Exhumation of the North American Cordillera revealed by multi-dating
of Upper Jurassic–Upper Cretaceous foreland basin deposits
Clayton S. Painter†, Barbara Carrapa, Peter G. DeCelles, George E. Gehrels, and Stuart N. Thomson
Department of Geosciences, University of Arizona, 1040 E. 4th Street, Tucson, Arizona 85721, USA
ABSTRACT
New low-temperature thermochronology and geochronology data from Upper
Jurassic–Upper Cretaceous strata from the
North American Cordilleran foreland basin in Utah, Colorado, Wyoming, and South
Dakota document rapid exhumation rates
of the adjacent Cordilleran orogenic belt to
the west. Both zircon (U-Th-[Sm])/He (zircon
He) and apatite fission track (AFT) thermochronology were applied to proximal and
distal synorogenic deposits in order to identify a thermochronometer suitable to record
source exhumation during the North America Cordilleran orogeny. AFT lag times from
Upper Jurassic–Upper Cretaceous deposits
are 0–5 m.y. and indicate a relatively steadystate to slightly increasing exhumation rate
between 118 Ma and 66 Ma. These lag-time
measurements are consistent with active
shortening and rapid exhumation rates of
~0.9–>1 km/m.y. of the North American Cordillera throughout the Cretaceous.
Double dating of the detrital AFT samples
was performed on apatites with young AFT
cooling ages, in order to test whether or not
the young cooling ages represent a signal
related to exhumation rather than volcanic
activity. Maximum depositional ages using
detrital zircon U-Pb geochronology match
existing ages on basin stratigraphy. This
study indicates that AFT is the most effective
thermochronometer to resolve source exhumation from Lower to Upper Cretaceous
foreland stratigraphy in the central Cordilleran foreland, and indicates that source material was exhumed from 4 to 5 km depths but
was never buried more than a few kilometers
(<4 km) since Cretaceous time. Zircon He
dates indicate that the orogenic hinterland
could not have been exhumed from depths
>8–9 km. Double dating of apatites (with
†
Now affiliated with ConocoPhillips; Clayton.S
.Painter@conocophillips.com.
AFT and U-Pb) shows that volcanic contamination is a significant issue that can, however,
be addressed by double dating.
INTRODUCTION
Foreland basin deposits are an important archive of orogenic growth and tectonic
processes (Aubouin, 1965; Dickinson, 1974;
Dickinson and Suczek, 1979; Jordan, 1981;
DeCelles and Giles, 1996; DeCelles, 2004;
Miall, 2009). Many researchers have used
coarse-grained foreland basin deposits to date
thrusting events, identify unroofing sequences,
and identify provenance. Examples of these
techniques are clast counting of synorogenic
conglomerates and sandstone petrographic
analysis (Dickinson, 1985; Graham et al., 1986;
Lawton, 1986; DeCelles, 1988; Steidtmann and
Schmitt, 1988; Horton et al., 2004).
Thermochronology applied to detrital minerals from foreland basin deposits is a powerful tool to infer the timing of sediment source
cooling and exhumation (Bernet et al., 2001;
Carrapa et al., 2003, 2006; Najman et al.,
2005; Reiners and Brandon, 2006; Carrapa,
2010). While traditional provenance techniques
provide information on the type of sediment
sources through time, thermochronology provides unique information on the timing and
rates of sediment source exhumation and on
the thermal history of the sedimentary basin as
well. In particular, detrital thermochronology
can be applied to measure lag time, which is the
difference between the depositional age of the
detrital minerals and their cooling ages (Garver
et al., 1999). Lag-time trends also provide information on the mode of orogenic growth (Bernet et al., 2001; Carrapa et al., 2003; Carrapa,
2009). Lag time of foreland basin deposits can
thus successfully measure the long-term exhumation history of orogenic belts over large
catchment areas (Cerveny et al., 1988; Coutand
et al., 2006; Spiegel et al., 2004). In addition,
many of the allochthonous thrust sheets in the
North American Cordillera have since been
eroded and later obscured by Basin and Range
extensional tectonics, leaving only the foreland
basin deposits as a record of exhumation history.
Despite the great potential of such an approach
in North America, to date, no detailed detrital
thermochronological study had been applied in
the retroarc foreland basin of the North American Cordillera. The goal of this study is to determine the timing, pattern, and rates of cooling of
the North American Cordillera in order to better
understand the modes of exhumation and contribute to models of fold- thrust belt and foreland
basin evolution. In this study we apply zircon
(U-Th-[Sm])/He (zircon He) and apatite fission
track (AFT) thermochronology and zircon U-Pb
geochronology to samples from Upper Jurassic–Upper Cretaceous coarse-grained foreland
basin deposits in Utah, Colorado, Wyoming,
and South Dakota, in order to determine provenance cooling history and maximum depositional ages (Table 1; Figs. 1, 2, and 3). Furthermore, U-Pb thermochronology can be used to
assess whether the young cooling-age populations were contaminated by young, Cordilleran
arc–derived apatites, and thus record cooling
related to magmatic events rather than exhumation ages of the Cordilleran thrust belt. Lag-time
patterns and exhumation rates calculated from
this study are here compared to basin-filling and
orogenic-growth models.
Coarse-grained deposits have been interpreted to represent contrasting tectonic processes. For example, some researchers have
asserted that proximal upward-coarsening successions represent orogenic growth, but that
distal upward-coarsening successions represent
periods of tectonic quiescence, flexural rebound,
and the reworking of proximal deposits into the
distal foreland (Beck et al., 1988; Blair and
Bilodeau, 1988; Heller et al., 1988). This model
has been called the two-phase stratigraphic
model (Heller et al., 1988). In contrast, others
have linked distal coarse-grained deposits to
times of active shortening and orogenic growth,
and propose that the increase in sediment supply during these periods of active orogenic
GSA Bulletin; Month/Month 2014; v. 1xx; no. X/X; p. 1–26; doi: 10.1130/B30999.1; 16 figures; 6 tables; Data Repository item 2014223.
For permission to copy, contact editing@geosociety.org
© 2014 Geological Society of America
1
Painter et al.
Sample
051101
051102
051103
051104
051105
051106
051107
051108
051201
051204
051205
051206
051207
051208
051209
051210
051211
051212
051213
051214
TABLE 1. SAMPLE LIST, LOCATION, AND ANALYSES DONE
Location
Latitude
Stratigraphic unit
Longitude
Sample type
Chilson Member,
N43.44490°
Detrital
Lakota Formation
W103.77887°
Chilson Member,
N43.44490°
Detrital
Lakota Formation
W103.83715°
N43.44717°
Morrison Formation
Detrital
W103.83905°
N43.69704°
Frontier Formation
Detrital
W106.69336°
N40.96244°
Frontier Formation
Detrital
W109.47128°
N40.95719°
Dakota Sandstone
Detrital
W109.47023°
N40.52022°
Cedar Mountain Formation
Detrital
W109.52075°
N40.54865°
Morrison Formation
Detrital
W109.52416°
N40.96344°
Echo Canyon Conglomerate
Conglomerate clast
W111.41634°
N40.76712°
Kelvin Formation
Detrital
W111.40012°
N41.58785°
Lazeart Sandstone
Detrital
W110.63001°
N41.87089°
Frontier Formation
Detrital
W110.52497°
N41.48659°
Detrital
Blair Formation
W108.96523°
Brooks Member,
N41.35810°
Detrital
Rocks Springs Formation
W108.93082°
Trail Member,
N41.32461°
Detrital
Ericson Formation
W108.94299°
Canyon Creek Member,
N41.31646°
Detrital
Ericson Formation
W108.92226°
N41.31762°
Almond Formation
Detrital
W108.90691°
Chimney Rock Tongue Member,
N41.39890°
Detrital
Rock Springs Formation
W108.93394°
N42.56673°
Detrital
Cloverly Formation (A interval)
W106.70624°
N42.52449°
Morrison Formation
Detrital
W106.74066°
Analysis type
DZ
U-Pb
Zircon He
AFT
DA
U-Pb
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
(continued )
growth is greater than the accommodation space
created by flexural subsidence in the proximal
foredeep and leads to rapid progradation into
the distal foreland basin (Burbank et al., 1988;
DeCelles and Giles, 1996; Horton et al., 2004).
We compare our exhumation trends and rates
based on lag-time measurements to predictions
made from both of these basin-filling models.
Active shortening and orogenic growth should
produce small lag times and rapid exhumation
rates, whereas flexural rebound and reworking
of stored deposits into the distal foreland should
produce larger lag times.
At a larger scale, lag times have been used
to interpret trends in orogenic wedge behavior
and to identify when orogenic wedges were
in subcritical or supercritical states (Carrapa,
2009); these predictions are based on the Coulomb wedge model, which describes orogenic
growth as a function of the wedge’s taper (Davis
et al., 1983; Dahlen, 1984). Decreasing lag
times are predicted during a subcritical wedge
2
state when the wedge is building internally,
whereas increasing lag times are predicted during a supercritical wedge state, when the wedge
is rapidly propagating into the foreland basin
(Carrapa, 2009). We use this model to interpret
our lag-time trends and identify the overall Cordilleran orogenic wedge behavior during the
Cretaceous.
GEOLOGIC BACKGROUND
Timing of the initial development of the Cordilleran retroarc thrust belt has been the source
of some debate. Some workers propose that
thrusting began during the Early Cretaceous
(Heller et al., 1986), whereas others state that
thrusting began during the Late Jurassic (ca.
155 Ma) (DeCelles and Burden, 1992; DeCelles
and Currie, 1996; Currie, 1997). Thrusting
within the Cordilleran retroarc thrust belt continued until ca. 50 Ma (DeCelles, 2004) (Fig. 1).
Early in the history of the adjacent foreland
basin, nonmarine sedimentation dominated and
included the Upper Jurassic Morrison Formation and Lower Cretaceous Cedar Mountain–
Cloverly–Kootenai Formations (Suttner, 1969;
Furer, 1970; Currie, 1997). Between ca. 110
Ma and ca. 71 Ma, marginal marine to fully
marine deposition dominated the foreland basin
while the epicontinental Western Interior Seaway extended from the Gulf of Mexico to the
Arctic Ocean north of Alaska. Isopach maps
show that from ca. 155 Ma to ca. 88 Ma, a
flexurally influenced to flexurally dominated
retroarc foreland basin was located east of the
North America Cordilleran orogenic belt in
the western U.S.A. (Jordan, 1981; Roberts and
Kirschbaum, 1995; Currie, 1997; DeCelles,
2004). Although flexural subsidence continued
to be influential after 88 Ma, the isopach pattern becomes diffuse, suggesting that dynamic
subsidence may have influenced the foreland’s
geometry (Pang and Nummedal, 1995; Roberts
and Kirschbaum, 1995; Mitrovica et al., 1989;
Geological Society of America Bulletin, Month/Month 2014
Exhumation of the North American Cordillera
TABLE 1. SAMPLE LIST, LOCATION, AND ANALYSES DONE (continued )
Location
Analysis type
Latitude
DZ
DA
Zircon He
AFT
Stratigraphic unit
Longitude
U-Pb
U-Pb
Sample
Sample type
N37.11554°
051218
Dakota Sandstone
Detrital
x
x
x
W111.85088°
N41.31892°
051219
Ericson Formation
Detrital
x
W108.93170°
N42.23242°
07.28.11
Adaville Formation
Detrital
x
W110.31064°
N39.96674°
060922
Price River Formation
Conglomerate clast
x
W111.47218°
N39.96532°
060923
Price River Formation
Conglomerate clast
x
W111.47127°
N40.00208°
Sam 3
Price River Formation
Conglomerate clast
x
W111.40743°
N40.00193°
Detrital
x
Sam 5
North Horn Formation
W111.40824°
N40.00498°
Sam 7
North Horn Formation
Detrital
x
W111.40840°
N40.00193°
Sam 8
North Horn Formation
Conglomerate clast
x
W111.40945°
N39.34931°
Sam 11
Inkom Formation
Paleozoic strata
x
W112.28324°
N39.51203°
Sam 13
Price River Formation
Detrital
x
W111.73695°
N40.16784°
Sam 15
Castlegate Formation
Detrital
x
W108.87477°
N40.16843°
Sam 16
Castlegate Formation
Detrital
x
W108.87371°
N40.20236°
Sego Sandstone Member:
Detrital
x*
x
x
x
Sam 17
Mesaverde Group
W108.86123°
Sego Sandstone Member:
N40.20167°
Sam 18
Detrital
x*
Mesaverde Group
W108.86312°
N39.88097°
Sam 19
Castlegate Formation
Detrital
x
W111.21610°
Sego Sandstone Member:
N40.17529°
NSD4 B
Detrital
x
x
Mesaverde Group
W108.82601°
Note: This is a comprehensive list of all samples presented in this paper and the analytical work performed on each sample (see Figs. 2 and 3 for a visual location
of each sample). Sample type indicates whether the sample was a detrital sandstone foreland basin sample, or a conglomerate cobble from wedge-top deposits.
DZ U-Pb—detrital zircon U-Pb; zircon He—zircon (U-Th-[Sm])/He thermochronology; AFT—apatite fission track thermochronology; DA U-Pb—detrital apatite
U-Pb thermochronology.
*Detrital zircon samples published by York (2010); all other analyses are new.
DeCelles, 2004; Liu and Nummedal, 2004).
By ca. 81 Ma, dynamic subsidence appears to
have been a significant control on basin geometry (Roberts and Kirschbaum, 1995; Pang and
Nummedal, 1995; Liu and Nummedal, 2004;
Painter and Carrapa, 2013). Even though the
cause of dynamic subsidence remains ambiguous (Pang and Nummedal, 1995), some have
modeled it as a result of a cold and shallowing
subducting slab (Mitrovica et al., 1989; Gurnis,
1993). Isopach thicknesses indicate that by the
Maastrichtian, ca. 71– 65 Ma, Laramide-style
basement-cored uplifts had begun to partition
the foreland and create isolated basins (Dickinson et al., 1988; DeCelles, 2004). During uplift
of basement-involved structures to the east, Cordilleran orogenic deformation continued in the
west (DeCelles, 2004).
During foreland basin development adjacent
to the North America Cordilleran orogenic
belt, coarse-grained deposits (i.e., sandstone to
conglomerate) episodically prograded past the
proximal foredeep and into the distal foreland,
hundreds of kilometers east of the contemporary
thrust front. The mechanism controlling deposition of these distal coarse-grained deposits has
been debated over the years. Some have proposed that whereas upward-coarsening successions in the proximal foreland basin represent
active shortening in the fold-thrust belt and are
synorogenic, upward-coarsening successions in
the distal foreland represent reworking of coarse
material from the proximal foreland following
isostatic rebound and reworking during times
of tectonic quiescence (Fig. 4) (Beck et al.,
1988; Blair and Bilodeau, 1988; Heller et al.,
1988). Heller et al. (1988) proposed that during
times of active shortening and tectonic loading,
flexural subsidence rates are high, and coarsegrained deposits are trapped in the proximal
foreland. After active shortening ceases, flexural
rebound replaces flexural subsidence, which
leads to exhumation and reworking of coarse
proximal deposits out into the distal foreland
basin (Fig. 4). In contrast, other researchers
interpret coarse-grained deposits that prograde
rapidly into foreland basins as being syntectonic
(Burbank et al., 1988; DeCelles and Giles, 1996;
Horton et al., 2004). This flux-driven model,
described by Paola et al. (1992), predicts that
orogenic growth supplies more sediment to the
foreland basin than the basin can accommodate
through flexural subsidence; this results in rapid
widespread progradation of sediments (Burbank
et al., 1988; Paola et al., 1992; DeCelles and
Giles, 1996; Horton et al., 2004). Accordingly,
exhumation in the fold-thrust belt should follow
the same predictions, and lag times should be
short as a response to rapid erosion and little
sediment storage.
Relatively little thermochronological work
has been done in the North American Cordillera
of the western U.S.A. Various thermochronological studies have focused on Laramide mountain ranges in the Rocky Mountains (Cerveny,
1990; Cerveny and Steidtmann, 1993; Omar
Geological Society of America Bulletin, Month/Month 2014
3
Painter et al.
104°W
thermal gradient (e.g., Turcotte and Schubert,
2002), and rapidly deposited in the foreland
basin. However, if tc > td, then tL > 0. Small lag
times represent rapid exhumation, whereas large
lag times represent slow exhumation (Garver
et al., 1999). Constant lag times over a long
period of time represent steady-state exhumation, whereas decreasing lag times represent
increasing exhumation rates, and increasing lag
times represent episodic or decreasing exhumation rates (Garver et al., 1999; Bernet et al.,
2001; Carrapa et al., 2003) (Fig. 6). If the lag
time of distal grains in coarse-grained foreland
deposits approximates zero, then the deposits
are assumed to be of syntectonic origin, implying no reworking from proximal foreland basin
strata. However, if tL of distal coarse-grained
foreland deposits is large, then reworking of
deposits from proximal parts of the foreland
basin during flexural rebound is plausible, as
predicted by the two-phase stratigraphic model
of Heller et al. (1988) (Fig. 4). This approach is
valid only if the thermochronological ages are
not reset or partially annealed after deposition.
In the case of this study, post-depositional partial annealing is unlikely because stratigraphic
thicknesses, ages, and subsidence histories in
the Cordilleran foreland basin system suggest
that sediment burial during the Early Cretaceous
to Cenozoic never exceeded 2–3 km in eastern
Utah (DeCelles and Currie, 1996).
49°N
N
PRB
B
BH
WRB
D-JB
GRB
U-PB
37° N
PB
SJB
Sevier fold-thrust belt
Cordilleran magmatic arc
Laramide foreland province
0
Major thrust fault
Study area
550
200
kilometers
Major basins − Abbreviations outlined in caption
Figure 1. Regional index map of the western U.S.A. including the
Sevier fold-thrust belt, Laramide province, Cordilleran magmatic
arc, and major basins (modified from DeCelles, 2004). Basins shown
are the San Juan (SJB), Paradox (PB), Uinta-Piceance (U-PB),
Denver-Julesburg (D-JB), Green River (GRB), Wind River Basin
(WRB), Big Horn (BHB), and Powder River (PRB).
et al., 1994; Crowley et al., 2002; Kelley, 2002;
Peyton et al., 2012) and on the Colorado Plateau
(e.g., Dumitru, et al., 1994; Flowers et al., 2007,
2008). Burtner and Nigrini (1994) and Burtner
et al. (1994) used vitrinite reflectance and AFT
thermochronology to study the Idaho-Wyoming
part of the Sevier fold-thrust belt and concluded
that anomalously high geothermal gradients
during the Late Jurassic–Early Cretaceous were
caused by gravity-driven fluid flow. Preliminary
fission track analyses from the Upper Jurassic
Morrison Formation and the Lower Cretaceous
Cloverly Formation in Wyoming indicate late
Neocomian–early Albian cooling ages (Heady,
1992; DeCelles and Burden, 1992; Swierc and
Johnson, 1996; Chen and Lubin, 1997). In addition, the experimental work of Guenthner et al.
(2013) includes some zircon He work from the
foreland basin and the Sevier fold-thrust belt
in Utah. However, to date, no detailed detrital
thermochronological study of Cordilleran foreland basin strata is available.
Zircon He and AFT thermochronometers
measure the time of cooling through the 170–
190 °C and 60–120 °C temperature windows
respectively, i.e., partial retention or annealing
zone (PRZ, PAZ) (Gleadow and Duddy, 1981;
Gleadow et al., 1983; Laslett et al., 1987; Wolf
4
et al., 1998; Reiners et al., 2004). At temperatures above the lower limit of the PRZ, the mineral system becomes open and begins to lose
the radiogenic daughter product. In the case of
zircon He, He diffuses out of the system. In the
case of AFT, ion disruption tracks, a record of
the spontaneous fission of 238U, begin to anneal
(i.e., shorten).
In order to determine pattern and rates of cooling and exhumation of the Cordilleran orogenic
belt, we use lag-time measurements. Lag time
(tL) is defined as the difference between the cooling age of a detrital mineral (tc) and the depositional age (td) of its hosting strata (Brandon and
Vance, 1992; Garver et al., 1999) (Fig. 5):
t L = tc − td .
(1)
To determine td, we use a combination of existing age controls based on published biostratigraphic and 40Ar/39Ar age controls and our new
detrital U-Pb geochronologic ages (Table 2).
Different lag-time patterns reveal different
exhumation behavior in the source area. If tc ≈
td, then tL ≈ 0, indicating a very small lag time
(Garver et al., 1999) (Fig. 5). This means that
for the AFT system, the mineral was exhumed
from 4 to 5 km depth, assuming a 20 °C/km geo-
Existing Stratigraphic Age Control
Stratigraphic age control in the retroarc foreland basin of the North America Cordillera is
based on radiometric dating and biostratigraphy. Ammonite and inoceramid biostratigraphic
zones and 40Ar/39Ar ages of bentonite beds have
been used in the past (Baadsgaard et al., 1993;
Obradovich, 1993; Obradovich et al., 2002;
Izett et al., 1998; Gradstein and Ogg, 2004).
Cobban et al. (2006) compiled these data and
provided a biostratigraphic zonal data table for
much of the Upper Cretaceous North America
Cordilleran foreland basin. The stratigraphic
age control of fluvial and alluvial-fan deposits
is instead based on palynology (e.g., Jacobson
and Nichols, 1982; DeCelles and Burden, 1992;
Kowallis et al., 1991; Horton et al., 2004). In
some cases, age control comes from proximal
marine biozones that are correlated to the fluvial deposits (Martinsen et al., 1999), as well
as 40Ar/39Ar and K-Ar geochronology on tuffs
within the fluvial deposits. Below is a discussion on the existing age control for the Upper
Jurassic–Upper Cretaceous stratigraphy in the
Utah-Wyoming-South Dakota area of the foreland basin. The stratigraphic units discussed
below are the horizons sampled for this study,
Geological Society of America Bulletin, Month/Month 2014
Exhumation of the North American Cordillera
45° N
BH
B
PRB
051101
051102
051103
051104
N
A′
WRB
051213
051214
07.28.11
051207
051208
051209
051211
051212
051219
051206
051205
051105
051106
051201
051204
060922
060923
051108
051107
Sam 19
Sam 13
D-JB
GRB
U-PB
41° N
Sam 16
Sam 18
NSD4 B
Sam 11
PB
A
051218
SJB
109°W0
250
500
Sevier fold-thrust front
km
Major basins − SJB (San Juan Basin), PB (Paradox Basin),
U-PB (Uinta-Piceance Basins), GRB (Green River Basin),
D-JB (Denver-Julesburg Basin), WRB (Wind River Basin),
PRB (Powder River Basin)
BHB (Big Horn Basin)
Sample location with sample ID
Figure 2. Index map of the study area showing Utah, Wyoming, Colorado, and western South Dakota in the western U.S.A. Map shows
sample distribution. Sample information can be found in Table 1.
