1
Tectonic significance of the Ericson Sandstone, Rock Springs, WY
2
Ryan Leary
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Abstract
The Ericson Sandstone was deposited in the distal Sevier foreland basin during Campanian time and is
now well exposed around the Rock Springs uplift in southwestern Wyoming. The formation is thin,
regionally extensive, and does not display the wedge shaped geometry typical of foreland basin
sediments. Devlin et al. (1993) inferred that the Ericson Formation was deposited during a period of
tectonic quiescence between movements on the Absaroka Thrust that coincided with uplift of local
Laramide structures. During this time, isostatic rebound in the thrust belt would have caused erosion in
the wedge top and proximal basin and pushed coarse sediment into the distal basin as predicted by Heller
et al. (1988). Two distinct pulses of local Laramide uplift are resolvable from sedimentary analysis of the
Ericson Sandstone. In this study, we establish a precise depositional age of the Ericson Sandstone through
detrital U-Pb zircon analysis and palynological analysis. Extensive paleocurrent analysis shows a
generally southeast transport direction, but northward indicators near the Flaming Gorge Reservoir
indicate that the Uinta Mountains were being uplifted and shedding sediment northward by Upper
Campanian time. Detailed petrographic analysis indicates that Ericson sediment was most likely derived
from erosion of Proterozoic quartzites of the Willard Thrust Sheet to the west.
18
19
20
Introduction
Extensive research has been conducted on the rocks of the Upper Cretaceous Sevier
21
foreland basin system (Roehler, 1990; DeCelles, 1994; Currie, 1997, and many others).
22
Emplacement of large thrust sheets in the Sevier fold-thrust belt exerted a first order control on
23
flexural subsidence and deposition in the basin (Liu et al., 2005; Devlin et al., 1993). Timing of
24
thrust faulting in the Sevier belt is relatively well understood (Royse et al., 1975; Wiltschko and
25
Dorr, 1983; DeCelles, 2004), and major cycles of basin sedimentation are relatively easily to
26
correlate to the established thrust history (Liu et al., 2005). However, no study has attempted to
27
directly link foreland basin strata to synorogenic rocks in the thrust belt, so correlation is
28
tentative (Devlin et al., 1993; DeCelles and Cavazza, 1999). During the Latest Cretaceous, uplift
29
of intrabasinal Laramide structures partitioned the basin and drastically changed subsidence and
2
30
sedimentation patterns (Dickinson et al., 1988; Devlin et al., 1993; Steidtmann and Middleton,
31
1991; Fan, et al., 2011). The Ericson Sandstone in the Rock Springs area is well situated both
32
geographically and temporally to record the effect on sedimentation of this major change in basin
33
architecture; deposition of the Ericson was affected not only by flexure associated with the thrust
34
belt but also by local Laramide tectonics.
35
In this study, we present detailed petrographic data and extensive paleocurrent analysis of
36
the Ericson Sandstone in order to determine sediment provenance. Detrital U-Pb zircon dating
37
aids in this interpretation and provides precise maximum depositional ages. Palynologic analysis
38
provides further depositional age information, and analysis of facies and sedimentary
39
architecture within the Ericson Sandstone provides information on basin subsidence and
40
paleogeography. Correlation of the Ericson Sandstone to equivalent strata in the thrust belt
41
requires additional work and is left to a future publication.
42
43
44
Geologic and Tectonic Setting
The Ericson Sandstone is exposed around the Rock Springs Uplift, a north-south oriented
45
doubly plunging anticline in the Green River Basin of southwestern Wyoming (Mederos et al,
46
2005). The uplift sits roughly 100 km to the east of the Sevier fold-thrust belt and was deposited
47
in the Cordilleran foreland basin (Fig. 1).
48
During the Cretaceous, subduction of the Farallon plate beneath the North American
49
continent produced a nearly continuous chain of magmatism and deformation along the western
50
edge of North American (Dickinson, 2004). The Sevier belt accommodated much of the
51
continental shortening in this system, and a large foreland basin system developed from New
3
52
Mexico into Canada (Cross, 1986). Deformation occurred in pulses along major thrust faults
53
such as the Willard, Ogden, Crawford, Absaroka, and Hogsback thrusts (Royse et al., 1975).
54
Beginning in the Campanian, basement cored Laramide uplifts began to partition the foreland
55
basin system (Dickinson and Snyder, 1978; DeCelles, 2004), drastically changing subsidence
56
and sedimentation patterns in the basin. Prior to the onset of Laramide deformation, subsidence
57
and sedimentation in the basin followed the pattern typical of flexural foreland basins in which
58
maximum subsidence takes place in the foredeep adjacent to the thrust front (Jordan, 1981;
59
Beaumont, 1981). As Laramide deformation began, dynamic subsidence rather than flexural
60
subsidence became the dominant source of sediment accommodation, and the locus of thick
61
deposition shifted ~400 km to the east (DeCelles, 2004). Deposition of the Ericson Sandstone
62
began during the late Campanian and was concurrent with this shift in deposition and with uplift
63
along early Laramide structures (Devlin et al., 1993). Although basement rocks of Laramide
64
uplifts such as the Wind River Range were not exposed until Paleocene time (Fan et al. 2011),
65
there is evidence that Laramide structures were experiencing uplift as early as 90 Ma
66
(Steidtmann and Middleton, 1991 and references therein). In particular, seismic data show that
67
strata in the Moxa Arch and the RSU are significantly truncated by base of the Ericson
68
Sandstone (Devlin et al., 1993) demonstrating that these structures were active before late
69
Campanian time.
70
71
72
73
Sedimentology and stratigraphy
The sedimentology of the Ericson Formation is documented in 36 detailed measured
sections. More than 800 paleocurrent measurements show regional paleodrainage patterns.
4
74
Measurements were made following the method outlined by DeCelles et al. (1983) in which
75
individual limbs of medium- to large-scale trough crossbeds are measured. Each paleocurrent
76
direction shown in Figs. 2-4 consists of an average of 10 individual limb measurements.
77
Standard lithofacies were documented and are listed along with physical process interpretations
78
in Table 1. The age of the Ericson Formation is based on palynology, ammonite biostratigraphy,
79
and detrital zircon U-Pb analyses.
80
81
Regional Stratigraphy
82
The Ericson Sandstone is part of the Campanian Mesa Verde Group which is composed
83
of the Blair, Rock Springs, Ericson, and Almond Formations. The Mesa Verde is a large
84
progradation-retrogradational foreland clastic wedge that thickens towards the Sevier foredeep to
85
the west (Roelher, 1990). It is bracketed by thick marine shale units: the Baxter Shale below and
86
the Lewis Shale above.
87
The Ericson Sandstone exposed in the Rock Springs Uplift is roughly 100 km east of the
88
Sevier fold-thrust belt and belongs to a group of units informally termed “long runnout coarse
89
facies.” These facies make up a set of relatively coarse-grained sandstone units that periodically
90
extend into the distal basin. Other “long runnout facies” in this basin include the Frontier
91
Formation and the Lazert/Airport Sandstone (Devlin et al., 1993, Fig. 3). These distal coarse-
92
grained facies have traditionally been interpreted as representing periods of tectonic quiescence
93
in the hinterland during which flexural rebound of the thrust belt caused reworking of proximal
94
sediments and progradation into the basin (Heller et al., 1988). During major episodes of
95
thrusting in the hinterland, tectonic loading in the thrust belt is thought to have caused rapid
5
96
flexural subsidence in the basin. This rapid increase in accommodation would have produced
97
strong retrogradation in the basin, and caused fine grained sediments to dominate the distal
98
foreland. As this new accommodation filled and the thrust belt was eroded and began to rebound,
99
coarser-grained facies would have prograded into the distal foreland.
100
Three significant thrust-controlled sedimentation cycles are exposed in the Rock Springs
101
Uplift. These cycles include the Lower Baxter Shale – Airport Sandstone, the Upper Baxter
102
Shale – Blair/Rock Springs Formation, and the Upper Almond Formation/Lewis Shale – Fox
103
Hills Formation/Lance Formation. These cycles have been proposed to correlate to movement of
104
the Crawford, Early Absaroka, and late Absaroka thrust sheets, respectively (Devlin et al., 1993;
105
Liu et al., 2005). Each cycle consists of marine shale overlain by a progradational succession of
106
marine deposits, and each is capped by a sandstone body. Although the Ericson Sandstone is
107
deposited above the Rock Springs Formation and caps the middle thrust controlled sedimentation
108
cycle, it differs significantly from other distal sandstones exposed in the Rock Springs Uplift and
109
is not considered part of the cycle (Devlin et al, 1993). The Ericson Sandstone is the coarsest unit
110
exposed in the Rock Springs Uplift, and beds containing grains up to granule size are exposed on
111
the northwest side of the uplift. Additionally, it is more erosive than any Mesa Verde unit below
112
it; Devlin et al. (1993) estimated that 150 m and 250 m of underlying strata were removed by the
113
Trail and Canyon Creek Members, respectively. This drastic shift in depositional style was likely
114
caused by Campanian uplift of the Rock Springs Uplift in conjunction with tectonic quiescence
115
in the thrust belt (Devlin et al., 1993). During this period, sediment supply would have been
116
relatively high because of continued erosion in the thrust belt, and local accommodation would
117
have been highly limited.
118
6
119
Ericson Stratigraphy
120
Trail Member
121
The Trail Member is the lowest of the three Ericson Members. It rests unconformably on
122
top of the Rock Springs Formation, and as much as 150 m of the Rock Springs Formation was
123
eroded at this surface (Devlin et al., 1993). The Trail Member is an amalgamated, very fine- to
124
medium-grained sheet sandstone with minor fine grained interbeds. It ranges in thickness from 8
125
to 134 m and is thickest in the southeast portion of the uplift (Fig. 2). Trough cross-stratified
126
sandstone (St) dominates in this member, but planar cross strata (Sp), horizontal laminations
127
(Sh), ripples (Sr), and massive units (Sm) are also present. Sandstone facies are arranged into
128
beds that are typically ~5 m thick, but some beds are as thick as 15 m and as thin as 10 cm. Most
129
beds have erosional bases; many show slight fining upward trends. Channel forms are rarely
130
preserved completely but are multistory in character. Lateral accretion elements (as described by
131
Miall, 1985) are rarely observed. Fine-grained facies consist of thin, organic-rich interbeds
132
which are most commonly present in exposures on the southeast side of the Rock Springs Uplift.
133
These interbeds are primarily composed of laminated gray or organic-rich siltstone (Fsl). Sparse,
134
poorly developed coal beds are also associated with fine-grained facies in this interval.
135
Paleocurrent indicators show a strong southeastward flow in outcrops around the Rock
136
Springs Uplift. However, northward flow is indicated in exposures near Flaming Gorge
137
Reservoir. The youngest U-Pb peak age in detrital zircon samples yields a maximum
138
depositional age of 93 Ma for the Trail Member; however, palynological and biostratigraphic
139
ages (Devlin et al., 1993) indicate that Trail deposition occurred during the Upper Campanian.
7
140
The dominance of the trough cross-bedded sandstone (St) in the Trail Member suggests
141
deposition by strong, unidirectional currents within channels (Ashley, 1990). Planar cross-
142
stratified sandstone (Sp) is interpreted to represent transverse or lingoid bars within channels
143
(Miall, 1985, Miall, 2006 p. 115). Massive and laminated sandstone (Sm, Sl) is interpreted as
144
representing rapid deposition and upper flow regime conditions in flash flood events (Miall,
145
1985, Miall, 2006 p. 120). Rippled sandstone (Sr) is interpreted to represent lower flow
146
conditions near main channel margins and in minor channels (Miall, 2006 p. 115). Sparsely
147
preserved laminated (Fsl) and massive (Fsm) silt in the Trail Member is interpreted to represent
148
overbank deposits. Erosionally based, fining-upward sequences of trough cross-beds, ripple
149
cross-stratified sandstone, and laminated shale are interpreted to represent preserved channels.
150
Complete channel sequences are rarely preserved in the Trail Member. The sheet-like
151
architecture of sandstone bodies within the Trail Member suggests that channels were laterally
152
mobile; however, the near absence of lateral accretion elements suggests that this system was not
153
meandering. The low preservation of fine grained sediments is consistent with this interpretation
154
and indicates that accommodation was low during the time of deposition.
155
We interpret the Trail Member to represent a sandy braided river system much like that
156
described as “Sand-dominated, deep perennial braided” by Miall (2006 p. 200) or of S.
157
Saskatchewan type (Cant and Walker, 1978). This interpretation is consistent with that made by
158
Devlin et al. (1993). Roehler (1990) interpreted the Trail Member to have been deposited by
159
meandering streams because of the presence of lateral accretion elements near its base. Although
160
the occasional occurrence of lateral accretion elements within the Trail Member was observed in
161
this study, these elements were not common. Additionally, the presence of such structures is not
162
necessarily inconsistent with a braided fluvial environment (Skelly et al., 2003).
8
163
164
Rusty Member
165
The Rusty Member conformably overlies the Trail Member. The Rusty Member is a
166
heterolithic interval of rocks ranging in thickness from 16 to 145 m; thickest exposures occur
167
along the southeast side of the Rock Springs Uplift (Fig. 2). This member contains the most fine-
168
grained material of any of the three Ericson members, but large sandstone bodies are still
169
present. These bodies are dominated by cross-stratified sandstone (St), but planar cross stratified
170
sandstone (Sp), massive sandstone (Sm), horizontally stratified sandstone (Sh), and rippled
171
sandstone (Sr) are also present in minor volumes. Most of the sandstone bodies in the Rusty are
172
thinner than those in the Trail or Canyon Creek Members, but laterally extensive, multi-story
173
sheet sandstones between 15 and 50 m thick are present in some locations. Tabular sandstone
174
bodies thinner than 1 m occur regularly in the Rusty Member and are mostly found within fine-
175
grained intervals. These bodies are typically very fine- to fine-grained sandstone and consist of
176
rippled (including climbing ripples), massive, or laminated sandstone. Fine grained material
177
found in the Rusty is primarily laminated or massive siltstone (Fsl or Fsm, respectively). Wood
178
fragments are common, and many of these intervals are highly organic-rich. Poorly developed
179
coal is present in some places.
180
Paleocurrent indicators show a predominantly eastward flow direction. This represents a
181
subtle shift form the dominantly southeastward flow direction in the Trail Member. The youngest
182
populations of U-Pb detrital zircon ages yield a maximum depositional age of 75 Ma (DeCelles,
183
unpublished data); these data are consistent with the palynological age of upper Campanian and
184
with previously published data (Devlin et al., 1993; Martinsen et al., 1999).
9
185
Interpretations of the sandy facies within the Rusty Member are the same as for the Trail
186
Member (above). Thick sandstone bodies dominated by trough cross-beds (St) are interpreted to
187
represent fluvial/distributary channels incising the finer grained overbank deposits. The sheet-
188
like architecture of these bodies suggests laterally mobile channels similar to those in the Trail
189
Member. However, channel sequences are more likely to be fully preserved in the Rusty Member
190
than in the Trail or Canyon Creek Members. Thin, tabular sandstone bodies dominated by
191
rippled (Sr), parallel laminated (Sl), and massive (Sm) sandstone are interpreted to represent
192
crevasses splay deposits. The abundance of these deposits indicates that natural levees were well
193
developed in this system and that avulsion events were common (Makaske, 2001). Siltstone (Fsl
194
and Fsm) is interpreted to represent overbank deposits; these deposits are much more organic
195
rich than the fine-grained intervals in the other two members. The abundance of fine grained
196
material and the more complete channel preservation indicate that sediment accommodation was
197
much higher during the deposition of the Rusty Member.
