm lithofacies are angular to subangular.
Beds of Sm, Fm lithofacies contain granules and pebbles. Thin beds of siltstone (Fm) in
the thick conglomerate sequence display no distinctive paleosol development.
The assemblage of lithofacies in the Indian Meadows Formation is characteristic of
gravel-bedded alluvial fan setting mixed with sediment gravity flows (DeCelles et al.,
1991; Stanistreet and McCarthy, 1993; Miall, 1996). The horizontal and cross-stratified
conglomerate and sandstone were deposited by small flashy, ephemeral braided rivers on
115
alluvial
fans
(Miall,
1978).
The
unstratified,
poorly-sorted,
matrix-supported
conglomerates represent debris flows triggered by catastrophic events, which occur
usually in the proximal parts of alluvial fans (Nemec and Steel, 1984; Schultz, 1984;
Stanistreet and McCarthy, 1993). The massive sandstones and conglomeratic siltstones
were deposited by sheet floods deposits. The stacked tabular beds of horizontal and crossstratified sandstone are crevasse-splay deposits (Miall, 1978; 1996). The thick
conglomerate beds are typical of shallow gravel-bed braided river channels, with crossbedding interpreted as accretion sets, and the upward-fining trend within conglomerates
reflecting a progressive decrease in flow strength (Hein and Walker, 1977; Miall, 1996).
Well-developed Calcisols are typical of floodplain deposits and represent relatively low
sedimentation rates (Kraus, 1999). Overall, the deposition environment of the Indian
Meadows Formation changes from debris flow-dominated to stream-dominated alluvial
fan. The change suggests surface slope of alluvial fan decreased (Stanistreet and
McCarthy, 1993; Miall, 1996).
Paleocurrent data show consistently southwestward paleoflow directions, suggesting
that the sediments were shed from the Washakie Range and/or western Owl Creek
Mountains by transverse rivers.
Wind River Formation: Braided River Association
The Wind River Formation contains intercalated grey pebble- to cobbleconglomerates (Gcm, Gcmi, Gcp, Gct, Gch) with basal scour surfaces, sandstones (Sh,
Sr, St, Sm), purple-red siltstones (Fr, Fm) and stacked Calcisols (P), totaling ~260 m in
thickness (Fig. 4.3C, Fig.4.4E). The conglomerates are generally ~20 m thick and occur
116
in depositional units of ~2-4 m thick. The sandstone beds usually display upward-fining
trend, and sandstone often caps fining-upward conglomerates. Calcisols are developed in
most siltstone intervals, and the thickness is ~1 m, in many instances, several paleosols
are stacked atop one another (Fig. 4.4F). Organic rich horizons up to 0.5 m thick are
occasionally preserved occasionally above the carbonate nodule layers.
The assemblage of lithofacies in the Wind River Formation is characteristic of lowsinuosity gravel-bedded braided river depositional systems (Miall, 1978; 1996). The
conglomerates represent braided channel deposits longitudinal bar deposits that filled
relatively shallow gravelly channel (Hein and Walker, 1977; Miall, 1977; 1996). Normal
grading of individual beds may have developed during waning flow. The sandstones were
deposited on the tops or flanks of bars during waning flow or in slack-water ponds, such
as abandoned channels (Miall, 1978). Thick paleosol carbonate horizon suggests that the
floodplain of the braided rivers was vegetated and the paleosols are well-developed when
the mean annual precipitation is high, and the climate has very strong seasonality
(Retallack et al., 2005).
The paleocurrent direction varies between eastward and southwestward, but mainly
eastward, suggesting that the sediments could have been shed from the Washakie Range
and/or western Owl Creek Mountains to north and the Wind River Range to southwest.
Large variation of paleocurrent directions may be explained by frequent crevassing and
bi-directional flows.
Overall, the deposition environment in the northwestern Wind River Basin changes
from alluvial fan into low-sinuosity river, with paleocurrent directions changing from
117
southwestward to mostly eastward during 55.5-51 Ma. Such evolution suggests that
surface slope between sediment source terrane and the basin changed from steep into
shallower angle (Stanistreet and McCarthy, 1993; Miall, 1996).
SANDSTONE PETROGRAPHY AND PROVENANCE
Methods and description
Standard petrographic thin sections were made from 16 medium-grained sandstone
samples that were collected while measuring stratigraphic sections. The thin sections
were stained for potassium and calcium feldspar and point-counted (450 counts per slide)
using a modified Gazzi-Dickinson method, in which crystals larger than silt-sized within
lithic fragments are counted as monocrystalline grains (Ingersoll et al., 1984). The pointcounting parameters are listed in Table 2, and modal data are given in Table 3. The modal
sandstone analyses are augmented by 11 clast-counts (at least 100 clasts per station).
Monocrystalline quartz is the primary constituent of all samples. Lithic grain
populations are dominated by micritic carbonate. Volcanic grains constitute <5% of total
lithic grains. Other lithic grains include phyllite, siltstone, and quartzite derived from
sedimentary and metasedimentary strata. Biotite, muscovite, pyroxene, olivine,
glauconite, and chlorite are the most common accessory minerals. The Indian Meadows
and Wind River Formation sandstones have average modal compositions of
Qm:F:Lt=57:10:33,
Qt:F:L=77:11:13;
and
Qm:F:Lt=41:26:33,
Qt:F:L=56:26:18,
respectively. The Indian Meadows Formation contains greater amounts of quartz and
glauconite, and lesser amounts of feldspar than the Wind River Formation (Fig. 4.5). All
of the Eocene sandstones that we studied are dominated by calcite cements (Fig. 4.6).
118
Clasts of dolostone, limestone, and sandstone dominate the conglomerates in the
Indian Meadows Formation. Carbonate clasts with brachiopod fossils are abundant in the
lower interval of the Indian Meadows Formation. The sandstone clasts are quartzose and
have distinct red color. Granite gneiss clasts first appear in the middle interval of the
Indian Meadows Formation, and the content increases upsection, reaching ~20% at the
top of the Indian Meadows Formation. Granite (~45%) and carbonate (~40%) clasts
dominate the conglomerates in the Wind River Formation.
Interpretation
The sandstone modal petrographic data show that the lower Eocene sandstones in the
northern Wind River basin were derived from a recycled orogenic provenance (Fig. 4.6).
Potential source terranes in Wyoming include: Cretaceous sandstone, siltstone, and chertpebble conglomerate; Jurassic and Triassic eolian sandstone and marine limestone;
Jurassic-upper Permian glauconitic siltstone, sandstone, and limestone; Permian-upper
Cambrian limestone, dolostone, and sandstone; middle-upper Cambrian micacous shale;
Cambrian coarse-grained quartzite; and Archean granite gneiss (Love and Christiansen,
1985).
Lithic grains of carbonate, sandstone, mudstone, and phyllite were probably derived
from the Phanerozoic sedimentary cover strata exposed along the northern and
southwestern flanks of the Wind River basin. The large amount of well-rounded
monocrystalline quartz grains in the Indian Meadows Formation suggests the sediment
was recycled from underlying quartzose sedimentary unites, mostly from Jurassic and
Triassic eolianite. The occurrence of glauconite suggests that nearby Mesozoic
119
sedimentary rocks were major sediment sources. The abundant feldspar grains in the
Wind River Formation were derived from Precambrian basement rocks.
The red sandstone clasts in the conglomerates are of recycled Jurassic and Triassic
eolian sandstones, and the limestone and dolostone clasts were derived from the
Phanerozoic marine carbonate units. The carbonate clasts with brachiopod fossils are of
Mississippian and Pennsylvanian age (Love and Christiansen, 1985). The granite clasts
were derived from the Precambrian basement rocks, which are now exposed in the
Laramide ranges.
Overall, the Eocene sandstones and conglomerates of the northwestern Wind River
Basin exhibit a simple unroofing sequence, with initial source terranes dominated by
Mesozoic and upper Paleozoic rocks giving way to lower Paleozoic and Precambrian
basement rocks upsection.
DETRITAL ZIRCON U-Pb GEOCHRONOLOGY
Samples and Methods
Six samples of medium- to coarse-grained sandstone from the Indian Meadows
Formation (3DB69, 4DB4.5, 4DB191, 2DB273) and Wind River Formation (2DB2,
2DB257), one sample of a granite cobble (2DB2cobble), and two samples of modern
river sands (East Fork-EF, Little Popo Agie River-LP) were collected and processed by
standard methods for separating zircons (Gehrels et al., 2000). Generally ~1000 detrital
zircon grains are extracted from ~1 kg of Eocene sandstone. These zircon grains are
mostly 30-100 m in diameter, vary from subheral to anhedral, and display varied colors
(Fig. 4.7).
120
The Little Popo Agie River and East Fork rise in Precambrian crystalline basement of
the Wind River Range and Washakie Range, respectively. The formmer cuts an ~2 km
thick Paleozoic and Mesozoic sedimentary section on the northeastern flank of the Wind
River Range, while no Paleozoic and Mesozoic sedimentary strata are exposed along East
Fork (Fig. 4.1B). One kg samples of medium-grained sand collected from the two rivers
yielded very different amounts of detrital zircons, with only 19 zircon grains derived
from the East Fork sample (EF) and abundant zircons in the Little Popo Agie samples.
Zircon grains in sample EF are dark brown euhedral, and ~150 m in diameter, whereas
those in sample LP are similar to those from Eocene sandstones, subhedral to anhedral,
and mostly 30-100 m in diameter (Fig. 4.7).
About 100 individual zircon grains were analyzed for the early Eocene sandstone
samples and sample LP. All 19 zircons in sample EF and 23 zircons from sample
2DB2cobble were analyzed. U-Pb geochronology of zircons was conducted by laserablation-multi-collector inductively coupled plasma-mass spectrometry (LA-MC-ICPMS) at the University of Arizona LaserChron Center. Details of analytical procedures
and data processes are described in Gehrels et al., 2006, and Dickinson and Gehrels,
2009. The ages presented are
for grains with
206
Pb/238U ages for grains <1000 Ma and
206
Pb/207Pb ages
206
Pb/238U ages >1000 Ma. Age uncertainties (1σ) of individual grains in
the data table include only measurement errors; systematic errors would increase age
uncertainties by 1-2%. Those analyses with >10% uncertainty (206Pb/238U ages) or more
than 30% discordance or 5% reverse discordance are not considered further. Analyses
that yielded isotopic data of acceptable discordance, in-run fractionation, and precision
121
are shown in Table DR4. A total of 712 zircon ages is reported here. The data are
displayed on concordia diagrams and age-probability plots in Figures 4.8, 4.9. Nine of the
19 zircon grains from sample EF show concordant ages. The discordia ages of magmatic
zircons of 2DB2cobble are shown in Figure 4.10. There is no systematic correlation
between shape, color, angularity and U-Pb age for zircons in the Eocene sandstones and
sample LP.
Results
The youngest detrital zircons recovered from the Eocene basin fill are in the 60-80
Ma range, which is older than the depositional age derived from North American Land
Mammal ages. Ages of pre-80 Ma zircons generally fall within the following intervals:
80-230 Ma, 230-300 Ma, 330-760 Ma, 1.0-1.3 Ga, 1.3-1.5 Ga, 1.6-1.8 Ga, and 2.5-3.0
Ga. The sources of each zircon population are summarized in Table 5. Zircons of
Proterozoic age constitute the largest population on age-probability diagrams. Sample
2DB2cobble has a mean zircon crystallization age of 2.61 Ga. A single zircon grain in
sample LP produce an age of 47.7±2.1 Ma, but the other age groups are similar to those
in the Eocene samples. The nine detrital zircon grains with concordant ages in sample EF
cluster at 2.7-3.2 Ga. The interpretation of detrital zircon ages in the western United
States is relatively well understood (Armstrong and Ward, 1993; Gehrels et al., 1995;
Roback and Walker, 1995; Stewart et al., 2001; Torres et al., 1999; Gehrels, 2000;
Gehrels, et al., 2000; DeGraaff-Surpless et al., 2002; Dickinson and Gehrels, 2003; Link
et al., 2005; Dickinson and Gehrels, 2009). Here, we summarize the sources of specific
age groups in Table 3. The major source terranes are presented in Fig. 4.1A.
122
Interpretation
The euhedral morphology and small percentage of zircon grains suggest most of
grains in sample EF were derived from weathered granite in the Washakie Range and/or
the Owl Creek Mountains. The small number of concordant zircon ages from sample EF
suggest that rocks in the Washakie Range were metamorphosed and suffered significant
radiation damage and Pb loss. Nevertheless, ages from sample EF are consistent with the
zircon U-Pb age of the west Owl Creek Mountains (~2.8 Ga) (Kirkwood, 2000). The
youngest zircon in sample LP is ~48 Ma; this grain was most likely derived from the
Absaroka Volcanic Field (Amstrong and Ward, 1993). Approximately 20% of the detrital
zircons analyzed in sample LP are in the 2.5-2.7 Ga age range, which is consistent with
zircon U-Pb ages of basement rocks in the Wind River Range (2.55-2.67 Ga) (Frost et al.,
2000). The anhedral morphology and small grain size suggest most of the zircon grains in
sample LP were recycled, presumably from Mesozoic sandstones. This is supported by
the fact that Mesozoic sandstones in western U.S. have similar age spectra, including: 1)
zircons from the Cordillera magmatic arc in California and Nevada (80-220 Ma) and
Permian-Triassic magmatic arc sources in eastern Mexico (230-280 Ma); 2) recycled
zircons from the Devonian-Mississippian Antler orogenic belt in Nevada and Idaho (330450 Ma); 3) zircons derived from the Appalachian orogenic belt (360-760 Ma), and
Grenville terrane (1.0-1.3 Ga) in the eastern U.S.; and 4) recycled zircons from the
Yavapai-Mazatzal orogen (1.6-1.8 Ga) (Roback and Walker, 1995; Dickinson and
Gehrels, 2003; 2009).
123
Detrital zircon geochronology of the modern river sands sheds light on the Eocene
detrital zircon age spectra in the following aspects: (1) zircon grains recycled from
Mesozoic sandstones with mostly Grenville and Yavapai-Mazatzal ages, dominate the
zircon population in fluvial basinal sediments; (2) basement exposures along the modern
basin margin contribute only ~20% of the total zircon grains to basinal sediment; and (3)
zircons from the Washakie Range (2.7-3.1 Ga) are older than zircons from the Wind
River Range (~2.6 Ga).
The detrital zircon age spectrum of the lower Indian Meadows Formation (3DB69,
4DB4.5) is similar to that of the Jurassic eolianite in Utah and Wyoming, with abundant
Grenville (~1.0-1.3 Ga) and lesser amounts of Yavapai-Mazatzal (1.6-1.8 Ga) age grains
(Dickinson and Gehrels, 2003; 2009). The proportion of grains derived from the
Cordilleran magmatic arc increases in the middle Indian Meadows Formation (sample
2DB273). This change corresponds to the inferred increase of fluvial discharge and
coarsening of clasts in the braided fluvial deposits. The detrital zircon age spectrum of
the upper Indian Meadows Formation (sample 4DB191) is dominated by grains of
Yavapai-Mazatzal age, reflecting a recycled source in Paleozoic strata (Gehrels et al.,
1995; Stewart et al., 2003) when the Washakie and/or western Owl Creek Ranges were
unroofed.
The ~2.61 Ga zircon age from the granite cobble from the lower Wind River
Formation matches the age of basement granite in the Wind River Range (Frost et al.,
2000). Abundant granite clasts and Archean zircons (~2.6 Ga) in the lower Wind River
Formation (sample 2DB2) suggest that Wind River Range basement rocks were a major
124
source terrane by early Eocene time. The detrital zircon age spectrum changes into the
shape of modern sand sample LP at the top of the Wind River Formation (sample
2DB257), with predominant Yavapai-Mazatzal ages a large component of Mesozoic ages
indicating derivation from magmatic arc, and ~20% Archean ages with sources in the
Wind River Range basement rocks.
In summary, detrial zircon geochronology of lower Eocene sandstones in the Wind
River basin shows: 1) the source terrane of the Indian Meadows Formation (~55.5-54.5
Ma) was most likely the Washakie Range and/or Owl Creek Mountains, as suggested by
southwestward paleoflow directions. Sediment derived from these sources records an
unroofing sequence from upper Mesozoic sandstone to lower Paleozoic strata; 2) grains
derived from the Wind River Range began to enter the depositional system by ~53-51
Ma; and 3) the basement of the Wind River Range was eroded and exposed to the extent
of present by 51 Ma.
STABLE ISOTOPE GEOCHEMISTRY
Methods
The basic approach of this study and the analytical methods for carbonate isotope
analysis follow that of DeCelles et al. (2007) and Leier et al. (2009). Modern soil
carbonate was collected from under cobbles from at least 50 cm depth in active soil
horizons. Paleosol carbonate nodules were collected from the middle of paleosol beds,
which are at least 50 cm below paleosurface. We also analyzed the δ13C values of eight
dominant plant species in the study area collected during the growing season. Organic
matter δ13C was measured using a Costech EA combustion unit connected to a Finnigan
125
Delta Plus XL mass spectrometer via a Conflo III split interface. The precision is better
than ±0.1% (1σ). All the isotope values of carbonate and organic matter are reported
relative to PDB, and that of water relative to SMOW.
Results
The δ18O (PDB) values of all marine and nonmarine carbonate in the Wind River
basin range from -17.6 to -1.5‰ (Table 6; Fig. 4.12). Recycled marine limestone clasts
and coral fossils have the highest δ18O values, -4.9 to -1.5‰, whereas Early Eocene
fluvial cements have the lowest values, from -17.6‰ to -11.5‰. Early Eocene paleosol
micrites have δ18O values between -9.8 and -8.5‰ and display little variability, and are
similar to the δ18O values of Early Eocene paleosol nodules in the Bighorn basin (Koch et
al., 1995). The δ18O values of secondary veins in the paleosol nodules are generally lower
than those of paleosol nodules, ranging from -14.1‰ to -9.4‰. The δ18O values of
modern soil carbonates vary between -10.3‰ and -6.3‰.
The δ13C (PDB) values of all marine and nonmarine carbonate in the Wind River
basin range from -9.5 to +4.4‰ (Table 6; Fig. 4.12). Recycled marine limestone clasts
and coral fossils have the highest δ13C values, of -4.9 to -1.5‰. Early Eocene paleosols
have δ13C values between -9.5‰ and -5.6‰, with the highest values in the middle and
lower Indian Meadows Formation (Fig. 4.13). These paleosol δ13C values are similar to
the values of Early Eocene paleosols in the Bighorn basin (Koch et al., 1995). The δ13C
values of modern soil carbonates are generally higher than paleosols, of -4.5‰ and 0.3‰. The δ13C values of secondary veins and fluvial cements vary between -9.3‰ and -
126
5.8‰, and -7.0‰ to -3.2‰, respectively. The δ13C values of eight species of modern
plants are -24.5±1.0‰, consistent with the values obtained from Holocene soil organic
matter by Amundson et al. (1996). The δ18O values of paleosols and isotope values of
fluvial cements do not show systematic change through the section, but the δ13C values of
paleosol are higher in the lower Indian Meadows Formation than the upper and Wind
River Formation (Fig. 4.13).
Evaluation of Diagenesis
Several lines of evidence argue that Early Eocene paleosol carbonate nodules and
fluvial carbonate cements are not diagenetically reset in the Wind River basin, and
therefore the isotopic results can be used to reconstruct paleoelevation and paleoclimate.
First, carbonate petrography study shows the paleosol carbonates are micritic. No
recrystallization or cement infilling is observed in thin sections. The sandstone cements
are a mix of micrite and sparite. Calcite cement constitutes up to ~50% of the sandstone,
consistent with the high porosity of weakly compacted sands (Fig. 4.11). Such high
percentages characterize early diagenetic calcite, since early cementation occurs prior to
significant compaction (Quade and Roe, 1999 and references therein; Sanyal et al., 2000).
These observations suggest that the Early Eocene carbonates in the Wind River basin
were formed very soon after burial. Second, the δ18O values of sparry calcite veins in
paleosol nodules are between -14.1‰ and -9.4‰, lower than the values of micrite in the
paleosol nodules (Fig. 4.12). This suggests that the calcite veins probably formed by
fluids at temperatures higher than at the Eocene soil surface. If paleosol nodule micrite
underwent diagenetic resetting during the formation of secondary sparry veins, the
127
isotopic values of micrite would be similar to the values of secondary veins. Third, the
δ18O and δ13C values of marine limestone clasts and fossil corals in conglomerates
immediately adjacent to paleosols range from -4.9 to -1.6‰, and -4.4 to -0.5‰,
respectively (Fig. 4.12). These recycled marine limestone clasts and fossils have isotopic
values similar to those from unaltered Mesozoic-Paleozoic marine carbonate (Veizer et
al., 1999), but significantly higher than the values from paleosol and fluvial carbonate
cement. The δ18O and δ13C values of soil nodules, secondary veins, fluvial cement, and
marine limestone are distinct from each other, and form clusters in the δ18O vs. δ13C
diagram (Fig. 4.12). Diagenesis would tend to homogenize the isotopic values of marine
limestones, micrites, and secondary spars. The large variation of fluvial cement δ18O
values may be due to the addition of marine limestone detritus through sampling, which
have relatively positive values (Figs.4.12, 4.13).
Oxygen Isotopes and Paleoaltimetry
In order to compare the isotopic composition of paleosols to modern soils, we must
apply a set of corrections to the δ13C and δ18O values of Eocene paleosols (Fig. 4.12).
The δ18O value of seawater was lower (~-1.0‰) and the mean annual temperature in the
Wind River basin was higher (18.6±2.4℃) in Early Eocene compared to present (Zachos
et al., 1994, Wilf, 2000). The higher temperature makes the δ18O values of Early Eocene
paleosol carbonate 2.5‰ lower than modern soil carbonate formed in water of same δ18O
value based on standard calcite fractionations (0.2‰/℃, Kim and O’Neil, 1997).
Therefore, combining the two factors, we have added 3.5‰ to the δ18O values of paleosol
128
carbonate for comparison purposes. The higher temperature also decreases the δ13C value
of Early Eocene paleosol carbonate by 1.5‰ compared to modern soil carbonate formed
in equilibrium with soil CO2 of same δ13C value (0.12‰/℃, Romanek et al., 1992). The
corrected paleosol δ18O and δ13C are higher than the most negative values from modern
soils (Fig. 4.12), which are formed in equilibrium with unevaporated local meteoric water
(Quade et al., 1989; Cerling and Quade, 1993; Quade et al., 2007). This suggests that the
δ18O value of ancient meteoric water is higher than that of modern rainfall.