A to A′ is the trend in which samples are plotted in Figure 3.
and all samples and sample locations are found
in Table 1 and Figures 2 and 3; age data are also
compiled and presented in Table 2.
The Upper Jurassic Morrison Formation was
sampled from three geographically distinct areas
in eastern Utah, central Wyoming, and western
South Dakota. In eastern Utah, the Morrison Formation spans 154.8 ± 0.6 Ma to 135.2 ± 5.5 Ma
(Kimmeridgian–Valanginian), based on both
40
Ar/39Ar dating and K-Ar techniques (Kowallis
et al., 1991, 1998; Peterson, 1992) (Tables 1, 2;
Figs. 2, 3).
In central Wyoming, near Alcova Reservoir,
the age of the Morrison Formation has been
demonstrated to be 154.8 ± 0.6 to ca. 145 Ma
(DeCelles and Burden, 1992; Currie, 1998). The
older control is based on stratigraphic ties to
the age reported in the lower Morrison Formation by Kowallis et al. (1991), and the younger
boundary is based on palynomorphs (DeCelles
and Burden, 1992) (Table 2). The far eastern
extents of the Morrison Formation in eastern
Colorado and Wyoming and western South
Dakota and Oklahoma have been constrained
with biostratigraphy. Litwin et al. (1998)
reported palynomorphs in the Morrison Formation of that region that span latest Oxfordian–
Tithonian time. On the basis of ostracodes and
charophytes, Schudack et al. (1998) reported the
same ages for the Morrison Formation as Litwin
et al. (1998) (Table 2).
The Kelvin Formation (equivalent of the
Cloverly Formation) in northeastern Utah, near
Rockport Reservoir, has been interpreted as
Aptian–Albian, ca. 126–112 Ma (Crittenden,
1963; Hale and Van de Graaf, 1964; Kauffman,
1969; Ryer, 1977), based on lateral stratigraphic
correlations that place the Kelvin Formation
above the nearby Upper Jurassic Morrison
Formation (Crittenden, 1963; Hale and Van
de Graaf, 1964; Ryer, 1977). The age control
on the upper boundary is from the overlying
Mowry and Aspen Shales that contain the lower
Cenomanian Neogastroplites cornutus (Kauffman, 1969; Ryer, 1977) (Table 2).
Multiple researchers have tried to date the
Cloverly Formation (a Kelvin Formation equivalent) in Wyoming with a variety of methods;
Zaleha (2006) reviewed existing age controls
and determined that palynology provides the
most reliable results. In Wyoming, the Cloverly
spans the Early Cretaceous (Valanginian) to midAlbian (DeCelles and Burden, 1992; DeCelles
et al., 1993; Furer et al., 1997; O’Malley, 1994;
Way, 1997; Currie, 1998; Burton et al., 2006).
The A interval (Meyers et al., 1992; May et al.,
1995; Zaleha, 2006) of the Cloverly Formation near Alcova Reservoir in central Wyoming
is Early Cretaceous (Valanginian–Barremian)
based on palynomorphs reported in DeCelles
and Burden (1992) (Table 2).
In western South Dakota, the Lakota Formation is the Cloverly Formation equivalent; it
spans Aptian to mid-Albian time (Waagé, 1959;
Post and Bell, 1961; Dahlstrom and Fox, 1995;
Way et al., 1998; Zaleha, 2006; Sames et al.,
2010). The lowest member of the Lakota Formation in the Black Hills is the Chilson Member, which is Aptian in age (Post and Bell, 1961;
Sames et al., 2010), ca. 126–113 Ma (Table 2).
The Aptian–Albian Cedar Mountain Formation in northeastern Utah has been constrained
with U-Pb dating of zircons to a maximum
depositional age of 117–109 Ma (Burton et al.,
2006) (Table 2). In the northern Uinta Basin
in Utah, palynology indicates that the Dakota
Formation is upper Albian (Currie et al., 2011,
2012). The Dakota Formation in south-central
Utah, west of Glen Canyon City, is ca. 95 Ma
(Kirschbaum and McCabe, 1992; Uličný, 1999)
(Table 2).
The Frontier Formation has been documented
throughout Utah and Wyoming. North of Vernal, Utah, and near Flaming Gorge Reservoir,
the sandstone deposits of the Frontier Formation
are Turonian in age and are within the Watinoceras devonense to Prionocyclus germari (ca.
93.2–89 Ma) biozones (Cobban and Reeside,
1952; Cobban et al., 2006). In the type locality
of the Frontier Formation in western Wyoming,
north of the city of Frontier, and in eastern Wyoming, just west of Kaycee, the Frontier Formation is Cenomanian to Turonian in age and spans
the Conlinoceras tarrantense to Prionocyclus
germari (95.73 ± 0.61–89 Ma) biozones (Cobban and Reeside, 1952; Merewether et al., 1976;
Cobban, 1990; Cobban et al., 2006) (Table 2).
The Echo Canyon Conglomerate is Coniacian–Santonian in age. Palynological studies
have produced ages between ca. 87 and 85 Ma
(Jacobson and Nichols, 1982; DeCelles, 1994)
(Table 2).
Geological Society of America Bulletin, Month/Month 2014
5
Painter et al.
central eastern
Utah
Sam 8
70
060923
80
85
90
95
051218
100
Stratigraphic age (Ma)
western
Colorado
eastern
Wyoming
central
Wyoming
western
South Dakota
North Horn Fm.
051211
Almond Fm.
051210 Canyon Creek
Mbr.
Sam 18 lower and upper
Sego Sandstone 051219 Rusty Mbr.
Adaville Fm.
Sam 17 Mbr.
060922
051209 Trail Mbr.
07.28.11
051208 051212
051207
051205 Lazeart SS. Mbr.
Brooks Mbr.
Adaville Fm.
Rock Springs Fm.
051201 Echo Cangon Cgl.
Chimney Rock Tongue
lower Rock Springs Fm.
basal Blair Fm.
051105
Frontier Fm.
Dakota SS
051104
051206
Frontier Fm.
Sam 13
75
western
Wyoming
Ericson Fm.
southern
Utah
Price River Fm.
65
051106
Dakota SS
051107
Cedar Mtn. Fm.
051204
Kelvin Fm.
Frontier Fm.
105
115
130
051102
051103
Morrison Fm.
051101
120
125
lower and upper
Chilson Mbr.
110
Black text = sandstone
sample
Gray and underlined
text = conglomerate
cobble sample
051213
the A interval
Cloverly Fm.
051214
Morrison Fm.
135
140
145
051108
Morrison Fm.
150
155
160
Figure 3. Graphical representation of the spatial and temporal distribution of samples within this study (Table 1). See Table 2 for detailed
citations and for age uncertainties associated with depositional ages presented in the literature. A to A′ in Figure 2 is the direction in which
samples are plotted. Detailed information on the age control is found in the text. Black text represents sandstone samples and gray text
represents conglomerate cobble samples.
In western Wyoming, the Upper Cretaceous
Adaville Formation is ca. 82.5 Ma at its base (the
Lazeart Sandstone Member), based on Scaphites hippocrepis I, and 81.86 ± 0.36 Ma at its
top, based on Scaphites hippocrepis II (Miller,
1977; Roehler, 1990; Devlin et al., 1993; Krystinik and Blakeney DeJarnett, 1995; Cobban
et al., 2006). Farther east, the Blair Formation
near Rock Springs, Wyoming, is coeval with the
Lazeart Sandstone Member, with an age of ca.
82.5 Ma (Scaphites hippocrepis I) (Smith, 1961;
Gill et al., 1970; Roehler, 1990; Krystinik and
Blakeney DeJarnett, 1995; Cobban et al., 2006)
(Table 2).
Both the Chimney Rock Tongue Member and
the Brooks Member of the Rock Springs Formation, near Rock Springs, Wyoming, are early
Campanian in age. The Chimney Rock Tongue
Member is ca. 81.5 Ma, constrained by Scaphites hippocrepis III, and the overlying Brooks
6
Two-phase stratigraphic model (anti-tectonic)
Thrust-Derived
Proximal
Distal
Molasse
Foreland
Foreland
Active
Thrust
Belt
Subsidence
Erosion
reworked
deposits
Thrust
Advance
Cessation
of
Thrusting
Inactive
Thrust
Belt
Rebound
Figure 4. Two-phase stratigraphic model as proposed by Heller et al. (1988).
The model asserts that upward-coarsening sequences in the proximal foredeep represent active shortening and tectonism in the thrust belt. In contrast, it asserts that upward-coarsening sequences in the distal foreland are
anti-tectonic, formed during times of tectonic quiescence and flexural rebound, and are reworked from proximal coarse-grained deposits.
Geological Society of America Bulletin, Month/Month 2014
Exhumation of the North American Cordillera
Figure 5. Stylized fold-thrust
belt, foreland basin, and geoexhumation
thermal gradient. Lag time (tL)
tL = tc – td
equals the difference between
cooling
depositional age t d
the cooling age (t c ) and the
age t c
depo sitional age (t d ) (Garver
~60 °C
apatite (U-Th-[Sm])/He
et al., 1999). The white dashed
~120 °C
apatite fission track
lines show the approximate clo~180 °C
zircon (U-Th-[Sm])/He
sure temperature of different
thermochronologic systems.
The black dashed line represents a stylized exhumation pathway, and the red dot represents an apatite-bearing sample passing through its
closure temperature, being exhumed, and then being deposited in the foreland basin.
Member is ca. 81 Ma, constrained by Baculites
sp. (weak flank ribs) (Smith, 1961; Gill et al.,
1970; Roehler, 1990; Krystinik and Blakeney
DeJarnett, 1995; Cobban et al., 2006) (Table 2).
The Sego Sandstone Member of Mesaverde
Group in the Book Cliffs area, Utah, overlies
Baculites perplexus and has Baculites scotti in
its upper part (ca. 78 Ma to 75.56 ± 0.11 Ma)
(Gill and Hail, 1975; Cobban et al., 2006). In
northwest Colorado, the age of the Sego Sandstone Member is less well understood than
it is in the Book Cliffs area, Utah. Baculites
perplexus has been identified below the Sego
Sandstone Member in northwest Colorado, but
no ammonite zone has been identified in the
upper portions of the Sego Sandstone Member
in northwest Colorado (Cullins, 1971; Molenaar
and Wilson, 1993; Painter et al., 2013). However, in a detrital zircon U-Pb study, a single
young zircon grain was dated at 76.6 ± 1.5 Ma
(York, 2010), suggesting a similar age to the
Sego Sandstone Member in the Book Cliffs area
in Utah (Table 2).
The Upper Campanian Ericson Formation,
near Rock Springs, Wyoming, sampled in this
study (Table 1; Figs. 2, 3), spans the biozones
Baculites mclearni to Baculites reesidei (ca.
80 to 72.94 ± 0.45 Ma) (Gill et al., 1970; Martinsen et al., 1999; Cobban et al., 2006). However, the Ericson Formation consists of fluvial
to estuarine deposits, and these biostratigraphic
horizons are correlated along strike from nearby
marine stratigraphy (Gill et al., 1970; Martinsen
et al., 1999; Leary, 2011). The Trail Member of
the Ericson Formation, its stratigraphically lowest member, spans the Baculites asperiformis
to Baculites sp. (smooth) biozones (ca. 79 Ma).
The overlying Rusty Member of the Ericson Formation has been correlated to the Baculites sp.
(smooth) to Baculites perplexus biozones (ca.
78 Ma). The uppermost member of the Ericson
Formation is the Canyon Creek Member, which
has been correlated to the Didymoceras cheyennese to Baculites reesidei zones (74.67 ± 0.15 to
72.94 ± 0.45 Ma) (Gill et al., 1970; Martinsen
et al., 1999; Cobban et al., 2006) (Table 2).
In north-central Utah, Upper Cretaceous to
Paleocene conglomerate deposits have been
dated using palynology (Horton et al., 2004);
the Castlegate–Price River Formation in the
Charleston-Nebo salient in north-central Utah
is mid- to upper Campanian (ca. 80–71 Ma)
(Fouch et al., 1983; Horton et al., 2004). The
overlying North Horn Formation is Maastrichtian–early Paleocene (ca. 70–61 Ma) (Horton
et al., 2004) (Table 2). The upper Campanian
to lower Maastrichtian Almond Formation, near
Rock Springs, Wyoming, is correlated to Baculites jenseni to Baculites baculus biozones (ca.
72–71 Ma) (Gill et al., 1970; Martinsen et al.,
1999; Cobban et al., 2006) (Table 2).
METHODS
Thirty-seven samples of conglomerate
cobbles and sandstones were collected from
proximal and distal Cordilleran foreland
basin deposits (Table 1). Detrital zircon U-Pb
geochronology was applied to all sandstone
samples (Table 1). Zircon He thermochronology was applied to one conglomerate cobble
sample, seven foreland basin sandstones, and
one paleozoic sandstone exposed in the thrust
belt (Table 1), and AFT thermochronology was
applied to four conglomerate cobbles and seven
sandstone samples (Table 1). All thirty-seven
samples presented in this paper were collected
from surface outcrops, and both the base and top
of the selected stratigraphic units were sampled.
Because of generally poor apatite yield in clasts
and sandstones derived from Cordilleran quartzites, ~50 pounds (20 kg) were collected for each
sandstone sample. All samples were processed
to separate both zircons and apatites. Zircon and
apatite crystals were extracted by standard mineral separation methods of crushing followed
by separation by Wilfley table, Frantz magnetic
separator, and heavy liquids. Every sample collected for this study produced zircons; however, only eleven samples produced apatites of
suitable quality and quantity for AFT thermochronology. The paucity of apatite could be a
result of low apatite content in the miogeoclinal
Paleozoic source rocks, or it could indicate that
apatite did not survive transport from the sourcing orogenic belt to the foreland basin because
of mechanical and/or chemical weathering.
U-Pb analysis on detrital zircon and detrital
apatite, zircon He analysis, and AFT methods
are explained below. More detailed information about laboratory procedures and analytical equipment can be found in the GSA Data
Repository1 (Expanded Methods).
Detrital Zircon and Apatite
U-Pb Geochronology
Zircon and apatite U-Pb ages were determined by laser ablation–multicollector–inductively coupled plasma mass spectrometry
(LA-MC-ICPMS) at the Arizona LaserChron
Center (Gehrels et al., 2006, 2008; Thomson
et al., 2012). Twenty-two new detrital zircon
samples were analyzed, producing 1874 new
U-Pb ages. The analytical data are reported in
the Data Repository (Table DR1). Uncertainties shown in these tables are at the one-sigma
level and include only measurement errors.
Analyses that are >20% discordant (by comparison of 206Pb/238U and 206Pb/207Pb ages) or >5%
reverse discordant are not considered further
(Gehrels, 2011).
The closure temperature for U-Pb in apatite
is 450–550 °C (Cherniak et al., 1991), classifying it as a medium-temperature thermochronometer. In quickly cooled volcanic rocks (e.g.,
ash-fall material), this temperature is attained at
nearly the same time as the crystallization age
and therefore yields an age near the crystallization age. Dates from metamorphic and plutonic
rocks can also record metamorphic events and
late-stage cooling of magmatic intrusions. In
1
GSA Data Repository item 2014223, which contains expanded methods, raw detrital zircon U-Pb
data (Table DR1), raw apatite U-Pb data (Table
DR 2), and concordia plots (Figure DR1), is available at http://www.geosociety.org/pubs/ft2014.htm
or by request to editing@geosociety.org.
Geological Society of America Bulletin, Month/Month 2014
7
8
Geological Society of America Bulletin, Month/Month 2014
Frontier
Formation
Echo Canyon
Conglomerate
Adaville
Formation
Rock Springs
Formation
Sego Sandstone
Member:
Mesaverde Group
Ericson
Formation
Price River
Conglomerate
ca. 82.5
ca. 82.5
Western
Wyoming
South-central
Wyoming
Lazeart
Sandstone
Member
Blair Formation
95.73 ± 0.61–89
95.73 ± 0.61–89
Western
Wyoming
Eastern
Wyoming
ca. 93.2–89
81.86 ± 0.36
Western
Wyoming
Upper Adaville
ca. 87–85
ca. 81.5
South-central
Wyoming
Chimney Rock
Tongue Member
Eastern
Utah
ca. 81
South-central
Wyoming
Brooks Member
North-central
Utah
ca. 78–76
ca. 79
South-central
Wyoming
Trail Member
Northwest
Colorado
ca. 78
74.67 ± 0.15–
72.94 ± 0.45
South-central
Wyoming
South-central
Wyoming
ca. 80–71
ca. 70–61
ca. 72–71
Age
(Ma)
Rusty Member
Canyon Creek
Member
North-central
Utah
North-central
Utah
North Horn
Formation
Location
South-central
Wyoming
Almond
Formation
Formation/Member
Equivalent
stratigraphy
Cenomanian–Turonian
Cenomanian–Turonian
Turonian
Coniacian–Santonian
Early Campanian
Early Campanian
Early Campanian
Early Campanian
Early Campanian
Campanian
Campanian
Campanian
Late Campanian
Mid–late Campanian
Maastrichtian–
early Paleocene
Late Campanian–
Maastrichtian
Geologic age
Ammonites, Ar/Ar
Ammonites, Ar/Ar
Ammonites
Palynomorphs
Ammonites
Ammonites
Ammonites, Ar/Ar
Ammonites
Ammonites
Stratigraphic correlations,
ammonites, DZ U-Pb
Stratigraphic correlations,
ammonites
Stratigraphic correlations,
ammonites
Stratigraphic correlations,
ammonites, Ar/Ar
Palynomorphs
Palynomorphs
Ammonites
Data type
TABLE 2. LATE JURASSIC TO LATE CRETACEOUS STRATIGRAPHIC AGES
25, 26,
27
25, 26,
27
25
28, 29
31, 33,
34, 35
30, 31,
32, 33
30, 31,
32, 33
30, 31,
32, 33
30, 31,
32, 33
36, 37,
38, 39
35, 40
35, 40
35, 40
41
41
35, 40
Source
None
None
None
76.6 ± 1.5
None
None
90.5 ± 2.0
N/A
84.3 ± 4.8
85.3 ± 1.3
b
None
None
72.1 ± 1.5
a
N/A
N/A
None
None
None
91.5 ± 2.5
N/A
85.6 ± 4.1
87.2 ± 4.8
None
None
None
None
None
None
N/A
N/A
N/A
None
None
None
94.0 ± 0.8
N/A
96.0 ± 0.8
96.9 ± 0.7
None
None
None
None
None
None
72.9 ± 4.8
a
N/A
N/A
None
DZ young ages MDA (Ma)
Youngest
Average of
Youngest
grain
young grains population
(conitnued)
051104
051206
051105
051201
051207
051205
07.28.11
051212
051208
Sam 17
051209
051219
051210
060922,
060923
Sam 8
051211
Sample(s)
Painter et al.
ca. 126–112
Eastern
Utah
ca. 126–113
154.8 ± 0.6–
135.2 ± 5.5
154.8 ± 0.6–
ca. 145
Central
Wyoming
Western
South Dakota
Eastern
Utah
Central
Wyoming
Chilson Mbr. of
the Lakota Fm.
ca. 139–126
117–109 Ma
ca. 102
Eastern
Utah
Eastern
Utah
ca. 95
A interval
Kelvin Fm.