198
Sparse indications of tidal influence including inclined heterolithic beds and paired
199
mudstone/siltstone drapes as reported in Shanley et al. (1992) were observed along the northwest
200
side of the Rock Springs Uplift. However, these facies are uncommon, and neither definitively
201
indicates tidal influence. As a result, we suggest that tidal influence on the Rusty Member
202
depositional system was minor.
203
Based on channel mobility, abundant overbank facies, and frequent avulsion events, we
204
interpret the Rusty Member to represent a meandering fluvial system. The abundance of organic
205
matter and coal in addition to minor estuarine facies in the Rusty Member suggests that it was
206
deposited in a delta plain setting. This interpretation is consistent with the work of Devlin et al.
207
(1993), Martinsen et al. (1999), and Roehler (1990). Roehler (1990) interpreted the Rusty
10
208
Member to have been deposited in a floodplain rather than delta plain environment; however,
209
differences between the two styles in the rock record are slight and it is likely that this system
210
was somewhat transitional between the two deposystems.
211
212
Canyon Creek Member
213
The Canyon Creek Member is an amalgamated sheet sandstone ranging in thickness from
214
20 to 98 m (Fig. 4). Typical sandstone bed thickness is 2 – 10 m; however, 2- 5 m beds are most
215
common, and beds are generally thinner than in the Trail and Rusty Members. Beds are nearly all
216
laterally continuous. Typical sediment grain size ranges from very-fine sand to granule with
217
minor fine-grained intervals preserved in some locations. The Canyon Creek Member is
218
significantly more amalgamated and significantly coarser-grained than the Trail and Rusty
219
Members. It sits atop a sharp unconformity which Devlin et al. (1993) estimated to represent
220
~240 m of erosion. Trough cross-stratified sandstone (St) dominates the Canyon Creek Member,
221
but planar cross-stratified (Sp), massive (Sm), rippled (Sr), and horizontally laminated sandstone
222
(Sh) are present as well. Fine grained material is nearly absent from the Canyon Creek Member
223
except over a limited area in sections exposed on the northern side of the Rock Springs Uplift.
224
Here, fine grained intervals make up a minor volume of the total member thickness.
225
Paleocurrent indicators around the RSU show a general east-southeast flow direction with
226
significantly greater variation than in the Trail or Rusty Members. Paleocurrent indicators
227
measured near Flaming Gorge Reservoir show strong northward flow, and this flow direction
228
also appears in the southernmost sections of the Rock Springs Uplift. Youngest peak ages form
229
detrital zircon U-Pb dating yield a maximum depositional age of 73 Ma. This is in agreement
11
230
with published ages of deposition (Devlin et al., 1993; Martinsen et al., 1999) and with recent
231
palynological dating.
232
Interpretations of the sandy facies present in the Canyon Creek Member are the same as
233
those for the Trail Member, and the two members share very similar architectural elements. The
234
dominance of trough cross-bedded sandstone (St) in the Canyon Creek Member is interpreted to
235
indicate deposition by fluvial channels. The coarseness of the sandstone indicates that these
236
channels were part of a depositional system with higher energy than those of the Trail and Rusty
237
Members. Complete channel facies assemblages are rarely preserved in the Canyon Creek
238
Member because erosive channel bases are so densely spaced. Like in the Trail Member, the
239
extensive lateral continuity of the sandstone bodies suggests a high level of channel mobility.
240
Densely spaced erosional surfaces and the absence of fine-grained material indicates that
241
sediment accommodation was very low during Canyon Creek deposition.
242
Based on facies and sedimentary architectural analysis, we interpret the Canyon Creek
243
Member to have been deposited in a braided, South Saskatchewan type (Cant and Walker, 1978)
244
fluvial environment similar to, but of higher energy than the Trail Member’s depositional
245
environment. This is consistent with the work of Devlin et al., (1993) who also interpreted the
246
Canyon Creek Member as having been deposited in a braided fluvial system. Roehler (1990),
247
however, interpreted it to have been deposited in a meandering environment. Martinsen et al.
248
(1999) split the Canyon Creek Member into two facies packages: the lower Canyon Creek,
249
interpreted to represent braided fluvial deposits and the upper Canyon Creek, interpreted to have
250
been deposited by meandering streams. This interpretation was justified by exposures at the
251
northern end of the Rock Springs Uplift in which the Canyon Creek Member contains more fine
252
grained material. In this study, the presence of fine grained intervals is attributed to local
12
253
variation in sediment accommodation due to minor local faults and is not taken to reflect changes
254
in fluvial style over the entire study area.
255
256
257
Regional Thickness Patterns
The Ericson Formation varies widely in thickness across the study area. It is thinnest on
258
the western side of the Rock Springs Uplift and thickens to the southeast (Fig. 5). The individual
259
members of the formation follow this pattern but display more local variation. The Trail Member
260
thickens to the southeast, but shows an embayed pattern especially in the northern part of the
261
uplift (Fig. 2). The Rusty Member follows a similar pattern although there is less local variation
262
(Fig. 3). The Canyon Creek thickens to the east and southeast but shows less north-south
263
variation than either of the members below it (Fig. 4). Correlated sections across the Rock
264
Springs Uplift (Figs. 6-7) show that the thickness of the Trail and Rusty Members is much less
265
consistent that that of the Canyon Creek Member.
266
The Thickness pattern of the Ericson Formation is unusual in that it follows nearly the
267
opposite of that expected of a foreland basin deposit. Foreland basin deposits typically display
268
wedge shaped geometry with the thickest sediment accumulation occurring close to the thrust
269
front in the foredeep depozone (DeCelles and Giles, 1996). Here, the thickest accumulation
270
occurs in the area farthest from the thrust front, and the formation thins toward the proximal
271
basin. This thinning occurs at least as far as the Moxa Arch (Fan, unpublished data). Local
272
variations in thickness are likely caused by movement on numerous small faults that cut the
273
Rock Springs Uplift as inferred by Martinsen et al. (1999). The Ericson Formation’s abrupt
274
thickening on the eastern side of the uplift cannot, however, be attributed to local faulting. By
13
275
late Campanian time, dynamic subsidence caused the locus of deposition in the Sevier foreland
276
basin to shift from the Sevier foredeep to what is now south-central Wyoming, ~500 km away
277
from the thrust front. At this time, structures such as the Moxa Arch and the Rock Springs Uplift
278
were experiencing episodic uplift. These uplifts would have prevented thick accumulations of
279
sediment from being deposited in the proximal basin, and deposits would have thickened
280
drastically to the east where uplift was not occurring. The marked thickening of the Ericson
281
Formation along the eastern side of the Rock Springs Uplift likely represents the point at which
282
dynamic subsidence began to rapidly outpace uplift. Subsurface data are in agreement with this
283
conclusion and show that the Ericson Formation continues to thicken into the distal basin (Fan,
284
unpublished data).
285
286
Provenance
287
Sandstone Petrography
288
Modal framework grain compositions of 117 fine- to coarse-grained sandstone samples
289
from the Ericson Formation were determined by point-counting standard thin sections stained for
290
K-feldspar and Ca-plagioclase. Slides were counted according to a modified Gazzi-Dickinson
291
method (Ingersoll et al., 1984), and 450 grains were counted in each sample. Point-counting
292
parameters are listed in Table 2, and the most important grain types are discussed below.
293
Complete petrographic data are presented in Table 3.
294
All samples are dominated by quartzose grains including monocrystalline (Qm),
295
polycrystalline (Qp), and foliated polycrystalline quartz (Qpt) (Fig. 8). Chert is also abundant in
296
these samples and was counted as either chert (C) or black chert (Cb) based on the presence or
14
297
absence of significant carbonaceous coloration. Volcanic grains are present only in small
298
amounts and were counted as either vitric (Lv), felsic (Lv), mafic (Lm), or microlitic (Lvm).
299
Vitric grains were distinguished by their pseudo-isotropic optical characteristics and extremely
300
fine-grained texture. Mafic and felsic grains are fine-grained, and classified based on their
301
mineral compositions. Microlitic grains are rarely found but contain lath-shaped plagioclase
302
grains. K-Feldspar is present in some thin sections and makes up as much as 26% of some
303
samples. Ca-plagioclase is almost entirely absent from the Ericson Formation; where present, it
304
typically makes up <1% of framework grains. Other minerals such as muscovite, tourmaline,
305
glauconite, and pyroxene are present in trace amounts. The Ericson Formation is very poorly
306
cemented, and matrix is typically clay rich if present at all. Some samples contain minor calcite
307
cement, and small amounts of kaolinite are sometimes present. All percentages reported below
308
are normalized to ternary plots.
309
The Ericson Formation is remarkably homogeneous in terms of its petrographic
310
composition. All samples plot within the Recycled Orogen provenance field as established by
311
Dickinson and Suczek (1979) and are dominated by either monocrystalline quartz or chert (Fig.
312
9). Samples were collected from four different stratigraphic intervals: the Gottsche Tongue
313
(below the Ericson Formation) and the Trail, Rusty, and Canyon Creek Members of the Ericson
314
Formation. Sandstone composition in the Gottsche Tongue is highly uniform. Lithic grains in
315
these samples (mostly chert) make up no more than 20%; K-feldspar makes up as much 15% of
316
the Gottsche framework grains. The Trail Member is of similar composition, but chert becomes
317
more abundant in some samples. K-feldspar makes up as much as 17% of some Trail sandstones,
318
but most contain <10% K-feldspar. The Rusty Member shows an increase in K-feldspar
319
abundance, and samples containing 10-20% K-spar are not uncommon. Sandstone within this
15
320
interval also shows a minor decrease in the abundance of chert compared to the Trail and Canyon
321
Creek Members. The Canyon Creek Member contains more chert than either of the two members
322
below it and contains up to 77% lithic grains. Most Canyon Creek samples contain 0-2% K-
323
feldspar; the most K-feldspar rich sample contains 9%.
324
Whereas the general composition of the Ericson Formation is highly uniform, subtle
325
upsection and geographic trends are present (Fig. 10). The Trail and Rusty Members of the
326
Ericson contain up to 20% K-feldspar. Upsection, most samples from Canyon Creek Member
327
generally contain <5% K-feldspar. The abundance of K-feldspar within each member does not
328
vary significantly with location around the RSU, but samples from near Flaming Gorge contain
329
almost no feldspar. This raises two questions: first, what is the source of the K-feldspar? and
330
second, what about the Ericson source area was changing to decrease the abundance of feldspar?
331
Possible sources of K-feldspar include Proterozoic arkosic quartzites such as the Mutual
332
Formation exposed in the Willard Thrust Sheet (Crittenden, 1971) and the Uinta Mountains
333
(Schoenfeld, 1969). Crystalline basement rocks exposed in the Wasatch Culmination (DeCelles,
334
1994) and Laramide uplifts such as the Wind River Range (Fan et al., 2011) are also possible
335
sources of K-feldspar.
336
Paleocurrent indicators directly north of the Uinta Mountains show a consistent
337
northward paleoflow; however, this source area can be ruled out based on the low abundance of
338
feldspar near Flaming Gorge. If the Uinta Mountains were a significant source of feldspar,
339
samples from their flanks would be richer in feldspar than in more distal locations. It is also
340
possible to dismiss the Wind River Range as a potential source of K-feldspar in the Ericson
341
Formation. Although a large area of crystalline basement is exposed in the modern Wind River
342
Range, the range was not likely stripped of its sedimentary cover until early Paleocene time
16
343
(Steidtmann and Middleton, 1991; Fan et al., 2011) and so could not have shed significant
344
volumes of feldspathic sediment during Ericson Formation deposition. Paleocurrent indicators
345
also show no indication of the southwestward transport necessary to deliver sediment from the
346
Wind River Range to the Rock Springs Uplift.
347
Basement rocks exposed in the Wasatch Culmination present another possible feldspar
348
source. The Wasatch Culmination is a large, basement-cored structural culmination in the Sevier
349
hinterland, and analysis of the Hams Fork Conglomerate, inferred to be the Ericson’s proximal
350
equivalent (Devlin et al., 1993; DeCelles and Cavazza, 1999), indicates that basement rocks
351
were being eroded there as early as Campanian time (DeCelles, 1994). Although erosion of this
352
structure would have produced feldspathic sediment, basement clasts make up only 3% of the
353
total conglomerate clast content. This suggests that an additional source is necessary to provide
354
feldspathic sediment to the Ericson Formation.
355
Proterozoic arkosic quartzites of the Willard thrust sheet are the most likely sources of K-
356
feldspar in the Ericson Formation. The Willard sheet carries a 4 km thick sequence of
357
Proterozoic rocks which were exposed at the surface by Coniacian time (DeCelles, 1994).
358
Analysis of the Hams Fork Conglomerate indicates that the Willard sheet was supplying large
359
volumes of sediment to the proximal foreland by Campanian time (DeCelles and Cavazza,
360
1999). An arkosic quartzite clast found on the west side of the Rock Springs Uplift (Fig. 11) is
361
identified as belonging to the Mutual Formation and supports the idea that material derived from
362
Proterozoic quartzite units was being delivered to this part of the foreland.
363
Although it is difficult to resolve the upsection decrease in feldspar content based purely
364
on data gathered in the basin, the upsection change likely resulted from a change in source rock
17
365
or from drainage reorganization in the hinterland. The change likely reflects the progressive
366
removal of feldspathic quartzites such as the Mutual Formation. If erosion removed most of the
367
Mutual Formation exposed at the surface between deposition of the Rusty and Canyon Creek
368
Members, the thrust belt would not have been supplying K-feldspar to the foreland. If on the
369
other hand, Ericson feldspar was derived from the Wasatch culmination, the upsection change
370
may represent a reorganization of the drainage system so that Wasatch-derived material was no
371
longer deposited in the Rock Springs area.
372
373
374
Paleontology and Palynology
The age of the Ericson Formation is established primarily through ammonite
375
biostratigraphy. Using regional correlation, Gill et al. (1970) reported that the deposition of the
376
Ericson Formation began at the base of the Baculites mclearni zone and ended in the middle
377
Baculites reesidei zone. Based on correlation with the Parkman Sandstone (Gill and Cobban,
378
1966), Devlin et al. (1993) reported that the base of the Ericson Formation was deposited during
379
the middle Baculites perplexus zone and that the top of the Ericson Formation was deposited
380
during the middle Baculites reesidei zone.
381
Palynological ages of fine grained intervals within the Ericson Formation are consistent
382
with existing biostratigraphic ages (Gill et al. 1970, Devlin et al., 1993). A sample from the
383
lower Trail Member collected at section 1RS contained palynomorphs consistent with lower
384
Campanian age; a sample collected from the middle Rusty Member at section 2RS yielded an
385
age of Upper Campanian, and a sample from the upper Canyon Creek Member yielded an upper
18
386
Campanian age with excellent pollen recovery. No palynomorphs specific to the Maastrichtian
387
were found.
388
389
Detrital Zircon U-Pb Analysis
390
Methods
391
Six samples of fine- to medium-grained sand were collected from the Ericson Formation
392
(two samples from each member). One sample was also collected from a tuff just below the base
393
of the Ericson formation. All seven samples were processed by standard methods for separation
394
of detrital and igneous zircon, respectively (Gehrels et al., 2000). Samples were analyzed at the
395
University of Arizona Laserchron center by laser-ablation-multi-collector-inductively coupled
396
plasma mass spectrometry. Detailed description of analytical procedures and data reduction can
397
be found in Gehrels et al. (2008).
