ABSTRACT

STRATIGRAPHY AND PALYNOLOGY OF THE ALBIAN-CENOMANIAN DAKOTA FORMATION AND MOWRY SHALE, UINTA BASIN, UTAH AND COLORADO by Justin Scott Pierson The Albian-Cenomanian Dakota Formation and Mowry Shale of the Uinta Basin consist of an overall transgressive sequence of continental and marine strata that were deposited in the medial part of the Cordilleran foreland-basin system. However, complex stratigraphic relationships within the Dakota Formation and Mowry Shale, as well as complexities between both older and younger strata, have led to different interpretations regarding the large-scale stratigraphic architecture of the basin. In order to provide a better understanding of the overall stratigraphic relationships between the Albian-Cenomanian rocks of the region, palynological samples from the Dakota Formation, Mowry Shale, and overlying units were collected from the northern and southern margins of the Uinta Basin. When combined with preexisting biostratigraphic studies and regional stratigraphic correlations of the Dakota-Mowry interval, this data can be used to construct a unifying stratigraphic model for Dakota and Mowry deposition. Results of this study indicate that Dakota Formation contains three, unconformity-bound depositional sequences. The first Dakota sequence is late Albian in age and was deposited above a regional unconformity that can be traced throughout the Uinta Basin. The second Dakota sequence was deposited above a second regional unconformity that formed during latest Albian time. In the northern part of the Uinta Basin, nonmarine deposition of second Dakota sequence was confined to the late Albian. Early Cenomanian-aged marine deposits of the overlying Mowry Shale comprise the upper parts of the sequence. In the southern part of the basin, the second Dakota sequence is entirely nonmarine. A regional decrease in relative sea level at the end of early Cenomanian time resulted in the development of a regional unconformity throughout the study area. In the southern Uinta Basin, incised fluvial channel complexes of the third Dakota sequence lie above the unconformity. The third Dakota sequence in this region is capped by the middle Cenomanian-Turonian Tununk Member of the Mancos Shale In the northern part of the basin, nonmarine deposits of the third Dakota sequence are absent. In this region the unconformity is situated at the erosional contact between the Mowry Shale and the middle Turonian Tununk Member.

STRATIGRAPHY AND PALYNOLOGY OF THE ALBIAN – CENOMANAIN DAKOTA FORMATION AND MOWRY SHALE, UINTA BASIN, UTAH AND COLORADO

A Thesis

Submitted to the

Faculty of Miami University

in partial fulfillment of

the requirements for the degree of

Master of Science

Department of Geology

by

Justin Scott Pierson

Miami University

Oxford, Ohio

2009

Advisor______

(Dr. Brian Currie)

Reader______

(Dr. Jason Rech)

Reader______

(Dr. Ellen Currano) TABLE OF CONTENTS

INTRODUCTION 1

METHODS 6

GEOLOGIC SETTING 7

REGIONAL STRATIGRAPHY 8 Northern Uinta Basin First Dakota Sequence 8 Second Dakota Sequence 9 Mowry Shale 11

Southern Uinta Basin First Dakota Sequence 12 Second Dakota Sequence 14 Mancos Shale Tununk Member 15

DEPOSITIONAL AGE 17

PREVIOUS AGE DETERMINATIONS 17 Northern Uinta Basin Dakota Formation 17 Mowry Shale 17 Mancos Shale Tununk Member 18

Southern Uinta Basin Dakota Formation 18 Mancos Shale Tununk Member 18

NEW BIOSTRATIGRAPHIC DATA 20 Northern Uinta Basin Steinaker Reservoir Location 20 Mowry Shale 20