The δ18O value of ancient local meteoric water can be calculated from paleosol δ18O
value and constrained temperature. Pedogenic calcite is thought to form in isotopic
equilibrium with soil water during the warm season (Quade et al., 1989; Cerling and
Quade, 1993; Quade et al., 2007; Breeker et al., 2009). The temperature of the warm
season is usually between the mean annual temperature and maximum summer
temperature. Soil water derives from rainfall that may undergo evaporative enrichment in
18
O, especially in arid settings. We assume the summer temperature in Wyoming in
Early Eocene is ~30℃ based on an early Middle Eocene temperature reconstruction in
France, which has a similar mean annual temperature as Wyoming (Andreasson and
Schmitz, 1995). The δ18O values of Early Eocene precipitation can then be derived by
using soil nodule formation temperature (18.6-30℃) and standard calcite fractionation
factors (Kim and O’Neil, 1997). The calculated δ18O values of Early Eocene precipitation
in the Bighorn and Wind River basins are -6.8±1.9‰ (SMOW), which are consistent with
the values derived from the δ18O values of mammal tooth enamel in the Early Eocene
129
Bighorn basin and Powder River basin (Fricke, 2003), and the values derived from
freshwater bivalve fossils in the lower Eocene in the Powder River basin (Fan and
Dettman, submitted). For comparison with modern water, 1‰ is added to the δ18O value
of Early Eocene precipitation to account for lower seawater δ18O value in Early Eocene
(Zachos et al., 1994).
The δ18O value of groundwater can be calculated from fluvial cement δ18O value and
constrained temperature. Early diagenetic cement in the river channels form in
equilibrium with local groundwater (Quade and Roe, 1999; Mack et al., 2000). The
deposition temperature of the early cements should be close to mean annual temperature
since it formed near the surface (18.6±2.4℃). The calculated δ18O value of groundwater
is -16.6±0.5‰ (SMOW), using the most negative δ18O value of fluvial cement (-17.6‰,
PDB). This value (-16.6‰) is comparable with the unweighted mean δ18O value of
modern precipitation in the south flank of the Wind River Range (-15.2‰, Pinedale,
Wyoming, elevation of 2.4 km) after the correction of lower Early Eocene seawater δ18O
value (Zachos et al., 1994) (http://www.uaa.alaska.edu/enri/usnip). The large difference
between the δ18O values of groundwater and local precipitation in the Early Eocene Wind
River basin suggests the groundwater was not sourced in local precipitation, but rather
from the surrounding highlands.
At present, rainfall in the high elevations of the Rocky Mountains is dominated by
winter precipitation from the Pacific Ocean and Arctic. The low elevation regions in the
Laramide province likely received abundant summer precipitation from the Gulf of
Mexico and small amount of winter precipitation from Arctic (Bryson and Hare, 1974,
130
Dutton et al., 2005). Today, the elevation along a west-east transect through the Rocky
Mountains, Laramide province, and Great Plains decreases from 3-4 km to 0.5 km, which
strongly influences the δ18O value of modern precipitation and the local isotopic lapse
rate (Fig. 4.14). In Early Eocene, the movement of Sevier fold-and-thrust belt caused
significant shortening and thickening, and formed an elevated hinterland plateau to the
west of the Laramide province (DeCelles, 2004). Therefore the paleotopgraphy of
Wyoming in Early Eocene was probably similar to present, and the main vapor source
from the ancestral Gulf of Mexico. This provides the justification for the comparison of
the δ18O values of the Early Eocene precipitation with the modern isotopic patterns.
Warmer global temperature in Early Eocene could affect the relationship between the
δ18O value of precipitation and local temperature. Therefore, we compare the δ18O values
of Early Eocene precipitation in the Wind River basin with modern summer precipitation
isotopic gradient in the region (Fig. 4.14). The δ18O values of Early Eocene precipitation
(-5.8‰±1.9‰ after correction) in the Wind River and Bighorn basins are similar the
values of the modern summer precipitation in the same latitude of the Great Plains (~5.5‰, Mead, Nebraska, elevation of 352 m) (Harvey, 2001), but significantly higher than
the values of modern summer precipitation in the Laramide province (-12.6‰, Butte,
Montana, elevation of 1653 m) (Gammons et al., 2006), suggesting the paleoelevation of
the Early Eocene Wind River basin and Bighorn basin was low (~500 m). The low
basinal elevation of the Wind River Basin was stable in Early Eocene as there is no
systematic variation of the δ18O value of paleosols through the stratigraphic section (Fig.
4.13). The difference (9.8±2.0‰) between the δ18O values of Early Eocene river water
131
and basinal precipitation suggests the elevation difference between the surrounding
Laramide ranges and basin floor is 3.4±0.7 km based on the isotopic lapse rate of
2.9‰/km derived from modern precipitation in the U.S. (Dutton et al., 2005). Such an
elevation difference is higher than the modern difference of 1.5-2.5 km. The high
estimated elevations of the Laramide ranges (~4 km) from our study are consistent with
the elevation estimates derived in previous paleobotanical studies for the Early Eocene
(Gregory and Chase, 1992; Wolfe et al., 1998).
Carbon Isotopes, Paleoclimate and pCO2
The δ13C value of soil carbonate is determined by the relative proportion of C3 to C4
plants in moist climate, and additionally by the extent of local plant cover in arid climate
where soil respiration rates are low (Quade et al., 1989; Cerling and Quade, 1993,
Breeker et al., 2009). Modern climate in the Wind River basin is semi-arid, with the mean
annual precipitation of ~200 mm. Our analyses show that the most common grasses and
the dominant plant, sagebrush, in the sparsely vegetated basin are C3, with the δ13C
values of -24.5±1.0‰. Soil carbonate formed in equilibrium with CO2 respired from pure
C3 plants will have a δ13C value of -12 to -10‰ (Cerling and Quade, 1993). The
relatively high δ13C values of modern soil carbonate in the Wind River basin (2.4±2.1‰) clearly suggests mixing of atmospheric CO2 with plant-derived CO2 owing to
low soil respiration rates in the local semi-arid climate (Fig. 4.12).
The δ13C values of Early Eocene paleosols (-7.0±2.0‰) in the Wind River basin are
higher than the values of pure C3-dominated soil carbonate, but significantly lower than
the values of modern soil (Fig. 4.12, Table 6). This can be explained by high proportion
132
of C4 plants, dry Eocene climate, and higher pCO2 in Early Eocene. There is no robust
evidence for the existence of C4 plants in Early Eocene (Cerling and Quade, 1993). The
lower δ13C values of paleosols relative to modern soils in the Wind River basin point to
more humid paleoclimate in Early Eocene than present in central Wyoming. This is
supported by several other lines of evidence: (1) shallow clast-supported braided river
channels with lithofacies of Gch, Gcp, Gct and sheet flood in the middle and upper India
Meadows Formation, are generally formed by high seasonal water and sediment
discharge in humid climate (Ritter et al., 1995; Miall, 1996; DeCelles and Cazavva,
1999); (2) Calcisols are well developed in the floodplain of braided rivers in Early
Eocene Wind River basin. The thick (>50 cm) reddish argillic horizons that typify Wind
River Formation paleosols point to a relatively moist setting; and (3) abundant plant leaf
fossils of mixed deciduous and evergreen in the Wind River Formation show high mean
annual temperature and paleoprecipitation up to 21℃ and 2000 mm/yr (Hickey and
Hodges, 1975; Wilf et al., 1998).
We therefore feel justified in using the δ13C values of paleosols estimate ancient
atmospheric pCO2 levels based on a diffusion-based model developed by Cerling (1992),
under the assumption of elevated soil respiration rates. During the Eocene δ13C value of
soil carbonate should be determined by the δ13C value of soil CO2, which is a mixture of
soil respired CO2 and atmosphere CO2. Therefore, the δ13C value of soil CO2 is a
function of the concentration (pCO2) and δ13C value of CO2 in atmosphere, and the
concentration and δ13C value of soil-respired CO2. The δ13C value of ancient soil CO2 can
be calculated from the measured δ13C value of paleosols, using the temperature-
133
dependent fractionation equation (Romanek et al., 1992; Breeker et al., 2009). The
concentration of soil-respired CO2 is a function of soil respiration rate and soil depth.
Carbonate nodules in our research were collected ~50cm below the paleosurface. In our
reconstruction we assume: (1) soil respiration rates ≥ 4 mmol/m2/hr (Ekart et al., 1999;
Quade et al., 2007; Leier et al., 2009); (2) The δ13C value of CO2 in atmosphere is
assumed to be near pre-industrial values of -6.5‰, and the values of plant derived CO2 be
-24.5‰; (3) an exponential CO2 production function (Quade et al., 2007).
Using the average value of the three most positive δ13C values of paleosols in the
lower Indian Meadows Formation, atmospheric pCO2 at ~55Ma is estimated to have been
2050 ±450 ppmV (based on 1σ of the δ13C value of the paleosol carbonate). Using the
average value of the more negative δ13C values in the upper Indian Meadows and Wind
River Formations, atmospheric pCO2 from 54 to 51Ma is estimated to have been
900±450 ppmV. The calculated high pCO2 values and declining Early Eocene trend,
based on paleosols in central Wyoming, are consistent with previous estimates of Ekart et
al. (1999) using the same method, and by Pearson and Palmer (2000) using boron isotope
ratios of planktonic foraminifer shells.
REGIONAL PALEOGEOGRAPHY
Our reconstruction of the paleogeography in the northwest Wind River basin in the
early Eocene is divided in three parts (Fig. 4.15). The temporal evolution is constrained
by the relative stratigraphic position of particular lithofacies associations and the
evolution of detrital zircon age spectra, and absolute ages are based on fossil assemblages
in the basin.
134
Lower Indian Meadows Formation was deposited unconformably on upper
Cretaceous Cody Shale in the East Fork Area. The depositional hiatus formed at least
partly by folding in front of the Washakie Range (Winterfeld and Conard, 1983).
Deposition evolved from small braided rivers into debris flows on proximal alluvial fans
along the range front. Southward-flowing debris flows delivered mainly Mesozoic and
late Paleozoic clastic materials. The gravitational force associated with steep slope is
important to the initiation of debris flows (Stanistreet and McCarthy, 1993; Coussot and
Meunier, 1996). Therefore, we infer that the Washakie Range to the north of the region
was high during the early Eocene.
Deposition in the upper Indian Meadows Formation was dominated by shallow
braided rivers on alluvial fans. Southward flow delivered Paleozoic clasts from the
Washakie Range mainly into the basin, and the Precambrian basement core in the
Washakie Range was gradually exposed to erosion. The change from debris flows to
braided rivers suggests the slope between the mountain range and basin floor decreased
(Stanistreet and McCarthy, 1993). Such a change of slope may have been caused by the
rapid erosion of the mountain range and accumulation of sediment in wet climate.
Braided rivers flowing northwest mainly dominate the sedimentary environment of the
Wind River Formation. We argue that the change of paleoflow direction was caused by
the development of a northward paleoslope along the Wind River Range. Such a slope
could be formed during or after the deposition of the Indian Meadows Formation, and
before deposition of the Wind River Formation. Paleoslopes along both Wind River
Range and Washakie Range formed a confined valley in early Eocene, and low-sinuosity
135
rivers were developed in the narrow deposition space when discharge and sediment is
high in wet season. The dominant northwestward paleocurrent direction and granite
cobbles derived from the Wind River Range suggest that the Wind River Range became
the major source terrane of sediment in the northwest Wind River basin during ~53-51
Ma. The abundance of basement granite clasts, feldspar, and Achaean zircons (Fig. 4.13)
suggest that the basement core of the Wind River Range was exposed before ~53 Ma.
Low-sinuosity rivers developed in upstream could have merged into a large eastward
flowing river in the Wind River basin. Therefore, a paleodrainage pattern similar to
present was developed by late early Eocene time in the northwest Wind River basin. The
local relief based on oxygen isotope ratios was 2.3±0.8 km.
IMPLICATIONS FOR TECTONICS
Rapid Late Paleocene - Early Eocene Uplift of Basement-Cored Ranges
Tectonic uplift of the Washakie Range produced steep slope between the Range and
basin in early Eocene to form southward flowing gravel-dominated alluvial fans. The
Wind River Range was also uplifted during the late Paleocene-early Eocene to shed off
basement crystalline clasts, and form drainage similar to present. Both of the Ranges had
an elevation contrast of 2.3±0.8 km relative to the basin, which stood at ~0.5 km in early
Eocene. The rapid tectonic uplift and growth of surface topography of the Wind River
Range and Washakie Range in late Paleocene-early Eocene in west Wyoming is
supported by three lines of evidence from the synorogenic sedimentation, reflection
seismic records, and thermochronology studies. Alluvial fan conglomerates of late
Paleocene-early Eocene age archiving intense unroofing of Laramide source terranes also
136
occurred along the east flank of the Beartooth Range, east of Bighorn Range, north of the
Uinta Mountains, and on the south flank of the Wind River Range (Gries, 1983; DeCelles
et al., 1991; Crews and Ethridge, 1993; Hoy and Ridgway, 1997). Seismic and borehole
records from the south flank of the Wind River Range show that Precambrain rocks
overlie lower Eocene sediments (Gries, 1983 and ref. therein). Thermochronological
studies of the Beartooth Range and Wind River Range also show large exhumation of 4-8
km happened in late Paloecene-early Eocene (Omar et al., 1994; Peyton and Reiners,
2007). This exhumation amount is significantly higher than the thickness of Phanerozoic
sedimentary cover on the Precambrian cores.
The tectonic uplift of the Wind River Range may have started in late Cretaceous
along a N-S trend as a paleosol developed at the base of the Paleocene deposits on the
east flank of the Wind River Range (Ritzma, 1957; Gries, 1983). The Hoback basin to the
west of the Washakie and Wind River ranges has thick uppermost Cretaceous and
Paleocene sediments with abundant conglomerates (Love, 1973). Such uplift should be
minor and did not produce high topography and influence the paleodrainage compared to
the Paleocene-early Eocene uplift. The major tectonic exhumation and unroofing of
Laramide ranges in western Wyoming in late Paleocene-early Eocene time could have
been enhanced by the relatively humid paleoclimate. Studies in the Himalaya and
Washington Cascades have shown that high precipitation is coupled with rapid erosion
and sediment denudation rate (Reiners et al., 2003; Thiede et al., 2005). Rapid erosion
could in turn reduce the mass of mountain ranges and cause isostatic rebound
(Champagnac et al., 2007). Therefore, it is possible that the fast exhumation of Laramide
137
ranges in western Wyoming was initiated by tectonic uplift and enhanced by climatically
enhanced erosional uplift in early Eocene.
Post-Early Eocene Regional Uplift
Currently the Laramide basins in Wyoming have an average elevation of ~1.5 km.
Oxygen isotope ratios of basinal precipitation recorded in paleosol nodules shows the
basinal elevation of the Wind River and Bighorn basins in early Eocene is comparable
with the modern Great Plains, in the order of ~0.5 km. Therefore, the basin floor of the
Laramide basins in Wyoming reached the present elevation after early Eocene.
A few mechanisms are proposed to explain the surface uplift of Laramide basins after
early Eocene: 1) removal of Farallon slab or thickened mantle lithosphere in western U.S.
in middle Cenozoic (Dickinson and Snyder, 1978; Humphreys, 1995; Sonder and Jones,
1999), 2) thickening lithosphere by lower crustal flow or crustal detachment faulting in
middle Cenozoic (Erslev, 1993; McQuarrie and Chase, 2001; Erslev, 2005), 3) isostatic
rebound of lithosphere due to climate induced sediment erosion and/or mantle dynamic
uplift in late Cenozoic (Hellar et al., 2003; Champagnac et al., 2007; Whipple, 2009).
The southward migration of post-Laramide magmatism in the northern Basin and
Range is argued as the evidence of southward removal of Farrallon slab or mantle
lithosphere (Humphreys, 1995; Sonder and Jones, 1999). The resulting asthenospheric
upwelling due to removal could bring asthenosphere and cause regional uplift by positive
buoyancy. The post-Laramide magmatism occurred in northwestern Wyoming and Idaho
at ~50 Ma (Amstrong and Ward, 1993), which predicts the timing of regional uplift in the
Laramide foreland in Wyoming. Lower crustal flow and crustal detachment requires a
138
topographic gradient between the Laramide foreland and the over-thickened Sevier
hinterland (McQuarrie and Chase, 2001). High topography gradient between the Sevier
hinterland and foreland existed before the Cordilleran fold-thrust belt began to extend and
gravitationally collapse; in turn, this requires that regional uplift in the foreland due to
lower crustal flow and/or crustal detachment should have been earlier than extensional
collapse of the thrust belt since ~45 Ma (Janecke, 1992; Constenius 1996). However,
there is no robust evidence suggesting high basinal elevation before early Eocene.
Therefore it is unlikely that either crustal shortening along a regional detachment or
crustal flow was the cause of post-Eocene regional elevation gain in the Laramide
foreland.
Abundant thermogeochronological and sedimentological evidence suggests Miocene
exhumation that could cause a regional surface uplift. Apatite fission track and (UTh)/He thermochonology studies of surface transacts in the Beartooth Range, Wind River
Range, Bighorn Range, and Black Hills show an exhumation of >1 km in late Miocene
(Cerveny and Steidtmann, 1993; Omar et al., 1994; Strecker, 1996; Crowley et al., 2001;
Peyton and Reiners, 2007). A recent reconstruction of post-Laramide basin fill from the
depositional remnants shows >1 km of incision occurred in the Laramide Rocky
Mountain basins and the western Great Plains during high local relief since late Miocene
time (McMillan et al, 2006). The timing of incision is consistent with the tilting of the
late Miocene-Pliocene Ogallala Group (McMillan et al., 2002; Heller et al., 2003). A
mass reduction in mountain belt could be regionally compensated by flexural uplift of the
underlying lithosphere, and hence cause flexural rebound and erosion of the foreland
139
basin (Champagnac et al., 2007; Whipple, 2009). Global cooling since middle Miocene is
associated with the development and expansion of Antarctic and North Hemisphere ice
sheets and the transition from C3 to C4 plants (Quade and Cerling, 1995; Zachos et al.,
2001). Resulting intense glaciations by global cooling in the mid-latitude continental
interior could cause isostatic rebound in the foreland basin and mountain ranges in the
Laramide Rocky Mountains (Champagnac et al., 2007; Whipple, 2009). A combination
of dynamic rebound and the regional lithospheric warming along the Rio Grade Rift in
late Cenozoic time have been proposed as a thermal driven mechanism for the tilting and
incision of the Ogallala Group (McMillan et al., 2002; Heller et al., 2003; McMillan et
al., 2006). The isostatic rebound of lithosphere due to both climate induced sediment
erosion and mantle dynamic upwelling could uplift the Laramide region and western
Great Plains in the late Miocene. However, more paleoelevation data covering Cenozoic
are required to evaluate the regional uplift amount in late Cenozoic, and our research can
not exclude any dynamic subsidence and uplift between early Eocene and late Miocene.
CONCLUSIONS
1. The northwestern corner of the Wind River basin in central Wyoming consists of
~700 m thick of early Eocene Indian Meadows Formation (55.5-54.5 Ma) and Wind
River Formation (~53-51 Ma). Petrographic, detrital zircon U-Pb geochronology data and
paleocurrent analysis show the Washakie Range/western Owl Creek Mountains to the
north of the basin experienced rapid unroofing at 55.5-54.5 Ma, and the Wind River
Range to the southwest became the dominant sediment source terrane by ~53-51 Ma.
Tectonic uplift of the Washakie Range/western Owl Creek Mountains and the Wind
140
River Range in the late Paleocene-early Eocene formed a confined valley between two
high ranges, and a paleodrainage similar to present with rivers flowing from both ranges
was formed in the northwestern Wind River basin by 51 Ma. The sedimentary
environment evolved from alluvial fan into braided rivers, and paleocurrents changed
from southwestward into mostly eastward due to the tectonic damming of the Wind River
Range.
2. Young zircon grains equivalent to the depositional age are absent in early Eocene
sediment. Recycled detrital zircon grains of Grenville and Yavapai-Mazatzal orogens
from Mesozoic and Paleozoic sedimentary rocks exposed in the Laramide ranges
dominate the zircon populations of both modern river sand and early Eocene sandstones
in the Wind River basin. Present extent of basement exposure in the Wind River Range
can only contribute ~20% of the total zircon grains to basinal sediments. Zircons of
different ages from Precambrian basement rocks exposed in Laramide ranges are
potentially useful to trace the sediment source terrane.
3. A more humid climate in the early Eocene Wind River basin is inferred from the
high soil CO2 respiration rate compared to today. Calcisols were extensively developed in
the floodplain deposits. Atmosphere pCO2 estimated from paleosol carbon isotope ratios
decrease from 2050±450 ppmV to 900±450 ppmV is early Eocene, consistent with
previous studies.
4. The elevation of the Wind River Basin was comparable with the modern Great
Plains, in the order of ~500 m, and the local relief between the Washakie Range/western
Owl Creek Mountains, Wind River Range and Wind River Basin was 2.3±0.8 km in early
141
Eocene. Post Laramide regional uplift up to 1 km is required to form the present
landscape in central Wyoming Miocene-Pliocene isostatic rebound of lithosphere due to
both global cooling induced sediment erosion and regional mantle dynamic upwelling
could uplift the Laramide region and western Great Plains to form the modern landscape.
142
Figure 4.1. A: General map of the United States showing location of study area relative to
the major tectonic features and source terranes of detrital zircons (Dickinson and Gehrels,
2009). WRB stands for the Wind River basin. B: General map of Wyoming showing the
age of Precambrian basement surrounding the Wind River basin (Frost et al., 2000;
Kirkwood, 2000). Grey lines represent the Wind River and its tributaries. Stars represent
locations of modern river sand for detrital zircon U-Pb age analysis, a: East Fork; b: Little
Popo Agie River. C: Geological map of northwestern Wind River basin. Squares
represent locations of measured sections (modified from Love and Christiansen, 1985).
143
Figure 4.2. Chronostratigraphic chart for the northwestern areas of the Wind River basin,
showing North America Land Mammal age control and sections measured in this study.
Vertically ruled areas are depositional lacunae, and question marks indicate poor age
control, see text for references.
144
(A)
145
(B,C)
146
Figure 4.3. A: Stratigraphic symbols used in the stratigraphic sections in B and C. B:
Measured sections of the Indian Meadows Formation in the northwestern Wind River
basin. C: Measured sections of the Wind River Formation in the northwestern Wind
River basin. B and C include lithofacies, paleocurrent directions, clast composition, and
stratigraphic correlations (dotted lines). Section locations are marked in Figure 1C.
Lithofacies descriptions are summarized in Table 1.
147
A
B
Indian Meadows Formation
20 m
SW
Wind River Formation
30 mm
C
D
20 mm
3m
E
F
3m
30 m
Figure 4.4. Photographs of northwestern Wind River basin outcrops. (A) Angular
unconformity between the Wind River Formation (below, horizontal) and the Indian
Meadows Formation (moderately dipping to the northeast). (B) Conglomerate in the
lower section 3DB (Gmm). (C) Conglomerate in the upper section 2DB (Gcmi). (D)
Sandstones containing pebbly lags in the upper part of section 4DB (Sm). (E) Overview
of the Wind River Formation. (F) Stacked Calcisols in the Wind River Formation.