398
399
400
Results
Sample EM11 was collected from the Trail Member near 1RS. Analysis of this sample
401
produced 91 usable zircon ages between 74 Ma and 1.9 Ga. The two most pronounced age
402
groups consist of 18 and 24 grains clustered about peak ages of 93 and 97 Ma (Fig. 12). The
403
youngest grain analyzed yielded an age of 74±2 Ma. Ages from this sample are not particularly
404
useful in establishing a maximum deposition age because the youngest population (~93 Ma) is
405
much older than the depositional age established by other dating methods (Devlin et al., 1993).
406
Although the youngest grain age is consistent with results from other dating methods, the
19
407
youngest age peak rather than youngest single grain analysis is used in this study, as single grain
408
analysis is much less reliable (Dickinson and Gehrels, 2009a). This sample also yielded
409
significant age peaks at ~400 Ma, 1.2 Ga, 1.5 Ga, 1.7 Ga, and 2.7 Ga.
410
Sample EM8 was collected in the same location from the Rusty Member. This sample
411
yielded 88 useable ages with the youngest peak at 75 Ma (10 grains); the youngest grain was
412
dated at 74±1 Ma. For this sample, the youngest age peak is a reliable indicator of maximum
413
depositional age and agrees with other dating methods (Martinsen et al., 1999). Older
414
populations are similar to those seen in sample EM11 with the notable absence of the population
415
at ~1.2 Ga.
416
Sample EM9 was collected from the Canyon Creek Member in section 1RS; it yielded 94
417
useable ages. The youngest age peak consists of 9 grains clustered around 73 Ma, and the
418
youngest grain yielded an age of 66±6 Ma. The youngest age peak is consistent with the
419
previously determined depositional age.
420
Sample 2RS#2 was collected from the Trail Member at section 2RS near the Flaming
421
Gorge Reservoir. This sample yielded 101 usable ages. The largest grain population clusters
422
around 97.5 Ma with other significant grain populations clustering around 400 Ma, 1.05 Ga, 1.42
423
Ga, 1.77 Ga. This sample did not yield a youngest population that is useful in determining
424
depositional age.
425
Sample 2RS#4 was collected from the Rusty Member at the same location and yielded 92
426
usable ages ranging from 95 Ma to 2.9 Ga. This sample’s youngest population clustered around
427
96 Ma, so accurate depositional age cannot be determined from this set of zircons. Other
428
significant populations cluster around 159 Ma, 1.05 Ga, 1.36 Ga, 1.78 Ga, 2.07 Ga.
20
429
Sample 2RS#5 was collected from the Canyon Creek Member at section 2RS. This
430
sample yielded 93 usable ages ranging from 160 Ma to 3.3 Ga. The youngest population of
431
grains clusters around 158 Ma, and the ~95 Ma population found in all other Ericson Formation
432
samples is absent. Because no young population was found, this sample cannot provide accurate
433
depositional age information. Other major populations clustered around 411 Ma, 1.1 Ga, 1.5 Ga,
434
and 1.85 Ga.
435
436
Interpretation
437
The source of the zircon grains with U-Pb ages in the 65-75 Ma range in sample from
438
section 1RS requires some explanation. These grains are likely sourced from the Cordilleran
439
magmatic arc. This arc was the only source of active magmatism at the time, and paleocurrent
440
indicators clearly show transport from the west. However, at the onset of the Laramide orogeny,
441
flat slab subduction caused an abrupt magmatic shutoff in the arc south of what is now Idaho
442
(Dickinson, 2004, Gaschnig et al., 2010), and the California arc was almost completely shut off
443
by 80 Ma (Armstrong and Ward, 1993, Dumitru, 1991). By 75 Ma (the approximate age of the
444
youngest Ericson Formation zircon), magmatism had migrated north, and the nearest potential
445
source of the young zircons found in these samples is the Idaho Batholith; this system was most
446
active between 83 and 67 Ma (Gaschnig et al., 2010). Significant southward transport of
447
sediment from the Idaho Batholith to the Rock Springs area would have been required if these
448
grains are from this system. Paleocurrent indicators measured around the Rock Springs Uplift do
449
not show as strong a southward signal as would be expected if this were the case, and the
450
Cordilleran foreland basin system was overfilled by Late Cretaceous time (Flemings and Jordan,
21
451
1989 and references therein) precluding significant axial drainage. It is also plausible that the
452
Idaho batholith zircons were transported to the Rock Springs Uplift in ash clouds. If volcanic
453
eruptions associated with this magmatism were large enough, air fall deposits containing zircon
454
could have easily been deposited in the basin near the Rock Springs Uplift or in the proximal
455
foreland to the west where they could have been reworked in eastward-flowing rivers.
456
Older age populations analyzed from 1RS samples represent a variety of source areas
457
from around the North American continent. The zircon age distributions of Trail and Canyon
458
Creek Member samples are very similar. Both show peaks clustering around 0.5, 1-1.3, 1.5, 1.7,
459
and 2.7 Ga. These zircon clusters are likely derived from the Appalachian and Grenville age
460
belts, the anorogenic granites of the Yavapai-Mazatzal terrane, and the Archean Wyoming
461
craton, respectively (Dickinson and Gehrels, 2009). Rusty Member zircons show similar patterns
462
with two exceptions: far fewer grains of Appalachian age are present, and this sample contains a
463
much stronger Yavapai-Mazatzal age peak. These subtle changes may reflect minor drainage
464
reorganization or changing source rocks. Our data do not allow us to speculate on the exact
465
nature of this shift, but this is consistent with Rusty Member paleocurrent indicators that show a
466
stronger eastward flow than indicators in the other two members.
467
Samples collected from 2RS show a different provenance than those collected from the
468
Rock Springs Uplift. Sample 2RS#2 (Trail Member) contains a significant number of Cordilleran
469
Arc age grains and shows a similar Paleozoic and Precambrian profile to samples from 1RS. This
470
suggests that the provenance of the Trail Member was the same for sediment deposited near the
471
Uinta Mountains as for that deposited around the Rock Springs Uplift. Although paleocurrent
472
data show a northward trend from sections near the Uinta Mountains, the signal is weak, and the
473
Uinta Mountains likely contributed only minor amounts of sediment at this time. In samples
22
474
2RS#4 and 2RS#5 (Rusty and Trail Members, respectively), the zircon age profile changes. The
475
number of young zircons decreases upsection, and 2RS#5 contains no grains younger than 160
476
Ma. The relative abundance of Proterozoic grains also increases upsection, and these grains
477
constitute a much stronger signal in these samples in 1RS. This suggests that the Uinta
478
Mountains, which contain large volumes of Proterozoic quartzite, became the dominant source of
479
sediment in this area by the time the Canyon Creek Member was deposited. The absence of
480
young, Cordilleran sourced grains and strong northward paleocurrent indicators further support
481
this conclusion.
482
483
Paleogeography
484
Our current understanding of the paleogeography of southwestern Wyoming during
485
deposition of the Ericson Formation is presented in Figure (Fig. 13). Sketches are based on
486
paleocurrent measurements, facies interpretation, thickness trends, and interpretations by
487
previous workers (DeCelles and Cavazza, 1999; Roehler, 1990, Devlin et al., 1993, Martinsen et
488
al. 1999).
489
During deposition of the Trail Member, braided alluvial streams flowed across a broad
490
alluvial plain east of the Sevier thrust front. Location and existence of fluvial megafans draining
491
the thrust belt is based on work on the Hams Fork Conglomerate by DeCelles and Cavazza
492
(1999); however correlation of the Ericson Formation with the Hams Fork Conglomerate is not
493
clear-cut because surface outcrops are absent between the Rock Springs Uplift and the thrust
494
belt.
23
495
The first pulse of active uplift of the Rock Springs Uplift began in the late Campanian.
496
Other Laramide structures in the basin were active before this time (Steidtmann and Middleton,
497
1991), but there is no indication that structures other than Rock Springs Uplift and Uinta
498
Mountains significantly affected Ericson sedimentation. Northward paleocurrent measurements
499
from near Flaming Gorge Reservoir indicate that rivers were draining northward from the rising
500
Uinta Mountains. Because this signal is weaker than that preserved in the Canyon Creek
501
Member, we infer that uplift of the Uinta Mountains was relatively minor during Trail Member
502
deposition.
503
During deposition of the Rusty Member, the amount of available sediment
504
accommodation increased due to a hiatus in deformation of the Rock Springs Uplift, and the
505
system experienced minor retrogradation. A flood plain and delta plain environment dominated
506
the study area, and preservation potential of fine-grained overbank materials was high. Because
507
of the non-amalgamated nature of Ericson channel deposits near Flaming Gorge Reservoir we
508
infer that the Uinta Mountains were not active at this time. However, paleocurrent measurements
509
still indicate northward flow along the northern flank of the Uinta Mountains.
510
Subsequent uplift of the Rock Springs Uplift and Moxa Arch leveled a regional
511
unconformity across much of the foreland basin (Devlin et al., 1993). This uplift, combined with
512
the already minor flexural subsidence in the basin caused the system to prograde eastward into
513
the more distal basin. As uplift and the resulting erosion came to a halt, the Canyon Creek
514
Member was deposited by braided fluvial channels. Abundant northward paleocurrent indicators
515
near Flaming Gorge Reservoir indicate that uplift of the Uinta Mountains was more active than
516
during Trail deposition. Major displacement along the Late Absaroka thrust (Royse et al., 1975)
24
517
marked the end of Canyon Creek deposition, and renewed flexural subsidence caused a major
518
regression in the Cordilleran foreland basin (Devlin et al., 1993).
519
520
521
Tectonic Implications
The timing of thrust sheet emplacement in Sevier fold-thrust belt exerted strong control
522
on the foreland basin system in which the Ericson Formation was deposited (Roelher 1990;
523
Devlin et al., 1993; DeCelles, 1994; Liu et al., 2005). Episodic loading of the foreland
524
lithosphere by movement along major faults caused rapid flexural subsidence and large-scale
525
retrogradation. During times inactivity in the thrust belt, low availability of sediment
526
accommodation caused progradation of more proximal units into the basin (Liu et al., 2005). At
527
the end of the Cretaceous, uplift of Laramide structures partitioned the basin and developed
528
smaller-order sedimentation cycles. The deposition of the Ericson Formation is thought to
529
represent a cycle controlled by Laramide uplifts superimposed onto the larger Sevier controlled
530
subsidence regime (Devlin et al., 1993).
531
Devlin et al. (1993) invoked uplift of the RSU to explain the unconformable bases of the
532
Trail and Canyon Creek Members, the coarseness of the Ericson Formation, and its high level of
533
amalgamation. Mederos et al. (2005) identified this uplift as the first of two major pulses of
534
uplift of the RSU; the second major pulse occurred in Paleocene-Early Eocene time.
535
Here, we argue that two separate, minor pulses of RSU exhumation are resolvable
536
through study of the Ericson Formation. The first pulse of uplift is recorded by the unconformity
537
at the base the Trail Member. During active uplift, the Rock Springs Formation was incised. As
538
uplift slowed, a small amount of sediment accommodation became available, and the Trail
25
539
Member was deposited. The Rusty Member was likely deposited during a period of structural
540
inactivity in the Rock Springs Uplift. Because the thrust belt was still experiencing a period of
541
tectonic quiescence and sediment accommodation was still low, the system retrograded only
542
slightly, and fine-grained sediments were preserved in the Ericson Formation. The unconformity
543
at the base of the Canyon Creek Member represents a second, larger pulse of uplift of the Rock
544
Springs Uplift. This movement occurred in conjunction with uplift of the Moxa Arch to the west,
545
and as much as 250 m of sediment was eroded from the Rusty Member near the Rock Springs
546
Uplift (Devlin et al., 1993). As this period of uplift slowed enough that some accommodation
547
became available, the Canyon Creek Member was deposited. In the mid-Maastrichtian, renewed
548
slip along the Absaroka thrust (late Absaroka thrusting) caused a drastic increase in flexural
549
subsidence in the basin (Devlin et al., 1993; DeCelles, 2004; Liu et al., 2005). Large amounts of
550
accommodation became available, and dominantly fine grained Almond Formation was
551
deposited as the system experienced the beginning of a major retrogradational period.
552
The Ericson Formation has been inferred to be the distal equivalent of the Hams Fork
553
Conglomerate, a Campanian-Maastrichtian syntectonic unit exposed in the Sevier thrust belt
554
(Devlin et al 1993; DeCelles and Cavazza, 1999). This correlation is based on palynological data
555
from the Hams Fork and other syntectonic conglomerates. However, more information is
556
required to positively correlate the two units. Recent preliminary paleomagnetic studies of the
557
Echo Canyon Conglomerate, believed to be Coniacian-Santonian, suggest that it may in fact be
558
Campanian in age (DeCelles and Ojha, unpublished data). This would suggest that the Echo
559
Canyon, not the Hams Fork is the proximal equivalent of the Ericson Formation.
560
26
561
Conclusions
562
1. Detrital U-Pb zircon dating and palynologic analysis of the Ericson Formation robustly
563
determine that it was deposited during late Campanian time during a time of structural inactivity
564
in the hinterland. This inactivity limited tectonic subsidence and diminished sediment
565
accommodation in the basin.
566
2. Two unconformities in the Ericson Formation record distinct pulses of uplift of the
567
Rock Springs Uplift, and paleocurrent measurements indicate that uplift of the Uinta Mountains
568
was taking place during Ericson deposition.
569
3. The Trail and Canyon Creek Members of the Ericson Formation were deposited in an
570
alluvial plain environment. The Trial and Canyon Creek Members have been inferred to
571
represent deposition in braided fluvial environments. The Rusty Member was deposited as a
572
floodplain or delta plain deposit during a minor transgressive period in the basin.
573
4. Sediment making up the Ericson Formation was derived primarily from the Sevier
574
fold-thrust Belt with minor contributions from the Uinta Mountains to the south. Composition of
575
up to 15% K-feldspar in some Ericson samples suggests that specific sources in the hinterland
576
included the Willard thrust sheet and the Wasatch culmination.
577
5. Detrital zircon grains younger than ~80 Ma were most likely derived from a magmatic
578
flare-up of the Idaho Batholith, as much of the Cordilleran magmatic arc was inactive after this
579
time.
580
581
6. Further work is required to directly correlate the Ericson to proximal synorogenic
conglomerates exposed in the Sevier wedge-top.
27
582
583
584
Acknowledgements
This research was supported by ExxonMobil, Chevron, and the University of Arizona.
585
Field assistance was provided by Matthew Morriss. Special thanks to Bill Devlin, Kurt Rudolf,
586
Damian O’Grady, and Jay Kalbas for help in the field, to Mark Pecha, Percival Gou, and
587
Gayland Simpson for help with detrital zircon analysis, and to Vladimir Torres and ExxonMobil
588
for palynomorph analysis.
589
590
References Cited
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
Armstrong, R. L., & Ward, P. L. (1993) Late Triassic to earliest Eocene magmatism in North American Cordillera:
Implications for the western interior basin, in Evolution of the Western Interior basin: Geological Association
of Canada Special Paper 39 (eds. by Caldwell, W. G. E., & Kauffman, E. G.) p. 49–72, Geological
Association of Canada.