Southern Uinta Basin Westwater Creek and Westwater Creek East Locations 20 Dakota Formation 23 Mancos Shale Tununk Member 23 Agate Wash Location 24 Dakota Formation 26 Mancos Shale Tununk Member 26 Yellow Cat Location 27 Dakota Formation 27

ii

TABLE OF CONTENTS –Continued

Green River East Location 27 Dakota Formation 27 Mancos Shale Tununk Member 30 Cottonwood Wash Location 30 Mancos Shale Tununk Member 30 Trapp Springs Well Core 30 Dakota Formation 32 Mancos Shale Tununk Member 33

BIOSTRATIGRAPHIC SYNTHESIS 33

STRATIGRAPHIC IMPLICATIONS 35 Dakota Formation and Mowry Shale 35 Mancos Shale Tununk Member 35

UINTA BASIN CORRELATIONS 37

REGIONAL STRATIGRAPHIC EVOLUTION 40

CONCLUSIONS 45

REFERENCES 46

APPENDIX A. Detailed palynological results 52 Plate 1. Detailed palynology for the Steinaker Reservoir Location 53 Plate 2. Detailed palynology for the Westwater Creek and Westwater 54 Creek East Location Plate 3. Detailed palynology for the Agate Wash Location 55 Plate 4. Detailed palynology for the Yellow Cat Location 56 Plate 5. Detailed palynology for the Green River East and Cottonwood 57 Wash Locations Plate 6. Detailed palynology for the Trapp Springs Core Location 58

iii

LIST OF TABLES

1. Uinta Basin outcrop and well locations 3

iv

LIST OF FIGURES

1. Location map of the study area 2 2. Time stratigraphic chart for Albian-Cenomanian time 5 3. Outcrop correlation in the northern Uinta Basin 10 4. Outcrop correlation in the southern Uinta Basin 13 5. Steinaker reservoir outcrop measured section 21 6. Westwater Creek and Westwater Creek East outcrop measured sections 22 7. Agate Wash outcrop measured section 25 8. Yellow Cat outcrop measured section 28 9. Green River East and Cottonwood Wash outcrop measured section 29 10. Trapp Springs Core description and geophysical log 31 12. North-to-south surface-to-subsurface cross-section 38 13. Stratigraphic evolution of the Dakota Formation and Mowry Shale 41-42

v

ACKNOWLEDGEMENTS

I would like to thank my advisor, Dr. Brian Currie, for all of the insight, time, effort, and guidance that he offered during the course of this project. Also, I would like to thank Mary and Steve McPherson for opening their home while I was conducting field work and for Mary’s technical guidance throughout this project. Thanks also go to Jared Gooley for assisting me in the field and to the Utah Geological Survey for providing funding for this research. Finally, I would like to thank my parents for their unending support through all of my academic career.

vi

INTRODUCTION The Dakota Formation and Mowry Shale of eastern Utah and western Colorado consists of an overall transgressive sequence of continental and marine strata that was deposited in the medial part of the Cordilleran foreland basin system during Albian-Cenomanian time (~105-96 Ma) (Currie, 2002). Surface exposures of these units occur in areas north and south of the Uinta Basin (Figure 1, Table 1). Previous studies of the Dakota Formation and Mowry Shale in the region have focused on the sedimentology, depositional environments, and regional stratigraphy (Young, 1960; Vaughn and Picard, 1976; Ryer, et al, 1987; Molenaar and Wilson, 1990). However, complex stratigraphic relationships within the Dakota Formation (Currie, 2002), between the Dakota Formation and the Mowry Shale (Quigley, 1959; Molenaar and Cobban, 1991), and between the Dakota/Mowry and the overlying Mancos Shale, have led to differing interpretations regarding the basin-scale stratigraphic architecture of these units. For example, Molenaar and Cobban (1991) postulated that a regional unconformity identified at the base of the Dakota in the southern part of the Uinta Basin correlates with an unconformity between the Mowry Shale and overlying Mancos Shale in the northern Uinta Basin. These same authors concluded that the Dakota Formation in the northern and southern parts of the basin makes up two separate depositional units, and that the older Dakota unit to the north is conformable with the underlying Cedar Mountain Formation. They also suggested that the upper parts of the older Dakota unit identified in the subsurface of the Uinta Basin correlate with the Mowry Shale, but that outcrop exposures of the Dakota in the southern parts of the basin are younger than the Mowry. Currie (2002), however, hypothesized the Dakota Formation in the northern parts of the Uinta Basin is separated from the underlying Cedar Mountain formation by a regional unconformity. He also speculated that the Dakota Formation in the northern basin contains a second intra-formational unconformity that divides the unit into distinct upper and lower depositional sequences, and that the two unconformities merge into a single unconformity at the base of the unit in the southern part of the basin. Currie (2002) concluded that the Dakota Formation exposed in outcrops along the southern part of the Uinta basin is laterally equivalent with the Mowry Shale to the north. One reason for disparate regional correlations of these units is that most of the chronostratigraphic control used by previous workers was based on molluscan biostratigraphic