148
Figure 4.5. Ternary diagrams showing modal-framework grain compositions of
sandstones from lower Eocene strata of the northwestern Wind River basin. Provenance
fields after Dickinson and Suczek (1979). RO—recycled orogen; CB—continental block;
MA—magmatic arc. Framework components are explained in Table 2, and Data are
listed in Table 4.3.
149
A
Plagioclase
B
Calcite
Glauconite
Weathered K feldspar
250 µm
500µ
µm
Plagioclase
Figure 4.6. Photos of petrographic thin sections of sandstone from the Indian Meadows
and Wind River Formation (all photos in across-polarized light).
150
2DB257
2DBpebble
2.62 Ga
1.77 Ga
2.71 Ga
2.52 Ga
2.59 Ga
1.71 Ga
2.62 Ga
100 µm
Little Popo Agie River
2.85 Ga
150 µm
200 µm
2.67 Ga
East Fork
2.96 Ga
2.99 Ga
200 µm
Figure 4.7. Photos of the zircon grains in early Eocene Wind River basin. Transmitted
light (A, B) and cathodoluminescence images (C, D) of representative zircon grains. The
detrital zircon grains from the recycled Phanerozoic rocks are generally anhedral,
whereas those from Precambrian basement are typically euhedral.
151
Figure 4.8. U/Pb concordia diagrams for detrital zircon samples of sandstones from the
early Eocene Indian Meadows and Wind River Formation and modern river sand. Error
ellipses are shown for 2σ level of uncertainty, and only analyses that are <30% discordant
are plotted. See text for discussion.
152
153
Figure 4.9. U-Pb age-probability diagrams of detrital zircons for samples in this study.
The curves represent a sum of the probability distributions of all analyses from a sample,
normalized so that the areas beneath the probability curves are equal for all samples.
Thick dashed line represents 2.61 Ga, which is marked as the reference of Archean
zircons from the Wind River Range (see. Figure 4.10). Sources of different zircon age
peaks in this study are summarized in Table 4.4.
154
Figure 4.10. U/Pb concordia diagrams for zircons from a granite pebble in the base of
section 2DB. The age fits the crystallization age of the granite in the Wind River Range.
155
A
micritic carbonate
B
organic rich A horizon
2mm
paleosol carbonate
0.2mm
Figure 4.11. Field photos and images of thin sections of the carbonate nodules in the
early Eocene Wind River basin. (A) paleosol in the Wind River Formation. (B) micritic
paleosol carbonate nodule with microsparite.
156
0
Evaporation
-2
-4
18
δ O (PDB)
-6
-8
-10
Paleosols
Secondary vein
Marine limestone and corral fossil
Modern soil
Fluvial cement
Corrected paleosols
-12
-14
Low
rateRate
Lowsoil
Soilrespiration
Respiration
or high pCO2
-16
-18
-15
-10
-5
0
5
10
13
δ C (PDB)
Figure 4.12. Results of the stable isotope analyses in this study. See text for an
explanation of the correction of paleosol isotope values.
157
Figure 4.13. Simplified stratigraphy, carbon and oxygen isotope values of paleosol and
fluvial cement, percentage of granite clasts, Achaean zircons, and feldspar through
section. Vertically ruled areas are depositional lacunae. Dotted line marks the overall
change of each proxy.
158
Figure 4.14. Oxygen isotope data of Early Eocene paleosol carbonate in the Wind River
basin compared to the oxygen isotopic gradient of modern precipitation along an
elevation transect of Rocky Mountains-Laramide province-the Great Plains. The light
gray curve is the modern elevation profile along 43°N. The two solid lines mark the trend
of the δ18O values of modern mean annual and summer precipitations along the elevation
transect (latitude range between 40°N and 46°N). Isotope data of Eocene paleosol
carbonate in the Bighorn basin are from Koch et al. (1995). Modern precipitation isotope
data are compiled from the dataset of the United States Network for Isotopes in
Precipitation (USNIP) (www.uaa.alaska.edu/enri/usnip); Simpkins 1995; Harvey and
Welker, 2000; Harvey, 2001; Harvey, 2005; Gammons et al. 2006.
159
Figure 4.15. Paleogeographic sketch maps of the northwestern Wind River basin in early
Eocene.
160
Table 4.1. Lithofacies and interpretations used in this study
Lithofacies
code
Gmm
Gcm
Gcmi
Gct
Gchi
Gch
?
Description
Massive, matrix-supported pebble to boulder
conglomerate, poorly sorted, disorganized,
unstratified
Pebble to boulder conglomerate, poorly sorted, clastsupported, unstratified
Pebble to boulder conglomerate, moderately sorted,
clast-supported, stratified, imbricated
Pebble to cobble conglomerate, well sorted, clastsupported, trough cross-stratified
Pebble to cobble conglomerate, well sorted, clastsupported, horizontally stratified, imbricated (long
axis transverse to paleoflow)
Pebble to cobble conglomerate, well sorted, clastsupported, horizontally stratified
Interpretation
Deposition by cohesive mud-matrix debris
flows
Deposition from sheet floods and clast-rich
debris flows
Deposition by traction currents in unsteady
fluvial flows
Deposition by large gravelly ripples under
traction flows in relatively deep, stable fluvial
channels
Deposition from shallow traction currents in
longitudinal bars and gravel sheets
Deposition from shallow traction currents in
longitudinal bars and gravel sheets
Deposition by large straight-crested gravally
ripples under traction flows in shallow fluvial
channels
Gcp
Pebble to cobble conglomerate, well sorted, clastsupported, planar cross-stratified
Sm
Massive very coarse- to medium-grained sandstone,
Deposition from small gravity flow
sometime contains gravel
Sr
Fine- to medium--grained sandstone with small,
asymmetric ripples
St
Medium-- to coarse grained sandstone with trough
cross-stratification
Sh
Fine- to medium-grained sandstone, horizontally
stratified
Fr
Siltstone, horizontally laminated, or small ripples
Fm
Massive siltstone, sometime bioturbated
P
Massive siltstone with carbonate nodules
Modified from Miall (1978) and DeCelles et al. (1991)
Migration of small 2D and 3D ripples under
weak unidirectional flows in shallow channels
Migration of large 3D ripples (dunes) under
moderately powerful unidirectional flows in
large channels
Upper plane bed conditions, or flash floods
under unidirectional flows, either strong or very
shallow
Deposition from suspension or weak traction
current in overbank area
Deposition from suspension in ponds and
floodplain
Calcic paleosol
161
Table 4.2. Modal petrographic point-counting parameters
Symbol
Description
Qm
Monocrystalline quartz
Qp
Polycrystalline quartz
Qpt
Foliated polycrystalline quartz
Qms
Monocrystalline quartz in sandstone or quartzite lithic grain
C
Chert
S
Siltstone
Qt
Total quartzose grains (Qm + Qp + Qpt + Qms + S + C)
K
Potassium feldspar
P
Plagioclase feldspar
F
Total feldspar grains (K + P)
Lvm
Mafic volcanic grains
Lvf
Felsic volcanic grains
Lv
Total volcanic lithic grains (Lvm + Lvf)
Lsh
Mudstone
Lph
Phyllite
Lc
Carbonate lithic grains
Ls
Total sedimentary lithic grains (Lsh + S + C + Qms + Lc)
Lt
Total lithic grains (Ls + Lv + Lph + Qpt + Qp)
L
Total nonquartzose lithic grains (Lv + Ls+ Lph +Lc)
Note: Accessory minerals: glauconite, chlorite, zircon, biotite, pyroxene, olivine
162
Table 4.3. Modal petrographic data
Sample Qm(%) Qp(%) Qms(%) Qpt(%) C(%) S(%) Lsh(%) Lc(%) K(%) P(%) Lvf(%) Lvm(%) Lph(%) O(%)*
1DB4
49.3
11.6
0.2
0.4
1.1
2.9
8.9
5.6
6.4 10.2
0.4
0.0
0.0
2.9
1DB79
34.2
6.8
1.1
0.2
3.5
1.8
3.1
4.2
19.6 18.8
1.8
0.7
0.0
4.2
2DB2
36.0
7.8
0.7
1.6
2.4
1.3
9.1
14.9
8.2 13.1
0.9
0.2
0.0
3.8
2DB52
36.2
6.4
0.0
0.2
3.1
1.3
4.7
12.4 14.9 15.8
0.9
0.0
0.0
4.0
2DB257
41.1
14.9
0.0
0.9
2.9
2.7
4.4
5.1
7.8 10.2
1.1
0.0
0.0
8.9
2DB68
49.1
8.7
0.7
0.0
1.6
1.6
1.6
4.2
13.3 14.7
0.2
0.7
0.0
3.8
2DB127
45.2
10.5
0.4
0.4
1.3
0.4
2.9
4.0
13.6 13.6
0.0
0.0
0.0
7.6
2DB210
45.5
6.5
0.0
0.0
1.8
0.0
1.1
1.1
10.5 15.8
0.2
0.0
0.0
17.4
2DB273
43.8
8.7
0.0
1.6
6.4
8.4
10.2
9.1
3.1
0.7
2.0
1.6
3.1
1.3
3DB69
73.6
14.2
0.0
0.0
2.7
0.0
1.6
2.9
2.2
1.8
0.2
0.0
0.2
0.7
3DB110
66.2
13.1
0.0
0.0
0.7
0.9
3.1
2.9
5.6
0.9
0.0
0.0
0.0
6.7
4DB4.5
73.3
6.9
0.0
0.0
1.1
0.2
0.4
2.0
6.2
7.6
0.0
0.0
0.0
2.2
4DB105
54.7
15.1
0.5
0.0
0.7
1.1
2.3
1.8
11.0 6.3
0.0
0.0
0.0
6.5
4DB191
57.8
14.9
0.7
0.4
0.9
1.3
0.4
0.4
10.7 7.6
0.7
0.2
0.0
4.0
†
Numbers beside section labels indicate stratigraphic height (in meters) above base of section.
*Accessory minerals
163
Table 4.4. U-Pb(zircon) geochronologic analyses by laser-ablation multicollector ICP Mass Spectrometery
Analysis
U
(ppm)
206Pb
204Pb
U/Th
Isotopic ratios
206Pb*
207Pb*
± (%)
207Pb*
235U*
± (%)
206Pb* ± error
(%) corr.
238U
Apparent ages (Ma)
206Pb*
207Pb*
206Pb*
± (Ma)
± (Ma)
238U*
235U
207Pb*
± (Ma)
3DB69
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
79.114112
61.502422
126.94035
32.118829
129.74484
89.604955
41.617139
51.888701
152.53847
393.37776
103.43117
235.10337
88.554717
166.95328
618.8097
144.72516
238.50799
248.19095
76.205445
302.04197
64.038949
142.35187
26.673199
83.924252
100.24106
131.56882
376.59246
229.62482
91.500837
59.875706
17.312367
159.45737
119.02737
334.42993
998.48009
259.87944
64.142384
319.06989
166.30991
157.06545
30.332198
722.34849
729.60184
84.712941
336.34347
46.299915
97.112164
35.258271
155.07433
83.833747
266.12431
283.01001
93.918621
603.67021
492.40043
497.15842
177.51964
801.63111
90.001035
731.90326
128.65972
344.43723
473.65291
115.04514
177.88166
101.81844
281.18697
275.12312
197.01706
55.065997
508.47158
10280
17985
53095
12485
23490
42655
14660
96870
74470
69490
59245
86130
23560
33475
54220
67885
23175
46270
6300
22610
13935
65255
7435
44925
120855
84585
86200
141670
33470
9105
6170
32290
42005
82055
79255
92575
77140
59415
40430
31970
12370
103130
140505
20060
208215
16805
23300
25330
58690
36270
53635
47480
33675
199840
308100
222605
50995
253440
35260
149515
40780
28255
135070
36960
51675
53760
24245
66080
100610
8965
37745
2.5
1.2
6.4
0.9
2.3
1.7
1.1
1.7
2.0
4.5
1.4
2.1
1.9
2.6
4.7
2.8
1.7
3.2
1.9
5.5
2.5
2.7
1.8
2.4
3.7
2.0
3.6
1.8
4.0
0.9
0.8
2.2
2.3
1.3
4.0
1.9
1.6
5.4
1.4
1.9
0.2
10.9
9.9
3.9
12.8
1.0
2.3
1.1
1.3
2.3
2.3
0.6
1.1
4.2
1.4
4.9
2.3
4.2
1.9
6.6
2.4
3.1
5.0
2.3
2.0
1.2
1.6
2.1
1.9
2.6
2.0
17.1750 6.7 0.6530 6.8 0.0813 0.8
9.8194 1.6 3.6841 2.5 0.2624 1.9
11.5078 2.7 2.4579 4.6 0.2051 3.7
12.9867 4.1 2.1298 4.3 0.2006 1.2
13.0826 1.4 1.8155 1.7 0.1723 0.9
13.3665 2.6 1.9067 2.7 0.1848 0.8
13.0967 3.7 2.0620 3.8 0.1959 0.9
3.6610 1.8 25.5518 2.0 0.6784 0.8
7.8751 1.4 6.5920 1.8 0.3765 1.2
13.7788 2.1 1.6216 2.6 0.1621 1.6
5.2940 1.8 13.4474 2.4 0.5163 1.6
10.3628 1.4 3.6175 2.7 0.2719 2.3
11.1066 1.6 3.1148 1.8 0.2509 0.8
13.5714 2.2 1.7624 2.9 0.1735 1.9
8.6629 2.3 4.0867 8.7 0.2568 8.4
8.1102 0.8 6.0174 1.4 0.3539 1.1
17.6414 1.7 0.5429 3.1 0.0695 2.6
13.0796 1.2 1.9221 1.8 0.1823 1.4
8.8635 18.1 1.6256 20.1 0.1045 8.8
17.5488 2.6 0.5263 3.4 0.0670 2.1
13.5771 3.7 1.7033 4.0 0.1677 1.6
8.0234 1.0 6.1204 2.0 0.3562 1.8
12.6643 5.4 1.9788 5.4 0.1817 0.8
13.1007 3.3 1.9102 3.5 0.1815 1.1
5.2609 1.6 13.0904 1.8 0.4995 0.9
5.1461 1.8 13.3058 2.2 0.4966 1.2
12.7784 1.8 2.0054 2.0 0.1859 0.9
4.5640 1.1 17.7833 1.6 0.5886 1.2
9.6611 1.7 4.3393 2.0 0.3040 1.0
13.6849 1.9 1.7355 2.1 0.1723 0.8
10.0641 4.4 4.0845 4.6 0.2981 1.3
12.3072 1.7 2.4123 2.3 0.2153 1.5
8.8166 1.3 5.1596 1.9 0.3299 1.3
9.9523 1.6 3.8715 2.7 0.2794 2.2
5.8862 1.1 8.0172 3.3 0.3423 3.1
9.1702 1.0 4.7625 2.2 0.3167 2.0
3.2290 11.0 31.1014 11.1 0.7284 2.0
12.9910 0.7 1.9280 2.9 0.1817 2.9
12.8993 1.5 2.0163 2.7 0.1886 2.2
13.5018 1.3 1.7703 1.7 0.1734 1.2
8.9223 1.5 4.9443 3.3 0.3199 2.9
12.6626 3.1 1.5381 4.8 0.1413 3.7
13.1995 1.6 1.9803 2.2 0.1896 1.6
13.8609 1.8 1.6865 5.1 0.1695 4.8
4.3465 1.2 19.2573 3.5 0.6071 3.3
10.7438 2.4 3.3938 2.9 0.2644 1.6
13.6926 2.0 1.7184 2.6 0.1707 1.7
4.9170 1.6 15.6204 2.5 0.5570 2.0
9.8249 1.7 4.1819 2.3 0.2980 1.6
8.8808 1.3 5.2051 1.9 0.3353 1.4
12.4169 0.9 2.2025 1.0 0.1983 0.5
12.9488 1.3 2.0395 2.5 0.1915 2.2
9.5434 0.9 4.3715 2.2 0.3026 2.0
8.9323 2.1 5.1257 2.7 0.3321 1.7
4.7721 1.4 16.5015 1.7 0.5711 1.0
8.1879 1.7 5.8147 1.8 0.3453 0.7
11.7515 1.5 2.6888 2.2 0.2292 1.6
9.3771 2.0 4.4045 2.7 0.2995 1.8
9.4397 1.2 4.3490 1.7 0.2977 1.1
13.6342 1.2 1.7573 3.1 0.1738 2.9
10.8255 1.6 3.3146 1.9 0.2602 1.1
17.1973 2.8 0.5463 3.1 0.0681 1.3
11.6618 1.5 2.7724 1.9 0.2345 1.2
10.2037 2.3 3.8775 2.3 0.2870 0.5
10.1223 1.7 3.8641 1.8 0.2837 0.7
5.0734 1.7 14.3307 2.2 0.5273 1.4
17.8325 3.6 0.5119 3.6 0.0662 0.6
12.8564 2.8 2.1176 3.0 0.1975 1.2
8.2781 1.0 5.9779 1.7 0.3589 1.3
14.3011 4.5 1.2676 4.8 0.1315 1.8
16.7543 1.6 0.6328 1.9 0.0769 1.2
0.11
0.76
0.81
0.29
0.53
0.30
0.23
0.41
0.65
0.61
0.67
0.86
0.47
0.66
0.96
0.80
0.84
0.75
0.44
0.63
0.39
0.88
0.14
0.33
0.49
0.57
0.46
0.74
0.51
0.40
0.27
0.67
0.72
0.82
0.95
0.88
0.18
0.97
0.82
0.67
0.88
0.77
0.71
0.93
0.93
0.55
0.64
0.78
0.68
0.73
0.50
0.86
0.92
0.63
0.58
0.39
0.73
0.68
0.68
0.92
0.55
0.43
0.64
0.21
0.38
0.65
0.16
0.38
0.79
0.37
0.59
504.2
3.7 510.3 27.2
1501.9 25.6 1567.9 20.2
1202.9 40.7 1259.8 33.2
1178.6 13.4 1158.5 29.8
1024.5
8.5 1051.1 11.1
1093.4
8.1 1083.4 18.3
1153.0
9.5 1136.3 26.3
3338.4 21.1 3329.5 19.5
2060.0 20.5 2058.3 15.8
968.2 14.4 978.6 16.5
2683.6 34.7 2711.6 22.4
1550.4 31.8 1553.4 21.4
1443.1 10.7 1436.3 13.6
1031.2 17.9 1031.7 18.5
1473.3 110.5 1651.6 71.1
1953.4 18.2 1978.4 11.8
432.9 11.0 440.3 11.1
1079.7 13.8 1088.8 12.3
640.7 53.4 980.2 126.9
418.0
8.7 429.3 11.8
999.6 14.7 1009.8 25.9
1963.9 30.3 1993.2 17.7
1076.5
7.4 1108.3 36.5
1075.1 11.3 1084.6 23.1
2611.5 18.5 2686.2 16.7
2599.2 26.5 2701.6 20.5
1098.9
9.5 1117.4 13.9
2983.9 27.9 2978.1 15.1
1711.4 15.6 1700.9 16.7
1024.5
7.8 1021.8 13.2
1682.1 18.5 1651.2 37.6
1257.1 17.4 1246.3 16.2
1838.0 21.4 1846.0 15.9
1588.6 31.0 1607.8 21.7
1897.5 51.5 2233.0 29.8
1773.8 30.4 1778.3 18.6
3527.3 53.0 3522.3 110.0
1076.0 28.3 1090.8 19.7
1114.0 22.4 1121.0 18.1
1030.6 11.1 1034.6 11.4
1789.5 45.0 1809.8 27.6
851.7 29.3 945.7 29.4
1119.1 16.0 1108.8 14.9
1009.6 44.6 1003.4 32.6
3058.2 79.4 3054.8 33.7
1512.6 21.2 1503.0 22.4
1015.7 15.8 1015.4 17.0
2854.4 45.0 2853.9 23.8
1681.3 23.7 1670.5 19.3
1863.8 22.5 1853.5 16.3
1166.4
5.3 1181.8
6.9
1129.7 22.8 1128.8 17.3
1704.1 30.5 1707.0 18.4
1848.3 27.0 1840.4 22.5
2912.4 23.0 2906.3 16.3
1912.1 11.7 1948.6 15.6
1330.1 19.6 1325.4 16.5
1689.1 27.3 1713.2 22.5
1680.1 16.9 1702.7 13.9
1032.8 27.4 1029.8 20.2
1491.1 14.0 1484.5 15.0
424.9
5.5 442.6 11.0
1358.0 15.1 1348.1 14.4
1626.3
7.2 1609.0 18.8
1609.9
9.8 1606.2 14.5
2730.1 31.8 2771.9 20.9
413.3
2.3 419.7 12.5
1161.6 12.2 1154.6 20.7
1977.0 22.5 1972.6 14.6
796.3 13.4 831.3 27.4
477.5
5.3 497.8
7.7
538.2
1657.9
1358.2
1121.2
1106.5
1063.5
1104.4
3324.2
2056.6
1002.1
2732.5
1557.5
1426.3
1032.8
1886.7
2004.5
479.3
1107.0
1845.3
490.9
1032.0
2023.6
1171.2
1103.8
2742.9
2779.1
1153.4
2974.1
1687.9
1016.0
1612.2
1227.6
1854.9
1632.9
2556.5
1783.6
3519.4
1120.6
1134.7
1043.2
1833.4
1171.4
1088.7
990.0
3052.5
1489.4
1014.8
2853.5
1656.9
1841.8
1210.1
1127.0
1710.5
1831.4
2902.1
1987.6
1317.7
1742.8
1730.6
1023.5
1475.1
535.3
1332.5
1586.5
1601.4
2802.4
455.4
1141.3
1968.1
926.1
592.2
147
31
52
82
29
53
75
29
24
42
29
26
30
43
42
15
37
24
330
58
75
17
106
66
25
29
36
17
32
38
83
33
23
29
18
19
170
14
30
26
28
61
31
38
20
45
41
25
32
24
17
26
16
37
23
30
30
37
23
24
31
61
29
43
31
27
80
55
18
92
34
164
Table4.4. (Cont'd)
Analysis
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
4DB4.5
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
U
(ppm)
280.28192
199.47363
272.70533
78.028479
66.288652
305.98542
48.549617
132.7971
52.997305
117.8508
150.66543
94.086702
103.07258
222.66884
184.88935
113.5712
214.82074
217.41954
97.008729
134.07711
309.903
135.4864
243.05839
125.14294
234.26645
205.1884
151.04038
529.43002
211.23932
51.859525
283.19102
733.14447
140.23146
125.99628
151.3119
217.39368
170.46023
148.48037
494.9863
218.36338
72.753315
89.419215
92.858416
206Pb
U/Th
204Pb
46645
2.2
44080
1.9
32265
1.2
22835
2.3
42110
2.0
137355
1.6
33295
2.1
41040
2.5
18500
1.1
31550
3.6
32665
2.1
23330
1.6
23110
1.9
36510
4.0
71175
2.9
39110
0.8
42610
2.8
61350
4.2
25965
3.5
76750
3.4
89780 16.3
26450
0.8
37445
2.5
45180
1.7
58205
2.1
114865
2.2
14150
1.8
150410
4.9
36255
4.4
39035
1.9
108275
3.9
240585
2.8
88395
1.1
61210
3.3
65485 173.2
83200
1.6
15210
1.7
71910
2.8
68085
3.7
64235
3.0
17715
1.5
43895
3.1
53635
1.8
229 62230
127 36225
339 80825
499 30560
133 69265
260 42730
136 33070
295 95980
230 23405
167 69435
251 26650
54 42445
107 81195
177 64615
235 36495
64 34085
310 110920
490 182515
1.5
2.7
1.6
4.3
2.0
4.9
2.8
1.7
1.0
1.0
3.7
1.5
1.0
2.4
2.3
1.2
2.4
1.3
Isotopic ratios
206Pb*
± (%)
207Pb*
13.5335 1.3
12.8590 3.1
17.8592 3.1
12.1809 1.8
5.0757 1.9
5.5463 1.3
4.6242 1.3
9.5273 0.8
9.9246 1.5
13.3249 2.1
13.0241 1.1
13.6172 1.7
13.8957 1.7
11.5802 1.8
9.4379 2.5
9.9444 0.7
12.9500 1.3
12.8572 1.7
12.8837 1.8
6.5563 1.6
12.7351 2.7
13.7288 1.4
13.3079 3.0
8.8455 1.2
12.7801 1.3
6.2610 1.4
18.2520 2.9
8.2577 1.7
13.4827 1.1
5.5514 1.2
8.6535 1.1
10.7212 1.3
5.8799 1.2
8.5836 0.8
8.9700 1.5
9.7549 1.1
18.0282 3.2
7.7660 0.9
10.7474 2.4
12.2109 1.7
13.0250 2.1
8.6702 1.4
9.8596 1.7
9.1291
9.0285
10.2110
14.6287
5.6920
9.0269
13.1584
9.1978
16.8171
9.9541
13.4977
5.0028
5.3365
7.7535
12.3336
5.4750
10.2310
5.3107
1.3
1.7
2.4
3.7
1.9
1.4
2.3
2.5
1.5
1.7
4.0
3.4
1.4
1.8
3.7
2.0
2.8
2.5
207Pb*
206Pb* ± error
± (%)
(%) corr.