Ashley, G. M., (1990) Classification of large-scale subaqueous bedforms: a new look at an old problem. Journal of
Sedimentary Petrology, 60, 160-172.
Cant, D. J., and Walker, R. G., (1978) Fluvial processes and facies sequences in the sandy braided South
Saskatchewan River, Canada. Sedimentology, 25, 625-648.
Crittenden, M. D., Schaeffer, F. E., Trimble, D. E., & Woodward, L. A. (1971) Nomenclature and correlation of
some Upper Precambrian and Basal Cambrian Sequences in Western Utah and Southeastern Idaho. Geological
Society Of America Bulletin, 82, 581-602.
Cross, T. A. (1986) Tectonic controls of foreland basin subsidence and Laramide style deformation, western United
States. Spec. Publ. Int. Ass. Sediment., 8, 15-39.
Currie, B. S. (1997) Sequence stratigraphy of nonmarine Jurassic – Cretaceous rocks , central Cordilleran forelandbasin system. Geological Society Of America Bulletin, 109, 1206-1222.
DeCelles, P. G. (1994) Late Cretaceous-Paleocene synorogenic sedimentation and kinematic history of the Sevier
thrust belt, northeast Utah and southwest Wyoming. GSA Bulletin, 106, 32-56.
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, 304, 105-168.
DeCelles, P. G., & Cavazza, W. (1999) A comparison of fluvial megafans in the Cordilleran (Upper Cretaceous) and
modern Himalayan foreland basin systems. Geological Society of America Bulletin, 111, 1315-1334.
DeCelles, P.G., & Giles, K.A. (1996) Foreland basin systems. Basin Research, 8, 105-123.
Decelles, P. G., Langford, R. P., and Schwartz, R. K. (1983) Two New Methods of Paleocurrent Determination from
Trough Cross-Stratification. Journal of Sedimentary Research, 53, 629-642.
Devlin, W.J., Rudolph, K.W., Shaw, C.A. & Ehman, K.D. (1993) The effect of tectonic and eustatic cycles on
accommodation and sequence- stratigraphic framework in the Upper Cretaceous foreland basin of
southwesternWyoming. Int. Assoc. Sedimentologists Spec. Publ., 18, 501-520.
Dickinson, W. R. (2004) Evolution of the North American Cordillera. Annual Review of Earth and Planetary
Sciences, 32, 13-45.
28
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
Dickinson, W. R., & Gehrels, G. E. (2009) U-Pb ages of detrital zircons in Jurassic eolian and associated sandstones
of the Colorado Plateau: Evidence for transcontinental dispersal and intraregional recycling of sediment.
Geological Society of America Bulletin, 121, 408-433.
Dickinson, W. R., & Gehrels, G. E. (2009a) 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, 288,
115-125.
Dickinson, W. R., & Suczek, C. A. (1979) Plate tectonics and sandstone compositions. Amer. Assoc. Petr. Geol.
Bull., 63, 2164-2182.
Dumitru, T. A., Gans, P. B., Foster, D. A., & Miller, E. L. (1991) Refrigeration of the western Cordilleran
lithosphere during Laramide shallow-angle subduction. Geology, 19, 1145-1158.
Fan, M., DeCelles, P. G., Gehrels, G. E., Dettman, D. L., Quade, J., and. Peyton, S. L (2011) Sedimentology, detrital
zircon geochronology, and stable isotope geochemistry of the lower Eocene strata in the Wind River Basin,
central Wyoming. Geological Society of America Bulletin, 123, 979-996.
Flemings, P. B., and Jordan, T. E. (1989) A synthetic stratigraphic model of foreland basin development. Journal of
Geophysical Research, 94, 3851-3866.
Gaschnig, R. M., Vervoort, J. D., Lewis, R. S., & McClelland, W. C. (2009) Migrating magmatism in the northern
US Cordillera: in situ U–Pb geochronology of the Idaho batholith. Contributions to Mineralogy and
Petrology, 159, 863-883.
Gehrels, G.E., (2000) Introduction to detrital zircon studies of Paleozoic and Triassic strata in western Nevada and
northern California. In: M.J. Soreghan and G.E. Gehrels, Editors, Paleozoic and Triassic Paleogeography and
Tectonics of Western Nevada and Northern California. Geol. Soc. Am. Spec. Pap., 347, 1–17.
Gehrels, G.E., Valencia, V., and Ruiz, J. (2008) Enhanced precision, accuracy, effi ciency, and spatial resolution of
U-Pb ages by laser ablation–multicollector–inductively coupled plasma–mass spectrometry. Geochemistry
Geophysics Geosystems, 9, p Q03017.
Gill, J. R., and Cobban, W. A., (1966) Regional unconformity in Late Cretaceous, Wyoming. U.S. Geol. Surv. Prof.
Pap. 550-B, 7p.
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. Geol. Surv. Prof. Pap. 667, 53p.
Heller, P. L., Angevine, C. H., and Winslow, N. S. (1988) Two-phase stratigraphic model of foreland-basin
sequences. Geology, 16, 501-504.
Ingersoll, R. V., Bullard, T. F., Ford, R. L., Grimm, J. P., Pickle, J. D., & Sares S.W. (1984) The effect of grain size
on detrital modes: a test of the Gazzi-Dickinson point-counting method. Journal of Sedimentary Petrology, 54,
103-116.
Liu, S.-F., Nummedal, D., Yin, P.-G., & Luo, H.-J. (2005) Linkage of Sevier thrusting episodes and Late Cretaceous
foreland basin megasequences across southern Wyoming (USA). Basin Research, 17, 487-506.
Love, J.D., Christiansen, A.C. (1985) Geologic map of Wyoming, US Geological Survey.
Makaske, B. (2001) Anastomosing rivers: a review of their classification, origin and sedimentary products. EarthScience Reviews, 53, 149-196.
Martinsen, O. J., Ryseth, A., Helland-Hansen, W., Flesche, H., Torkildsen, G., & Idil, S. (1999) Stratigraphic base
level and fluvial architecture: Ericson Sandstone (Campanian), Rock Springs Uplift, SW Wyoming, U.S.A.
Sedimentology, 46, 235-263.
Mederos, S., B. Tikoff, and V. Bankey (2005), Geometry, timing, and continuity of the Rock Springs uplift,
Wyoming, and Douglas Creek arch, Colorado: Implications for uplift mechanisms in the Rocky Mountain
foreland, U.S.A., Rocky Mountain Geology, 40, 167-191.
Miall, A. D., (1985) Architectural-element analysis: a new method of facies analysis applied to fluvial deposits.
Earth-Science Reviews, 22, 261-308.
Miall, A. D., (2006) The Geology of Fluvial Deposits. Springer Science + Business Media, 582p.
Pedersen, P. K., and Steel, R. (1999), Sequence stratigraphy and alluvial architecture of the Upper Cretaceous
Ericson Sandstone, Glades-Clay Basin are, Wyoming/Utah border, The Mountain Geologist, 36, 71-84.
Roehler, H. W. (1990) Stratigraphy of the Mesa Verde Group in the central and eastern Green River Basin,
Wyoming, Colorado, and Utah. U.S. Geological Survey Professional Paper, 1508, 52 p.
Royse, F. Jr., Warner, M. A., and Reese, D. L., (1975) Thrust belt structural geometry and related stratigraphic
problems Wyoming-Idaho-northern Utah. In Deep Drilling Frontiers of the Central Rocky Mountains (Ed.
Bolyard, D. W.) Rocky Mountain Assoc. Geol. 1975 Symp. 41-54.
Schoenfeld, M.J. (1969) Quaternary geology of the Burnt Fork area, Uinta Mountains, Summit County, Utah.
Master’s Thesis, University of Wyoming, 60 p.
29
676
677
678
679
680
681
682
683
684
Shanley, K. W., McCabe, P. J. & Hettinger, R. D. (1992) Tidal influence in Cretaceous fluvial strata from Utah,
USA: a key to sequence stratigraphic interpretation. Sedimentology, 39.
Skelly, R. L., Bristow, C. S., Ethridge, F. G., (2003) Architecture of channel-belt deposits in an aggrading shallow
sandbed braided river: the lower Niobrara River, northeast Nebraska. Sedimentary Geology 158, 249-270.
Steidtmann, J. R., and Middleton, L. T. (1991) Fault chronology and uplift history of the southern Wind River
Range, Wyoming: Implications for Laramide and post-Laramide deformation in the Rocky Mountain foreland.
Geological Society of America Bulletin, 103, 472-485.
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
Figure 1. Tectonic and simplified geologic map of the study area after Love and Christiansen
(1985) and DeCelles (1994).
Figure Captions
Figure 2. Paleocurrent and isopach data from the Trail Member. Shaded area represents Ericson
exposure; unfilled line represents Mesa Verde exposure.
Figure 3. Paleocurrent and isopach data from the Rusty Member. Shaded area represents Ericson
exposure; unfilled line represents Mesa Verde exposure.
Figure 4. Paleocurrent and isopach data from the Canyon Creek Member. Shaded area represents
Ericson exposure; unfilled line represents Mesa Verde exposure.
Figure 5. Isopach map of the Ericson Formation. Shaded area represents Ericson exposure;
unfilled line represents Mesa Verde exposure.
Figure 6. Correlated section across the central Rock Springs Uplift. See Fig. 1 for section
locations.
Figure 7. Correlated section across the northern Rock Springs Uplift. See Fig. 1 for section locations.
Figure 8. Photomicrographs of Ericson thin sections. Left hand image is under plane polarized
light; right hand image is under cross polarized light. Qm-monocrystalline quartz; Qppolycrystalline quartz; K-potassium feldspar; C-chert; Cb-black chert; Lvf-felsic volcanic. (A)
Section cut from Mutual Formation pebble found in 15RS (B) Coarse grained sample from 18RS
(C) Quartzite cobble found in channel fill in 18RS (D) Sample collected from 34RS.
Figure 9. . Ternary diagrams plotting modal-framework compositions of Ericson Samples. Provenance
fields after Dickinson and Suczek (1979). RO-recycled orogen; CB-continental block; MA-magmatic arc.
Figure 10. Ternary diagrams of modal-framework composition of Ericson samples plotted by
location. Shaded area represents Ericson exposure while unfilled line represents Mesa Verde
exposure. See Figure 7 for explanation of symbols.
Figure 11. Photographs of Ericson outcrops. (A) Planar cross-stratified (Sp) sandstone (B)
Climbing ripples (Sr) (C) Channel architecture from section 22aRS (D) Incised channel and fill
documented in 18RS (E) Basal Trail unconformity near section 4RS (F) Quartzite clast identified
as Mutual Formation found in section 15RS (G) Soft sediment deformation in the Trail Member
in section 18RS.
30
723
724
725
726
727
728
729
Figure 12. Normalized probability plot of U-Pb dated detrital zircon samples from the Ericson
Formation.
Figure 13. Paleogeographic sketch maps of the Late Cretaceous foreland basin system. (A)
During Trail, (B) Rusty, and (C) Canyon Creek deposition. RSU-Rock Springs Uplift. See text
for justification and interpretation.
Idaho Batholith
Tgl
Tgl
rP
e
ak
Sn
n
lai
Wind
River
Range
Study Area
Se
v ie
Kl
atio
rm
efo
r fo
ldthru
st b
Ke
n
e lt
Twm
Tb
R
Moxa
Arch
Twm
Kmv
ive
Are
Lar a of
am
ide
D
Qs
I-80
Kmv
Kba
Dune Sand and Loess
(Quaternary)
Tm Miocene Intrusives
Bishop Conglomerate
Tbi
(Oligocene)
Tb Bridger Fm.
(Eocene)
Tgl Green River Fm
(Eocene)
Twm Wasatch Fm
(Lower Eocene)
Fort Union Fm
Tfu (Paleocene)
Lance Formation
Kl
(Upper Cretaceous)
Mesa Verde Group
Kmv
(Blair, Rock Springs,
Ericson, and Almond Fms.)
Ke Ericson (Campanian)
Baxter Shale
Kba
(Upper Cretaceous)
Location of measured
section
Qs
Tm
Tfu
Kba
Tbi
Tb
Flaming
Gorge
Reservoir
Tgl
Tfu
Figure 1
20m
60m
40m
80m
Figure 2
Trail Member
20m
40m
60m
80m
100m
100m
Figure 3
Rusty Member
Figure 4
20m
40m
Canyon Creek Member
TABLE 1. LITHOFACIES AND INTERPRETATIONS USED IN THIS STUDY†
Lithofacies
Code
Fsl
Fsm
Description
Laminated red, green, or gray
siltstone
Massive, bioturbated, mottled
siltstone, usually red; carbonate
nodules common
Siltstone, horizontally laminated, or
small ripples
Massive medium- to fine-grained
sandstone; bioturbated
Fine- to medium-grained sandstone
with small, asymmetric, 2D and
3D current ripples
Interpretation
Suspension-settling in ponds and lakes
Paleosols, usually calcic or vertic
Deposition from suspension or weak
traction current in overbank area
Bioturbated or pedoturbated sand,
Sm
penecontemporaneous deformation
Migration of small 2D and 3D ripples
Sr
under weak (~20–40 cm/s),
unidirectional flows in shallow
channels
Medium- to very coarse grained
Migration of large 3D ripples (dunes)
St
sandstone with trough crossunder moderately powerful (40–100
stratification
cm/s), unidirectional flows in large
channels
Medium- to very coarse grained
Migration of large 2D ripples under
Sp
sandstone with planar crossmoderately powerful (~40–60 cm/s),
stratification
unidirectional channelized flows;
migration of sandy transverse bars
Fine- to medium-grained sandstone Upper plane bed conditions under
Sh
with plane-parallel lamination
unidirectional flows, either strong
(>100 cm/s) or very shallow
†Modified after Miall (1978) and DeCelles et al. (1991).
Fsr
Figure 5
100
50
300
Caynon
Creek
Member
200
c
s
vf
f
m
c vc g
p c
Section 13RS
c
s
vf
f
m
c vc g
200
p c
Section 14RS
c
s
vf
f
m
c vc g
p c
200
Section 12RS
Rusty
Member
100
100
Figure 6
100
Trail
Member
c
s
vf
f
m
c vc g
p c
Section 8RS
c
s
vf
f
m
c vc g
p c
Section 9RS
c
s
vf
f
m
c vc g
p c
Section 10RS
200
100
Canyon Creek Member
100
100
100
c s
c
100
c
s
vf
f
m c vc g
s
vf
f
m c vc g
vf
f
m c vc g
p c
Section 33RS
p c
p c
Section 27RS
Section 24RS
100
c
s
vf
f
m c vc g
100
p c
200
Section 23RS
Rusty Member
100
100
c
s
vf
f
m c vc g
p c
Section 20RS
100
0
c
s
vf
f
m c vc g
p c
Section 21RS
c
s
vf
f
m c vc g
p c
Section 22RS
Base Trail Member
c
s
vf
f
m c vc g
p c
Section 26RS
c
s
vf
f
m c vc g
p c
Trail Member
Section 22aRS
c
s
vf
f
m c vc g
c
p c
s
vf
f
m c vc g
p c
100
Section 31RS
Section 30RS
20
c
c
s
vf
f
m c vc g
p c
Section 32RS
c
Figure 7
s
vf
f
m c vc g
p c
Section 29RS
s
vf
f
m c vc g
p c
Section 25RS
c
s
vf
f
m c vc g
p c
Section 7RS
TABLE 2. MODAL PETROGRAPHIC
POINT-COUNTING PARAMETERS
Symbol
Description
Qm
Qp
Qpt
Qss
Monocrystalline quartz
Polycrystalline quartz
Foliated polycrystalline quartz
Monocrystalline quartz in sandstone or
quartzite lithic grain
C
Chert
Cb
Black Chert
Ch
Chalcedony
Qt
Total quartzose grains (Qm + Qp + Qms
+ C + Cb + Ch)
K
Potassium feldspar (including perthite,
myrmekite, microcline)
P
Plagioclase feldspar (including Na and
Ca varieties)
F
Total feldspar grains (K + P)
Lvm
Mafic volcanic grains
Lvf
Felsic volcanic grains
Lvv
Vitric volcanic grains
Lvx
Microlitic volcanic grains
Lv
Total volcanic lithic grains (Lvm + Lvf +
Lvv + Lvx )
Lsh
Mudstone
Lph
Phyllite
Lsm
Schist (mica schist)
Lc
Carbonate lithic grains
Musc.