1 R.103W R.01E R.20E R.01W R.25E North ID A NV B C A T.01N B WY T.01S T.05S Salt Lake City Vernal Vernal 1 T.05N 40 191 D E

Green F 40 River 2

3 UT CO AZ NM T.01N 4 40°T.01S T.06SExplanation Albian-Cenomanian 5 T.11S T.11S outcrops A Measured section location & number Uinta 6 7 1 Well location & number 129 9 8 13 Trapp Spring well location 11 10 Highway 12 T.05S Line of section, Figure 3 Line of section, Figure 4 13 T.15S Basin Line of section, Figure 11 30 miles 14 50 kilometers 15 16 R.03W

17 T.10S 191 6 T.01N T.20S G K H Green River 39° 70 San Rafael Swell J R.104W R.26E R.19E R.14E 110° I 109°

Figure 1. A) Uinta Basin study area location, eastern Utah and western Colorado. Grey shading shows location B. B) Simplified geologic map of the study area showing Albian-Cenomanian outcrop belt, measured section locations, and stratigraphic cross section lines for Figure 4, Figure 5, and Figure 11. See Table 1 for outcrop/well names and latitude/longitude locations.

2 Table 1. Uinta Basin study area outcrop and well locations. See Figure 1 for Letter/Number map locations. Outcrops Location Latitude Longitude Letter in Figure 1 Steinaker Reservoir 40.53204 -109.52003 A Steinaker Reservoir/US 191 40.51285 -109.52638 B Split Mountain Anticline 40.47579 -109.37415 C Cliff Creek/US 40 40.31575 -109.23116 D Bull Canyon 40.28436 -109.03550 E Monument Headquarters 40.24545 -108.96808 F Westwater Creek 39.10529 -109.14610 G Agate Wash 39.03566 -109.22353 H Yellow Cat 38.85725 -109.59582 I Green River East 38.96896 -110.10598 J Cottonwood Wash 39.05841 -110.34317 K

Wells API Number Operator Lease Well Latitude Longitude Number in Figure 1 43047156850000 STANOLIND O&G CO U S A 4 40.36458 -109.42232 1 43047301490000 CHEVRON U S A INC RED WASH UNIT 44-21-C 40.19074 -109.21081 2 43047373500000 QUESTAR EXPLOR&PROD RWS 6D-5-9-24 40.06714 -109.24028 3 43047109160000 JOHNSON ROY M WATSON 2 39.99793 -109.09472 4 05103092680000 MITCHELL ENERGY CORP H H FED 1-35-1-104 39.91050 -109.03102 5 05103091640000 MITCHELL ENERGY CORP P M FEDERAL 1-2-3-104 39.81982 -109.02794 6 05103096660000 MITCHELL ENERGY CORP P M FEDERAL 2-12-3-104 39.80019 -109.02143 7 05103088260000 COSEKA RES (USA) LTD COLUMBINE SPRINGS 13-12-4-104 39.73137 -109.02615 8 43047311340000 BEARTOOTH O&G CO ENI 7-1 39.70637 -109.05240 9 43047312310000 BEARTOOTH O&G CO ENT-HATCH 15-6 39.69058 -109.10626 10 43047109600000 RAYMOND C F OIL CO GOVT 1 39.69227 -109.14852 11 43047307730000 EXXON CORPORATION CROOKED CANYON UN3 39.64517 -109.25630 12 43047309780000 COSEKA RES (USA) LTD TRAP SPRING 3-25-14-23 39.57643 -109.29753 13 43019306450000 COSEKA RES (USA) LTD FEDERAL 6-4-16-25 39.44300 -109.16391 14 43019312300000 LONE MOUNTN PROD CO STATE-HANCOCK 2-16 39.35152 -109.10896 15 43019302790000 LANSDALE A LANSDALE FEDERAL 14-1 39.33152 -109.11252 16 43019304130000 LANSDALE A FEDERAL 1-23 39.22226 -109.10931 17