Location
South-central
Utah
Age
(Ma)
15
Ar/Ar, palynomorphs
3, 4
None
None
154.2 ± 3.8 157.0 ± 3.2
None
136.3 ± 8.8 147.6 ± 5.9 155.3 ± 4.1
Kimmeridgian–Tithonian
4, 5, 6
Ar/Ar, K-Ar
Kimmeridgian–Berriasian
051214
051108
051101,
051102
None
None
16, 17, 18,
19, 20, 21
Palynomorphs
Aptian
051213
None
None
3, 11,
12, 13, 14,
15, 20
Valanginian–Barremian
Palynomorphs
051204
118.0 ± 4.5
121.3 ± 3.2
117.2 ± 3.2
7, 8,
9, 10
051107
106.3 ± 2.8 107.3 ± 3.6 109.2 ± 2.5
051106
U-Pb on zircons
None
None
None
22, 42,
43
Stratigraphic correlations,
ammonites
051218
Sample(s)
None
23, 24
None
94.5 ± 2.9
Source
Data type
Stratigraphic correlations,
ammonites
Stratigraphic correlations,
ammonites
Aptian–Albian
Aptian–Albian
Albian
Cenomanian
Geologic age
DZ young ages MDA (Ma)
Youngest
Average of
Youngest
grain
young grains population
Geological Society of America Bulletin, Month/Month 2014
ca. 158–ca. 145
Depositional age
st
ea
dy
-st
at
e
e
co xhu
ns
m
ta
nt atio
n
la
r
g
tim ate
incre
asing
e
exhu
matio
co
n rat
ns
e
ta
nt
la
g
tim
e
rate
exhumation
decreasing
Western
South Dakota
Late Oxfordian–
Palynomorphs, ostracodes,
Tithonian (predominantly
1, 2
157.8 ± 6.6 160.2 ± 4.2 161.8 ± 3.3
051103
charophytes
Kimmeridgian)
Note: Stratigraphic ages of Late Jurassic–Paleocene sandstones to conglomerates that span Utah, Colorado, Wyoming, and South Dakota. Existing ages were gathered from literature, and the sources are
given below. Absolute ages of certain biozones are all from Cobban et al. (2006), which is a compilation of previous biostratigraphic and Ar/Ar work. New constraints from detrital zircon (DZ) U-Pb dating, presented
in this study, are shown also (asome DZ U-Pb grains from Leary [2011]; bDZ age from York [2010]). In the DZ age columns, “None” indicates that none were found during U-Pb analysis, and “N/A” indicates that
these are conglomerate cobbles so no DZ analysis was done. MDA—maximum depositional age. Sources: 1 (Litwin et al., 1998); 2 (Schudack et al.,1998); 3 (DeCelles and Burden, 1992); 4 (Kowallis et al., 1991);
5 (Kowallis et al., 1998); 6 (Peterson, 1992); 7 (Crittenden, 1963); 8 (Hale and Van de Graaf, 1964); 9 (Kauffman, 1969); 10 (Ryer, 1977); 11 (DeCelles et al., 1993); 12 (Furer et al., 1997); 13 (O’Malley, 1994);
14 (Way, 1997); 15 (Burton et al., 2006); 16 (Waagé, 1959); 17 (Post and Bell, 1961); 18 (Dahlstrom and Fox, 1995); 19 (Way et al., 1998); 20 (Zaleha, 2006); 21 (Sames et al., 2010); 22 (Johnson, 2003); 23
(Kirschbaum and McCabe, 1992); 24 (B.S. Currie, 2013, personal commun.); 25 (Cobban and Reeside, 1952); 26 (Merewether et al., 1976); 27 (Cobban, 1990); 28 (Jacobson and Nichols, 1982); 29 (DeCelles,
1994); 30 (Miller, 1977); 31 (Roehler, 1990); 32 (Devlin et al., 1993); 33 (Krystinik and Blakeney DeJarnett, 1995); 34 (Smith, 1961); 35 (Gill et al., 1970); 36 (Gill and Hail, 1975); 37 (Cullins, 1971); 38 (Molenaar
and Wilson, 1993); 39 (Painter et al., 2013); 40 (Martinsen et al., 1999); 41 (Horton et al., 2004); 42 (Currie et al., 2011); 43 (Currie et al., 2012).
Morrison
Formation
Cloverly
Formation
Cedar Mountain
Formation
Dakota Formation
Formation/Member
Equivalent
stratigraphy
TABLE 2. LATE JURASSIC TO LATE CRETACEOUS STRATIGRAPHIC AGES (conitnued)
Exhumation of the North American Cordillera
Cooling age
Figure 6. Three hypothetical lag-time trends
and what they suggest about exhumation
(Garver et al., 1999; Bernet et al., 2001).
Decreasing lag times indicate an increase
in exhumation, constant lag times indicate
a steady-state exhumation rate, and increasing lag times indicate a decreasing exhumation rate.
contrast to zircon, apatite is more difficult to
date using U-Pb because apatite has much lower
amounts of U, generally <100 ppm, and generally higher amounts of common lead. However,
recent advances have improved U-Pb thermochronology of apatites (Carrapa et al., 2009;
Thomson et al., 2012). Although the error is
much higher in U-Pb analyses of apatite than
of zircon, this technique can establish whether
the crystallization and/or metamorphic age of
an apatite grain is near the AFT cooling age of
the same apatite grain, and can thus discriminate between magmatic ages versus exhumation ages.
We followed the procedure developed and
outlined by Thomson et al. (2012) to analyze
U-Pb ages of apatite in seven detrital samples,
targeting ten apatite grains (with the youngest
individual AFT ages) from each sample, and the
complete analytical results can be found in the
Data Repository (Table DR2). Grains from the
youngest AFT age population were targeted in an
effort to test whether their ages record exhumation or timing of crystallization in the case of volcanogenic apatites. These apatites were mounted
on slides next to 485 Ma apatite standards from
Madagascar and NIST reference material glass,
to correct for elemental fractionation.
Although a large laser (>65 µm) spot size
is recommended for apatite (Thomson et al.,
2012), the grain size of the available apatites did
not allow this use of a large spot size. Instead,
a 40-µm-diameter laser was used on all but one
9
Painter et al.
of the samples analyzed; the remaining sample
was analyzed with a 25-µm-diameter laser
because of its small apatite crystals.
The resulting interpreted U-Pb ages are
shown on Pb/U concordia diagrams and relative
age-probability diagrams using the routines in
Isoplot software (Ludwig, 2008). The age-probability diagrams show each age and its uncertainty (for measurement error only) as a normal
distribution, and sum all ages from a sample into
a single curve. Composite age-probability plots
are made from an in-house Microsoft Excel
program (see Analysis Tools at www.laserchron
.org for link) that normalizes each curve according to the number of constituent analyses, such
that each curve contains the same area, and then
stacks the probability curves. Maximum depositional ages (MDAs) for detrital zircon U-Pb
analyses were calculated using three methods
(described by Dickinson and Gehrels, 2009);
(1) the youngest grain was selected from each
of the samples, (2) the average age of the youngest three zircons was calculated, and (3) the
weighted mean of the youngest Gaussian distribution of three or more grains was calculated.
All three of these calculations are presented in
Table 2. All analytical data are reported in the
Data Repository (Table DR1).
Zircon (U-Th-[Sm])/He Thermochronology
Zircon He analyses were conducted at the
University of Arizona following the method
described by Reiners (2005). Nine samples
were analyzed for this study (Table 1; Figs.
2, 3). Three zircons from each sample were
handpicked, and the dimensions of each crystal
were measured to approximate crystal volume
to ensure a tetragonal prism width of greater
than 60 µm. Each crystal was then packed in a
Nb foil tube and heated with a focused 10 µm
beam of a 1064 nm Nd:YAG laser for 15 min
intervals to degas the He content of the zircon.
Typically two to three intervals are required to
sufficiently degas the zircon.
The gas extracted from the zircon was then
spiked with approximately –0.1 to 1.0 pmol 3He
and was cryogenically concentrated and purified. This gas mixture was then expanded and
measured with a quadrupole mass spectrometer. The U and Th contents were then measured by isotope dilution and solution ICPMS
(Reiners, 2005).
Apatite Fission Track (AFT)
Thermochronology
Eleven samples were analyzed using AFT
thermochronology (Table 1; Figs. 2, 3). Here we
present data from two different sample types:
10
apatites from conglomerate cobble clasts, and
detrital apatites from sandstones. Cobble clasts
can be considered as basement samples and
have a uniform time-temperature history, and
for these samples, 20 apatite grains per sample
were analyzed and a mean age is presented
(where χ2 > 5%). For sandstone samples, 100
detrital apatite crystals were analyzed in order
to capture the different source cooling signals
of the catchment area; the software package
BINOMFIT was used to identify different age
populations (Galbraith and Green, 1990; Brandon, 2002), and we considered only populations containing more than five grains as significant. Unless the individual age populations
are contaminated with volcanogenic apatites,
these populations are generally assumed to be
an exhumation signal; in particular, the youngest age population is generally assumed to be a
source exhumation signal.
RESULTS
Detrital Zircon U-Pb Geochronology
The primary purpose of measuring the age
of detrital zircons with U-Pb techniques was to
determine the MDA of the collected samples
by independent methods. Furthermore, because
of the wide geographic area that these samples
represent, detrital zircon (DZ) U-Pb analyses
help to assess whether the analyzed samples
share a similar provenance history. The samples
that were analyzed using DZ U-Pb are found in
Table 1, and the raw data can be found in the
Data Repository (Table DR1). Two samples
from previous work (York, 2010) with 200 individual zircon ages are included here together
with four zircon ages from Leary (2011). In
Table 2, we present how these DZ U-Pb ages
compare to the existing stratigraphic age control
determined from biostratigraphy and 40Ar/39Ar
ages of bentonites. Figure 7 is a probability
density plot of detrital zircons in each sample
<200 Ma, and the youngest single zircon in each
sample is listed as the MDA.
Three samples from the Morrison Formation
in Utah (sample 051108), Wyoming (sample
051214), and South Dakota (sample 051103)
were analyzed (Fig. 7). In both Utah and Wyoming, the samples were taken from fluvial
deposits. In South Dakota, the Morrison Formation is predominantly lacustrine. A weighted
mean of the youngest statistically separable
population of zircons for the Utah sample produced a Late Jurassic (Kimmeridgian) MDA
of 155.3 ± 4.1 Ma. Sample 051214 from Wyoming does not have a young population with the
requisite number of zircons (more than three);
however, it does contain two young grains with
an average MDA of 157.0 ± 3.2 Ma, which is
consistent with sample 051108 from Utah.
Sample 051103 from South Dakota has a young
population with a weighted mean and Late
Jurassic (Oxfordian) MDA of 161.8 ± 3.3 Ma.
In all cases, these samples produce a Late Jurassic MDA (Oxfordian–Kimmeridgian).
Four samples from the Lower Cretaceous
Cloverly Formation, and its equivalents, were
analyzed from Utah (sample 051204), Wyoming
(sample 051213), and South Dakota (samples
051101 and 051102) (Fig. 7). Sample 051204
from Utah is from the Kelvin Formation, which
is equivalent to the Cloverly Formation. The
weighted mean of the youngest statistically separable population of zircons in the sample from
Utah produced an Early Cretaceous (Aptian)
MDA of 121.3 ± 3.2 Ma. A single young zircon
in this sample is 117.2 ± 2.4 Ma, but this is not
a statistically robust population. Sample 051213
from the A interval of the Cloverly Formation in
Wyoming contained no young, syndepositional
zircons. Two samples (051101 and 051102)
from the Chilson Member of the Lakota Formation (Cloverly Formation equivalent) in South
Dakota were analyzed; however, no syndepositional zircons are present. One sample from
the Lower Cretaceous Cedar Mountain Formation (sample 051107) in Utah, also equivalent
to the Cloverly Formation, was sampled. The
weighted mean of the youngest population of
zircons produced an Early Cretaceous (Albian)
MDA of 109.2 ± 2.5 Ma (Fig. 7).
Two samples (samples 051218 and 051106)
from the Lower to Upper Cretaceous Dakota
Formation were collected in Utah, one from
south-central Utah and the other from northeast
Utah (Fig. 7). Neither of these samples has a
population of more than three young zircons to
calculate a weighted mean. However, the sample
from south-central Utah (051218) contained one
young zircon with the age of 94.5 ± 2.9 Ma, suggesting a Late Cretaceous (Cenomanian) MDA.
Three samples from the Upper Cretaceous
Frontier Formation were collected and analyzed, one from Utah (sample 051105) and two
from Wyoming (samples 051206 and 051104).
In Wyoming, sample 051206 was collected
from the western part of the state, and sample
051104 was collected from the eastern side in
the Powder River Basin (Fig. 7). The weighted
mean of the youngest zircon population in sample 051105 from Utah is 94.0 ± 2.9 Ma, producing a Late Cretaceous (Cenomanian–Turonian)
MDA. However, there are younger grains in this
population that do not form a statistically separable peak. The average of the three youngest
grains is 91.5 ± 2.5 Ma, suggesting a Turonian
MDA. Neither of the Wyoming samples yielded
young, syndepositional zircons.
Geological Society of America Bulletin, Month/Month 2014
Exhumation of the North American Cordillera
Wyoming
Utah-Colorado
051211
Almond Fm.
051210
Canyon
Creek Mbr.
051219
Rusty Mbr.
051209
Trail Mbr.
n=100 Sam 18
upper
Sego Sandstone Mbr.
n=100 MDA=76.6±1.5
Sam 17
lower
Sego Sandstone Mbr.
n=83
n=79
051208
n=90
051212
Brooks Mbr.
Rock Springs Fm.
n=89
Chimney Rock Tongue
lower Rock Springs Fm.
07.28.11
Adaville Fm.
n=87 MDA=84.3±4.8 Ma
051207
basal Blair Fm.
051205
Lazeart SS. Mbr.
Adaville Fm.
n=80 MDA=85.3±1.3 Ma
n=86 MDA=90.5±2.0 Ma
051105
Frontier Fm.
n=86 MDA=94.5±2.9 Ma
051218
Dakota Fm.
n=71 MDA=106.3±2.8 Ma
051107
n=87 MDA=117.2±3.2 Ma
n=77 †MDA=147.6±5.9 Ma
0
50
100
Age (Ma)
n=80
n=86
051104
051206
Frontier Fm.
Cedar Mtn.
Kelvin Fm.
051204
051108
Ericson Fm.
n=87
n=87
MDA=72.1±1.5 Ma
n=87
maximum depositional age=MDA
n=number of single zircon ages in sample
South Dakota
Morrison Fm.
150
the A interval
Cloverly Fm.
051213
n=84 MDA=154.2±3.8 Ma
051214
n=84
200 0
50
100
Age (Ma)
Morrison Fm.
150
lower and upper
n=88 051101 Chilson Mbr.
n=89 051102
n=97 MDA=157.8±6.6 Ma 051103 Morrison Fm.
200 0
50
100
Age (Ma)
150
200
Figure 7. Probability density plots of all young detrital zircon (DZ) U-Pb analyses (0–200 Ma) presented here. See Table 1 for a comprehensive list of all the samples with DZ U-Pb. All curves are normalized to one another. Samples Sam 18 and Sam 17 come from York (2010). All
the other samples are new. Where applicable, maximum depositional age (MDA) is given (see Table 2 for more detailed MDA information);
n is the number of zircon grains analyzed from each whole sample (excluding those grains that have been filtered out given quality assurance standards). All data can be found in Table DR1 in the Data Repository [see footnote 1].
Two samples (051205 and 07.28.11) of the
Upper Cretaceous Adaville Formation in western Wyoming were analyzed (Fig. 7), one from
the Lazeart Sandstone Member and one in the
upper Adaville Formation. The Lazeart Sandstone Member sample (051205) has three young
zircons with an average age of 87.2 ± 2.2 Ma,
suggesting a Late Cretaceous (Coniacian–Santonian) MDA. However, these three grains do
not represent a statistically separable and robust
population from which a weighted mean can be
calculated. The sample from the upper Adaville
Formation did not yield any young, syndepositional zircons.
Three samples from the Rock Springs Formation in Wyoming were analyzed, one from
the basal Blair Formation (sample 051207),
one from the Chimney Rock Tongue Member
(sample 051212), and one from the Brooks
Member (sample 051208) (Fig. 7). Young zircons in the age range of 84.3–89.0 Ma are present in the Blair Formation sample, but they are
overwhelmed by 90–98 Ma zircons and do not
produce a statistically separable peak. However,
three young zircons produced an average age
of 85.6 ± 4.1 Ma, consistent with a Late Cretaceous (Santonian) MDA. The samples from the
Chimney Rock Tongue Member and the Brooks
Member did not yield young, syndepositional
age zircons.
Three samples from the Upper Cretaceous
(Campanian) Ericson Formation in Wyoming
were analyzed. Also, two samples from the
Campanian Sego Sandstone Member of the
Mesa Verde Group in northwest Colorado from
York (2010) are presented here. Out of the Trail
Member, Rusty Member, and Canyon Creek
Member of the Ericson Formation, only the Canyon Creek Member (sample 051210) yielded
young, near syndepositional age zircons, sample
051210, with an age of 73.3 ± 5.1 Ma. However,
a sample presented in Leary (2011) from the
Canyon Creek Member of the Ericson Formation in the same general geographic area yielded
five ca. 73 Ma grains, which have been included
in this data set in order to calculate a weighted
mean MDA; those grains have suffixes of “rl1–
rl5” in the data file in the Data Repository (Table
DR1). The combined grains have a Late Campanian MDA of 72.9 ± 0.8 Ma (Fig. 7).
One of the Sego Sandstone Member samples
(Sam 17) contained one young zircon of 76.6 ±
5.1 Ma. However this is a single age and is not
the more robust weighted mean of a population
or the average of three young grains.
One sample from the Upper Cretaceous
Almond Formation in Wyoming was analyzed (sample 051211) but did not contain any
young zircons with nearly syndepositional ages
(Fig. 7).
All of the calculated MDAs have been compared to existing depositional ages based on
biostratigraphy and 40Ar/39Ar ages of bentonites
(Table 2). In an effort to compare provenance of
all the samples analyzed, a second probability
density plot is presented (Fig. 8). In this prob-
Geological Society of America Bulletin, Month/Month 2014
11
Wopmay
Trans-Hudson
Yavapai
Mazatzal
3200
3000
2800
2600
2400
2200
2000
1800
1600
1.48–1.34 Ga magmatics
1400
1200
Grenville orogen
1000
800
Morrison Fm.
051214
0
3600
3400
3200
3000
2800
2600
2400
2200
2000
1800
1600
Age (Ma)
the A interval
051213 Cloverly Fm.
051205 Lazeart SS. Mbr.
Adaville Fm.
051104
Frontier Fm.
051206
basal Blair Fm.
200
051207
07.28.11
Adaville Fm.
400
Brooks Mbr.
Rock Springs Fm.
Chimney
Rock Tongue
051212
lower Rock Springs Fm.
600
Peri-cratonic orogens
Cordilleran magmatism
051208
Trail Mbr.
051209
051219
051210 Canyon Creek Mbr.
051211
Almond Fm.
Ericson Fm.
WYOMING
Peri-cratonic orogens
1400
1200
1000
800
600
400
Sam 17
1.48–1.34 Ga magmatics
Grenville orogen
051108 Morrison Fm.
0
3600
3400
3200
3000
2800
2600
2400
2200
2000
1800
1600
1400
1200
1000
800
Peri-cratonic orogens
600
Peri-cratonic orogens
Cordilleran magmatism
400
200
0
12
Age (Ma)
Wopmay
051105
Frontier Fm.
051106
Dakota SS
051218
051107Cedar Mtn. Fm.
051204
Kelvin Fm.
lower Sego Sandstone Mbr.
upper Sego Sandstone Mbr.
Archean crust
Trans-Hudson
Yavapai
Mazatzal
Sam 18
UTAH-COLORADO
200
Figure 8. Probability density plots (PDPs) of pre-Sevier detrital zircon U-Pb ages (>160 Ma) to assess provenance. In these PDP curves, grains
younger than 160 Ma (coeval with the Sevier orogeny) are excluded. All of the curves were then re-normalized and stretched uniformly along
the vertical axis to make peaks more visible. Orogenic province ages are from Whitmeyer and Karlstrom (2007) and Gehrels et al. (2011).
SOUTH DAKOTA
Archean crust
3600
3400
Age (Ma)
lower and upper
Chilson Mbr.
051101
051102
Morrison Fm.
051103
Painter et al.
ability density plot, all grains younger than
160 Ma, near the onset of the Sevier orogeny
(DeCelles, 2004), are excluded in order to eliminate magmatic and volcanogenic synorogenic
zircons and instead isolate zircons exhumed
from the Paleozoic strata in the Sevier foldthrust belt and its hinterland region (Dickinson
and Gehrels, 2008; Gehrels et al., 2011). The
data were then renormalized and uniformly
stretched vertically to make peak age differences
more apparent (Fig. 8). The amplitude of some
of the peaks varies (e.g., the 1.6–1.8 Ga peak);
however, the presence of peak age clusters is
similar throughout the 24 samples (Fig. 8), and
no significant trends are evident.
Zircon (U-Th-[Sm])/He Thermochronology
In order to identify the most effective thermochronometer able to record cooling related to
source exhumation in the North America Cordillera, nine samples from the Sevier fold-thrust
belt and Cordilleran foreland were analyzed
with zircon He thermochronology. These samples include Paleozoic strata in the fold-thrust
belt itself, conglomerate cobbles of wedge-top
deposits, and detrital samples in the proximal to
distal foreland basin. Three zircons from each
sample were picked and dated, except for sample Sam 11, from which only two zircons were
dated. Complete data from these analyses can be
found in Table 3.
Sample Sam 11 is from the Inkom Formation, a Proterozoic quartzite from the Canyon
Range Culmination in the Canyon Range, Utah
(DeCelles et al., 1995) (Table 1; Fig. 2). The
two zircon He ages are 22.8 ± 0.5 and 139.7 ±
3.1 Ma (Table 3; Fig. 9).
Samples Sam 19, Sam 16, and Sam 15 are
detrital samples from the Upper Cretaceous
Castlegate Formation in both Utah and northwest Colorado (Table 1; Figs. 2, 3). Sample Sam
19 produced three zircon He ages, 348.7 ± 13.7,
396.3 ± 14.3, and 152.2 ± 6.2 Ma. Sample Sam
16 records three ages, 64.5 ± 5.1, 249.5 ± 9.5,
and 357.2 ± 15.2 Ma. Sample Sam 15 records
three ages, 96.0 ± 5.2, 125.8 ± 5.5, and 177.4 ±
6.7 Ma (Table 3; Fig. 9).
Sample Sam 17 is a sandstone sample from
the Upper Cretaceous Sego Sandstone Member
of the Mesaverde Group in northwest Colorado
(Table 1; Figs. 2, 3). It produced three zircon
He ages that are 84.0 ± 3.6, 347.6 ± 12.1, and
506.9 ± 20.7 Ma (Table 3; Fig. 9).