Muscovite
Lm
Total metamorphic lithic grains (Lph +
Lsm + Qpt)
Ls
Total sedimentary lithic grains (Lsh + Lc
+ C + Cb + Qss)
Lt
Total lithic grains (Ls + Lv + Lm + Qp)
L
Total nonquartzose lithic grains (Lv + Ls
+ Lph + Lsm + Lc)
Note: Accessory minerals: glauconite, tourmaline
kaolinite, zircon, pyroxene.
Sample
1RS8
1RS32
1RS101
1RS163
1RS199
1RS237
1RS
2RS68
2RS74
2RS112
2RS144
2RS175
2RS266
2RS308
3RS16
3RS145
3RS194
3RS208
4RS6
4RS12
4RS23
4RS68
4RS164
5RS73
5RS129
5RS218
5RS244
5RS330
5RS416
6RS10
6RS38
6RS136
6RS184
6RS353
7RS74
7RS86
7RS105
7RS122
7RS272
8RS18
Qt %
92.7
84.7
88.4
70.4
76.5
89.3
88.0
97.6
97.1
87.1
86.2
91.1
85.1
90.2
90.7
87.3
84.9
87.1
94.2
77.4
88.9
87.8
83.6
90.4
91.3
78.8
81.9
95.5
91.2
92.6
97.3
93.5
92.8
98.0
91.0
73.0
89.7
94.4
99.1
93.1
TABLE 3. RECALCULATED PETROGRAPHY DATA†
F% Lt % Qm % F % Lt % Qm % P % K %
2.0 5.3 78.9 2.0 19.1 97.5 1.1 1.4
1.3 14.0 70.9 1.3 27.8 98.2 0.0 1.8
2.4 9.1 74.4 2.4 23.1 96.8 0.0 3.2
11.8 17.9 56.4 11.6 32.0 82.9 2.0 15.1
7.6 15.9 68.9 7.6 23.6 90.1 0.0 9.9
0.9 9.8 60.2 0.9 38.9 98.5 0.4 1.1
5.6 6.5 46.9 5.6 47.6 89.4 0.0 10.6
0.2 2.2 89.6 0.2 10.2 99.8 0.0 0.2
0.4 2.4 79.8 0.4 19.8 99.4 0.0 0.6
4.0 8.9 76.7 4.0 19.3 95.0 0.0 5.0
3.3 10.4 63.8 3.3 32.9 95.0 0.3 4.6
2.9 6.0 76.7 2.9 20.4 96.4 0.0 3.6
1.3 13.6 64.2 1.3 34.4 98.0 0.0 2.0
3.6 6.2 65.6 3.6 30.9 94.9 0.6 4.5
4.7 4.7 78.2 4.7 17.1 94.4 0.0 5.6
0.7 12.0 27.3 0.7 72.0 97.6 0.8 1.6
2.2 12.9 62.7 2.2 35.1 96.6 0.0 3.4
1.8 11.1 47.6 1.8 50.7 96.4 0.0 3.6
1.1 4.7 85.8 1.1 13.1 98.7 0.0 1.3
16.3 6.3 69.8 16.2 14.0 81.1 0.3 18.6
0.0 11.1 69.1 0.0 30.9 100.0 0.0 0.0
0.4 11.8 72.2 0.4 27.3 99.4 0.0 0.6
9.4 7.0 72.4 9.3 18.2 88.6 0.0 11.4
6.0 3.6 80.4 6.0 13.6 93.1 0.0 6.9
3.4 5.4 82.7 3.3 14.0 96.1 0.0 3.9
15.6 5.6 64.0 15.6 20.4 80.4 0.3 19.3
11.4 6.7 58.9 11.3 29.8 83.9 0.0 16.1
0.0 4.5 82.2 0.0 17.8 100.0 0.0 0.0
0.0 8.8 29.6 0.0 70.4 100.0 0.0 0.0
4.7 2.7 79.3 4.7 16.0 94.4 0.0 5.6
1.3 1.3 69.1 1.3 29.6 98.1 0.0 1.9
2.4 4.0 68.0 2.4 29.6 96.5 0.0 3.5
0.7 6.5 49.6 0.7 49.8 98.7 0.4 0.9
0.0 2.0 54.0 0.0 46.0 100.0 0.0 0.0
5.6 3.4 77.6 5.6 16.9 93.3 0.0 6.7
18.0 9.0 58.0 17.8 24.2 76.5 0.6 22.9
3.1 7.2 56.4 3.1 40.4 94.8 0.0 5.2
0.7 4.9 55.8 0.7 43.6 98.8 0.0 1.2
0.2 0.7 75.6 0.2 24.2 99.7 0.0 0.3
4.0 2.9 85.1 4.0 10.9 95.5 0.0 4.5
Ls % Lm %
72.1 1.2
49.6 0.0
62.1 1.0
44.3 3.6
34.0 1.9
74.9 0.6
86.4 0.0
78.3 0.0
87.6 0.0
53.5 1.2
68.9 0.7
70.7 0.0
60.6 0.0
79.9 0.0
74.0 2.6
83.3 0.0
66.5 0.0
78.5 0.0
64.4 0.0
55.0 1.7
64.0 0.0
56.9 0.0
62.8 3.8
75.0 0.0
61.7 0.0
73.3 0.0
81.1 3.8
76.3 2.5
87.7 0.0
84.5 2.8
95.5 0.0
87.2 0.0
86.9 0.0
96.1 0.0
80.6 1.4
61.5 2.9
82.9 0.6
88.8 0.5
97.2 0.0
73.5 0.0
Lv %
26.7
50.4
36.9
52.1
64.1
24.6
13.6
21.7
12.4
45.3
30.4
29.3
39.4
20.1
23.4
16.7
33.5
21.5
35.6
43.3
36.0
43.1
33.3
25.0
38.3
26.7
15.2
21.3
12.3
12.7
4.5
12.8
13.1
3.86
18.1
35.6
16.6
10.7
2.75
26.5
M
T
T
T
R
R
CC
CC
RS
T
R
R
R
CC
CC
T
CC
CC
CC
T
T
T
T
CC
RS
RS
RS
T
R
CC
T
T
R
R
CC
T
T
T
R
CC
T
TABLE 3. RECALCULATED PETROGRAPHY DATA (cont.)†
Sample Qt % F % Lt % Qm % F % Lt % Qm % P % K %
8RS94
87.7 5.6 6.7 67.6 5.6 26.9 92.4 0.0 7.6
8RS190
95.1 1.6 3.3 72.2 1.6 26.2 97.9 0.0 2.1
9RS10
97.5 0.4 2.0 85.6 0.4 14.0 99.5 0.0 0.5
9RS64
94.4 2.2 3.4 70.9 2.2 26.9 97.0 0.0 3.0
9RS194
95.7 2.0 2.2 69.6 2.0 28.4 97.2 0.0 2.8
9RS230
92.4 4.2 3.3 64.2 4.2 31.6 93.8 0.0 6.2
10RS8
97.8 1.1 1.1 84.9 1.1 14.0 98.7 0.0 1.3
10RS52
95.5 1.1 3.3 79.6 1.1 19.3 98.6 0.0 1.4
11RS20
97.1 0.0 2.9 75.3 0.0 24.7 100.0 0.0 0.0
11RS120 82.9 10.1 7.0 72.5 10.0 17.4 87.8 0.0 12.2
11RS186 92.6 1.6 5.8 51.1 1.6 47.3 97.0 0.0 3.0
12RS34
91.0 3.4 5.6 70.4 3.3 26.2 95.5 0.0 4.5
12RS72
73.7 15.7 10.6 57.3 15.1 27.6 79.1 0.0 20.9
12RS81
91.4 5.3 3.3 35.1 5.1 59.8 87.3 0.0 12.7
13RS2
93.3 0.9 5.8 66.4 0.9 32.7 98.7 0.0 1.3
13RS25
94.0 3.6 2.4 84.2 3.6 12.2 95.9 0.0 4.1
14RS6
95.1 1.3 3.6 67.6 1.3 31.1 98.1 0.0 1.9
14RS51
91.9 0.7 7.4 52.7 0.7 46.7 98.8 0.0 1.3
14RS61
92.8 1.8 5.4 67.6 1.8 30.7 97.4 0.0 2.6
15RSP
88.4 11.2 0.4 82.2 11.1 6.7 88.1 0.0 11.9
15RS0
91.5 3.6 4.9 55.6 3.6 40.9 94.0 0.0 6.0
15RS38
74.7 17.7 7.6 64.9 17.6 17.6 78.7 0.0 21.3
16RS14
80.2 0.2 19.6 40.7 0.2 59.1 99.5 0.5 0.0
16RS29
74.2 12.2 13.6 66.4 12.2 21.3 84.5 0.0 15.5
16RS71
91.1 0.2 8.7 77.3 0.2 22.4 99.7 0.0 0.3
17RS38
86.7 1.6 11.8 47.1 1.6 51.3 96.8 1.4 1.8
17RS89
70.7 10.7 18.7 42.7 10.7 46.7 80.0 0.4 19.6
17RS115 91.1 1.6 7.3 19.8 1.6 78.7 92.7 7.3 0.0
18RS20
94.8 0.5 4.8 30.7 0.4 68.9 98.6 0.7 0.7
18RS62
89.2 1.1 9.7 52.0 1.1 46.9 97.9 0.0 2.1
18RS99
60.1 26.0 13.9 40.9 25.8 33.3 61.3 0.3 38.3
18RS116 86.4 3.6 10.0 17.6 3.6 78.9 83.2 4.2 12.6
18RS128 95.5 1.1 3.4 14.7 1.1 84.2 93.0 2.8 4.2
19RS51
94.9 0.2 4.9 55.6 0.2 44.2 99.6 0.0 0.4
19RS82
86.7 4.7 8.6 66.4 4.7 28.9 93.4 0.3 6.3
19RS130 91.8 2.4 5.8 78.9 2.4 18.7 97.0 0.0 3.0
20RS39
86.0 2.5 11.5 42.7 2.4 54.9 94.6 0.5 4.9
20RS64
74.8 10.5 14.7 65.1 10.4 24.4 86.2 0.0 13.8
20RS84
92.6 1.1 6.3 58.9 1.1 40.0 98.1 0.7 1.1
20RS84P 91.1 4.4 4.4 86.9 4.4 8.7 95.1 0.0 4.9
Ls % Lm %
74.8 0.0
87.2 0.0
85.5 0.0
87.6 0.0
92.2 0.0
89.4 0.0
92.1 0.0
83.7 1.2
89.2 0.0
61.3 1.3
88.3 0.5
78.4 0.9
62.2 2.5
94.8 0.0
82.3 0.0
80.0 0.0
88.6 0.0
84.8 0.5
82.6 0.0
92.6 0.0
88.0 0.0
57.1 3.9
66.9 0.0
45.3 2.1
61.4 0.0
77.9 0.0
60.5 0.5
91.0 0.0
93.2 0.0
80.6 0.0
62.3 6.8
87.6 0.0
96.0 0.0
88.9 0.5
69.8 3.2
72.6 0.0
79.4 0.0
39.8 1.9
84.6 1.1
48.7 0.0
Lv %
25.2
12.8
14.5
12.4
7.81
10.6
7.94
15.1
10.8
37.3
11.3
20.7
35.3
5.2
17.7
20
11.4
14.8
17.4
7.41
12
39
33.1
52.6
38.6
22.1
39.0
9.0
6.8
19.4
30.8
12.4
4.0
10.6
27.0
27.4
20.6
58.3
14.3
51.3
M
R
CC
R
R
CC
CC
T
T
T
R
CC
T
R
R
CC
CC
T
CC
CC
CC
T
R
T
R
CC
T
R
CC
T
T
CC
CC
CC
T
R
CC
R
R
CC
CC
TABLE 3. RECALCULATED PETROGRAPHY DATA (cont.)†
Sample Qt % F % Lt % Qm % F % Lt % Qm % P % K % Ls % Lm %
20RS85
96.4 1.4 2.3 21.8 1.3 76.9 94.2 5.8 0.0 97.1 0.0
21RS22
98.2 0.9 0.9 84.0 0.9 15.1 99.0 0.0 1.0 94.1 0.0
21RS54
77.7 14.0 8.3 68.2 13.6 18.2 83.4 0.0 16.6 50.7 7.0
21RS116 93.3 1.1 5.6 74.0 1.1 24.9 98.5 0.3 1.2 79.3 0.0
22RS10
96.2 1.6 2.2 73.3 1.6 25.1 97.9 0.0 2.1 91.2 0.0
22RS24
96.0 0.0 4.0 18.2 0.0 81.8 100.0 0.0 0.0 95.1 0.0
23RS6
95.2 0.2 4.6 34.0 0.2 65.8 99.4 0.6 0.0 93.2 0.7
23RS32
83.1 6.7 10.1 66.7 6.7 26.7 90.9 0.0 9.1 62.6 0.9
23RS70
95.9 0.2 3.9 35.1 0.2 64.7 99.4 0.0 0.6 94.2 0.0
24RS25
76.3 8.6 15.1 54.9 8.4 36.7 86.7 0.4 13.0 57.9 0.0
24RS68
95.5 2.0 2.5 71.6 2.0 26.4 97.3 0.0 2.7 91.5 0.0
25RS16
90.9 5.1 4.0 77.1 5.1 17.8 93.8 0.0 6.2 77.5 1.3
25RS42
97.3 1.6 1.1 77.8 1.6 20.7 98.0 0.0 2.0 94.6 0.0
26RS52
70.9 14.4 14.6 53.8 14.2 32.0 79.1 0.0 20.9 52.9 0.0
26RS81
97.9 1.8 0.2 24.4 1.8 73.8 93.2 2.5 4.2 99.7 0.0
27RS16
95.5 0.4 4.0 65.1 0.4 34.4 99.3 0.3 0.3 88.4 0.0
27RS55