3 Cobban, 1991), coupled with limited palynological data (Carroll, 1992; Cushman, 1994). As the majority of these studies focused on marine strata, the regional stratigraphic correlations of the nonmarine Dakota Formation are equivocal due to lack of age control. The primary objective of this thesis is to provide a better understanding of the overall stratigraphic relationships between the Dakota Formation and Mowry Shale in the Uinta Basin region (Figure 2). In order to accomplish this, palynological samples from the Dakota Formation and overlying units were collected along the northern and southern margins of the Uinta Basin to provide chronostratigraphic constraints. When combined with preexisting biostratigraphic data from the Dakota Formation, the Mowry Shale, and the Mancos Shale, this data can used to construct a unifying stratigraphic model for Dakota and Mowry deposition. A regional stratigraphic correlation of these units, using both outcrop and geophysical log data from wells in the study area, helps to further elucidate the stratigraphic framework of the Albian-Cenomanian rocks of the Uinta Basin.

4 Southern Uinta BasinSouthern Uinta BasinNorthern Uinta BasinNorthern Uinta Basin Ma AGE This Study Molenaar and Cobban (1991) This Study Molenaar and Cobban (1991)

90 Mancos Shale Mancos Shale Tununk Shale Mbr./Frontier Fm. Tununk Shale/Frontier Fm. Turonian Coon Springs Sandstone Coon Springs Sandstone Tununk Shale Tununk Member Dakota Sandstone Middle Cretaceous Unconformity Middle Cretaceous Unconformity Third Dakota Sequence Cenomanian Middle Cretaceous UnconformityMiddle Cretaceous Unconformity Upper Cretaceous Upper

Mowry Shale Mowry Shale Second Dakota Sequence 100 Second Dakota Sequence Dakota Formation Dakota Fm. Dakota Formation First Dakota Sequence First Dakota Sequence Albian Cedar Mountain Fm. Cedar Mountain Fm.

Ruby Ranch Member

Lower Cretaceous Lower Ruby Ranch Member Cedar Mountain Fm. Cedar 110 Mountain Fm. Cedar Figure 2. Time-stratigraphic diagram of the Lower/Upper Cretaceous Dakota Formation, Mowry Shale, and Mancos Shale in the Uinta Basin area, Utah. Ages are based on palynomorphs from the Dakota Formation, palynomorphs and molluscs from the Mowry Shale and younger marine deposits, and regional stratigraphic relationships. Compiled from Kirkland and Madsen (2007), Currie, (2002), Carroll (1992), and Molenaar and Cobban (1991). Timescale from Gradstein et al. (2005).