Two samples from the Upper Cretaceous
Price River Formation were analyzed, one
sandstone and one conglomerate cobble (Table
1; Figs. 2, 3). The sandstone sample, Sam 13,
produced three zircon He ages that are 97.3 ±
3.8, 141.1 ± 4.8, and 272.4 ± 8.6 Ma. The con-
Geological Society of America Bulletin, Month/Month 2014
Stratigraphic unit
North Horn Formation
North Horn Formation
North Horn Formation
North Horn Formation
North Horn Formation
North Horn Formation
Sego Sandstone Member
Sego Sandstone Member
Sego Sandstone Member
Price River conglomerate
Price River conglomerate
Price River conglomerate
Price River conglomerate
Price River conglomerate
Price River conglomerate
Castlegate Formation
Castlegate Formation
Castlegate Formation
Castlegate Formation
Castlegate Formation
Castlegate Formation
Castlegate Formation
Castlegate Formation
Castlegate Formation
Inkom Formation
Inkom Formation
TABLE 3. ZIRCON (U-Th-[Sm])/He DATA
Mass
Half-width
U
Sample type
(μg)
(μm)
(ppm)
Detrital
2.93
45.50
538.71
Detrital
0.63
28.50
527.40
2.87
45.00
705.73
Detrital
0.97
31.50
62.83
Detrital
1.07
35.25
290.09
Detrital
Detrital
0.70
29.00
430.94
Detrital
2.56
43.50
209.77
Detrital
1.60
38.50
303.33
Detrital
5.03
41.25
24.46
Conglomerate cobble
2.10
41.25
99.32
Conglomerate cobble
2.78
43.25
192.13
Conglomerate cobble
3.39
44.25
293.47
Detrital
15.68
79.50
394.60
Detrital
1.75
34.25
261.95
Detrital
5.81
52.00
17.93
Detrital
0.39
23.75
211.81
Detrital
0.54
26.75
226.65
Detrital
0.46
24.75
172.01
Detrital
1.06
33.50
78.04
Detrital
32.25
0.95
297.05
Detrital
26.25
0.83
235.06
Detrital
42.25
2.51
165.95
Detrital
1.30
36.00
251.26
Detrital
1.75
37.00
113.72
Paleozoic strata
47.75
55.14
5.65
Paleozoic strata
6.46
45.50
117.77
Th
(ppm)
228.04
206.64
280.44
47.95
318.99
176.78
191.51
82.98
7.89
59.38
101.20
117.50
195.61
159.46
51.27
63.03
127.73
149.86
75.69
88.29
109.07
106.45
98.67
76.20
39.34
59.46
4
He
(nmol/g)
451.40
509.49
382.93
67.11
82.38
199.16
469.66
116.95
73.11
34.57
278.69
376.27
318.76
129.00
42.91
85.70
141.98
171.85
120.91
594.94
64.77
405.53
200.35
241.61
6.17
78.16
Ft
0.76
0.63
0.76
0.66
0.68
0.64
0.75
0.72
0.76
0.74
0.75
0.76
0.86
0.70
0.79
0.57
0.61
0.58
0.67
0.67
0.63
0.75
0.70
0.69
0.78
0.78
Corrected age
(Ma)
154.08
184.63
105.71
185.90
56.68
99.86
347.55
84.04
506.85
76.18
253.12
231.14
141.09
97.32
272.39
95.95
125.76
177.35
249.49
357.16
64.47
396.34
152.23
348.72
22.82
139.69
Analytical error ± 2σ
(m.y.)
5.64
7.63
3.77
8.12
2.03
3 .9 7
12.14
3.59
20.74
2.58
8.42
7.73
4.81
3 .7 9
8.56
5.15
5.45
6.71
9.54
15.20
5.08
14.27
6 .1 7
13.65
0.50
3.14
Note: Sample type identifies whether the sample was a sandstone (i.e., detrital), a conglomerate cobble, or Paleozoic strata in the thrust belt. Mass is the mass of the zircon, and half-width is the half width of the
zircon (one dimension used to approximate volume). Ft is the fraction of 4He retained within the crystal based on Farley et al. (1996).
Sample name–
zircon grain number
Sam 7-z1
Sam 7-z2
Sam 7-z3
Sam 5-z1
Sam 5-z2
Sam 5-z3
Sam 17-z1
Sam 17-z2
Sam 17-z3
Sam 3-z1
Sam 3-z2
Sam 3-z3
Sam 13-z1
Sam 13-z2
Sam 13-z3
Sam 15-z1
Sam 15-z2
Sam 15-z3
Sam 16-z1
Sam 16-z2
Sam 16-z3
Sam 19-z1
Sam 19-z2
Sam 19-z3
Sam 11-z1
Sam 11-z2
Exhumation of the North American Cordillera
glomerate cobble sample, Sam 3, recorded three
ages that are 76.2 ± 2.6, 231.1 ± 7.7, and 253.1 ±
8.4 Ma (Table 3; Fig. 9).
Two sandstone samples from the Upper Cretaceous North Horn Formation from Utah were
analyzed, samples Sam 5 and Sam 7 (Table 1;
Figs. 2, 3). Sample Sam 5 records three ages that
are 56.7 ± 2.0, 99.9 ± 4.0, and 185.9 ± 8.1 Ma.
Sample Sam 7 records three ages that are 105.7
± 3.8, 154.1 ± 5.6, and 184.6 ± 7.6 Ma. All
of the zircon He ages are plotted against their
stratigraphic age in Figure 9 (Table 3).
Apatite Fission Track Thermochronology
Four samples from conglomerate cobbles
(051201, 060922, 060923, and Sam 8) and
seven samples from sandstone samples from
foreland basin strata (051204, 051207, 051208,
051212, 051218, Sam 17, and NSD4 B) (Tables
1, 4) were analyzed with AFT thermochronology. These data are presented in stratigraphic
order below.
Sample 051204 is a sandstone sample from
the Lower Cretaceous Kelvin Formation in
north-central Utah (near Rockport Reservoir)
(Table 1; Figs. 2, 3). Because of poor apatite
yield and quality, only 30 apatite grains were
available to be analyzed for AFT in this sample,
instead of the desired 100 grains per detrital
sample. The individual grain cooling age distribution ranges from 34.0 to 247.2 Ma (Table 5).
Two populations are identified with BINOMFIT
(Brandon, 2002), one of 52.1 ± 11.9/9.7 Ma and
one of 122.9 ± 12.2/11.7 Ma (Table 5). However, we reject the 52.1 Ma population (Table 5;
Figs. 10, 11) because it is based on <5 grains,
its distribution does not appear to be Gaussian
in the probability-density plot, and it is younger
than the depositional age. Another interpretation
for the 52.1 Ma age population is that this sample has been partially reset by post-depositional
burial; however, given the magnitude of subsidence and stratigraphic thickness for the area, we
consider partial resetting unlikely. We report
122.9 ± 12.2/11.7 Ma as the youngest population in Table 5.
One hundred grains from sample 051218, from
the Dakota Formation, were analyzed. Three
binomial-fit peak ages are 88.8 ± 7.0/6.5 Ma,
155.6 ± 13.6/12.6 Ma and 310.3 ± 35.5/32.0 Ma
(Table 5; Figs. 10, 11).
Twenty grains from a conglomerate cobble
(sample 051201) from the Echo Canyon Conglomerate were analyzed, producing a central
age of 90.5 ± 14.0 Ma. The χ2 probability for
this population is 99.98%, indicating that this
sample is represented by a single age population, sharing the same cooling history (Table 4;
Figs. 10, 11).
Geological Society of America Bulletin, Month/Month 2014
13
Painter et al.
zircon (U-Th-[Sm])/He cooling age (Ma)
0
100
60
300
400
500
600
Legend
North Horn Fm. (Sam 7 detrital)
North Horn Fm. (Sam 5 detrital)
Price River Fm. (Sam 3 cobble)
Sego SS Mbr. (Sam 17 detrital)
Price River Fm. (Sam 13 detrital)
Castlegate Fm. (Sam 19 detrital)
Castlegate Fm. (Sam 15 detrital)
Castlegate Fm. (Sam 16 detrital)
Inkom Fm. (Sam 11 Proterozoic quartzite)
65
depositional age (Ma)
Figure 9. Depositional age versus zircon (U-Th-[Sm])/He data.
Detailed (U-Th-[Sm])/He data
are reported in Table 3. Note
the discordant ages of the nondetrital samples (i.e., Sam 3 and
Sam 11), which indicate that the
zircon (U-Th-[Sm])/He system
was not fully reset. Also note
that there is a break in the y axis
to accommodate the plotting of
the Proterozoic sample, Sam 11.
200
e
10 Myr lag tim
e
0 Myr lag tim
55
70
75
80
85
PC
One hundred grains from sample 051207,
from the Blair Formation in Wyoming, were
analyzed (Table 4). Three binomial-fit peak
ages were identified, 85.6 ± 9.7/8.7 Ma, 162.1 ±
50.6/38.7 Ma, 271.9 ± 147.0/96.1 Ma. These
three ages are reported in Table 5 (Figs. 10, 11).
One hundred grains from sample 051212,
from the Chimney Rock Tongue Member of
the Rock Springs Formation in Wyoming, were
analyzed. They produced three binomial-fit
peak ages, 90.3 ± 5.5/5.2 Ma, 172.0 ± 18.0/16.3
Ma, and 454.9 ± 121.1/96.3 Ma (Table 5;
Figs. 10, 11).
One hundred grains from sample 051208,
from the Brooks Member of the Rock Springs
Formation in Wyoming, produced three binomial-fit peak ages, 33.9 ± 21.2/13.3 Ma, 112.0 ±
6.2/5.9 Ma, and 327.7 ± 51.0/44.3 Ma. The
youngest peak age of 33.9 Ma was rejected
because it is based on three grain ages, which
statistically are not enough to constitute a robust
population (Table 4; Figs. 10, 11).
Two conglomerate cobble samples from the
Price River Formation were analyzed. Twenty
grains from sample 060922, from the lower Price
River Formation, have a central age of 79.8 ±
6.3 Ma. This population has a χ2 probability
of 79.2%. Twenty grains from sample 060923,
from the upper Price River Formation, have a
central age of 74.5 ± 6.3 Ma. This population has
14
a χ2 probability of 70.8%. The high χ2 probability of both of these samples suggests that they
are composed of single populations, sharing the
same cooling history (Table 4; Figs. 10, 11).
One hundred grains from the lower Sego
Sandstone Member (sample NSD4 B) of the
Mesaverde Group produced three binomialfit peak ages of 66.6 ± 7.3/6.6 Ma, 111.9 ±
11.0/10.1 Ma, and 382.2 ± 46.4/41.5 Ma. One
hundred grains from the upper Sego Sandstone
Member, sample Sam 17, produced three binomial-fit peak ages, 66.6 ± 6.0/5.5 Ma, 110.7 ±
22.5/18.7 Ma, and 204.3 ± 47.3/38.6 Ma; however, the 204.3 Ma peak consisted of <5 grains
and was rejected (Table 5; Figs. 10, 11).
Twenty grains from a conglomerate cobble
sample, Sam 8, from the North Horn Formation
produced a central age of 66.1 ± 6.2 Ma. These
ages have a χ2 probability of 30.6%, which
indicates it is a single population (Table 4;
Figs. 10, 11).
Detrital Apatite U-Pb Thermochronology
In order to interpret the youngest cooling age
population in detrital AFT analysis as a source
exhumation signal, it is important to ensure
that these apatites are not young volcanogenic
apatites derived from the Cordilleran magmatic
arc. To address this issue, apatite grains from
the youngest age populations, P1, were targeted
from each of the seven detrital AFT samples
(Table 5) for apatite U-Pb thermochronology.
At least ten grains were selected from the P1
population from each sample. All of the data
and concordia diagrams from these U-Pb apatite
ages can be found in the Data Repository (Table
DR2, Figure DR1). We compare all of these
apatite U-Pb ages to the sample’s depositional
age, the AFT P1 age, and the individual AFT
grain ages (Table 6).
Nine apatite grains from 051204, a sample
from the Lower Cretaceous Kelvin Formation in
Utah, were dated with U-Pb thermochronology.
The small grain size of these apatites required
a 25 µm laser diameter, instead of the preferred
40 µm diameter laser used on all of the other
samples. This increased the error on each analysis and makes some grains plot off of concordia.
Grain ages range from 134.3 ± 21.3 to 892.1 ±
23.6 Ma; six of the nine apatites are >160 Ma,
whereas the other three are <160 Ma (Table 6).
Nine apatite grains from sample 051218, from
the Dakota Formation in south-central Utah, produced reliable U-Pb ages ranging from 320.6 ±
6.7 to 1602.0 ± 17.0 Ma. All nine apatites are
older than the youngest AFT P1 of 160 Ma, and
most are Proterozoic in age (Table 6).
Eight apatite grains from sample 051207,
from the Cedar Mountain Formation in Utah,
Geological Society of America Bulletin, Month/Month 2014
TABLE 4. SAMPLES WITH APATITE FISSION TRACK DATA
Number of
Induced ρi
Dosimeter ρd
P(χ2)
Central age ± 1σ
Spontaneous ρs
Sample
Latitude
Longitude
Stratigraphic unit
Sample type
grains
(× 106 cm–2) [Ns ]
(× 106 cm–2) [Ni ]
(× 106 cm–2) [Nd ]
(%)
(Ma)
Conglomerate
North Horn
Sam 8
N40.20167
W108.86312
20
1.58 [203]
4.66 [599]
1.31
30.6
66.1 ± 6.2
cobble
Formation
Sego Sandstone
Sam 17
N40.20236
W108.86123
Detrital
100
0.919 [3186]
2.70 [9374]
1.36 [9253]
0.0
80.2 ± 6.8
Member
Sego Sandstone
NSD4 B
N40.17529
W108.82601
Detrital
100
0.923 [2064]
2.43 [5442]
1.68 [9253]
0.0
119.3 ± 12.1
Member
Price River
Conglomerate
060923
N39.96532
W111.47127
20
1.52 [193]
5.17 [658]
1.73
70.8
74.5 ± 6.4
cobble
Formation
Price River
Conglomerate
060922
N39.96674
W111.47218
20
2.06 [240]
6.46 [752]
1.71
79.2
79.8 ± 6.3
Formation
cobble
Brooks
051208
N41.35810
W108.93082
Detrital
100
0.686 [1521]
1.55 [3444]
1.50 [6202]
0.0
128.7 ± 8.8
Member
Chimney Rock
051212
N41.39890
W108.93394
Detrital
100
0.582 [1685]
1.50 [4354]
1.63 [6202]
0.0
123.4 ± 8.5
Tongue Member
051207
N41.48659
W108.96523
Blair Formation
Detrital
100
0.643 [1122]
1.47 [2568]
1.46 [6202]
0.0
130.3 ± 9.8
Echo Canyon
Conglomerate
051201
N40.96344
W111.41634
20
0.640 [62]
1.641 [159]
1.27
99.98
90.5 ± 14.0
Conglomerate
cobble
Dakota
051218
N37.11554
W111.85088
Detrital
100
1.01 [2076]
2.38 [4925]
1.76 [6202]
0.0
149.2 ± 10.1
Formation
Kelvin
051204
N40.76712
W111.40012
Detrital
30
0.759 [327]
1.87 [806]
1.37 [6202]
0.4
105.7 ± 10.2
Formation
Note: All samples with apatite fission track thermochronology. In all conglomerate cobbles, 20 grains were analyzed. In detrital samples, 100 grains were analyzed, except for in sample 051204 where only 30
apatite grains were analyzed because of the low apatite yield. ρs is the spontaneous track density, and Ns is the number of spontaneous tracks counted. ρi is the induced track density on the external detector
(muscovite), and Ni is the number of induced tracks counted. Nd and ρd are the number of tracks and density of tracks calculated from the CN-5 dosimeter glass. P(χ2) is the χ2 probability. Fission-track ages were
calculated using a weighted mean zeta calibration factor (Hurford and Green, 1983) based on IUGS age standards (Durango and Fish Canyon Tuff apatites). The ζ for C.S. Painter is 367.7 ± 14.1 (± 2σ); ζ is
a factor that accounts for analyst bias in fission track counting for apatite fission track thermochronology. Bold ages in the central age column indicate that it is from a conglomerate cobble, and is the only age
population for the sample.
Exhumation of the North American Cordillera
produced ages ranging from 89.0 ± 10.8 to
1869.0 ± 159.5 Ma. Although one grain is
Proterozoic in age, the other seven are all
approximately Jurassic and younger (Table 6).
Two samples from the Rock Springs Formation, near Rock Springs, Wyoming, were analyzed; one from the lower Chimney Rock Tongue
Member (sample 051212) and the other from the
overlying Brooks Member (sample 051208). Ten
grains from the Chimney Rock Tongue Member
produced ages that range from 100.2 ± 10.7 to
1571.2 ± 22.6 Ma. Only one grain (1571.2 ±
22.6 Ma) is older than Late Jurassic age. Eight
grains from the Brooks Member produced a
range of ages of 83.7 ± 6.0 to 143.3 ± 31.7 Ma,
indicating that all of the grains are Early Cretaceous and younger in age (Table 6).
Two samples, NSD4 B and Sam 17, from the
Upper Cretaceous Sego Sandstone Member in
northwest Colorado, were analyzed. Nine apatite grains from NSD4 B produced ages ranging from 89.2 ± 59.0 to 1687.4 ± 41.9 Ma.
Although two of the nine grains are >160 Ma,
the rest are all <120 Ma. Ten apatite grains from
Sam 17 have U-Pb ages of 85.0 ± 7.5 to 867.2 ±
17.5 Ma. Two of the ten grains are older than
the young Cordilleran arc magmatic signal (i.e.,
>160 Ma); however, the other eight grain ages
are all <160 Ma (Table 6).
DISCUSSION
Zircon U-Pb Geochronology
and Biostratigraphy
Out of 22 samples analyzed using DZ U-Pb,
10 yielded zircon U-Pb ages that are near syndepositional age, thus producing an MDA that
represents the stratigraphic age of the sampled
strata. The extent of biostratigraphic work conducted in the Cretaceous western U.S.A. is vast,
and DZ analysis is an independent test of precision and accuracy of the biostratigraphic ages
(Table 2; Fig. 12), thus testing the validity of
stratigraphic correlations. The MDAs presented
in this study are mostly concordant with the
stratigraphic ages derived from biostratigraphy
and 40Ar/39Ar age on bentonite beds (Table 2;
Fig. 12). Where there is slight disagreement
between the results of the different methods
(e.g., an MDA that is younger than the accepted
biostratigraphic age), the ages are within error
of one another (Table 2; Fig. 12). For example,
the youngest zircon in sample 051107, a sample
from the Lower Cretaceous Cedar Mountain
Formation in eastern Utah, is 106.3 ± 2.8 Ma,
whereas the accepted biostratigraphic age is
117–109 Ma; however, 106.3 ± 2.8 Ma is within
error of 109 Ma (Table 2; Fig. 12). These results
also indicate that DZ U-Pb analysis can be
Geological Society of America Bulletin, Month/Month 2014
15
Painter et al.
TABLE 5. DETAILED APATITE FISSION TRACK DATA—ALL POPULATIONS
Stratigraphic age
FT age range
P1
P2
P3
P4
Sample
Stratigraphic unit
(Ma)
N
(Ma)
(Ma)
(Ma)
(Ma)
(Ma)
North Horn
66.1 ± 6.2
Sam 8
65.5 ± 4.5
20 39.6–143.0
N/A
N/A
N/A
Formation
[100%]
Sego Sandstone
66.6 ± 6.0/5.5
110.7 ± 22.5/18.7
Sam 17
73 ± 1.5
100 34.2–268.4
xx
xx
Member
[72.0%]
[24.9%]
Sego Sandstone
66.6 ± 7.3/6.6
111.9 ± 11.0/10.1
382.2 ± 46.4/41.5
NSD4 B
76.6 ± 1.5
100 40.9–901.7
xx
Member
[33.1%]
[52.2%]
[14.7%]
Price River
74.5 ± 6.3
060923
77 ± 2
20 43.9–147.3
N/A
N/A
N/A
Formation
[100%]
Price River
79.8 ± 6.3
060922
78 ± 2
20 51.6–161.6
N/A
N/A
N/A
Formation
[100%]
112.0 ± 6.2/5.9
327.7 ± 51.0/44.3
051208
Brooks Member
81 ± 3
100 25.0–624.6
xx
xx
[82.8%]
[13.9%]
Chimney Rock Tongue
90.3 ± 5.5/5.2
172.0 18.0/16.3
454.9 ± 121.1/96.3
051212
81.5 ± 1
100 39.6–782.6
xx
Member
[64.2%]
[31.1%]
[4.7%]
Blair
85.6 ± 9.7/8.7
162.1 ± 50.6/38.7
271.9 ± 147.0/96.1
xx
051207
82.5 ± 1
100 39.6–1459.4
Formation
[52.8%]
[37.4%]
[8.8%]
Echo Canyon
90.5 ± 14.03
051201
86 ± 1
20 58.1–153.9
N/A
N/A
N/A
Conglomerate
[100%]
Dakota
88.8 ± 7.0/6.5
155.6 ± 13.6/12.6
310.3 ± 35.5/32.0
051218
94.5 ± 2.9
100 43.9–579.0
xx
Formation
[35.2%]
[46.4%]
[18.4%]
Kelvin
122.9 ± 12.2/11.7
051204
117.2 ± 3.2
30 34.0–247.2
xx
xx
xx
Formation
[78.1%]
Note: Binomial-fit peak ages (P1 –P4 ) are as determined with BINOMFIT (Brandon, 2002) and are indicated by their mean age ± 1σ (note that errors are asymmetrical).
Percentages listed in peak ages represent the percentage of the entire sample contained in that age population. For non-detrital samples, the weighted mean is listed
here for reference, and “N/A” is listed in the other populations, given that there is only one population. Where a population is absent in the detrital samples, “xx” is listed.
N represents the number of apatite grains analyzed in the sample. FT age range is the entire age range for single crystal apatite fission track ages in the sample.
crucial in areas where a biostratigraphic framework is sparse. Also, many stratigraphic units
are time transgressive, and establishing a MDA
with DZ U-Pb can better indicate the stratigraphic position of a sample within a section.
Sediment Provenance Constrained by
Zircon U-Pb Geochronology
Paleozoic stratigraphy exhumed in the Sevier
fold-thrust belt (Dickinson, 2004; Dickinson and
Gehrels, 2008; Gehrels et al., 2011; Laskowski
et al., 2013). We interpret all of our DZ curves to
represent recycled zircons from the Sevier foldthrust belt with variable contributions of young
volcanic zircons from the Cordilleran arc.