96.2 0.9 2.9 78.4 0.9 20.7 98.9 0.0 1.1 85.7 0.0
28RS40
90.6 5.4 4.0 71.3 5.3 23.3 93.0 0.0 7.0 83.7 0.0
28RS71
83.3 13.7 3.0 72.7 13.5 13.8 84.3 0.0 15.7 76.6 0.0
28RS116 96.6 0.2 3.2 55.3 0.2 44.4 99.6 0.0 0.4 93.0 0.0
28RS154 95.3 2.5 2.2 81.3 2.4 16.2 97.1 0.0 2.9 85.9 0.0
29RS18
96.6 0.9 2.5 59.6 0.9 39.6 98.5 0.0 1.5 93.8 0.0
29RS51
97.5 1.1 1.3 84.0 1.1 14.9 98.7 0.5 0.8 91.0 0.0
30RS46
80.0 13.1 7.0 72.7 12.9 14.4 84.9 0.0 15.1 49.2 1.7
30RS73
79.2 19.0 1.8 72.2 18.7 9.1 79.5 0.0 20.5 76.5 0.0
30RS130 97.8 0.2 2.0 74.4 0.2 25.3 99.7 0.3 0.0 92.1 0.0
30RS153 94.3 0.5 5.2 43.1 0.4 56.4 99.0 0.0 1.0 90.9 0.0
31RS38
95.3 2.0 2.7 72.2 2.0 25.8 97.3 0.6 2.1 89.7 0.0
31RS85
93.8 2.4 3.8 79.8 2.4 17.8 97.0 0.0 3.0 78.8 0.0
33RS12
82.0 5.6 12.4 64.9 5.6 29.6 92.1 0.9 6.9 58.0 2.3
33RS26
97.1 0.7 2.2 65.6 0.7 33.8 99.0 0.7 0.3 93.4 0.0
34RS28
95.1 1.8 3.1 76.2 1.8 22.0 97.7 0.0 2.3 85.9 1.0
34RS124 87.9 5.8 6.3 70.4 5.8 23.8 92.4 0.0 7.6 74.3 0.0
Lv %
2.9
5.9
42.3
20.7
8.8
4.9
6.1
36.5
5.8
42.1
8.5
21.3
5.4
47.1
0.3
11.6
14.3
16.3
23.4
7.0
14.1
6.2
9.0
49.2
23.5
7.9
9.1
10.3
21.3
39.7
6.6
13.1
25.7
M
CC
T
R
CC
T
T
T
T
CC
R
CC
T
T
R
CC
CC
CC
RS
RS
T
T
T
T
T
R
CC
CC
RS
T
CC
CC
T
R
Sample
34RS240
36RS9
36RS10
36RS35
†M marks Stratigraphic interval. RS: Rock Springs Formation, T: Trail Member, R: Rusty Member, CC; Canyon Creek Member
TABLE 3. RECALCULATED PETROGRAPHY DATA (cont.)†
Qt % F % Lt % Qm % F % Lt % Qm % P % K % Ls % Lm % Lv % M
93
98
98
85
1.8 5.6 66.9 1.8
1.3 0.9 84.4 1.3
0.2
2 44.4 0.2
7.6 7.3 61.1 7.6
31 97.4 0.3 2.3
14 98.4 0 1.6
55 99.5 0 0.5
31
89 0 11
82
94
96
76
0 18 CC
0 6.3 T
0 3.6 T
0 24 T
Figure 8
Figure 9
Qt
Qm
CB
CB
RO
RO
MA
F
Lt F
Qm
P
MA
Canyon Creek Member
Rusty Member
Trail Member
Rock Springs Formation
K Lv
Figure 10
L
Lm
Ls
Qm
Qm
Figure 11
24RS
22aRS
22RS
23RS
21RS
20RS
Long Canyon
28RS
32RS
19RS
18RS
27RS
26RS
33RS
25RS
17RS
31RS
Qm
F
LtF
30RS
Lt
29RS
36RS
16RS
7RS
15RS
6RS
14RS
12RS
13RS
Qm
34RS
4RS
1RS
8RS
Qm
F
Lt
9RS
10RS
11RS
F
5RS
F
3RS
Minnies
Lt
2RS
Lt
EM9 (CC)
Cordilleran
Appalachian
Yavapai-Mazatzal
Grenville
Anorogenic
1RS
EM8 (R)
Wopmay
EM11 (T)
2RS#5 (CC)
2RS
2RS#4 (R)
2RS#2 (T)
Figure 12
Age (Ma)
Trail Member
Utah
Rusty Member
A bsa
roka
Thru
st
Colorado
Absa
roka
Thru
st
Figure 13
Canyon Creek
Member
Appendix A: Measured Section
Key
n=17
Soft Sediment Deformation
Massively Bioturbated
Burrowed
Clay Clasts
Clay Drapes
Root Casts
Wood Fragment
Coarse Lag
Eroded/Scoured Base
Sand
Silt/Clay
Carbonaceous Silt/Clay
Coal
Covered Section
Formation/Member Boundary
Paleo Current Measurment
number of paleocurrent measurments
Petrographic Sample
U-Pb detrital zircon age
Pollen Sample
50
150
100
Sm
1RS100P
250
200
Src
300
1RS199
St
Fsl
St/Sh
Fsl
St
Sh/Sr
Rusty
Member
Sr
St
163. 14E
Sh/Sr
Sr
St
134
n=17
St
40
90
St
St
Sh
190
140
240
Fsl
290
Sr
St
1RS237
Sh
Sh
Sm
St
St
Sm
St
Sr/Sh
Src
Sh/St
Fsl
1RS32
St
St
30
Sr
Fsl
Sm
Sm
Sh
St
Sm
180
130
80
Fsl
Sh
230
280
Sm
Sh
Sh
Canyon Creek
Member
Sr
Sh
Fsm
Sh
Sm
163, 14E
St
Sm
St
St/Sr
St
St
93
n=17
Sm
Fsl
St
20
1RS19P
Sr
Sh
70
Fsl
170
120
220
St
270
Fsl
Sh
St
Sm
Sr
St
St
44
n=19
St
Sm
Fe Stone
Chips
1RS163
Sh/St
Fsl
Sm
Sh/Sr
Trail Member
10
60
Sm
160
110
St
Sr
210
Sm
8
1RS8
St
St/Sm
6
4
McCourt
2
14, 73E
0
260
Sr
St
Sh
Sr
St
Sr/Fsl
Fsl
St
Sh
94
n=14
Fsl
1RS55P
Fcl
Hcs
St
Hcs/Sr
Hcs
Sr/Hcs
Sh/Sr
Hcs
c s vf f m cvcg p c
Section 1RS
Elevation: 2073 m
N41.32527
W108.94436
Fsl
50
Sm
St/Sh
c s vf f m cvcg p c
St
Sr/Fsr
St
St
1RS101
100
c s vf f m cvcg p c
150
c s vf f m cvcg p c
200
c s vf f m cvcg p c
250
c s vf f m cvcg p c
50
150
100
Sr
St
200
250
St
Sr/Sh
Rusty
Member
Sh
2RS144
290
340
Sh
St
St
Sh
Fsl
Sr/Sh
80
n=13
Sr
40
350
St
Sr/Sh
Hcs
Gotche/
Transition
Member
300
90
Hcs
St
190
140
240
Sh
St
Fsl
Sr
St
Sh
St
Fsl
Sr
Fsl
St
Fsl
Large
Bar Forms
St
Sr (vf)
St
30
St (m)
Sm
Fsl
St
2RS26P
St
230
Canyon
Creek
Member
Sr
Fsl
280
Sr
Fsl
Sr
Sh/Sr
St
St
2RS175
2RS74
St
St
St
Fsl
St
170
120
70
St
Sh/Sr
2RS222P
St
Sh
Sr
St
Sh
St
Trail
Member
330
St
Fsm
2RS226
Sr
20
180
130
80
270
220
320
Fsl
Sr
St
Fsl
2RS68
Sh
St
Sr
St 295
n=7
St
St
St
St
McCourt
Sand
2RS112
Sh
Hcs?
Sh
Sh
St
St
10
Hcs
60
110
Sr
Sh
160
210
260
2RS308
Fsl
St
Sh
St
2
18, 0N
0
St
St
Sh
Sh
Sh
Sh
c s vf f m cvcg p c
50
Section 2RS
Elevation: 2055 m
N41.00649
W109.22824
Sr
Fsl
Sr
Fsl
Sr
Sr
c s vf f m cvcg p c
Sh
Sr/Sh
Sr
6
4
310
St
St
8
Sh
Sr
St
St
Sh
St
St
100
c s vf f m cvcg p c
150
c s vf f m cvcg p c
Sr
200
c s vf f m cvcg p c
250
St
c s vf f m cvcg p c
300
c s vf f m cvcg p c
50
St
150
100
200
St
250
St
Sh
Sr
337
n=7
Sr
Fsl
St
3RS194
332
n=10
3RS145
Fsl
St
Sh
St
40
140
90
Sr/Sh
190
36
n=11
240
Sh
St
Sr
Fsl
Sh
Sr
Sr
Sh/Sr
St
Sh/Sr
Fsl
Canyon
Creek
Member
Sr
St
St
Sm
Sr
30
Fsl
Sr
Sm
Sh
230
St
Sr
Sm
180
130
80
St
St
295
n=9
Sm
St
Sr
Rusty
Member
St
Fsl
Sr
Sh
Sh
St
Sh
20
322
n=7
Sm
Sr
Sr
170
120
70
220
Sm
St
Trail
Member
Poor
Exposure
3RS16
Sh
Sh
Sr
Sh
Sh
St
Sh/Sr
St
10
Hcs
60
110
Sm
210
St
Sh
8
160
Sr
Sh
St
Sm
St
6
3RS208
St
Sh
Fsl
4
St
Fsl
38, 181N
2
Sh
Sr
Sr
Fsl
0
Sh
c s vf f m cvcg p c
Section 3RS
Elevation: 1906 m
N40.99989
W109.51111
St
50
c s vf f m cvcg p c
100
c s vf f m cvcg p c
150
Sr
Sr/St
c s vf f m cvcg p c
200
c s vf f m cvcg p c
50
150
100
St
200
Sh
Sh
250
300
Sm
St
St
160
n=11
St
Sh
Sm
Fsl
St
Sh
Sr
St
Sr
140
90
St
St
Fsl
Sr
Fsl
Fsl
Sr
Sh
Sr
40
St
190
Fsl
St
Fsl
St
St
Sr
St
Sr
Sr
Sh
290
240
St
Sr
Sr
Fsl
St
Sh
St
St
St
St
St
St
St
St
30
130
80
St
Rusty
Member
St
St
St
4RS126
Sh
St
149
St n=14
St
Sh
Sh
Sh
St
St
St
St
St
St
Sr
20
St
70
Sm
280
230
St
St
4RS23
180
Sm
St
Sr
St
120
170
270
220
Sr/Sh
St
4RS68
Sh
St
Sr
St
Sr/Sh
St
Sr
Sr
St
Sm
Sh
Fsl
Sh
Trail
Member
10
Fsl
60
Sh
St
160
110
Sr/Sh
St
Sm
4
'Flaggy'
St
Sh
Sm
Fsl
St
St
St
Sh
Fsl
St
4RS2P
4, 94E
0
St
Sm
Sh
2
St
Sm
6
St
St
c s vf f m cvcg p c
Section 4RS
Elevation: 2073 m
N41.35558
W108.92689
260
210
St
St
4RS6
St
St
Sr
8
St
Canyon
Creek
Member
4RS164
50
c s vf f m cvcg p c
100
c s vf f m cvcg p c
150
c s vf f m cvcg p c
200
Sm
c s vf f m cvcg p c
'Flaggy'
250
c s vf f m cvcg p c
150
100
50
200
250
300
350
Sh
St
St
St
Sh
Sh
St
5RS244
Trail
Member
Sh
40
90
Sh
140
Sr/Sh
190
Sh
Sr
290
240
340
St
St
Sr
Sr
Sh
Sh
St
St
Sh
St
Hcs
St
Sr
Rusty
Member
St
30
130
80
Hcs
Sm/Sh
5RS129
Sm
180
280
230
330
St
5RS330
St
Sh
Sm
St
5RS73
Sh
St
170
120
70
20
St
Sm
Sh
270
220
320
Sm
5RS218
Sr
St
Sh
St
Sr
St
St
St
St
St
10
Sr
60
110
Sh
160
260
210
Sh
310
82
n=9
Sh
8
St
St
Hcs
6
Sh
Hcs
4
Hcs
Fsl
Sr
Sh
2
67, 2N
0
St
Sr Wave
Ripples
St
c s vf f m cvcg p c
Section 5RS
Elevation: 1863 m
N40.98739
W109.58135
Sh
Sh
Sr
50
c s vf f m cvcg p c
100
c s vf f m cvcg p c
150
c s vf f m cvcg p c
200
c s vf f m cvcg p c
250
c s vf f m cvcg p c
300
c s vf f m cvcg p c
450
400
St
St
440
390
St
St
St
380
430
370
420
Section hits water.