235U*
238U
1.7614 1.7 0.1729 1.1
0.63
2.1368 3.4 0.1993 1.4
0.43
0.5790 3.4 0.0750 1.4
0.40
2.4647 2.8 0.2177 2.2
0.77
13.6335 6.9 0.5019 6.6
0.96
12.1179 3.5 0.4875 3.2
0.93
17.2960 2.2 0.5801 1.8
0.82
4.3563 1.8 0.3010 1.7
0.90
4.0954 2.2 0.2948 1.7
0.74
1.8500 3.1 0.1788 2.3
0.74
1.9435 2.0 0.1836 1.7
0.85
1.7543 2.2 0.1733 1.4
0.65
1.6290 2.2 0.1642 1.4
0.63
2.6278 2.2 0.2207 1.3
0.59
4.4060 2.9 0.3016 1.5
0.53
3.8821 1.3 0.2800 1.1
0.83
2.0479 2.0 0.1923 1.5
0.75
2.0786 2.3 0.1938 1.6
0.69
2.0596 2.2 0.1924 1.3
0.57
8.7694 1.8 0.4170 0.7
0.40
2.0922 3.4 0.1932 2.1
0.62
1.7266 1.6 0.1719 0.6
0.41
1.7262 3.5 0.1666 1.9
0.53
5.1274 2.1 0.3289 1.7
0.80
2.0461 2.8 0.1897 2.4
0.88
9.3817 2.8 0.4260 2.4
0.87
0.5246 3.1 0.0695 1.1
0.37
5.0577 3.6 0.3029 3.1
0.88
1.4138 2.3 0.1383 2.1
0.89
11.2587 2.7 0.4533 2.4
0.89
5.1635 2.8 0.3241 2.6
0.92
3.1168 2.1 0.2424 1.6
0.77
10.5765 3.2 0.4510 3.0
0.93
5.5030 1.5 0.3426 1.3
0.85
4.7457 2.5 0.3087 2.1
0.82
3.7647 3.3 0.2663 3.1
0.94
0.5317 3.3 0.0695 0.8
0.24
6.5460 1.1 0.3687 0.6
0.54
2.7507 3.7 0.2144 2.9
0.77
2.3796 3.0 0.2107 2.6
0.84
2.0035 2.9 0.1893 1.9
0.67
5.4634 1.7 0.3436 1.0
0.55
4.0649 2.0 0.2907 1.1
0.57
4.8693
4.9699
3.6344
1.3142
12.2351
4.3484
1.9699
4.7820
0.7525
3.9666
1.5935
15.3235
13.1706
6.8536
2.2213
12.8531
3.8433
12.9334
3.2
2.6
3.8
3.9
3.3
4.5
3.7
4.3
1.8
2.1
4.2
3.7
1.8
2.0
4.1
3.3
3.5
6.2
0.3224
0.3254
0.2692
0.1394
0.5051
0.2847
0.1880
0.3190
0.0918
0.2864
0.1560
0.5560
0.5098
0.3854
0.1987
0.5104
0.2852
0.4982
3.0
1.9
2.9
1.4
2.7
4.3
2.9
3.5
1.0
1.2
1.2
1.5
1.2
1.0
1.9
2.7
2.1
5.7
0.91
0.75
0.78
0.35
0.82
0.95
0.78
0.82
0.55
0.57
0.29
0.42
0.65
0.49
0.45
0.80
0.60
0.92
Apparent ages (Ma)
206Pb*
207Pb*
206Pb*
± (Ma)
± (Ma)
± (Ma)
238U*
235U
207Pb*
1028.0 10.2 1031.4 11.0 1038.5
26
1171.5 15.4 1160.8 23.3 1140.9
61
466.2
6.1 463.8 12.6
452.1
69
1269.9 25.1 1261.7 20.4 1247.8
35
2621.9 143.1 2724.6 65.4 2801.6
31
2559.7 68.4 2613.6 32.7 2655.6
21
2949.0 42.4 2951.4 21.1 2953.0
21
1696.3 24.6 1704.1 15.2 1713.6
15
1665.4 24.5 1653.4 18.3 1638.1
28
1060.3 22.1 1063.4 20.2 1069.8
42
1086.5 17.1 1096.2 13.5 1115.5
21
1030.0 13.4 1028.7 14.0 1026.0
33
979.9 12.3 981.5 13.6
984.9
34
1285.6 15.4 1308.4 16.4 1346.1
35
1699.2 23.0 1713.5 24.0 1731.0
45
1591.3 14.9 1610.0 10.3 1634.4
13
1134.1 15.3 1131.6 13.4 1126.9
26
1142.1 16.6 1141.8 15.8 1141.2
33
1134.6 13.0 1135.5 14.9 1137.1
35
2246.8 13.5 2314.3 16.0 2374.4
27
1138.9 22.3 1146.2 23.6 1160.1
53
1022.7
6.1 1018.5 10.0 1009.5
29
993.4 17.2 1018.3 22.5 1072.3
59
1833.3 26.6 1840.7 17.7 1849.0
22
1119.5 24.8 1131.0 18.8 1153.1
26
2287.7 46.6 2376.0 25.5 2452.7
23
432.8
4.7 428.2 10.8
403.6
65
1705.7 46.9 1829.0 30.3 1972.5
31
834.8 16.1 894.8 13.7 1046.0
21
2409.9 48.7 2544.8 25.4 2654.1
21
1809.6 41.2 1846.6 24.1 1888.6
20
1398.9 20.2 1436.9 16.1 1493.4
25
2399.9 59.7 2486.7 29.8 2558.3
20
1899.1 20.6 1901.1 12.7 1903.2
14
1734.5 31.5 1775.3 21.2 1823.7
26
1522.2 42.3 1585.2 26.7 1670.1
21
433.3
3.3 433.0 11.7
431.1
72
2023.3 10.1 2052.1
9.5 2081.2
16
1252.3 32.9 1342.3 27.9 1488.8
45
1232.8 28.6 1236.5 21.8 1243.0
33
1117.4 19.5 1116.7 19.3 1115.3
43
1903.7 15.8 1894.9 14.9 1885.2
26
1644.9 16.6 1647.3 16.4 1650.3
31
1801.4 46.5
1816.2 30.5
1536.5 40.2
841.5 11.0
2635.7 58.8
1614.9 61.0
1110.5 29.1
1784.8 54.9
566.1
5.4
1623.4 16.9
934.5 10.7
2850.1 35.2
2655.6 25.5
2101.5 17.9
1168.4 19.8
2658.3 58.2
1617.4 30.6
2605.9 121.3
1797.0
1814.2
1557.1
852.0
2622.6
1702.6
1105.3
1781.7
569.7
1627.4
967.7
2835.6
2692.0
2092.7
1187.8
2668.9
1601.9
2674.8
27.3
21.6
30.1
22.6
31.0
37.2
24.6
36.1
7.9
16.7
26.1
35.1
17.1
18.0
29.0
31.5
28.5
58.3
1791.8
1811.9
1585.1
879.4
2612.5
1812.2
1095.0
1778.1
584.1
1632.6
1043.8
2825.3
2719.4
2084.0
1223.4
2677.0
1581.5
2727.3
24
31
45
76
31
26
46
45
33
31
81
55
23
31
73
33
53
41
165
Table4.4. (Cont'd)
Analysis
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
U
(ppm)
247
248
115
837
107
183
434
404
97
286
1173
320
278
66
414
63
115
253
75
185
181
55
198
52
616
246
161
88
206
341
103
261
124
116
432
141
354
79
338
629
87
267
273
885
50
169
115
188
163
136
148
83
176
131
313
673
327
178
58
73
212
414
127
362
51
381
817
206Pb
U/Th
204Pb
50365
3.2
96370
2.2
16640
1.9
150050
4.7
19885
1.9
24075
1.3
42335
1.0
120885
2.0
34665
2.5
132080
0.7
4070
1.0
117785
1.0
78820
2.9
20475
3.1
214860
2.9
38875
2.6
14035
3.1
115510
4.6
37940
2.3
128995
2.1
55410
3.4
7050
1.5
90875
1.1
4435
3.5
116745 20.4
20815
0.9
37710
3.0
17855
0.8
77550
2.5
27285
1.8
31060
1.8
44370
2.4
39575
0.8
32935
4.1
87535
2.7
7745
1.0
170680
2.9
18535
1.6
79220
3.4
134630
1.7
38980
1.0
67545
1.9
193690
1.9
241480
2.1
8245
2.1
63770
1.0
36695
2.1
60605
2.5
57465
2.8
71525
1.0
72345
1.7
55335
1.2
83485
2.0
79505
3.6
242215
1.2
73155
4.8
182520
5.1
22725
2.2
77150
1.2
12715
1.5
89010
2.0
121420
4.0
26515
1.4
179160
3.4
28835
1.9
64890
1.4
181230
3.3
Isotopic ratios
206Pb*
± (%)
207Pb*
13.6680 2.0
8.7996 2.2
12.2470 3.9
13.3428 2.2
12.8697 4.0
5.6603 3.4
8.7865 5.4
11.4087 2.8
13.0121 2.5
5.3399 2.1
12.9407 5.9
9.1118 2.2
12.8406 1.7
12.6193 1.8
9.1960 3.8
9.4232 3.1
17.4979 8.5
9.4138 3.9
9.6849 3.1
8.5681 3.2
12.5780 3.7
17.4625 8.8
9.8832 1.9
10.8173 6.2
13.0658 1.1
16.7743 3.6
10.0329 2.8
13.2921 4.0
10.6317 1.6
16.2023 6.1
10.9584 2.9
13.3336 2.4
9.8946 2.4
9.4094 3.3
8.1746 1.4
16.4553 11.2
9.0401 2.3
13.2266 2.5
13.3698 2.1
9.0152 1.8
9.0034 1.6
10.2715 1.6
5.0000 1.0
9.7931 1.7
12.2445 4.8
9.6575 1.6
11.5885 2.0
11.0129 1.4
13.2225 2.6
10.4672 2.1
9.7471 2.5
9.8849 2.7
9.0234 1.7
9.1051 2.8
4.9972 1.6
13.2109 3.0
10.0504 2.4
18.3145 3.8
4.5924 3.3
11.1808 3.1
10.9653 1.5
9.2679 1.5
17.0778 7.8
8.6206 4.7
9.4430 1.5
11.6472 2.0
12.9395 1.0
207Pb*
206Pb* ± error
± (%)
(%) corr.
235U*
238U
1.6674 3.5 0.1653 2.9
0.83
4.8946 3.8 0.3124 3.1
0.82
2.2450 4.0 0.1994 1.0
0.25
1.8717 2.6 0.1811 1.4
0.52
1.9819 4.4 0.1850 1.7
0.40
8.6884 4.7 0.3567 3.2
0.69
4.5919 5.6 0.2926 1.3
0.23
2.7489 3.0 0.2275 1.0
0.34
2.0897 2.7 0.1972 1.0
0.38
13.2545 3.5 0.5133 2.8
0.80
0.5216 6.0 0.0490 1.1
0.18
4.9284 3.0 0.3257 2.0
0.67
2.0624 2.8 0.1921 2.3
0.81
2.1810 2.8 0.1996 2.2
0.77
4.5850 4.1 0.3058 1.4
0.33
4.5325 3.6 0.3098 1.8
0.50
0.6155 8.6 0.0781 1.4
0.16
4.4594 4.0 0.3045 1.0
0.26
4.3907 3.3 0.3084 1.1
0.33
5.4170 4.5 0.3366 3.2
0.70
2.2652 3.8 0.2066 1.0
0.26
0.5552 9.0 0.0703 1.9
0.21
4.0265 2.4 0.2886 1.5
0.62
2.7440 6.3 0.2153 1.0
0.16
1.9500 1.7 0.1848 1.3
0.77
0.7102 4.3 0.0864 2.3
0.54
3.9031 4.5 0.2840 3.5
0.77
1.7906 4.6 0.1726 2.4
0.51
3.3258 1.9 0.2564 1.1
0.57
0.6783 6.7 0.0797 2.8
0.42
3.2270 3.2 0.2565 1.5
0.47
1.8908 2.9 0.1828 1.7
0.58
3.9041 3.0 0.2802 1.8
0.59
3.4965 4.2 0.2386 2.6
0.61
5.6175 1.7 0.3330 1.0
0.59
0.6086 11.3 0.0726 1.0
0.09
4.9657 3.8 0.3256 3.0
0.80
1.9479 3.7 0.1869 2.8
0.74
1.8563 3.2 0.1800 2.4
0.76
4.9070 4.6 0.3208 4.2
0.92
5.0061 3.3 0.3269 2.9
0.87
3.6961 2.6 0.2753 2.0
0.79
15.1312 3.6 0.5487 3.4
0.96
4.2259 2.0 0.3001 1.0
0.51
2.2749 5.1 0.2020 1.7
0.33
4.2212 2.3 0.2957 1.6
0.70
2.7646 3.1 0.2324 2.4
0.77
3.1778 1.8 0.2538 1.1
0.59
1.9676 3.7 0.1887 2.6
0.71
3.6392 3.1 0.2763 2.3
0.75
4.2332 3.2 0.2993 2.1
0.64
4.1387 3.3 0.2967 1.9
0.56
4.9862 2.8 0.3263 2.2
0.79
4.8468 3.1 0.3201 1.2
0.39
14.8828 1.9 0.5394 1.0
0.53
1.7652 3.5 0.1691 1.9
0.53
3.8988 2.8 0.2842 1.6
0.56
0.5143 4.2 0.0683 1.9
0.45
17.4912 3.7 0.5826 1.8
0.47
2.9334 3.5 0.2379 1.7
0.48
3.0701 2.2 0.2442 1.6
0.74
4.5878 2.8 0.3084 2.4
0.84
0.6991 7.9 0.0866 1.0
0.13
5.3358 5.0 0.3336 1.6
0.32
4.3892 2.1 0.3006 1.5
0.69
2.5896 2.5 0.2188 1.5
0.60
2.0314 2.0 0.1906 1.8
0.87
Apparent ages (Ma)
206Pb*
207Pb*
206Pb*
± (Ma)
± (Ma)
± (Ma)
238U*
235U
207Pb*
986.1 26.3 996.2 22.1 1018.5
40
1752.4 48.2 1801.3 32.3 1858.4
40
1172.2 10.7 1195.2 28.0 1237.2
76
1073.1 13.3 1071.1 17.1 1067.1
44
1094.2 17.4 1109.4 29.5 1139.3
80
1966.4 54.7 2305.9 42.9 2621.8
57
1654.6 19.0 1747.8 46.3 1861.1
98
1321.1 11.9 1341.8 22.0 1374.9
53
1160.3 10.7 1145.4 18.3 1117.3
49
2670.8 60.6 2697.9 32.8 2718.3
34
308.1
3.2 426.2 20.9 1128.3
118
1817.5 31.7 1807.1 25.2 1795.2
40
1132.6 23.4 1136.4 19.1 1143.7
33
1173.3 23.2 1175.0 19.6 1178.2
36
1720.0 20.5 1746.6 33.9 1778.5
70
1739.6 27.0 1737.0 29.6 1733.8
57
484.8
6.4 487.0 33.2
497.3
187
1713.4 15.6 1723.5 33.4 1735.6
71
1732.9 16.4 1710.6 27.3 1683.4
58
1870.4 52.0 1887.6 38.9 1906.5
58
1210.9 11.0 1201.5 27.0 1184.7
73
438.1
8.1 448.4 32.8
501.8
195
1634.6 21.9 1639.6 19.9 1645.9
36
1256.9 11.4 1340.5 46.7 1476.5
118
1093.1 13.2 1098.4 11.5 1109.1
22
534.2 11.7 544.9 18.0
589.6
78
1611.5 49.2 1614.3 36.0 1617.9
53
1026.5 22.3 1042.0 30.2 1074.7
80
1471.6 14.5 1487.1 15.0 1509.3
30
494.4 13.5 525.7 27.7
664.4
131
1471.8 19.9 1463.7 25.0 1451.9
54
1082.5 16.9 1077.9 19.6 1068.4
48
1592.2 25.3 1614.5 24.3 1643.7
45
1379.5 31.9 1526.4 33.2 1736.5
61
1853.1 16.1 1918.8 14.7 1990.5
25
452.0
4.4 482.7 43.3
631.1
242
1816.9 47.7 1813.5 31.8 1809.6
41
1104.4 27.9 1097.7 25.1 1084.6
51
1067.0 23.8 1065.7 21.0 1063.0
42
1793.8 65.9 1803.5 38.7 1814.6
33
1823.3 45.3 1820.4 27.8 1817.0
30
1567.9 28.1 1570.5 20.5 1574.1
30
2819.8 78.6 2823.5 34.1 2826.2
16
1692.0 14.9 1679.1 16.1 1662.9
31
1186.2 18.1 1204.5 35.7 1237.6
94
1669.8 23.7 1678.1 18.8 1688.6
30
1346.9 28.7 1346.0 22.8 1344.7
38
1458.1 13.8 1451.8 13.8 1442.5
27
1114.3 27.0 1104.5 25.0 1085.2
52
1572.5 32.2 1558.1 24.6 1538.7
39
1687.6 30.4 1680.5 26.3 1671.6
45
1675.0 27.3 1662.0 27.0 1645.6
51
1820.5 35.2 1817.0 23.9 1812.9
32
1790.0 18.8 1793.1 25.7 1796.6
51
2780.9 22.6 2807.8 18.1 2827.1
26
1007.3 17.5 1032.7 23.0 1087.0
60
1612.5 22.5 1613.4 23.0 1614.7
44
426.0
7.9 421.4 14.6
395.9
85
2959.3 41.8 2962.2 35.8 2964.1
53
1375.6 20.7 1390.6 26.5 1413.6
59
1408.3 20.7 1425.3 17.1 1450.7
29
1732.7 36.2 1747.0 23.6 1764.2
28
535.3
5.1 538.2 33.0
550.6
171
1855.9 26.0 1874.6 42.8 1895.5
85
1694.3 22.1 1710.3 17.7 1730.0
28
1275.3 17.5 1297.7 18.4 1335.0
39
1124.8 18.1 1126.1 13.7 1128.5
20
166
Analysis
86
87
88
89
90
91
92
93
94
2DB273
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
U
206Pb
U/Th
(ppm) 204Pb
194 120060
2.7
282 93425
3.0
164 39085
3.7
220
9300
1.0
434 47605
0.8
65 22895
3.4
118 89930
1.7
562 70665
1.5
383 60470
1.3
34
57
557
61
150
175
125
100
815
49
174
415
132
261
517
113
2031
540
134
479
835
289
203
339
960
286
138
792
471
196
174
229
94
457
133
514
65
105
257
72
811
341
129
226
247
79
242
23
87
132
219
82
323
166
175
205
127
15410
16710
47150
25805
18170
53765
58190
69095
28270
3170
48730
58215
40060
11250
11200
44685
31175
135275
11865
124320
84485
3740
59325
120970
155625
34155
38365
197655
21895
32525
58150
100705
22120
102670
35150
43240
6450
25705
105340
17490
14325
7075
39275
114175
17875
10080
7220
29180
5630
68770
18370
33555
15670
53740
61600
116670
35145
2.1
2.1
3.3
1.3
1.3
2.8
0.8
2.3
2.5
0.4
1.9
1.4
1.8
2.4
1.9
2.6
4.1
3.2
0.7
0.9
1.9
1.3
1.1
2.1
1.8
2.1
1.5
2.7
3.3
1.0
2.0
2.3
0.7
2.3
1.5
1.4
1.3
1.0
1.6
1.4
1.9
1.7
1.6
1.3
0.6
0.6
1.6
1.3
0.8
3.9
1.7
1.5
2.1
1.8
2.3
0.9
2.3
Table4.4. (Cont'd)
Isotopic ratios
206Pb*
207Pb*
206Pb* ± error
± (%)
± (%)
(%) corr.