Source-to-Sink Exhumation History
Zircon U-Pb geochronology can not only indicate the depositional age of the analyzed deposits, but also its provenance. Our study area covers ~600 km along strike of the Sevier fold-thrust
belt and ~400 km along depositional dip into the
foreland basin. Such a widespread geographical
area includes multiple catchments and drainage
areas. Despite this, the DZ signal is remarkably
uniform (Fig. 8). This indicates a similar source
and a well-connected drainage system without large geographic barriers to act as filters to
certain signals. For example, distal deposits in
South Dakota have similar-amplitude peaks of
Cordilleran magmatic zircons (Fig. 8), showing
that the forebulge did not block a westerly sediment supply derived from the Cordilleran arc.
This suggests that the forebulge was an area of
condensed deposition rather than erosion and
that the foreland basin was overfilled (Flemings and Jordan, 1989). All DZ curves contain
populations of Trans-Hudson, Yavapai, Mazatzal, 1.48–1.34 Ga magmatic rocks, Grenville,
and pericratonic orogenic-age zircons. Smalleramplitude populations include Wopmay- and
Archean-age zircons. This age distribution is
consistent with zircon ages from miogeoclinal
16
Zircon He thermochronology was initially
performed to identify the most effective thermochronometer to measure the timing of exhumation of Paleozoic strata during Mesozoic
Cordilleran tectonics. Both sandstone and conglomerate cobbles produced a mix of ages ranging from 506.9 Ma to 22.8 Ma (Table 3; Fig. 9).
Ages from individual samples vary widely,
with up to ~400 m.y. internal variation, indicating only partial resetting of the fold-thrust
belt sediment sources, and suggest that this
material, once incorporated into the orogenic
system and later deposited within synorogenic
deposits, was never fully reset by subsequent
basin burial; this implies exhumation depths of
<8–9 km, assuming a 20 °C/km geothermal gradient and a partial retention zone for zircon He
of 170–190 °C (Reiners et al., 2004). A sample
from the Proterozoic Inkom Formation in the
Canyon Range duplex structure also produced
mixed ages between 139.7 Ma and 22.8 Ma
(Table 3; Fig. 9). Another possibility for nonuniform zircon He ages is that Paleozoic and
Proterozoic strata were exhumed from temperatures greater than ~190 °C but that excess He
was being retained in these zircons because of
alpha-decay damage (Guenthner et al., 2013), as
diffusion of He is impeded in crystals with large
amounts of radiation damage (i.e., damage to
the crystal caused by alpha decay and spontaneous fission) (Shuster et al., 2006; Flowers et al.,
2009). Guenthner et al. (2013) documented that
He diffusion is impeded in zircons with moderate to high levels of radiation damage, but that in
zircons that have very high amounts of radiation
damage, He diffusion is accelerated.
In contrast, we interpret all of our AFT samples to contain fully reset populations that record
source exhumation (or volcanogenesis in the
case of some of the detrital samples) related to
Cordilleran tectonics. The age populations in the
conglomerate cobbles all have a χ2 probability
greater than 5%, suggesting a single population
and full resetting of the conglomerate source
during Cretaceous time (Table 4). The individual
populations in the detrital samples also have a
χ2 probability greater than 5%. Whereas burial
of conglomerate and sandstone may cause partial annealing, we do not think that the analyzed
samples were reheated enough to initiate significant annealing. This interpretation is based on the
observation that in general, our samples display
an upsection younging of cooling ages (populations). If post-depositional partial annealing was
significant, we should expect deeper samples
to record younger ages and vice versa, resulting in a downsection younging of cooling ages.
BINOMFIT (Brandon, 2002) identifies a young
AFT population of ca. 52.1 Ma in the ca. 118 Ma
Kelvin Formation (sample 051204) (Table 2),
Geological Society of America Bulletin, Month/Month 2014
Exhumation of the North American Cordillera
84
0
69
–1
57
47
–2
38
–3
32
–4
26
0.24
2.44
0.61
0.35
SE[z] (~RSE[age])
4
Density (% per delta z=0.1)
102
FT grain age (Ma)
123
2
1
176
d)
060923 Price River Fm.
3
109
1
93
0
79
–1
67
57
–2
–3
–4
2.01
12
0.50
0.29
SE[z] (~RSE[age])
051212 Chimney Rock
12
12
10
10
8
8
6
6
2
0
0
960
30
20
60
120
240
FT grain age (Ma)
480
051204 Kelvin Fm.
1
40
80
160
FT grain age (Ma)
320
12
12
Density (% per delta z=0.1)
16
4
4
0
20
40
80
160
FT grain age (Ma)
0
60
120
240
480
FT grain age (Ma)
960
189
e)
051208 Brooks Fm.
160
f)
12
12
10
10
136
2
116
1
98
0
83
–1
71
60
–2
51
43
2.07
37
0.21
0.52
0.30
SE[z] (~RSE[age])
8
8
6
6
4
4
2
2
0
20
40
3
h) 10
051207 Blair Fm.
8
8
6
6
4
4
80
160
320
FT grain age (Ma)
051201 Echo Canyon Cgl.
640
0
250
i)
209
174
145
1
120
100
0
83
–1
2
2
–2
0
0
–3
30
16
8
2
69
57
48
14
j) 20
8
3
2
0
Standardized variance
2
4
3
2
Density (% per delta z=0.1)
4
4
0
30
10
4
5
1
g) 12
6
5
0
–4
6
7
6
0
20
35
0.20
8
7
6
2
–3
Density (% per delta z=0.1)
Density (% per delta z=0.1)
8
8
2
42
10
c) 9
4
Tongue Mbr.
10
NSD4 B Sego Sandstone Mbr.
8
4
3
49
9
14
060922 Price River Fm.
128
2
b)
14
4
150
Standardized variance
Standardized variance
Sam 17 Sego Sandstone Mbr.
150
FT grain age (Ma)
Standardized variance
3
182
FT grain age (Ma)
a)
Density (% per delta z=0.1)
North Horn Fm.
Standardized variance
Sam 8
FT grain age (Ma)
4
60
120 240 480
FT grain age (Ma)
960
0.77
0.44
SE[z] (~RSE[age])
40
0.31
k) 14
051218 Dakota SS.
12
12
10
10
8
8
6
6
4
4
2
2
0
30
3.10
0
60
120
240
FT grain age (Ma)
480
Figure 10. Probability density plots for all detrital apatite fission track (AFT) samples, and radial plots for all conglomerate cobble AFT
samples (Table 5). Dashed lines outline grain populations as chosen by BINOMFIT (Brandon, 2002). Each plot is labeled with its corresponding sample name. Note that axis scales are variable. X-axis indicates the standard error (SE) of log of age (z). This is approximately
equal to the relative standard error (RSE).
Geological Society of America Bulletin, Month/Month 2014
17
Painter et al.
60
0
100
200
AFT cooling age (Ma)
300
400
500
600
70
90
100
g time
10 Myr la
g time
0 Myr la
Depostional age (Ma)
80
Figure 11. Depositional age versus apatite fission track cooling
age of all samples analyzed with
apatite fission track thermochronology (AFTT) (both detrital and non-detrital samples).
See Tables 4 and 5 for details.
0 m.y., 5 m.y., and 10 m.y. lag
times are shown with gray lines.
110
Legend
North Horn Fm. (Sam 8)
upper Sego SS Mbr. (Sam 17)
lower Sego SS Mbr. (NSD4 B)
Price River Fm. (060923)
Price River Fm. (060922)
Brooks Mbr. (051208)
Chimney Rock Tng. Mbr. (051212)
Blair Fm. (051207)
Echo Canyon Cgl. (051201)
Dakota Fm. (051218)
Kelvin Fm. (051204)
120
130
which could represent post-depositional partial
annealing. However, this age population is based
on <5 apatite grains, which is too few to determine an age population with confidence. Also,
sample 051204 was collected in northeastern
Utah, where the Kelvin Formation is overlain by
only ~2 km of Cretaceous to Cenozoic stratigraphy (Royse, 1993; DeCelles and Currie, 1996),
which is not enough to reach temperatures that
could partially anneal fission tracks in apatite
(Gleadow and Duddy, 1981). This independent
evidence suggests that the sampled conglomerate cobbles and detrital sandstone populations
represent sediment source cooling ages and
implies that the Paleozoic miogeoclinal sources
were exhumed during the Cretaceous from temperatures greater than 110 ± 10 °C (Gleadow
and Duddy, 1981), corresponding to ~4–5 km
depths assuming a 20 °C/km geothermal gradient. Detrital samples produce populations that
range from ca. 455 to 67 Ma (Table 5). The
youngest population, P1, has an age range from
ca. 133 Ma (sample 051204 from the Lower
Cretaceous Kelvin Formation) to ca. 67 Ma
(sample Sam 17 from the Upper Cretaceous
Sego Sandstone Member) (Tables 5). This suggests that AFT, on both conglomerate cobbles
and detrital foreland basin samples, is an effective thermochronometer to measure cooling and
exhumation related to the development of the
Cordilleran thrust belt.
18
Lag-time measurements (Fig. 5) are useful in identifying provenance (e.g., Hurford
and Carter, 1991; Ireland, 1992; Carter, 1999;
Garver et al., 1999). Also, lag times can provide
information on the long-term orogenic-scale
exhumation (e.g., Zeitler et al., 1986; Bernet
et al., 2001). A decrease in lag time can be correlated to an increase in source region exhumation
rates, whereas an increase in lag time indicates
a decrease in exhumation rates (Bernet et al.,
2001). Constant lag times are associated with
steady-state exhumation (Garver et al., 1999)
(Fig. 6). Lag-time trends can also be associated with exhumation in response to different
orogenic wedge dynamics (Davis et al., 1983;
Dahlen, 1984; Suppe and Medwedeff, 1990;
Carrapa, 2009) (Fig. 13). Orogenic wedge
theory treats the orogen as a wedge and associates its behavior to its taper angle (α + β), where
β is the angle of the basal detachment and α is
the angle of the topographic slope (Davis et al.,
1983). If α decreases because of erosion or
other process, then the wedge will build internally to restore critical taper. If the wedge builds
too much, then it will collapse and propagate
into the foreland (Davis, et al., 1983; Dahlen,
1984) (Fig. 13). Increased exhumation rates
have been predicted for a wedge in a subcritical state (where the wedge shortens internally to
achieve critical taper), whereas decreased exhumation trends have been predicted for a wedge
that is in a supercritical state and propagating
toward the foreland (Carrapa, 2009) (Fig. 13).
Different orogenic states and trends of exhumation also correlate with the behavior of the
rate of propagation of deformation through the
foreland. When a wedge is deforming internally,
the rate of foreland-ward propagation of deformation is expected to decrease, and vice versa
(Davis et al., 1983; Carrapa, 2009).
In detrital thermochronologic studies, the
youngest age is typically considered a source
exhumation signal and used to measure lag time
(Garver et al., 1999; Carrapa et al., 2004, 2006;
Spiegel et al., 2004; van der Beek et al., 2006)
(Fig. 14). However, this assumes that the youngest cooling age, P1, only includes minerals that
represent source exhumation rather than volcanic contamination. Our study shows that the
youngest detrital AFT component in the Cordilleran foreland basin often includes volcanogenic
grains (i.e., minerals that were erupted near the
time of exhumation). Volcanic minerals should
have a cooling age close to or the same as crystallization age. Our double dating results show
that all but two of the P1 populations of all of our
detrital samples are significantly contaminated
with apatites that have U-Pb ages within error
of the youngest AFT age component (Table 6).
An alternative explanation is that P1 for all the
samples represents rapidly exhumed plutonic
apatites, but the methodological error prevents
Geological Society of America Bulletin, Month/Month 2014
Exhumation of the North American Cordillera
TABLE 6. DOUBLE DATES—APATITE FISSION TRACK (AFT) AND U-Pb AGE OF SINGLE APATITE GRAINS
Depositional age
AFT P1 age
AFT grain age
6/8 U-Pb age
Sample name–apatite grain number
Stratigraphic unit
(Ma)
(Ma)
(Ma)
(Ma)
Sam 17-10
Sego Sandstone Member
73 ± 1.5
66.6 ± 6.0/5.5 [72.0%]
70.5 ± 50.7
93.5 ± 5.1
Sam 17-11
Sego Sandstone Member
73 ± 1.5
66.6 ± 6.0/5.5 [72.0%]
73.6 ± 48.6
142.1 ± 15.8
Sam 17-12
Sego Sandstone Member
73 ± 1.5
66.6 ± 6.0/5.5 [72.0%]
76.1 ± 24.4
510.7 ± 59.7
Sam 17-15
Sego Sandstone Member
73 ± 1.5
66.6 ± 6.0/5.5 [72.0%]
59.8 ± 26.3
100.6 ± 3.8
Sam 17-16
Sego Sandstone Member
73 ± 1.5
66.6 ± 6.0/5.5 [72.0%]
48.3 ± 28.9
85.0 ± 7.5
Sam 17-17
Sego Sandstone Member
73 ± 1.5
66.6 ± 6.0/5.5 [72.0%]
51.5 ± 28.9
95.2 ± 10.4
Sam 17-19
Sego Sandstone Member
73 ± 1.5
66.6 ± 6.0/5.5 [72.0%]
68.9 ± 49.6
867.2 ± 17.5
Sam 17-22
Sego Sandstone Member
73 ± 1.5
66.6 ± 6.0/5.5 [72.0%]
39.2 ± 22.2
150.9 ± 9.6
Sam 17-24
Sego Sandstone Member
73 ± 1.5
73.2 ± 45.0
99.8 ± 9.0
66.6 ± 6.0/5.5 [72.0%]
Sam 17-25
Sego Sandstone Member
73 ± 1.5
66.6 ± 6.0/5.5 [72.0%]
67.0 ± 51.4
131.0 ± 2.1
NSD4 B-5
Sego Sandstone Member
76.6 ± 1.5
58.2 ± 30.8
89.2 ± 59.0
66.6 ± 7.3/6.6 [33.1%]
NSD4 B-6
Sego Sandstone Member
76.6 ± 1.5
66.6 ± 7.3/6.6 [33.1%]
52.1 ± 19.3
101.7 ± 5.1
NSD4 B-10
Sego Sandstone Member
49.3 ± 22.2
1676.5 ± 80.0
76.6 ± 1.5
66.6 ± 7.3/6.6 [33.1%]
NSD4 B-13
Sego Sandstone Member
76.6 ± 1.5
66.6 ± 7.3/6.6 [33.1%]
67.4 ± 46.3
103.9 ± 3.7
NSD4 B-15
Sego Sandstone Member
53.0 ± 23.8
90.9 ± 8.7
76.6 ± 1.5
66.6 ± 7.3/6.6 [33.1%]
NSD4 B-21
Sego Sandstone Member
76.6 ± 1.5
66.6 ± 7.3/6.6 [33.1%]
48.8 ± 23.8
1687.38 ± 41.9
NSD4 B-22
Sego Sandstone Member
78.0 ± 54.7
116.8 ± 6.0
76.6 ± 1.5
66.6 ± 7.3/6.6 [33.1%]
NSD4 B-23
Sego Sandstone Member
76.6 ± 1.5
66.6 ± 7.3/6.6 [33.1%]
54.5 ± 13.2
98.0 ± 98.4
NSD4 B-25
Sego Sandstone Member
63.4 ± 36.8
119.4 ± 5.5
76.6 ± 1.5
66.6 ± 7.3/6.6 [33.1%]
051208-2
Brooks Member
81 ± 3
112.0 ± 6.2/5.9 [82.8%]
95.1 ± 49.0
92.6 ± 6.2
051208-8
76.8 ± 47.6
83.7 ± 6.0
Brooks Member
81 ± 3
112.0 ± 6.2/5.9 [82.8%]
051208-9
Brooks Member
81 ± 3
112.0 ± 6.2/5.9 [82.8%]
125.9 ± 34.0
132.5 ± 35.2
051208-10
Brooks Member
81 ± 3
112.0 ± 6.2/5.9 [82.8%]
54.0 ± 15.8
89.6 ± 8.4
051208-12
Brooks Member
81 ± 3
81.0 ± 29.1
143.9 ± 31.7
112.0 ± 6.2/5.9 [82.8%]
051208-21
Brooks Member
81 ± 3
112.0 ± 6.2/5.9 [82.8%]
114.3 ± 58.0
125.1 ± 19.0
051208-24
71.3 ± 29.8
108.7 ± 31.9
Brooks Member
81 ± 3
112.0 ± 6.2/5.9 [82.8%]
051208-25
Brooks Member
81 ± 3
112.0 ± 6.2/5.9 [82.8%]
85.3 ± 33.0
98.4 ± 51.3
051212-6
Chimney Rock Tongue Member
81.5 ± 1
90.3 ± 5.5/5.2 [64.2%]
54.9 ± 9.9
161.4 ± 14.1
051212-9
Chimney Rock Tongue Member
81.5 ± 1
90.3 ± 5.5/5.2 [64.2%]
63.1 ± 31.6
138.4 ± 9.1
79.4 ± 55.0
100.2 ± 10.7
051212-11
Chimney Rock Tongue Member
81.5 ± 1
90.3 ± 5.5/5.2 [64.2%]
051212-14
Chimney Rock Tongue Member
81.5 ± 1
90.3 ± 5.5/5.2 [64.2%]
39.8 ± 4.2
156.6 ± 41.4
124.0 ± 78.2
106.2 ± 5.0
051212-20
Chimney Rock Tongue Member
81.5 ± 1
90.3 ± 5.5/5.2 [64.2%]
051212-24
Chimney Rock Tongue Member
81.5 ± 1
90.3 ± 5.5/5.2 [64.2%]
86.7 ± 42.7
140.4 ± 17.7
051212-25
Chimney Rock Tongue Member
84.6 ± 24.1
135.6 ± 22.1
81.5 ± 1
90.3 ± 5.5/5.2 [64.2%]
051212-28
Chimney Rock Tongue Member
81.5 ± 1
90.3 ± 5.5/5.2 [64.2%]
68.5 ± 25.1
127.2 ± 8.7
051212-29
Chimney Rock Tongue Member
83.2 ± 66.9
1571.2 ± 22.6
81.5 ± 1
90.3 ± 5.5/5.2 [64.2%]
051212-30
Chimney Rock Tongue Member
81.5 ± 1
90.3 ± 5.5/5.2 [64.2%]
75.2 ± 37.3
148.7 ± 13.3
051207-2
Cedar Mountain Formation
111.4 ± 10.2
213.3 ± 26.0
82.5 ± 1
85.6 ± 9.7/8.7 [52.8%]
051207-3
Cedar Mountain Formation
82.5 ± 1
85.6 ± 9.7/8.7 [52.8%]
103.3 ± 17.2
102.8 ± 7.2
051207-5
Cedar Mountain Formation
105.2 ± 36.8
89.0 ± 10.8
82.5 ± 1
85.6 ± 9.7/8.7 [52.8%]
051207-10
Cedar Mountain Formation
82.5 ± 1
85.6 ± 9.7/8.7 [52.8%]
121.1 ± 78.3
171.1 ± 6.6
051207-14
Cedar Mountain Formation
44.2 ± 8.0
128.8 ± 12.6
82.5 ± 1
85.6 ± 9.7/8.7 [52.8%]
051207-16
Cedar Mountain Formation
82.5 ± 1
85.6 ± 9.7/8.7 [52.8%]
118.1 ± 40.8
100.8 ± 3.5
051207-17
Cedar Mountain Formation
75.5 ± 47.2
96.0 ± 5.6
82.5 ± 1
85.6 ± 9.7/8.7 [52.8%]
051207-18
Cedar Mountain Formation
82.5 ± 1
85.6 ± 9.7/8.7 [52.8%]
107.7 ± 45.9
1869.0 ± 159.5
051218-1
Dakota Formation
125.0 ± 76.2
1558.4 ± 26.4
94.5 ± 2.9
88.8 ± 7.0/6.5 [35.2%]
051218-2
Dakota Formation
94.5 ± 2.9
88.8 ± 7.0/6.5 [35.2%]
67.2 ± 37.8
1591.9 ± 40.9
051218-13
Dakota Formation
110.7 ± 66.4
1327.9 ± 15.3
94.5 ± 2.9
88.8 ± 7.0/6.5 [35.2%]
051218-17
Dakota Formation
94.5 ± 2.9
88.8 ± 7.0/6.5 [35.2%]
120.9 ± 74.6
1477.4 ± 30.0
051218-19
84.9 ± 30.8
1477.4 ± 30.0
Dakota Formation
94.5 ± 2.9
88.8 ± 7.0/6.5 [35.2%]
051218-20
Dakota Formation
94.5 ± 2.9
88.8 ± 7.0/6.5 [35.2%]
107.9 ± 79.6
320.6 ± 6.7
71.2 ± 38.5
1602.0 ± 17.0
051218-21
Dakota Formation
94.5 ± 2.9
88.8 ± 7.0/6.5 [35.2%]
051218-23
Dakota Formation
94.5 ± 2.9
88.8 ± 7.0/6.5 [35.2%]
107.1 ± 61.4
1578.1 ± 16.5
051218-24
Dakota Formation
94.5 ± 2.9
88.8 ± 7.0/6.5 [35.2%]
86.8 ± 51.5
1594.3 ± 12.5
051204-1
Kelvin Formation
117.2 ± 3.2
122.9 ± 12.2/11.7 [78.1%]
106.5 ± 40.1
227.4 ± 27.7
051204-2
Kelvin Formation
117.2 ± 3.2
122.9 ± 12.2/11.7 [78.1%]
35.3 ± 0.7
303.0 ± 71.0
051204-3
Kelvin Formation
117.2 ± 3.2
122.9 ± 12.2/11.7 [78.1%]
32.7 ± 12.3
141.8 ± 22.5
051204-4
Kelvin Formation
117.2 ± 3.2
122.9 ± 12.2/11.7 [78.1%]
87.6 ± 8.3
283.9 ± 37.7
051204-9
Kelvin Formation
117.2 ± 3.2
122.9 ± 12.2/11.7 [78.1%]
136.9 ± 61.7
333.5 ± 43.8
051204-10
Kelvin Formation
117.2 ± 3.2
122.9 ± 12.2/11.7 [78.1%]
110.7 ± 38.2
134.3 ± 21.3
051204-11
Kelvin Formation
117.2 ± 3.2
122.9 ± 12.2/11.7 [78.1%]
139.5 ± 57.5
892.1 ± 23.6
051204-13
Kelvin Formation
117.2 ± 3.2
122.9 ± 12.2/11.7 [78.1%]
48.2 ± 22.6
140.3 ± 18.2
051204-16
Kelvin Formation
117.2 ± 3.2
122.9 ± 12.2/11.7 [78.1%]
77.9 ± 13.4
184.2 ± 23.7
Note: Individual AFT population and grain ages compared to the U-Pb age. Detailed apatite U-Pb data and concordia plots can be found in the Data Repository.