Not top of Ericson
St
St
5RS416
St
360
410
Sh
St
St
St
St
Sm
350
Section 5RSpg2
Elevation: 1863 m
N40.98739
W109.58135
c s vf f m cvcg p c
400
c s vf f m cvcg p c
150
100
50
200
250
300
350
St
St
4, 303E
Sr
St
24, 75E
160
n=15
Sh
Fsl
St
St
St
St
St
Fsl
Sh
St
St
40
Sh
St
240
Sr
290
St
340
Elev. 2121m
N41.47308
W108.83605
St
St
6RS38
190
140
90
Sh
16, 100E
6RS136
68
St n=13
St
St
8, 78E
98
n=12
6RS184
St
Sr
180
130
80
Sm
Sh
Sr
Fsl
St
Sm
St
St
30
St
Sh
St
St
280
230
Laterally
Limited
St
330
Sr
Sr
St
Sr
St
St
St
Sr
Sr
Sh
Sr
20
Canyon
Creek
Member
Sr
Fsl
St
St
St
Epsilon
x-beds
6RS71P
120
70
Fsl
Sh
170
270
220
320
Sh
Sr
St
Sm
Fsl
St
Sh
Sr
St
Sm
Sr
St
St
Trail
Member
St
Sr
10
Fsl
60
Sh
6RS10
160
110
St
260
310
St
Fsl
8
210
Sl
20, 85E
6
4
Fsl
Sh
Sr
Fsl
Fsl
St
Rusty
Member
Sh
Sh
Sh
St
Sm
2
0
Fsl
Sr
Sl
c s vf f m cvcg p c
Section 6RS
Elevation: 2107 m
N41.47778
W108.85423
St
50
c s vf f m cvcg p c
Sh
Fsl
Sr
Fsl
100
c s vf f m cvcg p c
150
Sr
c s vf f m cvcg p c
200
c s vf f m cvcg p c
250
c s vf f m cvcg p c
300
c s vf f m cvcg p c
450
400
Sh
St
St
440
390
Sh
Sr
Sr
St
Sh
St
380
430
Sm
Sm
St
370
420
St
St
St
360
410
St
St
6RS353
St
350
St
c s vf f m cvcg p c
400
c s vf f m cvcg p c
Section 6RS pg2
150
100
50
200
250
300
Sr
Sr
St
Sh
St
Fsl
Sh
Fsl
Sh
Coal
Sr
Sr
Sh
Sh
Sm
St
Fsl
Sm
Sh
Fsl
40
90
Sh
190
140
St
240
St
290
St
Sl, Fsl
St
St
Sl, Fsl
St
St
Sh
7RS186
Sp
St
St
St
St
St
Sh
30
130
80
Sp
St
St
Canyon
Creek
Member
St
180
230
St
280
St
St
Sr
Sr
St
Sp
St
Sh
St
StS
Sr
St
70
20
St
St
Strong calcite
cement
St
Sr
7RS122
St
St
7RS272
St
St
Trail
Member
Strong silica
cement
170
120
Fe Stone
220
Sh
270
St
St
St
Fsl
St
St
Fsm
St
St
Sm
Rusty
Member
Fsm
10
Sh
Sh
St
Sh
60
St
Fsl
St
St
St
St
160
110
260
210
Sr
8
Sh
St
St
Sr
St
Sp
Fsl
Sh
6
Sm
c s vf f m cvcg p c
Section 7RS
Elevation: 2251 m
N41.54854
W108.81279
Sh
Fsl
Fsl
St
Fsl
Sr
Fsl
9, 74E
103
St n=17
7RS54P
Sr
Fsl
2
0
St
7RS105
Fsl
4
St
Sl
Fsl
50
c s vf f m cvcg p c
100
Sh
c s vf f m cvcg p c
Sh
150
c s vf f m cvcg p c
200
c s vf f m cvcg p c
250
13
n=15
c s vf f m cvcg p c
150
100
50
200
250
Sr
St
Sr
Sh
Sh/Sr
St
8RS94
Sh/Sr
Sm
40
Sh
St
Sh
Sh
190
140
90
St
Rusty
Member
Canyon
Creek
Member
St
80
30
240
St
Sh
Sr
St
St
St
8RS190
(error)
130
180
230
120
170
220
160
210
Sh
Sh
St
St
Sh
St
St
St
20
St
70
St 112
n=15
Sr
Sh
8RS18
St
Sh
Sh
Sh
St/Sp
12, 60N
Trail
Member
Sp
Sp
Sr/Sl
10
60
St
110
8, 91E
St
Sl
8
Fsl
St
St
St
St 62
n=16
St
6
Sr/Sl
St
4
St
Sp
Sh
Sp
2
15, 140 S
0
St
Sh
Sh/Fsl
c s vf f m cvcg p c
Section 8RS
Elevation: 2220 m
N41.29943
W108.97411
St
St
Sr
50
c s vf f m cvcg p c
100
c s vf f m cvcg p c
150
c s vf f m cvcg p c
200
c s vf f m cvcg p c
150
100
50
Sm
200
St
250
300
St
St
St
Sm
Sh
Sr
Sr
Sm
Sr
Canyon
Creek
Member
St
Fsl
Sm
St
9RS194
St
St
St
St
Flaggy
Sr
St
Sm
St
40
90
Sh
St
140
Fsl
190
St
Sh
St
Sr
St
80
St
Sh
St
Sl
St
Sm
130
Sr
St
Sr
180
Fh
Sm
Sh
Sm
St
170
120
Sm
St
Sr
Sr
Sh
Sh
Fsl
60
St
Sh/Fsl
Sr
St
St
Sr/Sh
Sm
Fsl
9RS64
9RS11P
Sp
St
Sm
St
110
Rusty
Member
Fsl
St
Elev: 2120m
N41.28163
W108.94429
160
260
210
Sl
St
St
Sl
St
St
St
Sh
Sr
Sl
Sh
Sl
Flaggy
Sh
Sp
2
Sh
St
St
Sr
St
St
St
St
St
9, 37N
0
St
Fsl
Sr
St
4
270
220
St
St
6
128
n=14
St
St
Sr/Sh
Sm
St
St
St
St
70
Trail
Member
280
St
St
St
20
8
St
Sl/Fsl
St
St
St
10
230
Sh
St
9RS10
St
9RS230
Sh
St
Sh
St
St
Sr
Sr
St
Sh
St
Sh/Fsl
30
Coaly
Fsl
St
Sh
290
St
Sl
Sm
St
Fsl
Fsl
St
240
St
St
St
Sm
Sl
80
n=15
Sh/Fsl
20, 25N
c s vf f m cvcg p c
Section 9RS
Elevation: 2108 m
N41.27413
W108.94288
50
St
c s vf f m cvcg p c
100
c s vf f m cvcg p c
150
St
c s vf f m cvcg p c
St
200
c s vf f m cvcg p c
250
St
c s vf f m cvcg p c
100
50
150
Sr
200
250
300
350
Sr
Sh/Sr
Sh
Sm
St
Fsl
Sh
St
St
Sh
Sh
St
Sm
St
22, 140S
(suspect)
Sh
Sh
Sm
Sh
Sh
Sr
St
St
Epsilon
x-strata
40
St
Sm
Sh
140
90
Sr
Sh
Sh
190
Fsl
St
St
Sh
290
240
Sr
Sm
Sm
Fsl
Sr
St
Sr
St
St
340
Sr
Sr
Sh
St
St
St
St
St
St
Sr
Sh
St
St
Sm
30
130
80
Sm
St 90
n=12
180
Sr
St
230
St
280
330
Sh
St
St
St
St
Sm
Sh
Sh
Sm
Sm
St
St
Sh
St
Sh
St
170
120
70
20
St
Sh
Sm
St
Sl
270
220
Sh
320
Sh/Sr
St
Sh/Sr
Sm
Sm
St
Sh
Sm
Sm
Sh
Canyon
Creek
Member
Sh
10RS312DZ
Sm
St
10
60
St
10RS8
160
110
Poor
Exposure
Sp
8
Sm
Sm
Sh
Sm
260
210
St
310
Sh
Sm
St
6
Sh
St
Rusty
Member
4
Trail
Member
St
2
12, 5S
0
St
Sh
Sr
10RS52
St May not be
Base Ericson
c s vf f m cvcg p c
Section 10RS
Elevation: 2121m
N41.23276
W108.998594
St
50
St
St
St
c s vf f m cvcg p c
100
Sm
Sr
Sr
c s vf f m cvcg p c
Sh
Sl
150
Sm
c s vf f m cvcg p c
Fsl
St
St
200
c s vf f m cvcg p c
250
c s vf f m cvcg p c
300
c s vf f m cvcg p c
50
Sr
150
100
St
St
St
200
250
Sm
Sh
Sr
St
Sh
Sm
St
Flaggy
St
St
St
Sh
Flaggy
St
St
Sh
Fsl
40
St
90
St
140
St
190
240
St
St
St
Sr
Sh
St
Sh
Fsl
St
St
Canyon
Creek
Member
St
Sr
St
26
n=17
Fsl
St
St
St
11RS180
St
St
St
180
130
80
30
Fsl
St
St
St
Sp
Sr
St
20
9, 22N
Flaggy
St
St
Fsl
Flaggy
St
St
8
n=17
St
Sr
St
11RS20
230
11RS120
St
170
120
70
St
Sm
St
St
Sr
Sh
220
Flaggy
Sh
Sh/Sr
St
St
Fsl
Fsl
St
St
St
St
St
St
Trail
Member
10
8
St
St
60
4
2
11RS0P
St
Sh
Sh
Sm
Sm
St
Sr
St
St
Sm
Sr/Sh
St
Coal
Fsl
0
210
Rusty
Member
Sr
Sh
Fsl
Sl
Sr
St
Sm
Sh
160
110
St
Sr
Sh
6
St
Sh
St
c s vf f m cvcg p c
Section 11RS
Elevation: 2220m
N41.21599
W108.98859
50
Sr
St
c s vf f m cvcg p c
100
c s vf f m cvcg p c
150
c s vf f m cvcg p c
200
Sr
Sm
c s vf f m cvcg p c
100
50
332
n=8
Flaggy
St
12RS97DZ
St
St
Rusty
Member
St
40
90
St 328
n=15
12RS38DZ
St
St
12RS34
Sr
12RS81
St
80
Sr
St
30
Sm
120
n=19
Sl
Sr
St
Sm
St
Trail
Member
Caynpn
Creek
Member
12RS74DZ
Sh
St
12RS72
St
12RS21DZ
Fsl
Sr
Coal
20
St
Fsl
Sr
Fsl
Sh
70
Sh
12RS79DZ
Sr/Fsl
Sr
Fsl
Fsl
Sr
St
Sm
Sm
10
60
Sr
St
8
Sr
Coal
Fsl
Sr
Sr
6
St
St
4
Coal
Elev. 2014m
N41.44011
W109.24607
Sr
2
St
3, 41S
0
12RS51DZ
Fsl
c s vf f m cvcg p c
Section 12RS
Elevation: 2237m
N41.44338
W109.23159
50
Sr
Sr
c s vf f m cvcg p c
50
St
34
n=16
Sr
St
40
St
St
St
30
St
Sh
St
13RS26
St
Fsl
20
10, 100W
St
St
St
Canyon
Creek
Member
10
St
Sr
St
8
6
St
4
St
St Not base of
CC Member
13RS2
2
0
St
St
101
n=13
c s vf f m cvcg p c
Section 13RS
Elevation: 2023m
N41.42309
W109.23912
100
50
Fsl
St
St
Sr
Fsl
40
90
St
Sr
80
30
Sm
Sm
Sm
Rusty
Member
Elev. 2032
N41.45501
W109.25237
3, 65S
St
St
20
70
352
St n=17
158
n=10
St
St
St
St
Sm
St
14RS61
St
10
60
St
8
St
St
St
14RS6
Trail
Member
0
St
St
4
2
St
St
6
St
Sr
Sr
Canyon
Creek
Member
14RS51
Fsl
c s vf f m cvcg p c
Section 14RS
Elevation: 2040m
N41.45559
W109.24684
50
St
St
St
c s vf f m cvcg p c
100
50
St
Sr
Fsl
Sm
40
90
Sh
15RS38
Fe Stone
Fsl
80
30
Sh
St
Sm
Sh
Rusty
Member
Elev. 2022m
N41.46615
W109.25935
70
20
6, 35S
St
St
St
Sh/Sr
St
St
(Large
clayclasts)
St
10
St
60
St
St
8
140
n=10
St
St
348
n=12
6
St
St
4
Sr
Trail
Member
2
15RS0
0
St
Sr
Canyon
Creek
Member
St
Base trail
Sm unexposed
c s vf f m cvcg p c
Section 15RS
Elevation: 2016m
N41.46725
W109.25591
50
St
Fsl
c s vf f m cvcg p c
100
50
Canyon
Creek
Member
St
St
Sr
Sr
Fsl/Sr
Fsl
Fe-Stone
Fsl
Fsl
40
Sr
90
Fsl
Sl
Fsl
Fsl
Sm
Sl
Fsl
Fe Stone
Sl
30
80
St
Sh
16RS29
Fsl
Top C.C.
St
Fsl
St
Fsl
Sm
Sl
Fsl
Rusty
Member
20
St
16RS71
Sl
70
Sl
St
Sr
St
Sr
St
Sr
Sr
Flaggy
Sp
16RS14
St
St
St
10
60
10, 290W
10, 330W
St
St
8
St
St
6
St
St
4
Trail
Member
St
St
2
0
St
Not Base Trail
c s vf f m cvcg p c
Section 16RS
Elevation: 1969m
N41.53159
W109.24911
St
50
c s vf f m cvcg p c
150
100
50
200
St
St
St
St
Sr
Sh
Flaggy
Fsl
St
10,105W
40
Fsl
190
140
90
Sh
Sp
17RS38
17RS89
17RS88P
Fsm
St
St
Sp
Flaggy
Sp
St
10, 100W
30
St
Sh
St
Fsl
Sh
80
St
180
130
St
100
n=14
St 95
n=17
St
Fsl
St
St
131
n=18
125
St
n=14
St
Sm
St
St
Sp
20
120
70
St
St
170
St
St
St
Sm
St
Canyon
Creek
Member
St
17RS115
Sm
St
St
St
Fsl
St
10
60
115
n=11
160
110
St
Sr
Sr
St
8
18, 45S
10, 60S
6
Rusty
Member
4
St
St
Sr
15, 105W
Trail
Member
St
Fe-Stone
Sl
Fsl
Sr
St
Sl
2
Top
C.C.
St
0
c s vf f m cvcg p c
Section 17RS
Elevation: 2009m
N41.69319
W109.19548
50
c s vf f m cvcg p c
100
c s vf f m cvcg p c
150
Sr
Fsl
St
c s vf f m cvcg p c
150
100
50
Sh
St
18RS99
Fsl
St
St
130
St
n=15
Sh
St
Rusty
Member
Sm
Sh
St
Fsl
40
140
90
Sl/Sr
St
St
St
Sp
St
St
80
n=13
St
St
130
80
30
St
St
18RS128
St
112
St
n=15
Canyon
Creek
Member
Sp
St
Sr
Sp
Sh
St
Sp
Coal
St
St
St
18RS20
St
St
12, 70S
St
20
Fsl
120
70
St
St
St
St
St
St 123
n=20
St
275
n=14
18RS116
St
Sp
Sh
St
St
St
Sm
18RS62
Sm
10
St
Trail
Member
8
60
110
Sm
Fsl
St
St
6
Sm
Sh
Sm
Fsl
4
Fsl
2
Sm
St
0
c s vf f m cvcg p c
Section 18RS
Elevation: 2030m
N41.72111
W109.18857
50
c s vf f m cvcg p c
100
c s vf f m cvcg p c
50
100
St
150
Fsl
St
Fsh
St
Sm
St
St
Fsl
St
St
40
140
90
St
Fsl
Sr
Sr
19RS87P
St
Fe-Stone
Sr
Fe-Stone
Fsl
Fsl
St
19RS82
St
19RS130
St
130
80
30
St
10, 87W
St
St
Fsl
St
Sh/Sr
St
St
Sh/Sr
Rusty
Member
Sr
Fe-Stone
Trail
Member
Flaggy
Sm
St
70
20
120
114
n=15
St
St 96
n=10
St
St
St
94
n=14
St
St
St
St
10
St
119
n=20
60
St
St
St
110
St
St
Black Shale
Fsl
8
St
St
6
4
Sp
St
St
144
n=12
2
St
0
19RS51
c s vf f m cvcg p c
Section 19RS
Elevation: 2050m
N41.73174
W109.18954
50
St
c s vf f m cvcg p c
Canyon
Creek
Member
100
St
St
Fsl
c s vf f m cvcg p c
150
100
50
Sr
Sp
Sr
Fsl
St
St
St
St
40
90
St
20RS98
Sh
St
Sh
99
St n=13
St
Sh
Sh
St
Sh
Sh
St
St
St
20RS85
St
Sh
20RS84
20RS84P
70
n=7
Sm
Sh
80
30
Rusty
Member
140
Sm
Fe Stone
Canyon
Creek
Member
Sm
Sh
130
Sm
Flaggy
Fe-Stone
St
106
n=17
Sh
St
15, 93W
Sh
St
St
20
70
Sp/St
258
n=17
120
St
Sh
St
St
Sm
Sh/Fsl
15, 85W
St
St
St
20RS64
Fsl
90
Sp n=14
Sh/Sr
10
Sp
8
60
St
110
Sr
Fe-Stone
Trail
Member
6
St
St
4
2
0
c s vf f m cvcg p c
Section 20RS
Elevation: 2097m
N41.82632
W109.16269
50
c s vf f m cvcg p c
100
c s vf f m cvcg p c
100
50
150
Sr
St
Fsl
Sr
Sm
St
21RS54
(54)
Sh
Sr
Sr
St
40
140
90
Sh
Fsl
Sr
Fsm
Rusty
Member
Sr
Fcm
Sm
Sr
30
130
80
St
Fsl
St
St
10cm Clay
Clasts
Fsl
St
St
St
St
St
St
21RS22
116
n=19
20
St
165
n=16
St
St
70
St
120
St
St
St
St
St
210
n=15
St
St
St
St
21RS116
Sr
St
St
265
St n=13
266
n=19
Sh
St
St
St
10
St
Fe-Stone
18, 45S
10, 60S
6
110
Canyon
Creek
Member
17, 120W
St
8
St
St
Fe-Stone
4
St
Sr
Chert
Coaly
Sr
116
n=14
St
Trail
Member
2
60
Fsl
St
Sh
Fe-Stone
Sh/Sr
St
0
c s vf f m cvcg p c
Section 21RS
Elevation: 2089m
N41.84151
W109.15666
50
c s vf f m cvcg p c
100
c s vf f m cvcg p c
50
100
Sr/Sh
St
100
n=16
St
40
90
St
St
St
30
80
St
St 38
22RS24
Fsl
St
n=17
St
20
70
Sh/Sr
St
St
St
St
St
Fsr
Sr
Sr
Sp
St 118
n=11
10
22RS10
60
St
Fsl
8
Sh/Sr
Trail
Member
6
Sm
12, 355N
4
2
0
St
Rusty
Member
Sh/Sr
St
St
Sh
Sm
Nodular
Weathering
Fsl
c s vf f m cvcg p c
Section 22RS
Elevation: 2147m
N41.88638
W109.09288
Fsl
St
50
St
c s vf f m cvcg p c
150
100
50
200
St
St
St
St
St
Sh
St
22aRS
145P
Fsl/Sh
St
Fsh
St
St
40
Fe-Stone
90
St
St
Fe-Stone
Canyon
Creek
Member
St
St
140
190
Sh/Sr
Fsl
St
Fsl
Sr
St
Fe-Stone
Fsl
St
30
22aRS
130P
130
80
St
Fsm
180
Sm
St
Fsl
St
120
n=18
St
Sm
St
Fe-Stone
Fsm
120
70
20
Sm
170
St
St
St
Fsm
St
St
Sh
St
St
St
Fsl
St
Trail
Member
St
Sl
Sh/Sr
Sh
Sh
Sp
Sh
Sp
10
60
Sh
Fsl
Sr
8
Rusty
Member
St
6
12, 355N
4
2
0
St
Fe-Stone
160
110
Sr
Sr
Fsl
St
Fsl
Flat
Pebble
congl.