207Pb*
235U*
238U
8.2220 1.3 5.8718 2.0 0.3501 1.6
0.76
13.7446 2.3 1.6276 3.5 0.1623 2.6
0.75
12.4515 2.2 2.2938 3.8 0.2071 3.1
0.82
13.9672 15.2 0.6028 15.4 0.0611 2.7
0.17
17.6138 3.6 0.5590 3.7 0.0714 1.0
0.27
14.0999 4.5 1.5467 4.6 0.1582 1.0
0.22
9.6749 2.6 4.1111 2.8 0.2885 1.1
0.40
17.9419 2.4 0.5139 3.0 0.0669 1.7
0.58
17.4416 1.9 0.6950 3.3 0.0879 2.7
0.83
8.5877
12.2972
13.5072
10.9021
17.6768
12.6433
9.7882
6.2368
19.6508
14.5663
13.2811
9.8376
13.0549
18.5993
19.8719
13.5174
20.7094
12.8133
17.9980
10.1213
17.7509
20.1038
10.0573
9.1997
14.2023
18.4885
12.9361
13.6064
10.6116
15.3655
11.3116
9.2713
12.5296
13.2435
11.8640
12.8814
19.6226
13.5471
8.1653
13.2418
20.6325
21.4599
9.4255
8.5064
18.4651
17.2735
23.6800
5.5841
19.0501
10.6434
19.0628
12.1886
19.6919
12.3000
10.8259
5.7004
12.1537
4.1 5.5241 4.2 0.3441 1.0
3.8 2.2617 4.0 0.2017 1.2
1.8 1.5009 2.5 0.1470 1.8
4.1 3.1759 4.2 0.2511 1.0
6.0 0.5332 6.1 0.0684 1.0
2.2 2.0900 2.4 0.1916 1.0
1.0 4.0911 1.5 0.2904 1.1
1.3 9.9195 2.1 0.4487 1.7
3.5 0.1798 4.1 0.0256 2.1
16.3 0.8578 16.4 0.0906 1.1
3.0 1.8956 3.1 0.1826 1.0
1.7 3.6169 4.4 0.2581 4.1
3.8 2.0397 4.1 0.1931 1.5
10.8 0.1959 10.9 0.0264 1.6
7.6 0.1058 7.7 0.0153 1.3
2.6 1.7741 3.1 0.1739 1.7
4.4 0.0895 4.6 0.0134 1.4
1.3 2.0369 2.9 0.1893 2.6
7.4 0.5159 8.5 0.0673 4.3
3.9 3.5572 4.1 0.2611 1.3
1.9 0.5429 3.7 0.0699 3.1
8.4 0.0983 8.7 0.0143 2.2
2.4 3.9675 3.5 0.2894 2.6
2.5 4.7303 3.7 0.3156 2.7
2.0 1.5036 2.7 0.1549 1.8
2.5 0.4750 3.3 0.0637 2.2
2.7 1.8909 4.4 0.1774 3.5
2.7 1.6780 4.3 0.1656 3.4
3.6 0.6498 4.2 0.0500 2.1
2.2 1.1051 6.0 0.1232 5.6
3.4 2.7963 4.3 0.2294 2.7
1.5 4.5475 4.3 0.3058 4.1
2.2 2.2551 2.7 0.2049 1.6
1.6 1.8835 3.0 0.1809 2.5
2.2 2.6288 2.9 0.2262 2.0
2.9 1.7075 7.5 0.1595 6.9
8.1 0.4584 8.3 0.0652 1.7
3.0 1.7975 3.4 0.1766 1.7
1.4 5.6699 4.8 0.3358 4.6
4.4 1.9246 4.7 0.1848 1.8
3.1 0.1008 3.8 0.0151 2.3
9.2 0.0969 9.7 0.0151 3.3
2.8 4.5169 3.6 0.3088 2.3
1.5 5.5829 2.4 0.3444 1.9
9.5 0.3764 9.8 0.0504 2.4
7.2 0.7200 7.6 0.0902 2.6
14.6 0.0826 14.8 0.0142 2.3
3.0 12.7471 3.2 0.5162 1.0
14.7 0.2615 14.8 0.0361 2.1
2.7 3.4283 2.9 0.2646 1.0
16.9 0.2750 17.0 0.0380 1.0
1.7 2.3996 2.1 0.2121 1.2
12.1 0.1832 12.2 0.0262 1.0
3.1 2.0261 3.3 0.1807 1.0
2.0 2.9653 2.2 0.2328 1.0
1.3 12.0061 3.3 0.4964 3.0
2.5 2.4249 4.2 0.2137 3.3
0.24
0.31
0.70
0.24
0.16
0.41
0.73
0.79
0.52
0.07
0.32
0.93
0.36
0.15
0.17
0.54
0.30
0.89
0.50
0.32
0.86
0.25
0.74
0.73
0.68
0.65
0.79
0.78
0.51
0.93
0.63
0.94
0.59
0.85
0.68
0.92
0.20
0.50
0.96
0.38
0.60
0.33
0.64
0.78
0.25
0.34
0.15
0.32
0.14
0.35
0.06
0.58
0.08
0.31
0.45
0.92
0.80
Apparent ages (Ma)
206Pb*
207Pb*
206Pb*
± (Ma)
± (Ma)
± (Ma)
238U*
235U
207Pb*
1935.3 25.9 1957.1 17.8 1980.2
24
969.3 23.5 980.9 22.0 1007.1
47
1213.6 34.3 1210.4 26.7 1204.6
42
382.1 10.0 479.0 59.0
974.5
311
444.7
4.3 450.9 13.5
482.7
79
946.6
8.9 949.2 28.2
955.2
91
1633.9 16.3 1656.5 22.9 1685.3
47
417.3
7.0 421.1 10.2
441.8
54
543.2 14.3 535.8 13.8
504.4
41
1906.2
1184.5
884.3
1444.2
426.3
1130.3
1643.7
2389.4
163.1
559.2
1081.1
1479.9
1138.3
168.1
97.6
1033.7
86.1
1117.5
420.1
1495.6
435.5
91.7
1638.5
1768.3
928.3
398.1
1052.8
987.8
314.6
748.7
1331.4
1719.9
1201.7
1072.0
1314.5
954.1
407.4
1048.4
1866.3
1093.3
96.5
96.5
1734.7
1908.0
317.0
556.7
90.8
2683.3
228.8
1513.6
240.6
1240.1
166.5
1071.0
1349.3
2598.2
1248.7
16.5
13.1
14.5
12.9
4.1
10.4
15.7
33.1
3.4
5.8
10.0
54.2
15.3
2.7
1.2
15.9
1.2
26.2
17.3
17.6
13.2
2.0
37.2
41.8
15.8
8.4
34.0
31.0
6.5
39.6
32.7
61.1
17.4
24.9
23.5
61.5
6.6
16.6
74.1
18.3
2.2
3.1
35.1
31.0
7.5
13.7
2.1
21.9
4.6
13.5
2.4
13.4
1.6
9.9
12.2
65.0
37.7
1904.4
1200.4
930.8
1451.3
433.9
1145.5
1652.5
2427.3
167.9
628.9
1079.6
1553.3
1128.9
181.6
102.1
1036.0
87.0
1127.9
422.4
1540.1
440.4
95.2
1627.6
1772.6
931.9
394.7
1077.9
1000.2
508.4
755.8
1354.6
1739.7
1198.4
1075.3
1308.7
1011.3
383.2
1044.6
1926.8
1089.7
97.5
93.9
1734.1
1913.5
324.4
550.7
80.5
2661.1
235.9
1510.9
246.7
1242.5
170.8
1124.3
1398.8
2604.9
1250.0
36.5
27.8
15.4
32.2
21.6
16.8
12.1
19.3
6.3
76.8
20.7
35.3
27.8
18.1
7.5
20.1
3.9
19.5
29.5
32.8
13.1
7.9
28.2
31.0
16.3
10.9
29.3
27.6
16.6
32.1
32.4
35.9
19.0
19.7
21.6
48.1
26.5
22.4
41.2
31.7
3.6
8.7
30.1
20.7
27.2
32.5
11.5
29.7
31.3
22.5
37.2
14.8
19.1
22.2
17.0
31.0
30.0
1902.4
1229.2
1042.4
1461.7
474.8
1174.5
1663.8
2459.2
235.8
888.3
1076.4
1654.5
1110.8
361.2
209.9
1040.9
113.3
1148.0
434.9
1601.6
465.6
182.9
1613.4
1777.7
940.4
374.7
1129.0
1027.6
1512.8
776.9
1391.3
1763.6
1192.3
1082.1
1299.2
1137.4
239.1
1036.4
1992.5
1082.3
122.1
28.7
1733.4
1919.4
377.5
525.7
-212.8
2644.4
306.9
1507.2
305.4
1246.5
230.9
1228.7
1475.0
2610.1
1252.2
74
74
37
77
133
44
19
21
81
339
59
31
76
243
177
53
105
26
165
73
42
197
44
46
40
57
54
55
67
47
65
27
43
31
42
58
188
60
25
88
72
220
51
27
214
158
369
50
336
51
388
33
281
61
38
22
49
167
Analysis
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
4DB191
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
U
(ppm)
216
191
422
546
106
229
186
273
574
126
176
94
267
105
934
411
282
122
339
108
184
260
110
145
409
391
216
291
290
285
146
114
172
210
164
242
187
487
277
262
201
460
560
419
167
306
741
95
187
245
119
278
829
325
153
480
186
419
149
264
125
324
321
235
253
348
206Pb
U/Th
204Pb
66490
1.9
24250
0.5
36935
0.6
113740
3.0
27505
2.6
65680
1.5
28565
2.7
49985
1.7
6675
0.9
44575
0.6
40590
1.6
9780
1.9
64245
5.9
24015
2.7
16590
2.7
163770
1.8
185780
2.1
44185
1.7
113285
3.2
47295
1.4
44565
0.9
30810
1.1
53285
1.3
63750
1.9
54940
1.2
114870
1.8
104190
2.6
27200
2.5
22515
1.4
107245
3.2
44560
1.8
32860
1.0
87015
102950
87655
124830
65140
118000
121860
104845
81680
162710
12295
134120
94435
85795
61695
56560
117670
156805
83770
144665
13865
160470
86685
13745
41350
164485
76045
34155
68260
140760
36735
87275
153445
185600
Table4.4. (Cont'd)
Isotopic ratios
206Pb*
207Pb*
206Pb* ± error
± (%)
± (%)
(%) corr.
207Pb*
235U*
238U
10.7355 1.2 3.1551 2.7 0.2457 2.4
0.89
9.3173 2.2 4.5491 2.5 0.3074 1.2
0.48
17.9541 4.5 0.5227 4.7 0.0681 1.4
0.31
12.4813 2.3 2.2806 3.5 0.2064 2.7
0.76
12.8549 2.1 2.1555 2.4 0.2010 1.0
0.43
11.1369 1.8 3.0476 3.6 0.2462 3.1
0.87
15.0413 1.8 1.2502 3.3 0.1364 2.8
0.84
12.6692 1.8 2.2205 2.1 0.2040 1.0
0.48
19.2416 20.6 0.1075 20.6 0.0150 1.8
0.08
9.6298 1.0 4.2951 2.2 0.3000 1.9
0.88
12.6969 1.8 2.1662 2.5 0.1995 1.8
0.71
17.2615 5.2 0.6690 5.5 0.0837 1.7
0.30
13.0299 1.2 1.8886 3.8 0.1785 3.6
0.95
12.9280 2.9 1.9418 3.8 0.1821 2.3
0.62
21.2373 2.9 0.0893 3.3 0.0138 1.6
0.49
9.9715 3.0 3.8136 4.5 0.2758 3.3
0.74
7.6356 1.5 7.0156 2.8 0.3885 2.3
0.83
13.3663 2.3 1.7726 2.7 0.1718 1.4
0.50
10.7679 2.5 3.2024 2.9 0.2501 1.5
0.50
9.0822 2.0 4.9021 4.2 0.3229 3.7
0.88
10.4474 2.0 3.5953 2.2 0.2724 1.0
0.45
14.9289 1.6 1.3085 2.4 0.1417 1.8
0.76
11.0800 2.5 3.0469 2.8 0.2448 1.4
0.50
10.8372 1.6 3.1787 2.1 0.2498 1.4
0.68
16.3572 2.2 0.9076 2.9 0.1077 1.9
0.66
8.2887 3.1 6.0847 3.2 0.3658 1.0
0.31
9.3333 2.0 4.7030 3.1 0.3184 2.4
0.77
20.2992 9.6 0.1723 9.7 0.0254 1.3
0.13
20.4035 7.0 0.1642 7.1 0.0243 1.0
0.14
13.0856 2.3 2.0360 2.5 0.1932 1.0
0.40
13.6288 2.9 1.7168 3.4 0.1697 1.8
0.52
13.6226 2.3 1.7353 2.7 0.1714 1.4
0.52
0.9 9.1223
2.9 8.8172
2.8 9.0214
2.1 9.1378
2.6 8.6580
2.7 11.1361
2.0 9.1573
1.0 9.0581
3.2 11.0179
3.3 9.2077
0.8 8.6480
2.5 9.0908
1.7 9.1014
4.1 9.1126
2.2 9.2880
2.7 8.9228
6.6 9.9059
2.7 9.0659
1.5 8.8522
2.1 8.9319
3.3 8.6837
1.4 9.1262
3.0 9.0581
1.6 8.5966
1.2 9.1479
1.9 9.1577
2.7 9.1380
0.6 5.6254
3.5 8.7812
0.8 9.0602
1.0 9.0910
2.4 11.3545
3.2 9.2388
1.3 9.1608
1.7 4.7870
1.9 5.0509
2.4 5.0552
2.5 4.7041
1.0 5.2501
1.1 2.8680
1.5 4.7903
1.9 5.0188
1.2 3.1117
1.3 4.7391
2.0 3.8511
3.0 4.9176
3.4 4.7344
3.2 4.7006
3.1 3.1288
1.9 5.1526
2.7 3.9078
4.5 5.0354
3.1 5.3070
1.2 5.0668
2.7 4.1183
2.3 4.8640
1.6 4.8058
1.0 4.0243
1.7 4.7470
1.7 4.5896
1.7 4.7298
1.2 11.0221
1.1 5.2422
1.3 4.8514
1.2 4.7458
1.7 2.9762
1.9 4.7837
1.0 4.8111
2.0
2.1
2.6
2.9
1.4
1.5
1.9
2.3
2.8
2.2
4.3
3.2
3.6
3.6
8.0
2.2
3.0
4.6
3.2
1.9
2.9
2.7
2.4
6.3
2.0
2.2
2.4
1.8
1.7
1.7
2.1
2.2
2.1
1.7
0.3167
0.3230
0.3308
0.3118
0.3297
0.2316
0.3181
0.3297
0.2487
0.3165
0.2415
0.3242
0.3125
0.3107
0.2108
0.3334
0.2808
0.3311
0.3407
0.3282
0.2594
0.3219
0.3157
0.2509
0.3150
0.3048
0.3135
0.4497
0.3339
0.3188
0.3129
0.2451
0.3205
0.3197
1.0
1.0
1.0
1.5
1.0
1.0
1.1
1.3
2.6
1.8
3.8
1.1
1.0
1.6
7.4
1.0
1.4
1.0
1.0
1.4
1.0
1.4
1.9
6.2
1.1
1.4
1.7
1.3
1.3
1.0
1.7
1.5
1.0
1.4
0.51
0.47
0.39
0.51
0.71
0.66
0.59
0.55
0.91
0.82
0.89
0.35
0.28
0.45
0.92
0.46
0.46
0.22
0.31
0.75
0.34
0.51
0.77
0.99
0.54
0.62
0.70
0.73
0.76
0.61
0.80
0.66
0.48
0.82
Apparent ages (Ma)
206Pb*
207Pb*
206Pb*
± (Ma)
± (Ma)
± (Ma)
238U*
235U
207Pb*
1416.0 30.9 1446.2 21.0 1490.9
23
1727.9 18.6 1740.0 21.1 1754.5
41
424.5
5.9 427.0 16.4
440.3
100
1209.9 29.6 1206.3 24.9 1199.9
45
1180.5 11.0 1166.8 16.3 1141.5
42
1418.7 39.6 1419.6 27.3 1421.1
34
824.2 21.6 823.5 18.8
821.6
38
1196.9 10.9 1187.5 14.7 1170.4
36
96.0
1.7 103.7 20.3
284.1
475
1691.2 28.7 1692.4 18.0 1693.9
19
1172.5 19.5 1170.3 17.7 1166.1
35
518.5
8.3 520.1 22.3
527.2
114
1058.6 34.9 1077.1 24.9 1114.6
23
1078.2 23.2 1095.6 25.1 1130.2
58
88.1
1.4
86.9
2.8
53.6
69
1570.2 46.0 1595.6 36.1 1629.4
57
2115.9 41.3 2113.4 24.5 2110.9
27
1022.3 12.9 1035.5 17.5 1063.5
47
1438.9 19.0 1457.7 22.7 1485.2
48
1803.9 57.6 1802.6 35.2 1801.1
37
1553.1 13.8 1548.5 17.6 1542.2
37
854.1 14.4 849.4 13.7
837.3
32
1411.8 17.8 1419.5 21.6 1430.9
47
1437.6 18.4 1452.0 16.3 1473.0
29
659.2 12.2 655.8 14.2
644.0
47
2009.5 17.3 1988.1 28.1 1965.8
55
1781.7 37.5 1767.8 26.3 1751.4
37
161.5
2.1 161.4 14.5
160.3
225
154.8
1.5 154.4 10.2
148.3
165
1138.9 10.4 1127.6 17.2 1106.1
46
1010.5 16.6 1014.8 21.9 1024.3
59
1020.1 13.1 1021.7 17.3 1025.2
47
1773.7
1804.4
1842.1
1749.4
1836.8
1343.1
1780.7
1837.0
1431.5
1772.5
1394.7
1810.4
1753.1
1744.0
1232.9
1855.1
1595.2
1843.7
1890.2
1829.8
1486.6
1799.2
1768.8
1443.1
1765.0
1715.2
1757.8
2393.9
1857.1
1783.8
1755.0
1413.1
1792.4
1788.0
15.5
15.7
16.0
22.2
16.0
12.1
17.3
20.3
33.1
28.2
48.2
17.8
15.3
24.6
82.9
16.1
19.9
16.0
16.4
22.1
13.3
21.2
28.6
80.7
16.7
20.8
26.2
26.4
20.8
16.1
25.4
18.8
15.6
22.2
1782.6
1827.9
1828.6
1768.0
1860.8
1373.6
1783.2
1822.5
1435.6
1774.2
1603.5
1805.3
1773.4
1767.3
1439.8
1844.8
1615.3
1825.3
1870.0
1830.6
1657.9
1796.0
1785.9
1639.1
1775.6
1747.4
1772.5
2525.0
1859.5
1793.9
1775.4
1401.6
1782.0
1786.8
16.4
18.1
21.8
24.0
12.1
11.4
15.9
19.4
21.7
18.6
34.7
27.3
30.0
30.1
61.6
18.5
24.6
39.3
27.7
15.8
23.8
22.4
20.3
51.5
16.8
18.5
20.3
16.7
14.4
14.2
17.3
17.0
17.7
14.6
1793.1
1854.8
1813.3
1790.0
1887.7
1421.2
1786.1
1806.0
1441.6
1776.1
1889.8
1799.4
1797.3
1795.0
1760.3
1833.3
1641.6
1804.4
1847.7
1831.4
1882.4
1792.3
1806.0
1900.5
1788.0
1786.1
1790.0
2632.1
1862.2
1805.5
1799.4
1384.0
1770.0
1785.4
31
34
43
45
18
22
28
35
22
23
35
55
63
58
56
35
50
82
56
22
49
42
28
18
31
32
31
20
20
24
22
32
34
18
168
Table4.4. (Cont'd)
Analysis
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
2DB2
1
2
3
U
(ppm)
454
312
226
294
350
410
274
246
364
271
89
516
486
474
208
83
192
384
386
275
309
262
370
163
384
235
85
468
175
258
93
163
195
248
187
366
413
272
233
397
753
321
72
293
199
179
220
228
231
54
93
366
150
112
164
231
341
580
356
229
202
371
354
206Pb
U/Th
204Pb
19770
1.7
26335
1.1
45855
1.5
130335
1.9
152825
1.8
222585
2.3
262740
1.7
194860
2.5
262705
3.9
70420
3.1
37310
1.2
174165
2.2
179565
3.3
195960
2.5
104870
1.7
39240
1.5
89410
0.5
9350
0.6
164995
3.0
169395
3.3
115680
2.3
60515
1.0
159790
1.6
136750
4.2
303390
1.7
109445
1.4
41025
2.1
205955
1.2
89170
0.7
9850
1.8
45195
2.0
82685
1.4
88350
1.9
119425
2.8
36745
0.7
110455
1.1
160060
2.7
156410
2.1
154640
3.0
215735
2.2
36160
4.8
238205
3.2
78925
1.0
105100
1.8
139510
1.7
110735
3.3
144805
1.9
152100
2.3
50515
0.9
34895
1.5
40260
2.2
7215
1.1
111230
1.7
37610
1.4
126700
1.4
80180
2.0
25660
1.9
21150
1.3
166020
2.8
107760
1.3
90230
2.7
137175
2.1
133225
0.8
116
3782
73
8858
503 117792
Isotopic ratios
206Pb*
± (%)
207Pb*
8.6519 1.8
8.8529 1.6
8.9754 1.7
9.1588 1.6
9.1803 1.3
8.6725 1.0
5.4358 2.4
9.0681 1.4
9.0440 2.4
9.1581 1.8
9.2280 1.4
9.1153 1.0
9.1605 1.0
9.1660 1.3
9.3154 1.2
9.1850 1.0
9.0977 1.0
8.5924 1.0
9.0384 2.7
9.1247 2.6
9.1508 1.8
5.5589 2.4
9.1894 1.8
5.1055 1.9
4.7967 2.1
9.1891 1.3
9.1179 1.1
9.0669 1.7
9.0951 3.1
8.4911 2.3
8.8036 1.3
9.1624 1.6
8.7759 1.6
9.0799 1.6
9.0197 1.0
8.1929 1.8
9.1586 1.2
9.1828 2.3
9.0857 1.8
9.2009 2.2
8.8594 2.5
9.0825 1.9
5.3213 2.3
9.0897 1.8
9.2289 1.4
9.1014 2.3
9.1513 1.7
9.0456 2.0
9.0108 2.2
9.2719 1.8
14.1722 2.3
8.1710 4.3
9.2106 1.9
12.7527 1.2
9.1161 1.3
9.2384 3.8
8.9913 1.1
8.8330 1.7
9.1516 1.0
9.1108 1.9
9.2160 1.0
9.2036 1.2
9.1958 1.0
1.7 18.3116
1.9 9.9420
3.9 5.6036
207Pb*
206Pb* ± error
± (%)
(%) corr.