Italicized percentages represent how many of the total analyzed apatites are within that AFT age population. 6/8 U-Pb age indicates the 206Pb/238U age. Errors are 2σ.
the differentiation between these and volcanogenic apatites.
In an attempt to calculate lag times for the
distal foreland basin sandstone samples, and
to avoid misinterpretation of possible volcanogenic apatites, we consider only P1 from two
samples: 051204 from the Lower Cretaceous
Kelvin Formation, and 051218 from the Upper
Cretaceous Dakota Formation (Table 5; Fig.
12). This is because the apatite U-Pb ages for
P1 in these two samples are significantly older
than the associated AFT ages. Plotting these P1
AFT ages that are not contaminated with volcanogenic apatites together with the conglomerate cobble AFT ages, versus depositional ages,
shows a lag time between ~0 and 5 m.y. from
118 to 66 Ma (Fig. 15). The lag-time trend (Fig.
15) appears to be relatively constant, or slightly
decreasing, which suggests either steady-state
or slightly increasing exhumation rate through
time in the source region (Garver et al., 1999;
Bernet et al., 2001). Our lag times are consistent
with rapid steady-state exhumation, suggesting
that the Cordilleran orogenic wedge was at or
Geological Society of America Bulletin, Month/Month 2014
19
Painter et al.
70
70
80
90
Depositional age from biostratigraphy and Ar/Ar (Ma)
100
110
120
130
140
80
MDA from youngest grain of DZ U-Pb (Ma)
90
100
110
U-
Pb
=
bio
s
tra
t
150
160
Legend
Canyon Creek Mbr. (051210)
Sego Sandstone Mbr. (Sam 17)
Lazeart SS Mbr. (051205)
Blair Fm. (051207)
Frontier Fm. (051105)
Dakota Fm. (051218)
Cedar Mtn. Fm. (051107)
Kelvin Fm. (051204)
Morrison Fm. (051108)
Morrison Fm. (051214)
Morrison Fm. (051103)
120
130
140
150
160
170
Figure 12. Depositional age from biostratigraphy and Ar/Ar versus maximum depositional
age (MDA) from detrital zircon (DZ) U-Pb. Gray dashed line is where U-Pb age equals that
from biostratigraphy. Detailed data are included in Table 2.
near critical throughout the Cretaceous (Fig.
15). However, as these techniques become more
refined (reducing error) and are further applied
to North America Cordilleran foreland deposits,
spatial and temporal resolution may improve,
and a more complex and detailed exhumation
history may emerge.
Lag-time measurements are also useful to
approximate exhumation rates, and we use mea-
sured lag times to estimate exhumation rates in
the Sevier fold-thrust belt using the following
equation (Garver et al. 1999):
⎡T − T ⎤
ε = ⎢ c s ⎥ tL ,
⎣ G ⎦
(2)
where ε is the effective exhumation rate in
km/m.y., Tc and Ts are the closure temperatures
of apatite and the surface temperature respectively, G is the geothermal gradient in °C/km,
and tL is the lag time in years. We have already
calculated tL as ~0–5 m.y. Given that a true lag
time of 0 m.y. is impossible, an assumption
of ~1–5 m.y. is more reasonable. Assuming a
closure temperature of ~110 °C (Gleadow and
Duddy, 1981), a surface temperature of 20 °C,
and a geothermal gradient of 20 °C/km results in
an average exhumation rate for the P1 source terrain of 0.9 km/m.y. during the Early Cretaceous
and >1 km/m.y. during the Late Cretaceous.
Exhumation rates of 0.9–>1 km/m.y. are
relatively high for non-collisional systems such
as the North America Cordillera, whereas they
are more typical of rates recorded in collisional
systems such as the Himalaya, the Pyrenees,
and the Alps. Lag times between 0 and 5 m.y.
have been recorded in Cenozoic foreland basin
deposits of the western Alps (e.g., Carrapa
et al., 2003). Garver et al. (1999) calculated
exhumation rates based on detrital thermochronology of modern sediments in the Indus River
draining the foothills of the Himalaya to be
0.6–1 km/m.y., whereas Najman et al. (2003)
measured much more rapid Miocene exhumation rates in the Pakistan Himalaya, up to 4.5
km/m.y. Thiede and Ehlers (2013) reported
highly varied exhumation rates through space
and time in the Himalaya, ranging from 0.5
to 3 km/m.y. In the Pyrenees, Fitzgerald et al.
(1999) measured exhumation rates to be ~0.2–
>2 km/m.y., depending on the location in the
orogen and time during the orogeny. In non-collisional systems such as the central Andes, the
modern counterpart to the North America Cordillera (Coney and Evenchick, 1994; Dickinson, 2004), relatively low exhumation rates, 0.2
km/m.y., have been measured from synorogenic
Mio-Pliocene deposits preserved on the south-
decreasing exhumation
Depositional age
g
la
Foreland basin
stratigraphic section
nt
e
tim
Geological Society of America Bulletin, Month/Month 2014
ta
ns
20
co
Exhumation of a crustal column
Figure 13. Orogenic wedge
Source exhumation and
theory applied to lag times and
deposition of eroded material
exhumation rates (from Carin the adjacent foreland
rapa, 2009). Orogenic wedge
Pro-wedge and/or retro-wedge behavior
2
theory treats the orogen as a
tA
st
wedge and associates its beea
dy
tC
tA
-st
havior to the angle of the deat
tB
e
tachment (β), the angle of the
ex
tB
120 °C
inc
tB
1
h
rea
um
topographic slope (α), and a
sing
tC
tA
2
at
c
exh
tC
io
critical angle (θc) (Davis et al.,
u
350 °C
ma
1
n
tion
1983). If the sum of β and α is
greater than θc then thrusting
e.g., tA: cooling age at time tA < tB < tC
rapidly propagates into the
Detrital cooling age
foreland; if the sum of β and α
is less than θc, then the orogen builds internally (Davis et al., 1983). Increased exhumation rates correspond to subcritical wedges, when
the wedge is building internally, and decreased exhumation trends correspond to times when the orogenic wedge is supercritical (Carrapa,
2009). “1” indicates that when the orogen builds internally (shown by the internal thrust fault), exhumation will increase (decreasing lag
times). “2” indicates that when the thrusting rapidly propagates into the foreland, exhumation with decrease (increasing lag times).
Exhumation of the North American Cordillera
50
60
70
80
AFT cooling age (Ma)
90
100
110
120
130
140
60
70
Depostional age (Ma)
80
90
100
110
120
130
Legend
North Horn Fm. (Sam 8)
upper Sego SS Mbr. (Sam 17)
lower Sego SS Mbr. (NSD4 B)
Price River Fm. (060923)
Price River Fm. (060922)
Brooks Mbr. (051208)
Chimney Rock Tng. Mbr. (051212)
Blair Fm. (051207)
Echo Canyon Cgl. (051201)
Dakota Fm. (051218)
Kelvin Fm. (051204)
0
M
10
yr
lag
M
tim
yr
lag
e
tim
e
Figure 14. All ages from the youngest apatite grain populations (P1) plotted against depositional ages. Note the scatter. Typically this would be used to interpret lag time, but as
stated, this population is contaminated with volcanogenic apatites (Table 6). Interpreting all of these as lag times would produce an erroneous exhumation interpretation.
that of the central Andean arc, Puna-Altiplano,
and eastern Cordillera zones (Dickinson, 2004;
DeCelles, 2004). Just as the high-elevation Puna
Plateau has been subject to low exhumation rates
(0.2 km/m.y.) since Eocene time (Deeken et al.,
2006), it is likely that the Nevadaplano expe-
50
50
60
AFT cooling age of young exhumed apatites (Ma)
70
80
90
100
110
120
130
140
60
70
80
Depostional age (Ma)
ern Puna Plateau (Carrapa et al., 2006). Similar exhumation rates to those presented in this
study (>1 km/m.y.) have instead been recorded
by Eocene–Oligocene wedge-top deposits on
the eastern side of the Puna Plateau (Carrapa
and DeCelles, 2008) and in Miocene deposits
of the Eastern Cordillera of northwest Argentina
(Coutand et al., 2006), suggesting that exhumation rates can be rapid and geographically concentrated during periods of tectonic activity.
These high exhumation rates could not have
been sustainable over the entire North American
Cordillera for long periods of time, indicated by
the fact that even low-grade metamorphic rocks
were not exposed in the Cordillera during the
Cretaceous (DeCelles, 2004; Long, 2012). Our
AFT and zircon He thermochronology data suggest that material was exhumed from between 5
and 8 km depths, at exhumation rates of 0.9–>1
km/m.y. from 118 Ma to 66 Ma; however, this
could not have taken place over the entire orogen without exhuming deep-crustal material.
Instead, we propose that high rates of exhumation were concentrated in the frontal foldthrust belt along the eastern margin of the North
America Cordillera (Fig. 16). DeCelles (2004)
divided the retroarc side of the North America
Cordillera into five zones: the Luning-Fencemaker thrust belt, central Nevada thrust belt, the
Nevadaplano (a >3-km-high plateau during the
mid- to Late Cretaceous), the frontal Sevier foldthrust belt, and the younger Laramide basementcored uplifts. This orogenic profile is similar to
rienced low exhumation rates, and that rapid
exhumation was instead concentrated along the
eastward-propagating Sevier fold-thrust belt
(Long, 2012). While the Sevier fold-thrust belt
was active, new material was constantly being
exhumed in the frontal part of orogenic wedge,
allowing consistently fast but localized exhumation rates of >1 km/m.y. (Fig. 16).
Multiple researchers have used subsidence
histories to document initial thrusting and flexural loading of the Sevier fold-thrust belt, total
subsidence, and flexural wave migration (e.g.,
Heller et al., 1986; Pang and Nummedal, 1995;
DeCelles and Currie, 1996; Allen et al., 2000;
Liu and Nummedal, 2004). Focusing on the samples that are free of volcanic contamination (Fig.
15), all are from units deposited in proximal to
distal foredeep depozones. Subsidence histories
show that these ca. 118–66 Ma samples come
from strata deposited during active shortening
and subsidence (Heller et al., 1986; DeCelles
and Currie, 1996; Pang and Nummedal, 1995;
Liu and Nummedal, 2004), and the consistent
small lag times (i.e., rapid exhumation) support
this (Fig. 15). Small lag times recorded in this
study are inconsistent with significant reworking and do not support the hypothesis that coarse
clastics are associated with tectonic quiescence
and reworking of more proximal foreland basin
material. Currently, there is no agreement on the
significance of distal upward-coarsening deposits. Horton et al. (2004) linked distal coarsegrained sedimentary rocks to active shortening
90
100
110
Legend
North Horn Fm. (Sam 8)
Price River Fm. (060923)
Price River Fm. (060922)
Echo Canyon Cgl. (051201)
Dakota Fm. (051218)
Kelvin Fm. (051204)
0
120
M
10
yr
l
ag
tim
e
M
yr
lag
tim
e
(2)
(1)
130
Figure 15. Lag time plot. All populations that have been contaminated with volcanic
apatites have been removed from the youngest grain populations (P1). Gray arrows
outline two possible exhumation interpretations: (1) constant lag time and steadystate exhumation; (2) decreasing lag times and increasing exhumation rates.
Geological Society of America Bulletin, Month/Month 2014
21
Painter et al.
low exhumation rates
~0.2 km/Myr
Nevadaplano
west
arc
high exhumation rates
0.9−>>1 km/Myr
Sevier
fold-thrust belt
east
North America
Fara
l
lon
Plat
e
Figure 16. Schematic of the North America Cordillera during the Cretaceous, outlining the position of the arc,
Nevadaplano, and Sevier fold-thrust belt and exhumation rates (modified from DeCelles, 2004). Exhumation rates
for the Nevadaplano are estimated using measurements from the Puna Plateau in Carrapa et al. (2006). The
dashed lines above the subducting slab represent the shallowing slab during the Late Cretaceous.
and exhumation in the Charleston-Nebo portion
of the Sevier fold-thrust belt, but others (Willis,
2000) used the two-phase stratigraphic model
as described by Heller et al. (1988) to explain
the progradation of the Castlegate Formation
and the Sego Sandstone Member as the result
of periods of tectonic quiescence (Fig. 4). The
two-phase stratigraphic model applies to retroarc foreland basins dominated by flexural processes (Heller et al., 1988). However, the North
America Cordilleran foreland was partitioned
by Laramide-style basement-cored uplifts by
Maastrichtian time (ca. 71 Ma) (Dickinson
et al., 1988; DeCelles, 2004), and Aschoff and
Steel (2011) proposed that Laramide deformation initiated during the Campanian, as early
as ca. 77 Ma. This implies that stratigraphic
and thermochronologic studies of Campanian
distal sandstones in the North America Cordilleran foreland may not be a good test for the
two-phase stratigraphic model. However, lagtime measurements presented here are small
(<5 m.y.) for all pre-Laramide samples (ca.
119 Ma–80 Ma) (Fig. 15). Data resolution is an
issue in detrital thermochronology studies, and
higher vertical (stratigraphic) and spatial lagtime resolution would be ideal; however, our
lag-time measurements do not support the existence of tectonically quiescent periods between
ca. 95 and 66 Ma and arguably between ca. 118
and 66 Ma (Fig. 15), but instead suggest active
tectonics within the North American Cordillera
throughout those time intervals.
SUMMARY AND CONCLUSIONS
The combination of DZ U-Pb geochronology,
detrital AFT, and zircon He thermochronology
provides constraints on the depositional ages of
22
synorogenic deposits. Our new data show good
agreement between the youngest DZ U-Pb grain
ages and existing 40Ar/39Ar ages of ashes and
biostratigraphic ages of ammonite zones, supporting and further refining the stratigraphic age
of Upper Jurassic to Upper Cretaceous foreland
basin deposits in Western Interior U.S.A.
Zircon He thermochronology on conglomerate cobbles from the Price River Conglomerate
produced mixed ages of 76.2 ± 2.6 Ma, 253.1 ±
8.4 Ma, and 231.1 ± 7.7 Ma, which indicates
maximum exhumation of source material from
depths with temperatures <190 °C and from
no deeper than ~8–9 km, assuming a 20 °C/km
geothermal gradient, during the development of
the North American Cordillera. In contrast, AFT
ages of conglomerate cobbles in wedge-top
deposits produce single near-syndepositional
age populations, indicating that fission tracks
were completely annealed in the thrust belt
prior to exhumation. This suggests that source
material was exhumed from depths with temperatures >120 °C, ~4–5 km deep. Zircon He
and AFT limit exhumation depths to between ~4
and 9 km. None of the detrital foreland basin
samples appears to be significantly annealed
following deposition, so burial in these areas
likely did not exceed 3–4 km, which is also supported by independent stratigraphic information
(DeCelles and Currie, 1996).
Although AFT proves to be an effective
thermochronometer in the North America Cordilleran foreland basin, measuring lag time is
challenged by several factors, including: (1) low
yield of apatite grains in foreland basin deposits—only 11 out of the >37 samples processed
for apatite yielded enough for AFT analysis, even
with >10 kg sample size; and (2) young volcanic
or arc-derived contamination. The prevalence of
young volcanic or arc-derived apatites indicates
that the assumption that volcanic contamination
in the foreland basin deposits is negligible is not
always applicable, and U-Pb thermochronology
needs to be routinely applied on detrital apatites
to identify co-magmatic apatites versus older
exhumed apatites.
Future thermochronologic studies of foreland basin deposits may be key in identifying
whether orogenic growth of the North American
Cordillera initiated during the Late Jurassic or
Early Cretaceous (Heller et al., 1986; DeCelles
and Burden, 1992; DeCelles and Currie, 1996;
Currie, 1997). Small lag times (i.e., rapid exhumation rates) measured in the Upper Jurassic Morrison Formation would indicate Late
Jurassic orogenic growth. However, none of the
samples included in this study yielded sufficient
apatite to measure lag time.
Our measurements indicate small lag times
of ~0–5 m.y. throughout Cretaceous time.
Though the spatial and temporal resolution is
limited, the short lag times are consistent with
overall steady-state to slightly increasing source
exhumation at rates of 0.9 to >1 km/m.y. Lag
times are similar in both synorogenic wedge-top
conglomerates (i.e., the Price River Conglomerate and the North Horn Formation) and distal
foredeep sandstones (i.e., the Kelvin and Dakota
Formations), suggesting that both proximal and
distal foreland basin coarse-grained deposits
represent periods of active tectonics and exhumation, rather than tectonic quiescence, in the
Cordilleran foreland basin. These data also
indicate that apatites in distal sandstones in
the Cordilleran foreland basin were likely not
stored in the proximal part of the foreland for a
measureable amount of time and then reworked
into the distal foreland basin. Furthermore, these
Geological Society of America Bulletin, Month/Month 2014
Exhumation of the North American Cordillera
consistently rapid exhumation rates indicate that
exhumation was likely focused along the eastern
flank of the Nevadaplano and the Sevier foldthrust belt, and that the hinterland experienced
much slower exhumation rates.
ACKNOWLEDGMENTS
We thank the team at the Arizona LaserChron Center. Particularly we thank Mark Pecha, Clayton Loehn,
Nicky Geisler, Intan Yokelson, and Chelsi White.
Also, we thank Peter Reiners and Stefan Nicolescu for
support during our zircon (U-Th-[Sm])/He data acquisition. Xennephone Hadeen was of great help during
some of the sample preparation steps.
Facilities at the Arizona LaserChron Center are
supported by National Science Foundation awards
NSF-EAR 0732436 and 1032156. We thank Shell
Oil, ExxonMobil, and a 2012 GSA research grant for
funding support.
We thank Brian S. Currie and Shari A. Kelley for
their thorough and constructive reviews. We also
thank Timothy F. Lawton, the Associate Editor, for
his detailed comments and review. All of their input
helped with the clarity of this manuscript. In addition,
we thank Heidi Carroll for reading the manuscript and
giving technical writing feedback.
REFERENCES CITED
Allen, P.A., Verlander, J.E., Burgess, P.M., and Audet, D.M.,
2000, Jurassic giant erg deposits, flexure of the United
States continental interior, and timing of the onset of
Cordilleran shortening: Geology, v. 28, p. 159–162, doi:
10.1130/0091-7613(2000)28<159:JGEDFO>2.0.CO;2.
Aschoff, J., and Steel, R., 2011, Anomalous clastic wedge
development during the Sevier-Laramide transition,
North American Cordilleran foreland basin, USA: Geological Society of America Bulletin, v. 123, no. 9/10,
p. 1822–1835, doi:10.1130/B30248.1.
Aubouin, J., 1965, Geosynclines: New York, Elsevier, 335 p.
Baadsgaard, H., Lerbekmo, J.F., and Wijbrans, J.R., 1993,
Multimethod radiometric age for a bentonite near
the top of the Baculites reesidei Zone of southwestern Saskatchewan (Campanian-Maastrichtian stage
boundary?): Canadian Journal of Earth Sciences, v. 30,
p. 769–775, doi:10.1139/e93-063.
Beck, R.A., Vondra, C.F., Filkins, J.E., and Olander, J.D.,
1988, Syntectonic sedimentation and Laramide basement thrusting, Cordilleran foreland: Timing of deformation, in Schmidt, C.J., and Perry, W.J., Jr., eds.,
Interaction of the Rocky Mountain Foreland and the
Cordilleran Thrust Belt: Geological Society of America Memoir 171, p. 465–488, doi:10.1130/MEM171
-p465.
Bernet, M., Zattin, M., Garver, J.I., Brandon, M.T., and
Vance, J.A., 2001, Steady-state exhumation of European Alps: Geology, v. 29, p. 35–38, doi:10.1130/0091
-7613(2001)029<0035:SSEOTE>2.0.CO;2.
Blair, T.C., and Bilodeau, W.L., 1988, Development of
tectonic cyclothems in rift, pull-apart, and foreland
basins: Sedimentary response to episodic tectonism:
Geology, v. 16, p. 517–520, doi:10.1130/0091-7613
(1988)016<0517:DOTCIR>2.3.CO;2.
Brandon, M.T., 2002, Decomposition of mixed grain age
distributions using BINOMFIT: On Track, v. 24,
p. 13–18.
Brandon, M.T., and Vance, J.A., 1992, Tectonic evolution
of the Cenozoic Olympic subduction complex, Washington State, as deduced from fission track ages for
detrital zircons: American Journal of Science, v. 292,
p. 565–636, doi:10.2475/ajs.292.8.565.
Burbank, D.W., Beck, R.A., Raynolds, R.G.H., Hobbs, R.,
and Tahirkheli, R.A.K., 1988, Thrusting and gravel
progradation in foreland basins: A test of post-thrusting
gravel dispersal: Geology, v. 16, p. 1143–1146, doi:10
.1130/0091-7613(1988)016<1143:TAGPIF>2.3.CO;2.
Burtner, R.L., and Nigrini, A., 1994, Thermochronology of
the Idaho-Wyoming thrust belt during the Sevier orogeny: A new, calibrated multiprocess thermal model:
American Association of Petroleum Geologists Bulletin, v. 78, p. 1586–1612.
Burtner, R.L., Nigrini, A., and Donelick, R.A., 1994, Thermochronology of Lower Cretaceous source rocks in
the Idaho-Wyoming thrust belt: American Association
of Petroleum Geologists Bulletin, v. 78, p. 1613–1636.