Sh
St
St
128
n=12
St
Not Base
St Trail
c s vf f m cvcg p c
St
St
St
50
Section 22aRS
Elevation: 2173m
N41.89120
W109.09089
c s vf f m cvcg p c
100
c s vf f m cvcg p c
150
St
c s vf f m cvcg p c
50
100
Sr
Sr
Fe-Stone
Rusty
Member
Fsl
40
90
St
Fsl
St
Sr
St
St
Fsl
Sp
23RS32
St
80
30
St
Sh/Sr
St
St
St
Sr
St
Sh
Sm
St
Sm
St
St
St/Sh
St
70
20
162
n=16
72
n=13
St
Sh
23RS70
Sm
St
Sh
Fe-Stone
Sr
Sh
Sr
Trail
Member
Sr
Sr
St
St
St
10
8
12, 96W
6
St
St
60
St
23RS6
Fe-Stone
St
St 112
n=12
Canyon
Creek
Member
Sm
Sr
St
Fsl
Sr
4
Fsl
St
Sr
Sr
2
0
Not Base
Trail
c s vf f m cvcg p c
Section 23RS
Elevation: 2154m
N41.86188
W109.14443
Fsl
50
c s vf f m cvcg p c
100
50
Sr/Sh
St
St
St
Sh
Sr
Fsl
40
90
St
St
Canyon
Creek
Member
St 252
n=13
St
St
St
80
30
St
Sm
Sm
24RS25
Fe-Stone
Fsl
20
70
Fsl
Fe-Stone
St
Sr
24RS68
Fsl
Sp
Sr
Fe-Stone
Fsl
St
Sr
St
Rusty
Member
Sm
Sm
St
10
60
St
3, 50N
Sm
8
6
Trail
Member
4
Sh
St
Fsl
St
St
Sr
St
Sm
St
Sole Marks
2
St
0
c s vf f m cvcg p c
Section 24RS
Elevation: 2180m
N41.90022
W109.08164
50
c s vf f m cvcg p c
150
100
50
Sr
St
Rusty
Member
Sh/Sr
Sr
Fsl
St
St
St
St
25RS42
St
St
40
90
146
n=12
St
Sh/Sr
St
140
St
Sh
St
Sr
Sh
St
Sr
St
Sp
Sm
St
Sh
St
30
80
Sp
130
Sr
Sh
Sr
5, 100E
St
St
Sr
Sm
St
Sr
St
St
St
Sr
St
120
70
20
St
Fsr
Sh
St
25RS16
St
St
St
Trail
Member
St
10
60
St
8
6
Fcm
St
Sh
St
110
St
304
n=18
110
n=19
Fsl
St
Sh/Sr
St
Sr
St
4
Fsl
St
Sr
2
0
St
Fsl
c s vf f m cvcg p c
Section 25RS
Elevation: 2036m
N41.71047
W108.84378
St
St
50
St
c s vf f m cvcg p c
Sm
100
c s vf f m cvcg p c
100
50
Fsl
Not top C.C.
Sh/Sr
St
Sr
Fsl
St
St
Sr
Sm
St
40
90
Sh/Sr
St
Sh
Sr
St
Sm
St
St
Rusty
Member
St
Fe-Stone
St
Canyon
Creek
Member
St
St
St
26RS81
80
30
St
Fsl
Sm
St
Sr/Sh
St
20
Sr
Sm
70
St
St
St
Sm
St
St
30cm
Clay Clasts
10
60
Concretions
St
8
St
Fsl
6, 50N
6
Fsl
St
Trail
Member
4
Sr
Fsl
Sr
St
Sh/Sr
2
26RS52
St
0
c s vf f m cvcg p c
Section 26RS
Elevation: 2046m
N41.71525
W109.83076
50
Sh
Fsl
c s vf f m cvcg p c
50
100
St
St
St
Sr
St
St
40
90
Sh
Sr
Sr
St
Sh/Sr
80
30
St
Sr/St
27RS16
St
Sh
Sh
70
20
Fsm
St
Sh/Sr
27RS16
Sh/Sr
St
Sh/Sr
10
6, 50N
Sh
60
Fsl
Sr
8
6
4
Canyon
St
St
Fe-Stone
St
27RS55
Flaggy
Creek
Member
St
2
0
St
c s vf f m cvcg p c
50
St
c s vf f m cvcg p c
Section 27RS
Elevation: 2068 m
N41.71522
W109.82368
50
Sh/Sr
100
Fsl
150
Fsl
Sh/Sr
200
Fsl
Fsm
Fsl
Sh
Fsl
Sh/Sr
St
Sr
St
St
40
90
140
Sr
28RS40
Sr
St
Fe-Stone
Sh
St
Sr
St
190
Sr/Sh
Sh/Sr
St
Sr
Sh/Sr
Sh/Sr
Sh
St
Sm
Sm
30
80
Fsl
Sm
180
130
St
St
Sr
St
Fsl
St
St
Fsm
St
St
St
St
4, 55N
28RS71
Sh
20
Rock
Springs
Fm.
St
Sr
Fsm
St
St 6
n=13
120
70
Trail
Member
Fsl Leafy
St
Fe-Stone
Fe-Stone
St
Sh/Sr
Fsl
170
Rusty
Member
Sr/Sl
St
28RS116
Sm
Fsl
Hcs
Sr
Sr
St
St
Fsl
Sr
Hcs
Fsh
10
60
160
110
Fsl
St
St
8
St
Sr
Sh/Sr
6
Sm
Sh/Sr
4
2
0
Fsh
Sh
Sm
Sm
Fsl
Fsl
Sr/Sh
c s vf f m cvcg p c
Section 28RS
Elevation: 2191m
N41.77125
W108.94257
Sr
28RS154
50
Sr/Sh
c s vf f m cvcg p c
Fsm
100
c s vf f m cvcg p c
150
St
Fsl
c s vf f m cvcg p c
50
Sh/Sr
100
Sr
Sr
Sr
Sr
Sl
St
40
90
St
St
Sh
116
n=18
St
Sr
Fe-Stone
30
80
St
St
132
n=11
St
St
St
St
St
20
Sl
70
St
29RS18
St
St
Sr/Sh
St
Sh
Fe-Stone
Trail
Member
St
Sr
St
Sh/Sr
Sm
10
60
St
5, 70N
8
Sr/Fsl
6
Sm
Fe-Stone
4
St
Sh
2
St
29RS51
Sh
0
c s vf f m cvcg p c
Section 29RS
Elevation: 2051m
N41.64733
W108.79042
50
Sh
Sl
Sm
Fsl
c s vf f m cvcg p c
150
100
50
200
Fsh
5, 45N
St
St
130
n=20
30RS46
St
Sh
Sr/Sl
St
St
St
Coal
Fe-Stone
St
Sr
Sr
Sr
Sr
St
40
140
90
St
190
Sr
Sr
St
St
Sh
Sr
St
Sr
St
Canyon
Creek
Member
Sr
Sr
80
Sm
130
St
30RS130
Sm
Fsl
Sm
St
30
Sr
St
Fe-Stone
180
St
St
Sr
St
Sr
Fsl
Sr/Sh
Fsr
Fe-Stone
Sh
Sr
Sh
Sr
Sr
St
Sr
30RS73
Fsl
St
St
20
70
St
120
Fsl
Sr/Sl
170
St
Sr
St
Sh
Sr
Sm
St
Rusty
Member
St
60
St
8
2
0
Fsl
Sm
160
St
Sr
Sr
Sm
Fsh
Sh
Sh
4
110
Sh
St
St
Trail
Member
Sh
Fsl
Sh
Fsl
Sr
Sr
Sr
Fsl
Fe-Stone
Sr
St
6
St
Sr
Sr
10
St
Sh
Sr
St
St
St
Sp
Sp
Sh
Not base
Trail
c s vf f m cvcg p c
Section 30RS
Elevation: 2003m
N41.64853
W108.77113
St
St
30RS153
St
c s vf f m cvcg p c
St
St
St
50
St
100
Fsh
Sr
c s vf f m cvcg p c
150
St
c s vf f m cvcg p c
50
St
100
150
Sh
St
Sm
St
Sm
St
St 35
n=17
St
St
St
Sm
40
31RS38
140
90
St
St
Fsm
Sl/Sh
Sr
31RS34P
31RS85
St
St
St
Sm
St
30
St
80
Sh/Sr
Sr
130
St
Sr
Fsl
Sh
Sh
Sr/Sh
St
Sr
Fsl
Fsl
20
70
St
Sr
120
Fsl
Fsl
St
Sr
Sh/Sr
St
Sr
Sm
Trail
Member
Lacustrine
5, 45N
Sh
10
Fsl
Sr/Fsl
Rusty
Member
60
Sm
6
110
St
8, 50N
St
St
Fsl
8
St
Not top Rusty
St
21
n=16
St
St
4
Fsl
2
Sr
Fsm
St
Sr
St
Sh
31RS0P
0
Fsm
c s vf f m cvcg p c
Section 31RS
Elevation: 2005m
N41.68922
W108.81937
Sp
50
Sp
c s vf f m cvcg p c
St
100
c s vf f m cvcg p c
50
Sp
150
100
St
St
St
200
St
St
Sm
Fsm
Low angle
X-Strata
Fsm
St
Sr
Sm
Low angle
X-Strata
St
40
Sr
90
140
Fsl
Sm
St
190
St
Sr
Sr
Sm
Sm
17RS38P
Fsh
Sm
Sr
Sr
Sp
Swails?
180
130
80
30
Sp
Fe-Stone
St
102
n=14
St
Sh
Sh
Not top C.C.
Sh
Sh
St
Sh
Sh
St
St
20
170
120
70
St
St
Sm
St
St
Sm
St
St
St
Sm
164
n=16
St
Sr
St
Fsr
Sr
10
Fsl
St
60
6
St
St
310
n=11
Sp
Sp
Sm
Trail
Member
Fsl
c s vf f m cvcg p c
Section 32RS
Elevation: 2022m
N41.76779
W108.94262
St
Low angle
X-Strata
Sr/Sh
2
160
St
St
Sm
St
4
49
n=16
110
Sm
8
5, 65N
0
Rusty
Member
Canyon
Creek
Member
50
Sr/Sp
c s vf f m cvcg p c
100
St
c s vf f m cvcg p c
Sh
St
150
c s vf f m cvcg p c
100
50
St
Fsl
Sr
Fsl
Sr/Sh
St
40
90
St
St
1
n=10
St
Sp
St
St
St
30
Sh
80
St
St
33RS26
St
Sp
Sm
St
20
70
Sr
St
St
St
Sh
St 201
n=9
St
Fsl
St
33RS12
Fsl
10
60
8, 30N
Sh
St
8
St
6
Canyon
Creek
Member
St
4
Sp
Sr
Sh
2
Sr
Fsl
0
St 111
n=12
c s vf f m cvcg p c
Section 33RS
Elevation: 2046m
N41.69152
W108.79384
50
St
c s vf f m cvcg p c
150
100
50
200
250
300
350
Sh
Sh
Sm
Sh
St
St
Sm
St
34RS96P
St
St
Fsl
St
102
n=11
St
Sr
Rusty
Member
40
90
140
34RS240
St
190
St
St
17RS38
Fsl
290
240
Sr
St
St
Sh
Sh
Sh
Sm
St
St
Sh
St
167
n=17
Caynon
Creek
Member
Sh
St
Sr
St
Sm
Sh
Sm
St
Sm
34RS230
St
80
30
St
Sp
180
130
230
St
St
Sr
280
Fsl
330
Sh
Sh
St
Sr/Sh
St
St
Sh
Fsl
Sr/Sh
20
St
34RS230P
34RS28
Trail
Member
340
Sr
Sm
Sr
Sh
Sm
Sr
Sm
34RS124
St
St
St
St
Sh
7
n=12
St
120
70
170
St
270
220
St
320
St
St
Sr
Sh
St
St
Sr
Fsl
Sm
St
Sr/Sh
St
St
Sh
Sp
St
116
n=18
St
St
St
Sr/Fsl
St
10
60
15, 310S
Sm
Sr
Sm
Sr
Sm
260
210
St
Sh
8
160
110
310
St
St
Sm
Sh
St
6
St
Sm
4
St
St
Section 34RS
Elevation: 2108m
N41.37660
W108.91854
97
n=13
St
Fsl
c s vf f m cvcg p c
Sp
Sr
Sm
2
St
St
Sm
Fsl
34RS0P
0
St
50
c s vf f m cvcg p c
100
c s vf f m cvcg p c
150
c s vf f m cvcg p c
200
c s vf f m cvcg p c
250
St
Sp
Sp
St
c s vf f m cvcg p c
300
c s vf f m cvcg p c
50
40
36RS35
St
30
St
109
n=10
St
Sh
20
St
Sm
St 127
n=15
St
St
Sr
15, 295W
10
36RS10
36RS9
8
Sr
St
Sm
Sr
6
Fsl
4
Sr
St
Trail
Member
2
0
Sr
Bar forms
St/Fsl
Sl
c s vf f m cvcg p c
Section 36RS
Elevation: 1909m
N41.57650
W109.23797
Appendix B: U-Pb Zircon Data
EM11
EM11
EM11
EM8
EM8
EM8
EM9
EM9
EM9
2RS#2
2RS#2
2RS#2
2RS#4
2RS#4
2RS#4
2RS#5
2RS#5
2RS#5