235U*
238U
4.5934 5.1 0.2882 4.8
0.93
3.6922 6.8 0.2371 6.6
0.97
4.7963 2.9 0.3122 2.4
0.82
4.7843 1.9 0.3178 1.0
0.52
4.7678 2.5 0.3174 2.1
0.86
5.3256 1.4 0.3350 1.0
0.71
13.1886 2.6 0.5199 1.0
0.39
4.9143 1.7 0.3232 1.0
0.59
4.8606 2.6 0.3188 1.0
0.39
4.3943 2.1 0.2919 1.0
0.49
4.6162 1.9 0.3090 1.3
0.67
4.6591 1.4 0.3080 1.0
0.71
4.5288 1.6 0.3009 1.2
0.77
4.4797 3.1 0.2978 2.8
0.91
4.3777 1.6 0.2958 1.0
0.63
4.4688 2.1 0.2977 1.8
0.88
4.7221 2.1 0.3116 1.9
0.88
4.0300 4.6 0.2511 4.5
0.98
4.7002 3.2 0.3081 1.8
0.55
4.6243 2.8 0.3060 1.0
0.36
4.6355 2.4 0.3077 1.5
0.65
10.6125 2.9 0.4279 1.6
0.55
4.8061 2.5 0.3203 1.7
0.68
14.0111 2.2 0.5188 1.0
0.47
16.1125 2.3 0.5605 1.0
0.43
4.7785 2.0 0.3185 1.5
0.77
4.8378 1.5 0.3199 1.0
0.68
4.6821 2.5 0.3079 1.8
0.73
4.7197 3.4 0.3113 1.4
0.41
5.2873 2.7 0.3256 1.5
0.54
5.2127 1.6 0.3328 1.0
0.62
4.7946 2.5 0.3186 1.9
0.76
4.9871 2.6 0.3174 2.1
0.80
4.8805 1.8 0.3214 1.0
0.54
4.7093 2.1 0.3081 1.8
0.87
5.0712 2.1 0.3013 1.2
0.58
4.7459 2.3 0.3152 2.0
0.86
4.6928 2.5 0.3125 1.0
0.40
4.7882 2.1 0.3155 1.0
0.48
4.6130 2.7 0.3078 1.6
0.58
4.3813 2.7 0.2815 1.0
0.39
4.8200 2.1 0.3175 1.0
0.47
13.3427 3.0 0.5149 1.9
0.62
4.7803 2.4 0.3151 1.7
0.69
4.7165 1.7 0.3157 1.0
0.59
4.8122 2.7 0.3177 1.5
0.56
4.6702 2.2 0.3100 1.5
0.66
4.6329 3.6 0.3039 2.9
0.83
4.5901 3.6 0.3000 2.9
0.80
4.6901 2.1 0.3154 1.1
0.52
1.5005 2.5 0.1542 1.0
0.40
4.5700 5.4 0.2708 3.2
0.59
4.8450 2.1 0.3237 1.0
0.48
2.0802 1.6 0.1924 1.0
0.64
4.7157 1.6 0.3118 1.0
0.61
4.5061 4.0 0.3019 1.3
0.33
4.4085 1.5 0.2875 1.0
0.68
3.9036 7.0 0.2501 6.8
0.97
4.7250 1.4 0.3136 1.0
0.71
4.7111 2.2 0.3113 1.0
0.47
4.6843 1.7 0.3131 1.4
0.82
4.5570 2.1 0.3042 1.7
0.82
4.6294 1.8 0.3088 1.5
0.83
7.2 0.6139
1.1 4.0219
1.0 11.6668
7.3 0.0815 1.0
1.5 0.2900 1.0
1.4 0.4741 1.0
Apparent ages (Ma)
206Pb*
207Pb*
206Pb*
± (Ma)
± (Ma)
± (Ma)
238U*
235U
207Pb*
1632.7 69.1 1748.1 42.8 1888.9
33
1371.4 81.3 1569.7 54.1 1847.5
28
1751.6 36.5 1784.2 24.3 1822.6
30
1779.0 15.5 1782.1 16.1 1785.8
30
1777.3 33.2 1779.2 20.9 1781.6
23
1862.4 16.2 1873.0 12.1 1884.7
18
2699.0 22.1 2693.2 24.1 2688.9
39
1805.4 15.7 1804.7 14.3 1803.9
25
1784.0 15.6 1795.5 21.8 1808.8
43
1650.9 14.6 1711.3 17.0 1786.0
33
1735.5 19.3 1752.2 15.8 1772.1
26
1730.9 15.2 1759.9 11.8 1794.5
18
1695.7 17.9 1736.3 13.0 1785.5
18
1680.4 41.4 1727.2 25.7 1784.4
24
1670.3 14.7 1708.1 13.1 1754.9
23
1679.9 27.2 1725.2 17.4 1780.6
18
1748.5 28.8 1771.2 17.8 1798.0
18
1444.4 58.2 1640.3 37.5 1901.4
18
1731.4 26.7 1767.3 26.6 1809.9
48
1721.1 15.1 1753.7 23.0 1792.6
47
1729.1 23.4 1755.7 19.9 1787.4
33
2296.1 30.5 2489.8 26.8 2651.8
40
1791.3 26.6 1786.0 20.9 1779.8
33
2694.1 22.7 2750.5 20.8 2792.1
32
2868.8 23.2 2883.5 22.2 2893.7
34
1782.2 23.8 1781.1 16.8 1779.8
23
1789.4 15.6 1791.5 12.4 1794.0
20
1730.3 27.2 1764.1 20.5 1804.2
31
1747.3 21.1 1770.7 28.2 1798.6
56
1817.1 23.4 1866.8 23.4 1922.6
41
1852.1 16.1 1854.7 13.8 1857.6
23
1782.9 29.3 1784.0 20.8 1785.1
29
1777.1 32.6 1817.1 22.2 1863.3
29
1796.5 15.7 1798.9 15.5 1801.6
28
1731.2 27.2 1768.9 17.3 1813.7
19
1697.9 18.4 1831.3 18.1 1986.5
31
1766.5 30.9 1775.4 19.6 1785.9
22
1753.2 15.4 1765.9 20.9 1781.1
42
1767.8 15.5 1782.8 17.4 1800.4
33
1730.0 24.0 1751.6 22.7 1777.5
41
1599.0 14.7 1708.8 22.2 1846.2
45
1777.5 15.5 1788.4 17.9 1801.1
34
2677.7 40.5 2704.2 28.1 2724.1
38
1766.0 25.8 1781.4 20.4 1799.6
32
1768.7 15.5 1770.2 14.3 1771.9
25
1778.2 23.8 1787.0 23.1 1797.3
42
1740.6 22.4 1761.9 18.7 1787.3
31
1710.8 44.2 1755.2 29.7 1808.5
36
1691.2 42.8 1747.5 30.1 1815.5
40
1767.2 17.2 1765.5 18.0 1763.4
34
924.6
8.6 930.6 15.2
944.7
47
1545.0 43.6 1743.8 44.8 1991.3
77
1807.5 15.8 1792.7 17.7 1775.6
34
1134.4 10.4 1142.3 10.7 1157.4
24
1749.5 15.3 1770.0 13.7 1794.3
24
1700.8 19.9 1732.1 33.4 1770.1
69
1628.9 14.4 1713.9 12.2 1819.4
20
1438.9 88.0 1614.4 56.8 1851.6
30
1758.5 15.4 1771.7 11.9 1787.3
18
1747.1 15.6 1769.2 18.3 1795.4
35
1755.9 21.7 1764.4 14.5 1774.5
18
1712.0 26.0 1741.4 17.6 1776.9
22
1734.6 22.4 1754.6 14.8 1778.5
18
0.14 505.3
0.69 1641.6
0.72 2501.7
4.9 486.0
14.5 1638.6
21.6 2578.0
28.1
11.9
13.6
396.3
1634.9
2638.6
162
20
17
169
Table4.4. (Cont'd)
Analysis
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
U
206Pb
U/Th
(ppm) 204Pb
513 46382
5.9
402 11158
1.1
334 48556
2.2
257 13110
2.5
193 18290
3.0
136 19294
3.9
278
7066
2.0
40
4826
1.1
404 56014
3.5
350 30620
3.4
112 13714
2.3
257 36696
2.8
105 12140
3.8
251 24780
3.9
472 48932
6.9
185 26448
1.9
89 14414
1.1
97 14258
1.5
220 18796
3.1
397 53974 51.6
122 16940
0.5
121 24154
1.2
602 36144
2.0
70
8302
1.9
131 16644
2.7
295 30000
0.9
310 28232
1.0
53 12038
2.8
442 51864 17.6
432 57066
1.7
361 54362
2.8
353 55718
3.4
246 47098
2.0
127 26168
1.6
23
6456
0.8
90 17304
0.9
392 68948
3.7
211 19752
0.8
163 16592
1.0
370 30822
1.4
155 12724
1.6
122
7552
2.0
299 24832
2.5
787 48150 12.4
187
5080
1.2
184
3740
1.4
188 20944
1.4
224
4576
1.5
369 22608
1.2
572 48128
2.5
264
9748
0.9
122 11848
2.8
74
6094
1.0
190 23178
0.4
357
7164
0.8
243 18132
1.7
177 12940
4.2
248 23220
0.6
280
6412
3.7
338 41050
1.7
218 20294
2.8
274 35040
1.8
613 73736
3.0
161 42836
3.9
222 20432
1.8
321 51968
1.5
1286 18536
4.3
Isotopic ratios
206Pb*
± (%)
207Pb*
13.3004 1.0
17.6471 1.2
7.7833 1.1
12.8251 1.7
13.5221 1.0
10.6319 1.7
16.9276 1.3
9.7323 3.9
9.0104 1.3
13.4019 1.0
10.9731 1.6
5.3408 1.4
11.8065 3.5
13.5491 1.7
12.4101 1.9
9.0632 1.3
9.1566 1.7
9.8251 1.4
12.5345 2.2
9.4188 1.9
10.5452 1.8
3.6787 3.0
13.1477 2.4
12.1747 1.2
10.9060 1.4
8.9839 4.5
5.6216 2.0
8.4925 1.9
12.6881 3.7
10.8471 2.2
9.1108 4.0
9.1083 2.1
9.0537 1.8
8.5443 2.6
8.8122 2.3
9.1104 1.2
9.0426 2.5
9.1597 1.3
5.2145 1.7
9.1501 1.4
10.7344 1.4
13.7412 2.0
10.4935 1.4
13.6426 1.0
18.2622 2.5
18.4504 1.7
9.0773 1.0
18.3278 2.3
12.4603 1.3
9.0269 1.1
8.6149 2.1
9.0159 1.0
12.2937 2.1
9.2132 3.9
17.8710 2.2
13.4199 1.2
12.4479 1.0
9.7669 1.0
12.8578 12.9
8.0771 1.0
11.6919 1.3
9.0962 1.4
8.7034 1.0
4.8170 2.6
13.2726 1.7
9.2685 1.0
9.2396 1.5
207Pb*
206Pb* ± error
± (%)
(%) corr.
235U*
238U
1.8902 1.4 0.1823 1.0
0.71
0.5952 1.5 0.0762 1.0
0.65
6.8491 1.5 0.3866 1.0
0.68
1.9701 2.0 0.1833 1.0
0.50
1.7824 1.4 0.1748 1.0
0.71
3.4072 1.9 0.2627 1.0
0.51
0.6664 2.5 0.0818 2.2
0.85
4.1782 4.1 0.2949 1.3
0.32
4.9305 1.6 0.3222 1.0
0.62
1.8102 1.8 0.1760 1.5
0.84
3.1258 1.9 0.2488 1.0
0.53
12.4357 1.9 0.4817 1.2
0.65
2.4885 3.7 0.2131 1.0
0.27
1.7575 2.0 0.1727 1.0
0.51
2.2921 4.1 0.2063 3.7
0.89
4.4561 1.6 0.2929 1.0
0.61
4.7968 1.9 0.3186 1.0
0.52
3.9351 1.7 0.2804 1.0
0.59
2.2390 3.1 0.2035 2.2
0.71
4.0518 2.9 0.2768 2.2
0.77
3.3420 2.0 0.2556 1.0
0.50
22.7599 4.4 0.6072 3.1
0.72
1.8906 2.9 0.1803 1.6
0.54
2.5342 1.6 0.2238 1.0
0.62
3.2594 2.4 0.2578 1.9
0.80
4.7420 4.6 0.3090 1.1
0.23
11.4650 5.8 0.4674 5.4
0.94
5.7257 2.2 0.3527 1.0
0.46
2.1204 4.2 0.1951 2.1
0.50
3.2302 2.6 0.2541 1.5
0.56
4.7721 4.2 0.3153 1.3
0.30
4.7612 2.8 0.3145 1.9
0.68
4.8792 2.3 0.3204 1.5
0.63
5.3879 2.8 0.3339 1.0
0.36
5.2641 3.5 0.3364 2.6
0.75
4.4895 1.5 0.2966 1.0
0.65
4.8390 2.7 0.3174 1.0
0.37
4.6720 2.7 0.3104 2.3
0.87
9.8226 5.1 0.3715 4.8
0.94
4.7600 1.7 0.3159 1.0
0.58
3.0832 1.9 0.2400 1.4
0.72
1.7317 2.5 0.1726 1.6
0.62
3.5023 1.8 0.2665 1.1
0.60
1.6865 1.5 0.1669 1.1
0.75
0.5287 2.7 0.0700 1.1
0.41
0.4509 5.7 0.0603 5.4
0.95
4.7839 1.9 0.3149 1.6
0.85
0.5010 2.5 0.0666 1.0
0.39
2.1360 1.8 0.1930 1.2
0.65
4.8434 1.5 0.3171 1.0
0.68
3.8652 2.4 0.2415 1.2
0.50
4.8353 1.6 0.3162 1.2
0.77
2.4332 2.3 0.2169 1.0
0.43
4.8038 4.4 0.3210 2.1
0.47
0.5446 2.4 0.0706 1.1
0.44
1.8277 2.2 0.1779 1.9
0.86
2.3174 1.5 0.2092 1.1
0.73
4.1371 1.4 0.2931 1.0
0.71
1.0452 13.5 0.0975 3.9
0.29
6.0024 2.0 0.3516 1.8
0.87
2.6824 2.1 0.2275 1.7
0.79
4.9740 1.7 0.3281 1.0
0.59
5.3540 1.4 0.3380 1.0
0.71
15.8528 2.8 0.5538 1.0
0.36
1.9428 2.2 0.1870 1.4
0.63
4.7528 1.9 0.3195 1.6
0.85
4.1313 2.8 0.2768 2.3
0.85
Apparent ages (Ma)
206Pb*
207Pb*
206Pb*
± (Ma)
± (Ma)
± (Ma)
238U*
235U
207Pb*
1079.7
9.9 1077.6
9.4 1073.4
20
473.3
4.6 474.2
5.8
478.6
26
2107.2 18.0 2092.1 13.1 2077.3
19
1084.7 10.1 1105.3 13.6 1146.2
35
1038.5
9.6 1039.1
9.2 1040.2
20
1503.8 13.4 1506.1 15.3 1509.2
32
506.9 10.5 518.5 10.3
569.9
29
1666.1 19.4 1669.8 33.6 1674.4
72
1800.5 15.7 1807.5 13.7 1815.6
23
1044.8 14.8 1049.2 12.0 1058.2
20
1432.1 12.8 1439.1 14.6 1449.3
31
2534.7 25.1 2637.9 17.4 2718.0
23
1245.2 11.3 1268.7 26.6 1308.6
68
1027.0
9.5 1029.9 12.7 1036.1
34
1209.1 40.4 1209.8 29.2 1211.2
38
1656.1 14.6 1722.8 13.5 1804.9
23
1782.7 15.6 1784.3 16.3 1786.3
30
1593.4 14.1 1620.9 13.6 1656.8
25
1194.3 24.3 1193.3 21.9 1191.5
43
1575.1 31.3 1644.7 23.8 1734.7
34
1467.3 13.1 1490.9 15.8 1524.7
33
3059.0 76.5 3216.7 42.5 3316.6
47
1068.5 15.3 1077.8 19.0 1096.6
48
1301.8 11.8 1281.9 11.7 1248.8
24
1478.6 25.2 1471.4 18.6 1461.0
27
1735.7 16.0 1774.7 38.4 1820.9
81
2472.4 110.7 2561.7 53.9 2633.2
34
1947.3 17.0 1935.3 18.8 1922.4
35
1149.1 22.1 1155.5 29.2 1167.5
73
1459.7 18.9 1464.4 20.1 1471.3
41
1766.9 19.5 1780.0 35.5 1795.4
74
1762.9 29.0 1778.1 23.3 1795.9
37
1791.6 22.7 1798.7 19.5 1806.9
33
1857.2 16.1 1882.9 23.6 1911.4
46
1869.5 42.7 1863.1 29.9 1855.9
42
1674.6 14.7 1729.0 12.8 1795.5
21
1776.8 15.5 1791.7 22.9 1809.1
46
1742.5 35.4 1762.2 22.2 1785.7
24
2036.4 84.3 2418.3 47.3 2757.4
28
1769.6 15.5 1777.9 14.5 1787.6
26
1386.9 17.3 1428.5 14.9 1491.1
26
1026.3 14.8 1020.4 16.3 1007.6
40
1523.2 14.4 1527.7 14.0 1533.9
27
994.8 10.4 1003.4
9.6 1022.2
20
436.3
4.7 431.0
9.6
402.3
56
377.7 19.8 377.9 17.9
379.3
38
1765.0 24.7 1782.1 15.8 1802.1
18
415.6
4.0 412.4
8.6
394.3
52
1137.8 12.0 1160.5 12.2 1203.2
26
1775.5 15.5 1792.5 12.4 1812.2
20
1394.5 15.3 1606.4 19.7 1896.7
38
1771.1 18.7 1791.1 13.2 1814.5
18
1265.7 11.5 1252.5 16.7 1229.7
41
1794.6 32.1 1785.6 36.7 1775.0
70
439.7
4.5 441.4
8.6
450.6
48
1055.4 18.7 1055.4 14.7 1055.5
23
1224.7 11.8 1217.6 10.3 1205.2
20
1656.8 14.6 1661.7 11.6 1667.8
19
599.5 22.6 726.5 70.0 1141.1
257
1942.3 29.9 1976.2 17.8 2011.8
18
1321.2 19.7 1323.6 15.5 1327.5
25
1829.4 15.9 1814.9 14.3 1798.3
25
1876.8 16.3 1877.5 12.1 1878.3
18
2841.1 23.0 2868.0 26.3 2886.9
42
1105.2 13.9 1095.9 14.6 1077.6
34
1787.2 25.3 1776.6 16.0 1764.1
18
1575.5 32.7 1660.5 22.6 1769.8
27
170
Analysis
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
2DB257
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
U
206Pb
U/Th
(ppm) 204Pb
200 35592
2.1
106 25570
1.1
309 39296
1.6
340 35208
3.2
80
6850
1.8
195 23658
1.7
54
5532
0.2
397 29882
2.3
725 44792
6.0
333 27448
3.0
269 24552
2.0
167
4702
0.8
195 14462
1.2
117 11796
2.1
387 53776
1.9
279 31172
1.3
118
9398
1.3
238 21710
1.9
Table4.4. (Cont'd)
Isotopic ratios
206Pb*
207Pb*
206Pb* ± error
± (%)
± (%)
(%) corr.