Burton, D., Greenhalgh, B.W., Britt, B.B., Kowallis, B.J.,
Elliott, W.S., Jr., and Barrick, R., 2006, New radiometric ages from the Cedar Mountain Formation, Utah,
and the Cloverly Formation, Wyoming: Implications
for contained dinosaur faunas: Geological Society of
America Abstracts with Programs, v. 38, no. 7, p. 52.
Carrapa, B., 2009, Tracing exhumation and orogenic wedge
dynamics in the European Alps with detrital thermochronology: Geology, v. 37, p. 1127–1130, doi:10
.1130/G30065A.1.
Carrapa, B., 2010, Resolving tectonic problems by dating
detrital minerals: Geology, v. 38, p. 191–192, doi:10
.1130/focus022010.1.
Carrapa, B., and DeCelles, P.G., 2008, Eocene exhumation and basin development in the Puna of northwestern Argentina: Tectonics, v. 27, TC1015, doi:101029
/2007TC002127.
Carrapa, B., Wijbrans, J., and Bertotti, G., 2003, Episodic
exhumation in the Western Alps: Geology, v. 31,
p. 601–604, doi:10.1130/0091-7613(2003)031<0601:
EEITWA>2.0.CO;2.
Carrapa, B., Wijbrans, J., and Bertotti, G., 2004, Detecting provenance variations and cooling patterns within
the western Alpine orogen through 40Ar/ 39Ar geochronology on detrital sediments: The Tertiary Piedmont
Basin, northwest Italy, in Bernet, M., and Spiegel,
C., eds., Detrital Thermochronology: Provenance
Analysis, Exhumation, and Landscape Evolution of
Mountain Belts: Geological Society of America Special Paper 378, p. 67–104, doi:10.1130/0-8137-2378
-7.67.
Carrapa, B., Strecker, M.R., and Sobel, E.R., 2006, Cenozoic orogenic growth in the Central Andes: Evidence
from sedimentary rock provenance and apatite fission
track thermochronology in Fiambala Basin, southernmost Puna Plateau margin (NW Argentina): Earth and
Planetary Science Letters, v. 247, p. 82–100, doi:10
.1016/j.epsl.2006.04.010.
Carrapa, B., DeCelles, P.G., Reiners, P.W., Gehrels, G.E.,
and Sudo, M., 2009, Apatite triple dating and white
mica 40Ar/39Ar thermochronology of syntectonic detritus in the Central Andes: A multiphase tectonothermal
history, v. 37, p. 407–410, doi:10.1130/G25698A.1.
Carter, A., 1999, Present status and future avenues of source
region discrimination and characterization using fission track analysis: Sedimentary Geology, v. 124,
p. 31–45, doi:10.1016/S0037-0738(98)00119-5.
Cerveny, P.F., 1990, Fission track thermochronology of the
Wind River Range and other basement cored uplifts in
the Rocky Mountain foreland [Ph.D. thesis]: Laramie,
University of Wyoming, 189 p.
Cerveny, P.F., and Steidtmann, J.R., 1993, Fission track
thermochronology of the Wind River Range, Wyoming: Evidence for timing and magnitude of Laramide
exhumation: Tectonics, v. 12, p. 77–91, doi:10.1029
/92TC01567.
Cerveny, P.F., Naeser, N.D., Zeitler, P.K., Naeser, C.W., and
Johnson, N.M., 1988, History of uplift and relief on the
Himalaya during the past 18 million years: Evidence
from fission-track ages of detrital zircons from sandstones of the Siwalik Group, in Kleinspehn, K., and
Paola, C., eds., New Perspectives in Basin Analysis:
New York, Springer-Verlag, p. 43–61.
Chen, Z.Q., and Lubin, S., 1997, A fission-track study of
the terrigenous sedimentary sequences of the Morrison
and Cloverly Formations in the northeastern Bighorn
Basin, Wyoming: The Mountain Geologist, v. 34,
no. 2, p. 51–62.
Cherniak, D.J., Lanford, W.A., and Ryerson, F.J., 1991,
Lead diffusion in apatite and zircon using ion implantation and Rutherford Backscattering techniques: Geochimica et Cosmochimica Acta, v. 55, p. 1663–1673,
doi:10.1016/0016-7037(91)90137-T.
Cobban, W.A., 1990, Ammonites and some characteristic bivalves from the Upper Cretaceous Frontier Formation,
Natrona County, Wyoming: U.S. Geological Survey
Bulletin 1917-B, 13 p.
Cobban, W.A., and Reeside, J.B., Jr., 1952, Frontier Formation, Wyoming and adjacent areas: American
Association of Petroleum Geologists Bulletin, v. 36,
p. 1913–1961.
Cobban, W.A., Walaszczyk, I., Obradovich, J.D., and McKinney, K.C., 2006, A USGS zonal table for the Upper
Cretaceous middle Cenomanian–Maastrichtian of the
Western Interior of the United States based on ammonites, inoceramids, and radiometric ages: U.S. Geological Survey Open-File Report 2006-1250, 46 p.
Coney, P.J., and Evenchick, C.A., 1994, Consolidation of
the American Cordilleras: Journal of South American
Earth Sciences, v. 7, p. 241–262, doi:10.1016/0895
-9811(94)90011-6.
Coutand, I., Carrapa, B., Deeken, A., Schmitt, A.K., Sobel,
E.R., and Strecker, M.R., 2006, Propagation of orographic barriers along an active range front: Insights
from sandstone petrography and detrital apatite fissiontrack thermochronology in the intramontane Angastaco
basin, NW Argentina: Basin Research, v. 18, p. 1–26,
doi:10.1111/j.1365-2117.2006.00283.x.
Crittenden, M.D., Jr., 1963, Emendation of the Kelvin Formation and Morrison(?) Formation near Salt Lake
City, Utah, in Geological Survey Research 1963: Short
Papers in Geology and Hydrology: U.S. Geological
Survey Professional Paper 475-B, p. B95–B98.
Crowley, R.D., Reiners, P.W., Reuter, J.M., and Kaye, G.D.,
2002, Laramide exhumation of the Bighorn Mountains,
Wyoming: An apatite (U-Th)/He thermochronology
study: Geology, v. 30, p. 27–30, doi:10.1130/0091
-7613(2002)030<0027:LEOTBM>2.0.CO;2.
Cullins, H.L., 1971, Geologic map of the Rangely quadrangle, Rio Blanco County, Colorado: U.S. Geological
Survey Geologic Quadrangle GQ-812, scale 1:24,000.
Currie, B.S., 1997, Sequence stratigraphy of nonmarine
Jurassic–Cretaceous rocks, central Cordilleran foreland-basin system: Geological Society of America
Bulletin, v. 109, p. 1206–1222, doi:10.1130/0016-7606
(1997)109<1206:SSONJC>2.3.CO;2.
Currie, B.S., 1998, Upper Jurassic–Lower Cretaceous Morrison and Cedar Mountain Formations, NE Utah–NW
Colorado: Relationships between nonmarine deposition and early Cordilleran foreland basin development:
Journal of Sedimentary Research, v. 68, p. 632–652,
doi:10.2110/jsr.68.632.
Currie, B.S., McPherson, M.L., Pierson, J.S., Dark, J.P.,
Hokanson, W.H., Homan, M.B., Purcell, R.M., Pyden,
T.J., and Schellenbach, W.L., 2011, Sequence stratigraphy of the mid-Cretaceous Dakota Formation and
Mowry Shale, Uinta Basin, Utah and Colorado: Geological Society of America Abstracts with Programs,
v. 43, no. 5, p. 602.
Currie, B.S., McPherson, M.L., Hokanson, W., Pierson, J.S.,
Homan, M.B., Pyden, T., Schellenback, W., Purcell,
R., and Nicklaus, D., 2012, Reservoir characterization
of the Lower Cretaceous Cedar Mountain and Dakota
Formations, northern Uinta Basin, Utah: Utah Geological Survey Open-File Report 597, 33 p.
Dahlen, F.A., 1984, Noncohesive critical coulomb
wedges: An exact solution: Journal of Geophysical Research, v. 89, p. 10,125–10,133, doi:10.1029
/JB089iB12p10125.
Dahlstrom, D.J., and Fox, J.E., 1995, Fluvial architecture of
the Lower Cretaceous Lakota Formation, southwestern
flank of the Black Hills uplift, South Dakota: U.S. Geological Survey Bulletin 1917-S, 20 p.
Davis, D., Suppe, J., and Dahlen, F.A., 1983, Mechanics of
fold-and-thrust belts and accretionary wedges: Journal
of Geophysical Research, v. 88, p. 1153–1172, doi:10
.1029/JB088iB02p01153.
DeCelles, P.G., 1988, Lithologic provenance modeling applied to the Late Cretaceous synorogenic Echo Canyon
Conglomerate, Utah: A case of multiple source areas:
Geology, v. 16, p. 1039–1043.
DeCelles, P.G., 1994, Late Cretaceous–Paleocene synorogenic sedimentation and kinematic history of the
Sevier thrust belt, northeast Utah and southwest Wyoming: Geological Society of America Bulletin, v. 106,
Geological Society of America Bulletin, Month/Month 2014
23
Painter et al.
p. 32–56, doi:10.1130/0016-7606(1994)106<0032:
LCPSSA>2.3.CO;2.
DeCelles, P.G., 2004, Late Jurassic to Eocene evolution of
the Cordilleran thrust belt and foreland basin system,
western U.S.A.: American Journal of Science, v. 304,
p. 105–168, doi:10.2475/ajs.304.2.105.
DeCelles, P.G., and Burden, E.T., 1992, Non-marine sedimentation in the overfilled part of the Jurassic–Cretaceous Cordilleran foreland basin: Morrison and
Cloverly Formations, central Wyoming, USA: Basin
Research, v. 4, p. 291–314, doi:10.1111/j.1365-2117
.1992.tb00050.x.
DeCelles, P.G., and Currie, B.S., 1996, Long-term sediment
accumulation in the Middle Jurassic–early Eocene
Cordilleran retroarc foreland-basin system: Geology,
v. 24, p. 591–594, doi:10.1130/0091-7613(1996)024
<0591:LTSAIT>2.3.CO;2.
DeCelles, P.G., and Giles, K.A., 1996, Foreland basin systems: Basin Research, v. 8, p. 105–123, doi:10.1046/j
.1365-2117.1996.01491.x.
DeCelles, P.G., Pile, H.T., and Coogan, J.C., 1993, Kinematic history of the Meade thrust based on provenance
of the Bechler conglomerate at Red Mountain, Idaho,
Sevier thrust belt: Tectonics, v. 12, p. 1436–1450, doi:
10.1029/93TC01790.
DeCelles, P.G., Lawton, T.F., and Mitra, G., 1995, Thrust
time, growing of structural culminations, and synorogenic sedimentation in the type Sevier orogenic belt,
western United States: Geology, v. 23, p. 699–702, doi:
10 .1130 /0091 -7613 (1995)023 <0699: TTGOSC>2.3
.CO;2.
Deeken, A., Sobel, E.R., Coutand, I., Haschke, M., Riller, U.,
and Strecker, M.R., 2006, Development of the southern Eastern Cordillera, NW Argentina, constrained by
apatite fission track thermochronology: From Early
Cretaceous extension to middle Miocene shortening:
Tectonics, v. 25, TC6003, doi:10.1029/2005TC001894.
Devlin, W.J., Rudolph, K.W., Ehman, K.D., and Shaw, C.A.,
1993, The effect of tectonic and Eustatic cycles on accommodation and sequence stratigraphic framework in
the Upper Cretaceous foreland basin of southwestern
Wyoming, in Posamentier, H.W., Summerhayes, C.P.,
Haq, B.U., and Allen, G.P., eds., Stratigraphy and Facies Associations in a Sequence Stratigraphic Framework: International Association of Sedimentologists
Special Publication 18, p. 501–520.
Dickinson, W.R., 1974, Plate tectonics and sedimentation,
in Dickinson, W.R., ed., Tectonics and Sedimentation:
Society of Economic Paleontologists and Mineralogists Special Publication 22, p. 1–27.
Dickinson, W.R., 1985, Interpreting provenance relations
from detrital modes of sandstones, in Zuffa, G.G.,
ed., Provenance of Arenites: Dordrecht, Netherlands,
Reidel, p. 333–361.
Dickinson, W.R., 2004, Evolution of the North American
Cordillera: Annual Review of Earth and Planetary Sciences, v. 32, p. 13–45, doi:10.1146/annurev.earth.32
.101802.120257.
Dickinson, W.R., and Gehrels, G.E., 2008, Sediment delivery to the Cordilleran foreland basin: Insights from
U-Pb ages of detrital zircons in Upper Jurassic and
Cretaceous strata of the Colorado Plateau: American
Journal of Science, v. 308, p. 1041–1082, doi:10.2475
/10.2008.01.
Dickinson, W.R., and Gehrels, G.E., 2009, Use of U-Pb ages
of detrital zircons to infer maximum depositional ages
of strata: A test against a Colorado Plateau Mesozoic
database: Earth and Planetary Science Letters, v. 288,
p. 115–125, doi:10.1016/j.epsl.2009.09.013.
Dickinson, W.R., and Suczek, C.A., 1979, Plate tectonics
and sandstone compositions: American Association of
Petroleum Geologists Bulletin, v. 63, p. 2164–2182.
Dickinson, W.R., Klute, M.A., Hayes, M.J., Janecke, S.U.,
Lundin, E.R., McKittrick, M.A., and Olivares, M.D.,
1988, Paleogeographic and paleotectonic setting of
Laramide sedimentary basins in the central Rocky
Mountain region: Geological Society of America Bulletin, v. 100, p. 1023–1039, doi:10.1130/0016-7606
(1988)100<1023:PAPSOL>2.3.CO;2.
Dumitru, T.A., Duddy, I.R., and Green, P.F., 1994, Mesozoic–Cenozoic burial, uplift, and erosion history of
the west-central Colorado Plateau: Geology, v. 22,
24
p. 499–502, doi:10.1130/0091-7613(1994)022<0499:
MCBUAE>2.3.CO;2.
Farley, K.A., Wolf, R.A., and Silver, L.T., 1996, The effects
of long alpha-stopping distances on (U-Th)/He ages:
Geochimica et Cosmochimica Acta, v. 60, p. 4223–
4229, doi:10.1016/S0016-7037(96)00193-7.
Fitzgerald, P.G., Muñoz, J.A., Coney, P.J., and Baldwin,
S.L., 1999, Asymmetric exhumation across the Pyrenean orogen: Implications of the tectonic evolution
of a collisional orogen: Earth and Planetary Science
Letters, v. 173, p. 157–170, doi:10.1016/S0012-821X
(99)00225-3.
Flemings, P.B., and Jordan, T.E., 1989, A synthetic stratigraphic model of foreland basin development: Journal
of Geophysical Research, v. 94, p. 3851–3866, doi:10
.1029/JB094iB04p03851.
Flowers, R.M., Shuster, D.L., Wernicke, B.P, and Farley,
K.A., 2007, Radiation damage control on apatite
(U-Th)/He dates from the Grand Canyon region, Colorado Plateau: Geology, v. 35, no. 5, p. 447–450.
Flowers, R.M., Wernicke, B.P., and Farley, K.A., 2008, Unroofing, incision, and uplift history of the southwestern
Colorado Plateau from apatite (U-Th)/He: Geological
Society of America Bulletin, v. 120, p. 571–587, doi:
10.1130/B26231.1.
Flowers, R.M., Ketcham, R.A., Shuster, D.L., and Farley,
K.A., 2009, Apatite (U-Th)/He thermochronometry
using a radiation damage accumulation and annealing model: Geochimica et Cosmochimica Acta, v. 73,
p. 2347–2365, doi:10.1016/j.gca.2009.01.015.
Fouch, T.D., Lawton, T.F., Nichols, D.J., Cashion, W.B., and
Cobban, W.A., 1983, Patterns and timing of synorogenic sedimentation in Upper Cretaceous rocks of central and northeast Utah, in Reynolds, M.W., and Dolly,
E.D., eds., Mesozoic Paleogeography of West-Central
United States: Tulsa, Oklahoma, Society of Economic
Paleontologists and Mineralogists Rocky Mountain
Paleogeography Symposium 2, p. 305–336.
Furer, L.C., 1970, Petrology and stratigraphy of nonmarine
Upper Jurassic and Lower Cretaceous rocks of western Wyoming and southeastern Idaho: American
Association of Petroleum Geologists Bulletin, v. 54,
p. 2282–2304.
Furer, L.C., Kvale, E.P., and Engelhardt, D.W., 1997, Early
Cretaceous hiatus much longer than previously reported, in Campen, E.B., ed., Bighorn Basin: 50 Years
on the Frontier: Evolution of the Geology of the Bighorn Basin: Billings, Montana Geological Association,
1997 Field Trip and Symposium Guidebook, p. 47–58.
Galbraith, R.F., and Green, P.F., 1990, Estimating the component ages in a finite mixture: Nuclear Tracks and Radiation Measurements, v. 17, p. 197–206, doi:10.1016
/1359-0189(90)90035-V.
Garver, J.I., Brandon, M.T., Roden-Tice, M.K., and Kamp,
P.J.J., 1999, Exhumation history of orogenic highlands
determined by detrital fission track thermochronology,
in Ring, U., Brandon, M.T., Willett, S.D., and Lister,
G.S., eds., Exhumation Processes: Normal Faulting,
Ductile Flow, and Erosion: Geological Society [London] Special Publication 154, p. 283–304.
Gehrels, G.E., 2011, Detrital zircon U-Pb geochronology:
Current methods and new opportunities, in Busby, C.,
and Azor, A., eds., Tectonics of Sedimentary Basins:
Recent Advances: Chichester, UK, John Wiley & Sons,
Ltd, p. 47–62, doi: 10.1002/9781444347166.ch2.
Gehrels, G.E., Valencia, V., and Pullen, A., 2006, Detrital
zircon geochronology by laser-ablation multicollector ICPMS at the Arizona LaserChron Center, in
Loszewski, T., and Huff, W., eds., Geochronology:
Emerging Opportunities: Paleontology Society Short
Course: Paleontology Society Paper 11, 10 p.
Gehrels, G.E., Valencia, V., and Ruiz, J., 2008, Enhanced
precision, accuracy, efficiency, and spatial resolution
of U-Pb ages by laser ablation–multicollector–inductively coupled plasma–mass spectrometry: Geochemistry Geophysics Geosystems, v. 9, Q03017, doi:10
.1029/2007GC001805.
Gehrels, G.E., Blakey, R., Karlstrom, K.E., Timmons, J.M.,
Dickinson, B., and Pecha, M., 2011, Detrital zircon
U-Pb geochronology of Paleozoic strata in the Grand
Canyon, Arizona: Lithosphere, v. 3, p. 183–200, doi:
10.1130/L121.1.
Gill, J.R., and Hail, W.J., Jr., 1975, Stratigraphic sections
across Upper Cretaceous Mancos Shale–Mesaverde
Group boundary, eastern Utah and western Colorado:
U.S. Geological Survey Oil and Gas Investigations
Chart OC-68, 1 sheet.
Gill, J.R., Merewether, E.A., and Cobban, W.A., 1970, Stratigraphy and nomenclature of some Upper Cretaceous
and Lower Tertiary rocks in south-central Wyoming:
U.S. Geological Survey Professional Paper 667, 53 p.
Gleadow, A.J.W., and Duddy, I.R., 1981, A natural longterm track annealing experiment for apatite: Nuclear
Tracks and Radiation Measurements, v. 5, p. 169–174,
doi:10.1016/0191-278X(81)90039-1.
Gleadow, A.J.W., Duddy, I.R., and Lovering, J.F., 1983,
Fission track analysis: A new tool for the evaluation
of thermal histories and hydrocarbon potential: Australian Petroleum Explorer Association Journal, v. 23,
p. 93–102.
Gradstein, F.M., and Ogg, J.G., 2004, Geologic time scale
2004—Why, how, and where next: Lethaia, v. 37,
p. 175–181, doi:10.1080/00241160410006483.
Graham, S.A., Tolson, R.B., DeCelles, P.G., Ingersoll, R.V.,
Bargar, E., Caldwell, M., Cavazza, W., Edwars, D.P.,
Follo, M.F., Handschy, J.R., Lemke, L., Moxon, I.,
Rice, R., Smith, G.A., and White, J., 1986, Provenance
modeling as a technique for analyzing source terrane
evolution and controls on foreland sedimentation, in
Homewood, P., and Allen, P.A., eds., Foreland Basins:
International Association of Sedimentologists Special
Publication 8, p. 141–152.
Guenthner, W.R., Reiners, P.W., Ketcham, R.A., Nasdala, L.,
and Giester, G., 2013, Helium diffusion in natural zircon: Radiation damage, anisotropy, and the interpretation of zircon (U-Th)/He thermochronology: American
Journal of Science, v. 313, p. 145–198, doi:10.2475/03
.2013.01.
Gurnis, M., 1993, Depressed continental hypsometry behind
oceanic trenches: A clue to subduction controls on sealevel change: Geology, v. 21, p. 29–32, doi:10.1130
/0091-7613(1993)021<0029:DCHBOT>2.3.CO;2.
Hale, L.A., and Van de Graaf, F.R., 1964, Cretaceous stratigraphy and facies pattern—Northwest Utah and adjacent areas, in Guidebook to the Geology and Mineral
Resources of the Uinta Basin: Utah’s Hydrocarbon
Storehouse, Thirteenth Annual Field Conference:
Intermountain Association of Petroleum Geologists
Guidebook 13, p. 115–138.
Heady, E.C., 1992, Stratigraphic and fission track study of
the Morrison and Cloverly sediments, Bighorn County,
Wyoming [M.S. thesis]: Hanover, New Hampshire,
Dartmouth College, 52 p.