207Pb*
235U*
238U
9.3322 1.9 4.7317 2.1 0.3203 1.0
0.47
5.1706 1.3 14.2662 1.8 0.5350 1.2
0.67
9.1746 1.6 4.9965 1.9 0.3325 1.0
0.53
9.0970 1.5 4.7518 1.8 0.3135 1.0
0.56
11.6705 3.6 2.8307 3.7 0.2396 1.1
0.30
9.8234 1.6 4.1614 2.2 0.2965 1.4
0.67
9.9499 2.5 3.9906 2.9 0.2880 1.4
0.47
12.7446 1.8 2.1468 2.4 0.1984 1.5
0.65
13.1627 1.0 1.9156 2.1 0.1829 1.8
0.87
12.5331 1.1 2.1767 1.9 0.1979 1.6
0.82
11.5589 1.5 2.6725 2.3 0.2240 1.7
0.76
18.5267 2.1 0.5253 2.5 0.0706 1.4
0.56
12.7651 1.0 2.0867 2.0 0.1932 1.7
0.87
12.3292 1.7 2.2803 2.0 0.2039 1.1
0.52
8.7597 1.4 5.1400 2.4 0.3266 1.9
0.80
9.7170 2.3 3.9535 2.8 0.2786 1.6
0.57
13.4246 1.4 1.8598 2.2 0.1811 1.7
0.77
12.9732 2.8 1.8617 3.0 0.1752 1.0
0.34
169 33770
1.0 9.4527
418 58956
2.8 9.1828
323 35920
4.4 9.4688
118 20410
1.1 9.9147
126 38674
1.8 5.3600
251 35298
2.8 11.4330
120
6722
2.3 17.1875
187 63214
3.3 7.6904
279 95960
3.3 5.0313
583 39974 13.1 9.2971
518 58002
1.9 11.5792
166 11602
2.6 17.7927
216 13948
3.0 8.2914
191
9594
2.0 18.7161
219 40828
3.1 10.8027
196 26352
1.4 10.0390
402 12034
5.7 5.9361
203 23960
1.7 11.2595
194 34058
3.3 9.2308
913 36864
3.5 9.0131
206 35624
3.2 9.3085
291 47178
1.3 9.6039
133 28836 101.6 9.5598
872 20288
1.8 5.3850
65
7736
1.0 8.2649
361 43538
1.6 9.4377
620 109898
4.2 9.5016
464 11522
2.2 18.8112
216 32004
2.1 11.5862
693
5418
1.2 15.3428
206 16758
2.8 10.7143
149 33136
6.4 9.0082
170 13388
2.8 8.9812
257 41818
2.6 9.4267
699
3428
2.0 22.9897
191
5678
2.3 9.2717
337 40530
1.2 9.8699
647 70006
1.6 9.1566
518 69900
2.8 9.5757
330 13914
1.2 5.6571
39
5700
1.7 9.2748
389 17026
2.2 7.4251
80
3206
1.4 19.9569
415 73260
3.9 6.3898
59 19498
1.2 3.7506
362 29670
2.4 9.0951
144 37668
1.5 3.9010
1.9
2.4
1.6
1.0
1.1
1.8
3.2
1.6
2.1
1.5
1.9
3.9
9.7
3.6
4.4
3.2
1.5
2.4
1.7
1.2
1.8
1.8
1.0
2.1
1.3
1.1
2.2
2.9
1.4
2.6
1.4
2.6
2.1
1.4
7.1
6.5
2.0
1.4
2.2
1.4
2.5
4.0
3.9
3.3
1.7
1.4
1.0
4.6378
4.5073
4.6214
4.0127
13.5056
2.8570
0.7280
7.0371
14.8985
4.5946
2.7121
0.6199
5.8532
0.5212
3.2368
3.1578
9.5632
2.9337
4.6452
4.7497
4.7480
4.1324
4.4711
10.8705
4.9588
4.5320
4.4859
0.4210
2.8798
0.8134
3.1981
5.0127
5.0192
4.4787
0.0690
3.6468
4.0316
4.7808
4.2015
8.7692
4.8875
6.9527
0.5726
9.5821
24.9647
4.1945
22.4089
2.9
4.6
2.2
4.2
1.9
2.2
3.4
2.2
2.8
5.2
3.6
4.0
9.8
4.4
4.8
3.9
2.9
3.0
3.3
2.5
3.0
2.2
2.1
3.7
3.7
3.4
2.9
3.4
2.4
3.2
2.7
5.2
2.8
3.2
7.3
6.8
3.2
2.5
3.3
3.7
2.7
4.2
5.3
5.6
2.8
2.7
3.1
0.3180
0.3002
0.3174
0.2885
0.5250
0.2369
0.0908
0.3925
0.5437
0.3098
0.2278
0.0800
0.3520
0.0708
0.2536
0.2299
0.4117
0.2396
0.3110
0.3105
0.3205
0.2878
0.3100
0.4246
0.2972
0.3102
0.3091
0.0574
0.2420
0.0905
0.2485
0.3275
0.3269
0.3062
0.0115
0.2452
0.2886
0.3175
0.2918
0.3598
0.3288
0.3744
0.0829
0.4441
0.6791
0.2767
0.6340
2.2
3.9
1.5
4.0
1.6
1.3
1.3
1.5
1.8
5.0
3.0
1.0
1.5
2.6
2.0
2.2
2.5
1.9
2.8
2.1
2.4
1.3
1.8
3.1
3.4
3.2
1.9
1.8
2.0
1.8
2.3
4.5
1.9
2.9
1.6
1.9
2.5
2.1
2.5
3.4
1.1
1.1
3.6
4.5
2.2
2.3
2.9
0.76
0.85
0.68
0.97
0.81
0.58
0.38
0.68
0.65
0.95
0.84
0.25
0.15
0.59
0.41
0.57
0.87
0.62
0.85
0.86
0.81
0.60
0.88
0.83
0.93
0.94
0.67
0.52
0.82
0.57
0.85
0.87
0.68
0.90
0.22
0.29
0.77
0.84
0.75
0.93
0.40
0.25
0.68
0.81
0.80
0.84
0.95
Apparent ages (Ma)
206Pb*
207Pb*
206Pb*
± (Ma)
± (Ma)
± (Ma)
238U*
235U
207Pb*
1791.0 15.6 1772.9 17.7 1751.6
34
2762.5 26.3 2767.6 16.7 2771.3
21
1850.3 16.1 1818.7 16.0 1782.7
29
1758.0 15.4 1776.4 15.1 1798.2
27
1384.6 14.0 1363.7 28.0 1331.1
69
1673.8 21.2 1666.5 17.6 1657.1
30
1631.4 19.5 1632.3 23.3 1633.4
47
1166.9 16.4 1164.0 16.5 1158.6
36
1082.6 18.2 1086.5 14.0 1094.3
20
1163.8 16.9 1173.6 13.5 1191.8
22
1303.2 20.4 1320.9 16.8 1349.7
29
439.6
6.0 428.7
8.8
370.0
47
1138.6 18.2 1144.4 13.8 1155.5
20
1196.3 11.5 1206.2 14.4 1224.0
34
1821.6 29.8 1842.7 20.0 1866.6
26
1584.4 22.6 1624.7 23.0 1677.3
43
1072.8 16.3 1066.9 14.2 1054.8
28
1040.5
9.6 1067.6 19.6 1123.3
56
1779.7
1692.2
1776.9
1634.3
2720.4
1370.6
560.0
2134.4
2798.7
1739.8
1322.8
496.1
1944.0
440.7
1457.0
1334.1
2222.8
1384.5
1745.6
1743.1
1792.4
1630.7
1740.7
2281.1
1677.6
1741.7
1736.4
360.0
1397.0
558.6
1430.8
1826.2
1823.5
1722.0
73.7
1413.8
1634.5
1777.5
1650.5
1981.2
1832.4
2050.1
513.3
2368.8
3340.9
1574.6
3165.4
33.7
57.9
23.3
58.2
34.8
15.8
7.0
27.6
41.5
75.6
36.4
4.8
24.7
11.1
25.6
26.8
47.4
23.5
43.3
32.4
37.6
18.9
27.8
59.0
50.7
48.5
29.5
6.2
25.2
9.7
29.0
71.6
30.7
43.1
1.2
24.6
35.5
32.9
36.1
58.0
17.4
18.4
17.7
89.8
58.4
31.4
72.3
1756.1
1732.3
1753.1
1636.8
2715.7
1370.7
555.4
2116.1
2808.8
1748.3
1331.8
489.8
1954.3
426.0
1466.0
1446.9
2393.6
1390.6
1757.4
1776.1
1775.8
1660.7
1725.6
2512.1
1812.3
1736.9
1728.4
356.7
1376.6
604.4
1456.7
1821.5
1822.6
1727.0
67.7
1559.8
1640.6
1781.5
1674.3
2314.3
1800.1
2105.4
459.7
2395.5
3306.8
1672.9
3201.6
24.0
38.0
18.5
33.8
18.3
16.7
14.6
19.8
26.7
43.3
26.8
15.6
84.9
15.4
37.4
30.0
26.7
23.0
27.8
20.6
24.9
17.9
17.2
34.4
31.1
28.1
24.0
10.3
18.4
14.4
20.5
43.9
23.9
26.3
4.8
54.1
25.9
21.3
27.0
33.4
22.8
37.1
19.6
51.5
27.3
21.9
29.7
1728.1
1781.1
1725.0
1640.0
2712.1
1370.8
536.6
2098.4
2816.0
1758.5
1346.3
460.4
1965.2
347.1
1479.1
1616.8
2542.4
1400.1
1771.6
1815.0
1756.2
1698.9
1707.4
2704.5
1970.9
1731.0
1718.6
335.6
1345.1
780.0
1494.6
1816.0
1821.4
1733.1
-139.1
1763.5
1648.4
1786.3
1704.3
2622.8
1762.9
2159.8
200.0
2418.2
3286.3
1798.6
3224.4
35
44
30
19
19
35
69
29
35
28
37
86
173
81
83
59
24
45
32
23
32
32
18
34
24
21
40
66
27
54
26
47
37
25
176
119
37
25
40
23
45
71
91
56
26
26
16
171
Table4.4. (Cont'd)
U
(ppm)
48
193
49
271
50
72
51
373
52
224
53
684
54
315
55
211
56
189
57
95
58
278
59
125
60
339
61
96
62
122
63
252
64
374
65
121
66
214
67
77
68
188
69
694
70
632
71
145
72
398
73
120
74
1406
75
113
76
248
77
247
78
283
79
141
80
361
81
143
82
181
83
53
84
548
85
390
86
614
87
474
88
345
89
308
90
173
91
225
92
733
93
52
94
61
95
209
96
475
97
70
98
592
99
349
100
876
101
665
102
180
103
272
104
210
105
963
106
357
107
277
108
689
Little Popo Agie River
1
282
2
99
3
339
4
43
5
134
Analysis
206Pb
204Pb
26948
44256
18742
3022
27116
152644
53586
42516
57108
5768
32318
16598
93382
13496
51182
37816
47330
18392
52628
24570
31432
83096
41774
50442
5224
51508
12288
21984
49748
27960
60926
54432
76058
16760
27560
5586
60028
43312
81680
4308
46514
73536
18898
34810
117596
13368
6544
33606
112874
10236
81300
40740
73340
16230
41944
41942
17446
85014
77082
20370
4594
59485
44555
23115
23080
47850
Isotopic ratios
206Pb*
U/Th
± (%)
207Pb*
1.0 5.9885 1.2
3.1 11.1671 1.4
4.0 9.3368 1.5
24.2 26.3451 8.8
3.2 13.0532 1.0
5.3 5.4505 1.6
5.6 9.0996 1.8
2.5 9.4004 2.7
3.6 6.1801 3.3
1.2 18.7750 5.3
1.6 12.9941 1.3
2.0 13.2265 2.1
4.2 8.8176 1.7
2.2 9.2317 2.2
1.9 5.5972 1.6
2.1 9.1425 2.7
3.3 8.7488 2.8
2.7 12.5855 2.5
4.6 9.5397 4.2
1.6 5.0648 3.4
1.7 10.5507 1.5
7.4 11.1664 1.3
11.3 5.6380 3.5
2.7 5.3711 3.7
2.4 22.5549 7.5
3.4 4.5860 2.4
17.7 9.0136 1.7
1.1 9.4585 2.5
2.2 8.9157 1.4
2.4 9.3369 1.5
4.1 9.1167 1.0
1.1 5.3606 1.7
2.1 9.6839 1.4
3.7 12.9193 3.0
1.2 9.3566 1.0
1.2 12.6958 2.0
4.2 11.1265 1.2
3.6 8.7577 1.0
0.8 9.7340 1.8
1.6 23.5501 4.4
1.5 9.2322 2.8
2.2 6.0290 1.0
1.3 9.1954 2.0
1.3 8.8755 2.1
8.3 5.4143 1.4
1.0 5.4260 1.0
1.4 13.4004 2.1
1.4 9.5488 1.7
4.4 6.5844 1.0
1.0 11.1732 1.5
2.7 6.2800 1.0
1.4 12.2883 1.0
13.0 9.4850 3.1
1.2 17.8550 2.7
2.3 5.4847 1.1
2.9 9.2351 1.9
1.3 12.7437 1.7
1.1 11.3012 1.5
4.8 6.1359 1.1
3.5 9.2225 1.3
1.5 22.3120 2.7
2.8
4.2
0.3
0.9
2.9
8.9527
9.2856
8.7181
8.7934
9.2834
2.1
1.9
2.1
2.1
1.6
207Pb*
206Pb* ± error
± (%)
(%) corr.
235U*
238U
8.3039 3.9 0.3607 3.7
0.95
2.8466 1.8 0.2305 1.2
0.65
4.5506 2.5 0.3082 2.0
0.81
0.0508 9.1 0.0097 2.1
0.23
1.9742 1.5 0.1869 1.1
0.72
12.6993 2.9 0.5020 2.5
0.85
4.6867 3.0 0.3093 2.4
0.80
4.3608 3.4 0.2973 2.1
0.60
10.4751 3.8 0.4695 1.8
0.49
0.5589 5.9 0.0761 2.5
0.43
2.0231 1.9 0.1907 1.3
0.71
1.8648 2.4 0.1789 1.3
0.53
5.1159 2.3 0.3272 1.6
0.68
4.0091 3.1 0.2684 2.2
0.71
12.4820 1.9 0.5067 1.0
0.54
4.5216 3.6 0.2998 2.4
0.68
4.9012 3.7 0.3110 2.4
0.66
2.2602 2.9 0.2063 1.5
0.52
4.3140 4.7 0.2985 2.1
0.44
13.4218 8.4 0.4930 7.6
0.91
3.4283 2.3 0.2623 1.7
0.74
2.8953 2.4 0.2345 2.1
0.85
11.5602 6.1 0.4727 5.1
0.82
13.2596 6.0 0.5165 4.7
0.78
0.0955 7.7 0.0156 1.9
0.25
17.0696 3.1 0.5677 1.9
0.61
4.6663 2.1 0.3050 1.3
0.62
4.3312 3.2 0.2971 2.0
0.63
5.0580 1.9 0.3271 1.2
0.65
4.5277 3.5 0.3066 3.1
0.91
5.0225 2.9 0.3321 2.8
0.94
12.3728 3.0 0.4810 2.5
0.83
4.1479 1.9 0.2913 1.2
0.65
2.0689 3.2 0.1939 1.0
0.31
4.4465 2.4 0.3017 2.2
0.91
2.0544 3.8 0.1892 3.3
0.86
3.0255 2.1 0.2442 1.7
0.80
5.2089 2.7 0.3309 2.5
0.93
4.0816 3.0 0.2881 2.5
0.81
0.0905 6.0 0.0155 4.2
0.69
4.7014 4.2 0.3148 3.1
0.75
10.8698 1.6 0.4753 1.3
0.78
4.8075 2.3 0.3206 1.0
0.44
5.0217 3.2 0.3233 2.4
0.75
13.2633 4.1 0.5208 3.9
0.94
13.2035 2.7 0.5196 2.5
0.93
1.8810 3.9 0.1828 3.3
0.85
4.6235 4.5 0.3202 4.2
0.93
9.4424 4.0 0.4509 3.8
0.97
3.1934 2.2 0.2588 1.5
0.71
9.5037 2.6 0.4329 2.4
0.92
2.3443 2.0 0.2089 1.8
0.87
4.1567 4.4 0.2859 3.1
0.71
0.5309 3.2 0.0687 1.6
0.51
12.6681 1.8 0.5039 1.4
0.78
4.7952 2.7 0.3212 1.9
0.71
2.2362 2.0 0.2067 1.0
0.50
2.7625 3.9 0.2264 3.6
0.92
10.3323 1.5 0.4598 1.0
0.69
3.9141 4.9 0.2618 4.8
0.97
0.0830 5.7 0.0134 5.0
0.88
4.6324
4.7117
4.7261
5.2592
4.6368
3.0
2.2
3.0
2.4
2.6
0.3008
0.3173
0.2988
0.3354
0.3122
2.1
1.1
2.2
1.2
2.0
0.72
0.52
0.73
0.49
0.78
206Pb*
238U*
1985.3
1337.4
1731.6
62.3
1104.5
2622.4
1737.3
1678.0
2481.5
472.8
1124.9
1060.9
1824.6
1532.8
2642.5
1690.4
1745.6
1209.1
1683.8
2583.8
1501.8
1357.9
2495.4
2684.4
100.0
2898.5
1716.3
1677.0
1824.1
1724.0
1848.5
2531.8
1648.1
1142.2
1699.9
1116.9
1408.2
1842.5
1632.3
98.9
1764.3
2506.7
1792.8
1805.6
2702.7
2697.5
1082.3
1790.7
2399.3
1483.6
2318.6
1223.1
1621.2
428.6
2630.6
1795.5
1211.1
1315.7
2438.7
1499.1
86.0
1695.2
1776.6
1685.5
1864.5
1751.5
Apparent ages (Ma)
207Pb*
206Pb*
± (Ma)
± (Ma)
235U
207Pb*
63.2 2264.7 35.2 2527.7
20
14.0 1367.9 13.4 1415.9
26
30.8 1740.3 20.8 1750.7
27
1.3
50.3
4.4
-488.2
235
10.7 1106.7
9.8 1111.0
20
53.2 2657.6 27.5 2684.5
26
36.7 1764.9 25.1 1797.7
33
30.7 1705.0 28.4 1738.2
50
37.9 2477.7 35.0 2474.6
56
11.4 450.8 21.5
340.0
121
13.7 1123.3 12.7 1120.1
26
12.6 1068.7 16.1 1084.6
41
24.8 1838.7 19.5 1854.7
30
30.0 1636.0 25.3 1771.4
40
22.5 2641.4 17.9 2640.5
27
36.3 1734.9 30.0 1789.1
48
36.7 1802.5 30.9 1868.9
50
16.6 1200.0 20.4 1183.5
49
30.4 1696.0 38.4 1711.2
77
162.2 2709.8 79.2 2805.1
56
22.6 1510.9 18.0 1523.7
29
25.3 1380.7 18.4 1416.0
24
104.7 2569.5 57.5 2628.4
58
103.2 2698.3 56.8 2708.7
62
1.9
92.7
6.9
-92.0
184
43.9 2938.8 29.4 2966.4
39
20.0 1761.2 17.9 1814.9
30
29.7 1699.3 26.2 1727.0
45
19.5 1829.1 16.1 1834.7
26
47.3 1736.1 28.7 1750.7
27
44.2 1823.1 24.8 1794.2
18
52.1 2633.1 28.3 2711.9
28
17.6 1663.8 15.1 1683.6
26
10.5 1138.6 21.8 1131.6
60
33.3 1721.0 20.3 1746.8
18
33.6 1133.8 26.2 1166.2
39
21.0 1414.1 15.8 1422.9
24
40.1 1854.1 22.9 1867.0
18
35.6 1650.6 24.8 1674.1
33
4.1
88.0
5.1
-199.0
109
48.3 1767.5 35.1 1771.3
51
26.0 2512.1 14.9 2516.3
17
15.8 1786.2 19.1 1778.6
37
38.0 1823.0 27.1 1842.9
38
86.1 2698.6 39.1 2695.5
23
54.2 2694.3 25.1 2691.9
17
32.9 1074.4 25.9 1058.4
42
65.2 1753.5 37.6 1709.5
31
76.7 2382.0 36.4 2367.1
17
20.4 1455.6 16.8 1414.9
29
46.0 2387.9 23.6 2447.6
17
19.6 1225.8 14.4 1230.6
20
44.6 1665.5 36.0 1721.8
57
6.7 432.4 11.2
452.6
61
29.6 2655.3 16.5 2674.1
18
29.5 1784.1 22.4 1770.7
35
11.0 1192.5 14.0 1158.8
34
43.0 1345.5 29.3 1393.0
30
20.3 2465.0 13.5 2486.7
18
63.5 1616.6 39.8 1773.2
23
4.3
80.9
4.4
-65.5
65
± (Ma)
31.6
17.4
32.8
18.8
30.7
1755.1
1769.3
1771.9
1862.3
1755.9
24.7
18.2
25.3
20.2
21.6
1827.2
1760.8
1875.2
1859.7
1761.2
37
34
37
37
30
172
Table4.4. (Cont'd)
Analysis
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
U
(ppm)
1621
253
356
246
192
59
218
103
176
290
749
261
129
206
273
120
111
234
291
624
72
315
257
225
189
259
165
222
48
260
65
151
93
307
282
78
40
65
88
160
38
183
78
236
57
153
362
167
84
121
99
110
325
37
178
94
328
225
52
83
176
189
290
97
540
753
306
206Pb
204Pb
547025
5160
125490
139120
87260
23865
118130
36750
48000
14700
34105
15075
44540
84855
34790
12305
46160
144635
265115
187100
14465
100030
92900
2160
43895
108480
57060
73425
26600
80690
23395
44070
41150
9590
69360
92630
64370
54835
26615
198745
51345
80255
38475
95360
37030
63030
31590
72070
34940
88525
4255
33990
16440
10970
51160
18325
101875
128895
30745
5530
61250
55385
20295
30965
64060
175785
54200
Isotopic ratios
206Pb*
U/Th
± (%)
207Pb*
3.1 5.3047 1.8
1.7 4.9413 9.2
1.1 5.5722 3.0
2.5 5.4757 0.9
1.6 8.8267 2.0
0.7 8.3050 1.4
4.4 5.2405 2.0
1.6 9.1601 2.6
1.4 9.1095 2.0
4.0 19.3723 6.4
5.0 19.4308 2.0
6.3 19.1558 9.6
1.3 10.1112 2.1
1.7 9.2840 2.3
10.3 17.4270 4.0
1.1 18.6721 11.4
3.9 12.4075 2.6
2.1 5.6243 2.4
3.3 5.5356 3.1
1.2 5.5472 2.3
3.1 13.9749 2.7
2.7 9.7742 1.9
2.0 8.7691 1.8
1.7 27.0674 44.7
3.0 13.5704 1.8
7.4 9.0654 1.8
1.4 9.1378 2.8
1.8 9.1857 1.6
1.7 7.7244 2.9
9.6 13.9969 2.5
1.0 9.4145 3.2
3.2 13.7829 2.7
1.6 11.1473 2.0
0.5 17.1493 8.4
1.7 9.8076 5.1
3.1 9.2620 3.5
1.2 4.5139 3.4
3.3 13.7448 3.3
2.0 11.0948 6.3
2.7 9.0470 2.7
2.3 7.4870 2.3
1.4 9.5737 2.3
1.7 9.7560 3.3
2.0 8.9382 1.6
1.0 9.0326 5.0
2.8 13.5233 2.7
3.7 13.3443 2.8
1.9 5.4777 4.3
2.0 13.1326 5.0
1.2 9.2084 3.0
3.0 16.4743 27.4
0.5 8.6933 1.1
1.0 18.3438 2.8
0.9 8.9612 2.2
1.7 9.8455 1.9
3.5 11.9605 2.2
2.9 9.5998 1.4
1.6 4.7679 3.4
3.2 12.6414 2.2
2.0 15.2275 16.7
3.9 8.8571 2.4
1.0 10.6503 1.6
1.0 17.6722 2.8
1.0 9.6962 1.4
3.5 5.4297 0.8
1.6 9.6998 1.2
4.4 13.4203 1.5
207Pb*
235U*
13.6835
14.0394
12.8546
12.7283
5.2805
5.9374
14.0684
4.7850
4.7991
0.3016
0.3072
0.2883
3.7482
4.6776
0.3727
0.4745
2.2525
12.3446
12.7639
12.4299
1.6601
4.1223
5.1169
0.0378
1.7263
4.7919
4.6669
4.7019
6.9042
1.5766
4.6351
1.7704
3.0663
0.4703
3.4563
4.6574
17.2629
1.7400
2.8316
5.0796
7.3614
3.9875
3.8969
4.6305
4.6429
1.8278
1.7996
12.1607
2.0556
4.8441
0.2216
5.1130
0.4458
4.6797
3.9869
2.4726
4.1018
12.9330
1.9779
0.3112
4.7851
3.1116
0.5069
3.9485
12.5664
4.0735
1.7079
± (%)
3.7
9.3
3.2
1.3
4.0
3.1
3.5
3.9
2.7
6.9
3.2
10.0
2.7
4.1
6.7
12.4
3.6
3.5
3.5
3.7
2.9
3.1
2.0
44.9
2.3
2.2
3.0
2.2
4.6
3.5
3.8
3.0
2.2
8.4
5.7
3.7
3.5
3.7
6.6
2.8
2.4
2.6
5.0
2.8
5.2
2.7
2.8
5.7
5.2
3.1
27.4
2.3
3.7
3.3
3.3
3.1
4.4
4.6
3.8
17.2
2.6
2.2
3.6
2.3
4.2
2.6
2.7
206Pb*
238U
0.5264
0.5031
0.5195
0.5055
0.3380
0.3576
0.5347
0.3179
0.3171
0.0424
0.0433
0.0401
0.2749
0.3150
0.0471
0.0643
0.2027
0.5036
0.5124
0.5001
0.1683
0.2922
0.3254
0.0074
0.1699
0.3151
0.3093
0.3132
0.3868
0.1601
0.3165
0.1770
0.2479
0.0585
0.2459
0.3129
0.5652
0.1735
0.2279
0.3333
0.3997
0.2769
0.2757
0.3002
0.3042
0.1793
0.1742
0.4831
0.1958
0.3235
0.0265
0.3224
0.0593
0.3041
0.2847
0.2145
0.2856
0.4472
0.1813
0.0344
0.3074
0.2404
0.0650
0.2777
0.4949
0.2866
0.1662
± error
(%) corr.