Heller, P.L., Bowdler, S.S., Chambers, H.P., Coogan, J.C.,
Hagen, E.S., Shuster, M.W., and Winslow, N.S., 1986,
Time of initial thrusting in the Sevier orogenic belt,
Idaho-Wyoming and Utah: Geology, v. 14, p. 388–391,
doi: 10 .1130 /0091 -7613 (1986)14 <388: TOITIT>2 .0
.CO;2.
Heller, P.L., Angevine, C.L., Winslow, N.S., and Paola, C.,
1988, Two-phase stratigraphic model of foreland-basin
sequences: Geology, v. 16, p. 501–504, doi:10.1130
/0091-7613(1988)016<0501:TPSMOF>2.3.CO;2.
Horton, B.K., Constenius, K.N., and DeCelles, P.G., 2004,
Tectonic control on coarse-grained foreland-basin sequences: An example from the Cordilleran foreland
basin, Utah: Geology, v. 32, p. 637–640, doi:10.1130
/G20407.1.
Hurford, A.J., and Carter, A., 1991, The role of fission track
dating in discrimination of provenance, in Morton,
A.C., Todd, S.P., and Haughton, P.D.W., eds., Developments in Sedimentary Provenance Studies: Geological
Society [London] Special Publication 57, p. 67–78.
Hurford, A.J., and Green, P.F., 1983, The zeta age calibration of fission-track dating: Isotope Geoscience, v. 1,
p. 285–317.
Ireland, T.R., 1992, Crustal evolution of New Zealand:
Evidence from age distributions of detrital zircons
in Western Province paragneisses and Torlesse greywacke: Geochimica et Cosmochimica Acta, v. 56,
p. 911–920, doi:10.1016/0016-7037(92)90036-I.
Izett, G.A., Cobban, W.A., Dalrymple, G.B., and Obradovich, J.D., 1998, 40Ar/39Ar age of the Manson impact structure, Iowa, and correlative impact ejecta in
Geological Society of America Bulletin, Month/Month 2014
Exhumation of the North American Cordillera
the Crow Creek Member of the Pierre Shale (Upper
Cretaceous), South Dakota and Nebraska: Geological
Society of America Bulletin, v. 110, p. 361–376, doi:
10 .1130 /0016 -7606 (1998)110 <0361: AAAOTM>2 .3
.CO;2.
Jacobson, S.R., and Nichols, D.J., 1982, Palynological dating of syntectonic units in the Utah-Wyoming thrust
belt: The Evanston Formation, Echo Canyon Conglomerate, and Little Muddy Creek Conglomerate, in
Powers, R.G., ed., Geologic Studies of the Cordilleran
Thrust Belt: Denver, Colorado, Rocky Mountain Association of Geologists, p. 735–750.
Johnson, R.C., 2003, Depositional framework of the Upper
Cretaceous Mancos Shale and the lower part of the
Upper Cretaceous Mesaverde Group, western Colorado and eastern Utah, in Petroleum Systems and Geologic Assessment of Oil and Gas in the Uinta-Piceance
Province, Utah and Colorado: U.S. Geological Survey
Digital Data Series DDS-69-B, Chapter 10, 23 p.
Jordan, T.E., 1981, Thrust loads and foreland basin evolution, Cretaceous, western United States: American
Association of Petroleum Geologists Bulletin, v. 65,
no. 12, p. 2506–2520.
Kauffman, E.G., 1969, Cretaceous marine cycles of the Western Interior: The Mountain Geologist, v. 6, p. 227–245.
Kelley, S.A., 2002, Unroofing of the southern Front Range,
Colorado: A view from the Denver Basin: Rocky
Mountain Geology, v. 37, p. 189–200, doi:10.2113/7.
Kirschbaum, M.A., and McCabe, P.J., 1992, Controls on
the accumulation of coal and on the development of
anastomosed fluvial systems in the Cretaceous Dakota
Formation of southern Utah: Sedimentology, v. 39,
p. 581–598, doi:10.1111/j.1365-3091.1992.tb02138.x.
Kowallis, B.J., Christiansen, E.H., and Deino, A.L., 1991,
Age of the Brushy Basin Member of the Morrison Formation, Colorado Plateau, western USA: Cretaceous
Research, v. 12, p. 483–493, doi:10.1016/0195-6671
(91)90003-U.
Kowallis, B.J., Christiansen, E.H., Deino, A.L., Peterson, F.,
Turner, C.E., Kunk, M.J., and Obradovich, J.D., 1998,
The age of the Morrison Formation: Modern Geology,
v. 22, p. 235–260.
Krystinik, L.F., and Blakeney DeJarnett, B., 1995, Lateral
variability of sequence stratigraphic framework in the
Campanian and early Maastrichtian of the Western
Interior Seaway, in Van Wagoner, J.C., and Bertram,
G.T., eds., Sequence Stratigraphy of Foreland Basin
Deposits: Outcrop and Subsurface Examples from the
Cretaceous of North America: American Association
of Petroleum Geologists Memoir 64, p. 11–26.
Laskowski, A.K., DeCelles, P.G., and Gehrels, G.E., 2013,
Detrital zircon geochronology of Cordilleran retroarc
foreland basin strata, western North America: Tectonics,
v. 32, p. 1027–1048, doi:10.1002/tect.20065.
Laslett, G.M., Green, P.F., Duddy, I.R., and Gleadow,
A.J.W., 1987, Thermal annealing of fission tracks in
apatite: 2. A quantitative analysis: Chemical Geology,
v. 65, p. 1–13, doi:10.1016/0168-9622(87)90057-1.
Lawton, T.F., 1986, Compositional trends within a clastic
wedge adjacent to a fold-thrust belt: Indianola Group,
central Utah, U.S.A., in Homewood, P., and Allen,
P.A., eds., Foreland Basins: International Association
of Sedimentologists Special Publication 8, p. 141–152.
Leary, R.J., 2011, Tectonic significance of the Ericson Sandstone, Rock Springs, WY [M.S. thesis]: Tucson, University of Arizona, 204 p.
Litwin, R.J., Turner, C.E., and Peterson, F.P., 1998, Palynological evidence on the age of the Morrison Formation, Western Interior U.S: Modern Geology, v. 22,
p. 297–319.
Liu, S., and Nummedal, D., 2004, Late Cretaceous subsidence
in Wyoming: Quantifying the dynamic component:
Geology, v. 32, p. 397–400, doi:10.1130/G20318.1.
Long, S.P., 2012, Magnitudes and spatial patterns of erosional exhumation in the Sevier hinterland, eastern
Nevada and western Utah, USA: Insights from a Paleogene paleogeologic map: Geosphere, v. 8, p. 881–901,
doi:10.1130/GES00783.1.
Ludwig, K., 2008, Isoplot 3.60: Berkeley Geochronology
Center Special Publication 4, 77 p.
Martinsen, O.J., Ryseth, A., Helland-Hansen, W., Flesche,
H., Torkildsen, G., and Idil, S., 1999, Stratigraphic
base level and fluvial architecture: Ericson Sandstone
(Campanian), Rock Springs Uplift, SW Wyoming,
USA: Sedimentology, v. 46, p. 235–263, doi:10.1046
/j.1365-3091.1999.00208.x.
May, M.T., Furer, L.C., Kvale, E.P., Suttner, L.J., Johnson,
G.D., and Meyers, J.H., 1995, Chronostratigraphy
and tectonic significance of the Lower Cretaceous
conglomerates in the foreland of central Wyoming,
in Dorobek, S.L., and Ross, G.M., eds., Stratigraphic
Evolution of Foreland Basins: Tulsa, Oklahoma, Society for Sedimentary Geology (SEPM) Special Publication 52, p. 97–110.
Merewether, E.A., Cobban, W.A., and Spencer, C.W., 1976,
The Upper Cretaceous Frontier Formation in KayceeTisdale Mountain area, Johnson County, Wyoming, in
Laudon, R.B., Curry, W.H., III, and Runge, J.S., eds.,
Geology and Energy Resources of the Powder River:
Wyoming Geological Association 28th Annual Field
Conference Guidebook, p. 33–44.
Meyers, J.H., Suttner, L.J., Furer, L.C., May, M.T., and
Soreghan, M.J., 1992, Intrabasinal tectonic control
on fluvial sandstone bodies in the Cloverly Formation (Early Cretaceous), west-central Wyoming, USA:
Basin Research, v. 4, p. 315–335, doi:10.1111/j.1365
-2117.1992.tb00051.x.
Miall, A.D., 2009, Initiation of the Western Interior foreland basin: Geology, v. 37, p. 383–384, doi:10.1130
/focus042009.1.
Miller, F.X., 1977, Biostratigraphic correlation of the Mesaverde Group in southwestern Wyoming and northwestern Colorado: Rocky Mountain Association of
Geologists 1977 Symposium, p. 117–137.
Mitrovica, J.X., Beaumont, C., and Jarvis, G.T., 1989, Tilting of continental interiors by the dynamical effects of
subduction: Tectonics, v. 8, p. 1079–1094, doi:10.1029
/TC008i005p01079.
Molenaar, C.M., and Wilson, B.W., 1993, Stratigraphic cross
section of Cretaceous rocks along the north-flank of the
Uinta Basin, northeastern Utah, to Rangely, northwestern Colorado: U.S. Geological Survey Miscellaneous
Investigations Series Map I-1797-D, scale 1:218,000.
Najman, Y., Garzanti, E., Pringle, M., Bickle, M., Stix, J.,
and Khan, I., 2003, Early-Middle Miocene paleodrainage and tectonics in the Pakistan Himalaya: Geological
Society of America Bulletin, v. 115, p. 1265–1277, doi:
10.1130/B25165.1.
Najman, Y., Carter, A., Oliver, G., and Garzanti, E., 2005,
Provenance of Eocene foreland basin sediments,
Nepal: Constraints to the timing and diachroneity of
early Himalayan orogenesis: Geology, v. 33, p. 309–
312, doi:10.1130/G21161.1.
Obradovich, J.D., 1993, A Cretaceous time scale, in
Caldwell, W.G.E., and Kauffman, E.G., eds., Evolution
of the Western Interior Basin: Geological Association
of Canada Special Paper 39, p. 379–398.
Obradovich, J.D., Matsumoto, T., Nishida, T., and Inoue, Y.,
2002, Integrated biostratigraphic and radiometric study
on the lower Cenomanian (Cretaceous) of Hokkaido,
Japan: Proceedings of the Japan Academy, ser. B, v. 78,
no. 6, p. 149–153.
O’Malley, P.J., 1994, The influence of subtle tectonic movement along basement-rooted lineaments on deposition
of the Lakota Formation, northeastern Wyoming [M.S.
thesis]: Bloomington, Indiana University, 186 p.
Omar, G.I., Lutz, T.M., and Giegengack, R., 1994, Apatite
fission-track evidence for Laramide and post-Laramide
uplift and anomalous thermal regime at the Beartooth
overthrust, Montana-Wyoming: Geological Society of
America Bulletin, v. 106, p. 74–85, doi:10.1130/0016
-7606(1994)106<0074:AFTEFL>2.3.CO;2.
Painter, C.S., and Carrapa, B., 2013, Flexural versus dynamic processes of subsidence in the North America
Cordillera foreland basin: Geophysical Research Letters, v. 40, p. 4249–4253, doi:10.1002/grl.50831.
Painter, C.S., York-Sowecke, C.C., and Carrapa, B., 2013,
Sequence stratigraphy of the Upper Cretaceous Sego
Sandstone Member reveals spatio-temporal changes in
depositional processes, northwest Colorado, U.S.A.:
Journal of Sedimentary Research, v. 83, p. 323–338,
doi:10.2110/jsr.2013.21.
Pang, M., and Nummedal, D., 1995, Flexural subsidence and
basement tectonics of the Cretaceous Western Interior
basin, United States: Geology, v. 23, p. 173–176, doi:
10 .1130 /0091 -7613 (1995)023 <0173: FSABTO>2 .3
.CO;2.
Paola, C., Heller, P.L., and Angevine, C.L., 1992, The
large-scale dynamics of grain-size variation in alluvial
basins, 1: Theory: Basin Research, v. 4, p. 73–90, doi:
10.1111/j.1365-2117.1992.tb00145.x.
Peterson, F., 1992, Chronology of the Jurassic system in the
Western Interior Basin: SEPM (Society for Sedimentary Geology) Theme Meeting, Mesozoic of the Western Interior, Fort Collins, Colorado, p. 53.
Peyton, S.L., Reiners, P.W., Carrapa, B., and DeCelles,
P.G., 2012, Low-temperature thermochronology of the
northern Rocky Mountains, western U.S.A.: American
Journal of Science, v. 312, p. 145–212, doi:10.2475/02
.2012.04.
Post, E.V., and Bell, H., III, 1961, Chilson Member of the
Lakota Formation in the Black Hills, South Dakota and
Wyoming, in, Short Papers in Geologic and Hydrologic Sciences, Articles 293–435: Geological Survey
Research 1961: U.S. Geological Survey Professional
Paper 424-D, p. D173–D178.
Reiners, P.W., 2005, Zircon (U-Th)/He thermochronometry,
in Reiners, P.W., and Ehlers, T.A., eds., Low-Temperature Thermochronology: Techniques, Interpretations, and Applications: Mineralogical Society of
America Reviews in Mineralogy and Geochemistry 59,
p. 151–179.
Reiners, P.W., and Brandon, M.T., 2006, Using thermochronology to understand orogenic erosion: Annual Review
of Earth and Planetary Sciences, v. 34, p. 419–466, doi:
10.1146/annurev.earth.34.031405.125202.
Reiners, P.W., Spell, T.L., Nicolescu, S., and Zanetti, K.A.,
2004, Zircon (U-Th)/He thermochronometry: He diffusion and comparisons with 40Ar/39Ar: Geochimica et
Cosmochimica Acta, v. 68, p. 1857–1887, doi:10.1016
/j.gca.2003.10.021.
Roberts, L.N.R., and Kirschbaum, M.A., 1995, Paleogeography of the Late Cretaceous of the Western Interior of
middle North America: Coal distribution and sediment
accumulation: U.S. Geological Survey Professional
Paper 1561, 115 p.
Roehler, H.W., 1990, Stratigraphy of the Mesaverde Group
in the central and eastern greater Green River basin,
Wyoming, Colorado, and Utah: U.S. Geological Survey Professional Paper 1508, 52 p.
Royse, F., Jr., 1993, An overview of the geologic structure of
the thrust belt in Wyoming, northern Utah, and eastern
Idaho, in Snoke, A.W., Steidtmann, J.R., and Roberts,
S.M., eds., Geology of Wyoming: Geological Survey
of Wyoming Memoir 5, p. 272–311.
Ryer, T.A., 1977, Patterns of Cretaceous shallow-marine sedimentation, Coalville and Rockport areas, Utah: Geological Society of America Bulletin, v. 88, p. 177–188,
doi: 10 .1130 /0016 -7606 (1977)88 <177: POCSSC>2 .0
.CO;2.
Sames, B., Cifelli, R.L., and Schudack, M.E., 2010, The nonmarine Lower Cretaceous of the North American Western Interior foreland basin: New biostratigraphic results
from ostracod correlations and early mammals, and
their implications for paleontology and geology of the
basin—An overview: Earth-Science Reviews, v. 101,
p. 207–224, doi:10.1016/j.earscirev.2010.05.001.
Schudack, M.E., Turner, C.E., and Peterson, F., 1998,
Biostratigraphy, paleoecology and biogeography of
charophytes and ostracodes from the Upper Jurassic
Morrison Formation, Western Interior, USA: Modern
Geology, v. 22, p. 379–414.
Shuster, D.L., Flowers, R.M., and Farley, K.A., 2006, The influence of natural radiation damage on helium diffusion
kinetics in apatite: Earth and Planetary Science Letters,
v. 249, p. 148–161, doi:10.1016/j.epsl.2006.07.028.
Smith, J.H., 1961, A summary of stratigraphy and paleontology, upper Colorado and Montanan Groups, southcentral Wyoming, northeastern Utah, and northwestern
Colorado, in Wiloth, G.J., ed., Symposium of Late
Cretaceous Rocks, Wyoming and Adjacent Areas:
Wyoming Geological Association 16th Annual Field
Conference Guidebook, p. 101–112.
Spiegel, C., Siebel, W., Kuhlemann, J., and Frisch, W., 2004,
Toward a comprehensive provenance analysis: A multimethod approach and its implications for the evolution
Geological Society of America Bulletin, Month/Month 2014
25
Painter et al.
of the Central Alps, in Bernet, M., and Spiegel, C., eds.,
Detrital Thermochronology: Provenance Analysis,
Exhumation, and Landscape Evolution of Mountain
Belts: Geological Society of America Special Paper
378, p. 37–50, doi:10.1130/0-8137-2378-7.37.
Steidtmann, J.R., and Schmitt, J.G., 1988, Provenance and
dispersal of tectogenic sediments in thin-skinned
thrusted terranes, in Kleinspehn, K., and Paola, C.,
eds., New Perspectives in Sedimentary Basin Analysis:
New York, Elsevier, p. 353–366.
Suppe, J., and Medwedeff, D.A., 1990, Geometry and kinematics of fault propagation folding: Eclogae Geologicae Helvetiae, v. 83, p. 409–454.
Suttner, L.J., 1969, Stratigraphic and petrologic analysis
of Upper Jurassic–Lower Cretaceous Morrison and
Kootenai Formations, southwest Montana: American
Association of Petroleum Geologists Bulletin, v. 53,
p. 1391–1410.
Swierc, J.E., and Johnson, G.D., 1996, A local chronostratigraphy for the Morrison Formation, northeastern Bighorn Basin, Wyoming, in Bowen, C.E., Kirkwood,
S.C., and Miller, T.S., eds., Resources of the Bighorn
Basin: Wyoming Geological Association 47th Annual
Field Conference Guidebook, p. 315–327.
Thiede, R.C., and Ehlers, T.A., 2013, Large spatial and temporal variations in Himalayan denudation: Earth and
Planetary Science Letters, v. 371–372, p. 278–293, doi:
10.1016/j.epsl.2013.03.004.
Thomson, S.N., Gehrels, G.E., Ruiz, J., and Buchwaldt, R.,
2012, Routine low-damage apatite U-Pb dating using
laser ablation–multicollector–ICPMS: Geochemistry
Geophysics Geosystems, v. 13, Q0AA21, doi:10.1029
/2011GC003928.
26
Turcotte, D.L., and Schubert, G., 2002, Geodynamics (2nd
edition): New York, Cambridge University Press, 458 p.
Uličný, D., 1999, Sequence stratigraphy of the Dakota Formation (Cenomanian), southern Utah: Interplay of
eustasy and tectonics in the foreland basin: Sedimentology, v. 46, p. 807–836, doi:10.1046/j.1365-3091
.1999.00252.x.
van der Beek, P., Robert, X., Mugnier, J.-L., Bernet, M.,
Huyghe, P., and Labrin, E., 2006, Late Miocene–Recent exhumation of the central Himalaya and recycling
in the foreland basin assessed by apatite fission-track
thermochronology of Siwalik sediments, Nepal: Basin
Research, v. 18, p. 413–434, doi:10.1111/j.1365-2117
.2006.00305.x.
Waagé, K.M., 1959, Stratigraphy of the Inyan Kara Group
in the Black Hills: U.S. Geological Survey Bulletin
1081-B, 90 p.
Way, N., 1997, Incipient structural development of the Western Interior foreland as inferred from tectonostratigraphic analysis of the Lakota Formation (Early
Cretaceous) [Ph.D. thesis]: Bloomington, Indiana University, 195 p.
Way, N.J., O’Malley, P.J., Suttner, L.J., and Furer, L.C.,
1998, Tectonic controls on alluvial systems in a distal
foreland basin: The Lakota and Cloverly Formations
(Early Cretaceous) in Wyoming, Montana and South
Dakota, in Shanley, K.W., and McCabe, P.J., eds.,
Relative Role of Eustasy, Climate, and Tectonism in
Continental Rocks: SEPM (Society for Sedimentary
Geology) Special Publication 59, p. 133–137.
Whitmeyer, S.J., and Karlstrom, K.E., 2007, Tectonic model
for the Proterozoic growth of North America: Geosphere, v. 3, p. 220–259, doi:10.1130/GES00055.1.
Willis, A., 2000, Tectonic control of nested sequence architecture in the Sego Sandstone, Neslen Formation and upper
Castlegate Sandstone (Upper Cretaceous), Sevier foreland basin, Utah, USA: Sedimentary Geology, v. 136,
p. 277–317, doi:10.1016/S0037-0738(00)00087-7.
Wolf, R.A., Farley, K.A., and Kass, D.M., 1998, Modeling
of the temperature sensitivity of the apatite (U-Th)/
He thermochronometer: Chemical Geology, v. 148,
p. 105–114, doi:10.1016/S0009-2541(98)00024-2.
York, C.C., 2010, Sedimentological characterization of
flood-tidal delta deposits in the Sego Sandstone, subsidence analysis in the Piceance Creek Basin, and U-Pb
geochronology (NW Colorado, USA) [M.S. thesis]:
Laramie, University of Wyoming, 84 p.
Zaleha, M.J., 2006, Sevier orogenesis and nonmarine basin
filling: Implications of new stratigraphic correlations
of Lower Cretaceous strata throughout Wyoming,
USA: Geological Society of America Bulletin, v. 118,
p. 886–896, doi:10.1130/B25715.1.
Zeitler, P.K., Johnson, M.N., Briggs, N.D., and Naeser,
C.W., 1986, Uplift history of the NW Himalaya as recorded by fission-track ages of detrital Siwalik zircons,
in Jiqing, H., ed., Proceeding of the Symposium on
Mesozoic and Cenozoic Geology: Beijing, Geological
Publishing House, p. 481–494.
SCIENCE EDITOR: NANCY RIGGS
ASSOCIATE EDITOR: TIMOTHY LAWTON
MANUSCRIPT RECEIVED 13 SEPTEMBER 2013
REVISED MANUSCRIPT RECEIVED 6 APRIL 2014
MANUSCRIPT ACCEPTED 6 MAY 2014
Printed in the USA
Geological Society of America Bulletin, Month/Month 2014