3.3
0.88
1.3
0.14
1.2
0.36
1.0
0.76
3.5
0.87
2.7
0.89
2.9
0.83
2.9
0.74
1.8
0.67
2.7
0.39
2.5
0.78
3.0
0.29
1.8
0.66
3.4
0.83
5.4
0.80
4.8
0.39
2.6
0.70
2.6
0.73
1.5
0.44
3.0
0.79
1.0
0.35
2.5
0.80
0.9
0.44
4.4
0.10
1.5
0.66
1.2
0.56
0.8
0.27
1.6
0.69
3.6
0.78
2.5
0.71
2.2
0.56
1.3
0.45
1.0
0.45
0.5
0.06
2.4
0.43
1.2
0.33
0.8
0.22
1.7
0.46
2.2
0.33
0.5
0.18
0.9
0.36
1.2
0.46
3.7
0.74
2.3
0.82
1.3
0.25
0.5
0.18
0.5
0.18
3.9
0.67
1.5
0.29
0.8
0.24
1.5
0.05
2.0
0.89
2.4
0.65
2.5
0.75
2.8
0.83
2.2
0.71
4.2
0.95
3.1
0.68
3.1
0.82
4.1
0.24
1.0
0.38
1.5
0.67
2.3
0.64
1.8
0.80
4.2
0.98
2.3
0.89
2.2
0.83
Apparent ages (Ma)
206Pb*
207Pb*
206Pb*
± (Ma)
± (Ma)
± (Ma)
238U*
235U
207Pb*
2726.5 72.3 2728.1 34.9 2729.2
29
2627.3 28.9 2752.4 88.1 2845.4
150
2697.1 26.0 2669.1 30.6 2647.9
50
2637.3 22.1 2659.8 12.6 2676.8
14
1877.2 56.7 1865.7 34.1 1852.9
35
1970.9 46.4 1966.7 26.8 1962.3
25
2761.3 64.7 2754.3 33.0 2749.2
32
1779.4 45.1 1782.3 32.9 1785.6
48
1775.4 28.2 1784.7 22.9 1795.7
37
267.5
7.0 267.6 16.3
268.6
147
273.2
6.8 272.0
7.7
261.7
47
253.2
7.3 257.2 22.8
294.3
219
1565.5 25.2 1581.7 21.9 1603.5
38
1765.1 53.1 1763.2 34.7 1761.1
42
296.7 15.6 321.7 18.6
506.2
89
401.5 18.6 394.3 40.5
352.4
259
1189.8 27.9 1197.6 25.7 1211.6
51
2629.1 55.1 2631.0 33.0 2632.4
40
2667.0 33.4 2662.4 32.6 2658.8
52
2614.2 63.4 2637.4 35.1 2655.3
38
1002.5
9.4 993.4 18.4
973.3
56
1652.7 35.7 1658.7 25.1 1666.4
34
1816.2 14.1 1838.9 17.3 1864.7
33
47.7
2.1
37.7 16.6
-560.5 1259
1011.6 14.4 1018.4 15.1 1033.0
36
1765.6 18.7 1783.5 18.3 1804.5
33
1737.2 12.3 1761.3 24.7 1790.0
52
1756.7 23.8 1767.6 18.7 1780.5
29
2107.9 64.2 2099.2 40.8 2090.6
51
957.1 22.0 961.0 21.7
970.1
50
1772.5 33.3 1755.6 31.9 1735.5
58
1050.4 13.0 1034.7 19.4 1001.5
54
1427.7 12.7 1424.3 17.0 1419.3
38
366.5
1.8 391.4 27.2
541.5
183
1417.1 31.0 1517.3 44.8 1660.1
95
1754.8 18.4 1759.6 30.8 1765.4
64
2887.9 17.9 2949.6 33.8 2991.9
55
1031.1 16.3 1023.5 23.9 1007.1
67
1323.2 25.8 1363.9 49.7 1428.3
120
1854.3
8.1 1832.7 23.4 1808.2
49
2167.8 16.0 2156.3 21.7 2145.3
40
1575.6 16.8 1631.7 21.4 1704.7
43
1569.8 51.4 1613.0 40.1 1669.9
61
1692.2 34.2 1754.8 23.4 1830.2
29
1711.9 19.5 1757.0 43.4 1811.1
91
1063.0
4.9 1055.5 17.8 1040.0
54
1035.0
4.8 1045.3 18.4 1066.8
56
2540.9 81.3 2616.9 54.0 2676.2
70
1152.7 16.0 1134.2 35.7 1098.9
100
1806.9 11.8 1792.6 26.2 1776.0
55
168.5
2.5 203.2 50.5
628.6
600
1801.3 31.9 1838.3 19.4 1880.4
19
371.4
8.7 374.3 11.6
392.3
63
1711.8 37.0 1763.6 27.4 1825.5
39
1614.9 39.4 1631.5 27.0 1653.0
34
1252.7 24.8 1264.1 22.2 1283.5
42
1619.4 60.3 1654.7 36.2 1699.7
26
2382.9 62.6 2674.8 43.4 2903.5
55
1074.3 30.4 1108.0 25.4 1174.7
43
217.8
8.8 275.1 41.6
795.9
353
1727.8 15.2 1782.3 21.9 1846.7
44
1388.5 18.2 1435.6 16.6 1506.0
30
405.8
9.2 416.4 12.4
475.4
61
1579.6 25.2 1623.7 18.3 1681.3
25
2591.7 88.6 2647.7 39.7 2690.8
12
1624.4 33.0 1649.0 21.0 1680.6
22
991.3 20.5 1011.5 17.3 1055.4
30
173
Table4.4. (Cont'd)
Analysis
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
East Fork
1
2
3
4
5
6
7
8
9
2DBpebble
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Isotopic ratios
206Pb*
U/Th
± (%)
207Pb*
0.7 13.0042 2.2
1.6 5.4232 1.7
2.2 8.6453 2.2
0.9 8.5937 1.3
8.3 5.4867 1.4
2.4 9.1609 1.8
2.6 5.5381 3.2
1.9 15.9855 8.3
1.4 9.1388 1.0
1.9 8.9075 1.4
2.9 12.6076 2.0
1.0 4.9570 1.7
0.5 8.7486 2.3
3.4 8.2844 0.8
1.2 5.2586 3.6
1.3 13.0340 2.1
2.4 12.9583 3.2
3.3 8.6775 1.3
1.1 10.8512 1.2
2.2 10.7925 2.4
1.7 10.6018 4.3
1.5 22.8321 19.7
2.8 5.3901 1.5
3.6 18.0437 3.3
7.0 19.1792 4.2
2.2 13.3598 1.9
1.8 8.3662 3.8
1.7 5.4710 1.5
1.0 18.6052 20.4
1.8 9.0272 1.3
3.1 18.1827 5.5
2.1 8.8863 3.0
3.7 8.9238 3.0
7.0 5.9670 2.8
1.5 16.4052 6.8
2.1 5.2107 3.0
1.1 15.9678 1.9
1.8 10.3480 1.0
1.5 5.5492 3.5
2.3 11.6172 1.6
2.1 5.1363 1.4
207Pb*
206Pb* ± error
± (%)
(%) corr.
235U*
238U
1.9868 3.1 0.1874 2.3
0.72
10.9060 2.7 0.4290 2.1
0.77
5.4810 2.3 0.3437 0.8
0.34
4.9668 2.7 0.3096 2.4
0.88
12.8263 2.6 0.5104 2.1
0.83
4.7783 2.6 0.3175 2.0
0.75
12.8887 4.8 0.5177 3.6
0.75
0.4128 9.0 0.0479 3.6
0.40
4.8134 2.1 0.3190 1.9
0.89
4.9829 2.6 0.3219 2.2
0.85
2.0848 2.9 0.1906 2.1
0.71
15.3190 2.6 0.5507 1.9
0.75
5.1978 2.9 0.3298 1.9
0.64
5.7877 1.7 0.3477 1.5
0.89
9.6188 8.9 0.3669 8.1
0.92
1.9729 3.0 0.1865 2.1
0.70
1.9762 3.3 0.1857 0.9
0.27
5.3798 1.8 0.3386 1.3
0.71
3.1319 1.4 0.2465 0.7
0.53
3.0948 2.7 0.2422 1.3
0.49
3.2752 4.8 0.2518 2.1
0.43
0.3084 19.7 0.0511 0.7
0.04
12.5415 2.2 0.4903 1.7
0.75
0.4806 3.7 0.0629 1.6
0.44
0.3063 4.5 0.0426 1.5
0.34
1.6393 3.1 0.1588 2.5
0.79
5.8949 3.9 0.3577 0.6
0.17
11.8533 2.1 0.4703 1.5
0.70
0.4979 20.5 0.0672 2.1
0.10
4.6787 2.6 0.3063 2.3
0.88
0.2943 6.1 0.0388 2.7
0.44
5.1386 3.2 0.3312 1.1
0.35
5.1684 3.1 0.3345 0.6
0.19
11.3106 2.9 0.4895 0.5
0.17
0.7401 6.8 0.0881 1.0
0.14
13.6700 3.1 0.5166 0.9
0.29
0.9274 2.0 0.1074 0.8
0.41
3.4937 2.4 0.2622 2.2
0.91
12.7144 4.4 0.5117 2.7
0.60
2.6305 2.6 0.2216 2.1
0.81
14.4840 1.7 0.5396 0.9
0.54
Apparent ages (Ma)
206Pb*
207Pb*
206Pb*
± (Ma)
± (Ma)
± (Ma)
238U*
235U
207Pb*
1107.2 23.1 1111.0 21.3 1118.5
44
2301.0 40.6 2515.1 25.3 2692.8
29
1904.3 13.0 1897.6 19.9 1890.3
39
1738.6 36.6 1813.7 23.2 1901.1
24
2658.3 46.0 2667.0 24.1 2673.5
24
1777.4 30.8 1781.1 22.2 1785.4
32
2689.4 79.6 2671.5 45.2 2658.1
52
301.4 10.6 350.9 26.8
693.2
177
1785.0 29.5 1787.2 17.8 1789.8
17
1799.1 35.0 1816.4 22.2 1836.4
25
1124.8 21.4 1143.8 19.9 1180.0
40
2828.3 44.2 2835.3 24.6 2840.3
28
1837.4 30.2 1852.3 25.0 1868.9
41
1923.8 25.1 1944.6 14.7 1966.7
14
2014.6 140.3 2399.0 81.7 2743.6
59
1102.4 21.0 1106.3 20.0 1114.0
43
1098.2
9.3 1107.4 22.6 1125.6
64
1879.8 20.7 1881.6 15.4 1883.6
23
1420.3
9.4 1440.6 10.7 1470.6
22
1398.3 16.5 1431.4 20.7 1480.9
45
1447.9 27.0 1475.2 37.5 1514.6
82
321.1
2.3 273.0 47.2
-122.0
490
2571.9 35.8 2645.8 21.1 2702.9
24
393.2
6.1 398.5 12.1
429.2
74
269.0
4.0 271.3 10.6
291.5
96
950.3 21.8 985.4 19.7 1064.5
38
1971.2 10.9 1960.5 33.5 1949.2
68
2485.0 30.5 2592.9 19.8 2678.3
25
419.2
8.6 410.3 69.4
360.5
465
1722.6 34.9 1763.4 22.0 1812.2
23
245.5
6.4 262.0 14.1
412.1
123
1844.1 18.0 1842.5 27.4 1840.7
55
1860.2
9.4 1847.4 26.1 1833.1
55
2568.5 10.6 2549.1 26.7 2533.7
47
544.0
5.1 562.5 29.5
637.7
146
2684.8 19.8 2727.1 29.2 2758.6
48
657.6
5.2 666.3 10.0
695.5
40
1501.1 29.7 1525.8 19.2 1560.2
18
2663.9 58.0 2658.7 41.6 2654.8
59
1290.5 24.8 1309.2 19.4 1340.0
30
2781.6 21.0 2782.0 16.3 2782.2
24
U
(ppm)
332
284
188
166
334
223
285
1015
189
151
92
104
106
745
320
162
379
115
144
239
483
69
60
440
299
294
46
311
41
193
603
77
178
143
98
70
320
221
342
532
247
206Pb
204Pb
50325
18035
67780
59020
89355
80720
180770
12080
66080
47675
21445
60880
43715
201015
90910
38050
75910
46935
37680
55635
120305
4270
39780
28440
13550
54495
33015
35700
2990
78240
21415
80555
151480
186240
57935
106540
34105
60075
75285
75675
132720
403
340
529
371
187
66
695
158
223
6916
22612
11780
41840
17584
50040
19676
26440
61660
2.2
2.5
2.5
1.4
1.8
1.4
4.9
2.3
1.7
5.3087
4.6070
4.5118
4.9088
4.0151
4.3324
5.2356
4.7212
4.8812
3.1
0.7
1.8
2.5
2.7
1.0
6.0
4.1
0.9
10.1638
16.2834
12.5591
12.8086
19.4758
19.2725
12.2068
15.5482
15.4082
6.2
3.0
5.6
3.6
4.0
1.9
6.0
7.7
1.5
0.3913
0.5441
0.4110
0.4560
0.5671
0.6056
0.4635
0.5324
0.5455
5.4
3.0
5.3
2.7
3.0
1.6
0.6
6.6
1.2
0.87
0.97
0.95
0.73
0.75
0.86
0.11
0.85
0.81
2129.0 98.3 2449.8
2800.5 67.0 2893.6
2219.4 99.7 2647.2
2421.9 53.5 2665.7
2896.0 70.2 3065.7
3052.3 39.6 3055.6
2455.1 13.1 2620.4
2751.5 147.4 2849.4
2806.3 28.0 2840.8
57.8
29.0
52.9
34.1
38.8
18.3
56.6
73.9
14.4
2728.0
2959.0
2992.6
2856.2
3178.8
3057.7
2750.8
2919.4
2865.4
51
11
29
40
42
15
99
66
14
644
493
826
1012
897
566
789
414
578
545
664
509
545
552
584
55450
401145
239440
103010
212720
24530
21205
67575
433665
206500
403520
150530
263525
286935
155140
1.9
3.8
2.2
3.3
2.5
2.8
1.3
2.5
3.5
3.2
2.9
3.1
3.1
3.3
4.4
5.6750
5.7378
5.6357
5.6398
5.6589
5.6760
5.5915
5.6847
5.7113
5.7757
5.4721
5.6067
5.6429
5.6741
5.5400
1.1
0.6
1.2
0.9
1.6
0.8
1.0
1.2
1.4
1.9
1.1
1.0
1.6
1.1
4.2
12.0168
11.8276
11.3188
11.8252
11.8473
11.7562
11.2236
11.8109
11.8250
10.9292
13.0247
12.3631
12.0057
11.6482
11.6015
1.7
2.2
1.6
2.3
4.4
2.0
2.3
1.9
3.2
2.3
2.7
1.9
2.3
3.1
9.0
0.4946
0.4922
0.4626
0.4837
0.4862
0.4840
0.4552
0.4870
0.4898
0.4578
0.5169
0.5027
0.4914
0.4794
0.4661
1.3
2.1
1.1
2.1
4.1
1.9
2.1
1.4
2.8
1.4
2.4
1.6
1.6
2.9
7.9
0.77
0.96
0.68
0.92
0.93
0.93
0.90
0.76
0.89
0.60
0.92
0.84
0.71
0.93
0.89
2590.6 27.5
2580.2 44.2
2451.2 22.2
2543.3 43.7
2554.4 87.1
2544.5 39.1
2418.1 41.3
2557.5 30.0
2569.9 59.8
2429.9 28.3
2686.1 53.6
2625.5 34.5
2576.5 34.4
2524.4 60.8
2466.7 162.8
15.7
20.3
15.0
21.1
41.5
18.8
21.3
17.5
29.6
21.7
25.1
17.9
21.3
29.2
84.0
2617.5
2599.2
2629.1
2627.9
2622.2
2617.2
2642.2
2614.7
2606.9
2588.2
2677.9
2637.7
2626.9
2617.8
2657.5
18
10
20
15
27
13
17
20
24
31
18
17
26
19
69
2605.7
2590.8
2549.8
2590.7
2592.4
2585.2
2541.9
2589.5
2590.6
2517.1
2681.4
2632.4
2604.9
2576.6
2572.8
174
Table4.4. (Cont'd)
Analysis
16
17
18
19
20
21
22
23
U
(ppm)
344
763
528
288
759
337
337
336
206Pb
204Pb
141370
166160
49290
386010
37250
65370
161730
261480
Isotopic ratios
206Pb*
U/Th
± (%)
207Pb*
1.0 5.0032 1.1
2.9 5.7069 1.6
2.5 5.5069 3.2
2.6 5.6177 1.6
2.4 5.6644 1.3
1.2 5.6761 2.1
2.5 5.3530 2.1
2.8 5.7799 2.6
207Pb*
206Pb* ± error
± (%)
(%) corr.
235U*
238U
13.4801 2.0 0.4891 1.6
0.83
12.0115 4.1 0.4972 3.8
0.92
11.3537 3.9 0.4535 2.3
0.59
12.4087 2.6 0.5056 2.0
0.78
10.8778 1.7 0.4469 1.1
0.67
12.0545 2.5 0.4962 1.3
0.54
13.5856 2.6 0.5274 1.5
0.60
11.7695 3.0 0.4934 1.5
0.50
Apparent ages (Ma)
206Pb*
207Pb*
206Pb*
± (Ma)
± (Ma)
± (Ma)
238U*
235U
207Pb*
2567.0 34.7 2713.9 18.7 2825.2
18
2601.6 80.9 2605.3 38.5 2608.2
27
2410.7 46.3 2552.6 36.6 2667.4
53
2637.7 43.3 2635.8 24.2 2634.4
27
2381.4 22.5 2512.7 15.7 2620.6
21
2597.6 28.6 2608.7 23.3 2617.2
35
2730.7 34.3 2721.3 24.3 2714.3
34
2585.2 32.6 2586.2 28.5 2587.0
44
175
Table 4.5. Major age populations of detrital zircons in modern river sand and the early Eocene sediment
Minimum
age (Ma)
Maximum
age (Ma)
42
60
Sourth-central Idaho,Northwest Wyoming, sourtheast
Montana (Armstrong and Ward, 1993)
80
220
Central and southern California, Nevada, South-central
Idaho (Armstrong and Ward, 1993)
230
280
East Mexico (Torres et al., 1999)
330
450
Antler allochthon, central Idaho and northern Nevada
Appalachian orogenic belt
360
760
South and eastern United States, recycled from Mesozoic to
paleozoic miogeocline (Dickinson and Gehrels, 2003; 2009)
Grenville orogeny
950
1300
Midcontinent magmatism
1304
1532
Yavapai朚 azatzal Province
1600
1800
Archean Wyoming Province
2500
3200
Population
Challis and Absaroka Volcanic
Supergroup
Cordilleran magmatic arc (mainly
Sierra Nevada batholith, and Idaho
batholith)
Permian-Triassic magmatic arc
Devonian and Mississippian Antler
orogenic belt
Source regions
recycled from Neoproterozoic to paleozic miogeocline
(Dickinson and Gehrels, 2003; 2009)
Recycled from Cordilleran miogeocline (Dickinson and
Gehrels, 2003; 2009)
Recycled from Cordilleran miogeocline (Dickinson and
Gehrels, 2003; 2009)
Mainly from exposed Archean craton; also recycled through
Cordilleran miogeocline (Frost et al., 2000; Kirkwood, 2000;
Dickinson and Gehrels, 2003; Frost and Fanning,
2006;Dickinson and Gehrels, 2009)
176
Table 4.6. Isotope results
Sample
13
δ C (PDB)
18
δ O(PDB)
paleosol carbonate
1DB1.5
-5.7
-9.0
1DB6
-6.2
-9.4
1DB10
-6.5
-9.3
1DB20
-6.7
-8.8
1DB35
-6.7
-8.8
1DB55
-8.2
-9.2
1DB68
-8.0
-9.8
1DB71
-7.8
-8.7
1DB88
-7.2
-9.6
1DB95
-6.6
-9.1
1DB113
-7.0
-8.9
1DB114
-7.7
-9.2
1DB119
-7.5
-9.6
2DB30
-7.5
-9.4
2DB33
-7.0
-9.1
2DB46
-9.5
-9.6
2DB48.8
-8.8
-8.6
2DB62
-7.3
-8.9
2DB67
-7.9
-8.9
2DB87
-8.0
-9.4
2DB102
-8.8
-8.5
2DB132
-8.8
-9.3
2DB143
-9.0
-9.2
2DB163
-8.9
-8.6
2DB170
-8.4
-8.7
2DB221
-7.0
-9.0
2DB227
-7.6
-9.0
3DB22
-4.6
-9.6
3DB81
-5.6
-8.5
4DB113
-7.9
-8.9
4DB116
-5.6
-8.8
4DB152
-8.4
-8.5
4DB154
-7.9
-8.8
4DB159
-8.2
-8.8
4DB172
-7.2
-8.9
4DB175
-7.4
-9.3
fluvial cement
1DB69
-7.0
-11.5
2DB2
-3.8
-15.8
2DB52
-4.9
-17.6
2DB68
-6.7
-16.4
2DB96
-3.9
-16.1
2DB127
-5.4
-17.2
2DB210
-4.2
-12.7
4DB4.5
-4.9
-12.5
4DB195
-3.2
-11.7
secondary vein, limestone clasts, and corral fossil
1DB71C
-9.3
-12.0
1DB88C
-7.7
-14.1
1DB119C
-8.3
-11.8
4DB175P
-5.8
-12.8
4DB175C
-7.8
-9.4
1DB119P
-0.5
-4.9
2DB0L
1.2
-4.2
2DB0C1
4.4
-2.5
2DB0C2
2.5
-1.5
Description
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
paleosol nodule
fluvial cement
fluvial cement
fluvial cement
fluvial cement
fluvial cement
fluvial cement
fluvial cement
fluvial cement
fluvial cement
secondary vein
secondary vein
secondary vein
secondary vein
secondary vein
limestone clast
limestone clast
corral fossil
corral fossil
177
Table 4.6. (Cont'd)
modern soil carbonate
1DB118 MS
-4.5
2DB0
-4.1
MS1A
-4.2
MS1B
-3.5
MS1C
-3.9
MS2A
-2.8
MS2B
-0.3
MS2C
-1.8
MS2D
-3.4
modern plant
-24.9
1
-26.2
2
-25.8
3
-28.4
4
-25.1
5
-26.3
6
-25.8
7
-25.2
8
-10.0
-10.3
-10.3
-9.3
-9.2
-6.5
-6.3
-7.1
-6.6
modern soil-pebble coating
modern soil-pebble coating
modern soil at 50cm depth, elevation of
modern soil at 50cm depth, elevation of
modern soil at 50cm depth, elevation of
modern soil at 50cm depth, elevation of
modern soil at 50cm depth, elevation of
modern soil at 50cm depth, elevation of
modern soil at 50cm depth, elevation of
fountain grass
needle leaf sedge
rabbit brush
unkown species
sagebrush
unkown species
unkown species
Aster
2218m
2218m
2218m
2218m
2218m
2218m
2218m
178
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