5 METHODS Eight stratigraphic sections were measured using a Jacob’s staff and Brunton compass. At each outcrop location lithologies, grain-size, bedding geometries, sedimentary structures and paleocurrent orientations were documented. In addition, outcrop gamma-ray logs were created at some measured section locations in order to correlate stratigraphic units with subsurface data in the Uinta Basin. Gamma-ray measurements were taken with an Exploranium hand-held scintillometer at 30 cm intervals through each measured section. Five readings were recorded and averaged at every interval and plotted in a graph to produce a gamma-ray log for each section. Palynological samples were collected from the Dakota Formation, Mowry Shale, and Mancos Shale outcrops in the study area and from one drill core archived at the Utah Geological Survey Core Research Center in Salt Lake City. Samples were taken from approximately 10-20 cm thick intervals of unweathered carbonaceous mudstone devoid of modern plant material. For each outcrop sample, approximately 100-200 grams of mudstone was collected and cataloged with the section name and the corresponding position (in meters) above the base of the measured section. Core samples consisted of ~3 grams of carbonaceous shale and labeled by their depth (in feet) in the subsurface. Sub-samples were then selected by a visual estimation of organic content to maximize the potential for palynomorph recovery. Three to five grams from each sample were then sent to Gerald Waanders, consulting palynologist, for age, kerogen and thermal alteration index analyses.

6 GEOLOGIC SETTING The study area is located in the southern part of the Cretaceous Cordilleran foreland basin system (Jordan, 1981; Villien and Kligfield, 1986; Currie, 2002; DeCelles and Coogan, 2006). This retroarc foreland basin developed in response to eastward subduction of the Farallon Plate under the North American Plate. Convergence between these plates produced crustal thickening and associated thrust faulting in the Cordillera between Late Jurassic and Eocene time (DeCelles, 2004). Thrusting produced topographic loading in the Sevier thrust belt and corresponding flexural subsidence in the foreland basin to the east (Jordan, 1981; Currie, 2002). Long- wavelength “dynamic” subsidence associated with subduction-related mantle circulation beneath the western of North America, also contributed to the overall basin subsidence (Currie, 1998; Liu and Nummedal, 2004). While flexural and dynamic subsidence were likely the primary tectonic driving factors on overall foreland basin deposition, smaller-scale, eustacy-driven, transgressive- regressive accommodation cycles are also preserved in the Albian-Cenomanian rocks of the Western Interior seaway (Kauffman and Caldwell, 1993; Gale et al., 2008). Three unconformity- bound, transgressive-regressive, depositional sequences have been recorded in the Albian to Cenomanian deposits of Utah, Wyoming, and Colorado (Dolson and Muller, 1994; Oboh- Ikuenobe, et al., 2007).

7 REGIONAL STRATIGRAPHY The Dakota Formation is comprised of fluvial channel, overbank, and marginal-marine deposits. In the northern Uinta Basin, outcrops of the Dakota Formation are between <25-45 m (~80-150 ft) thick. In the southern Uinta Basin, the formation thickens from west to east from a zero-edge on the east flank of the San Rafael Swell (Molenaar and Cobban, 1991) to ~50 m (~160 ft) near the Utah-Colorado state line (Currie et al., 2008a). Based on the architecture of fluvial sandstones, overbank mudstones, and associated marginal/shallow marine deposits, the Dakota Formation has been previously subdivided into two stratigraphic units (Vaughn and Picard, 1976; Currie, 2002; Currie et al., 2008a). Throughout the study area, the oldest Dakota sequence unconformably overlies overbank and fluvial channel deposits of the Albian-age Ruby Ranch Member of the Cedar Mountain Formation (Figure 2) (Vaughn and Picard, 1976, Currie, 2002; Kirkland and Madsen, 2007). The second Dakota sequence unconformably overlies the lower Dakota sequence (Ryer et al., 1987; Currie, 2002; Currie et al., 2008b). In the northern Uinta Basin, the second Dakota sequence is capped by the lower Cenomanian Mowry Shale (Molenaar and Cobban, 1991). The Mowry Shale consists of up to 40 m (~130 ft) of marine shale, siltstone, and sandstone. The top of the Mowry represents a regional unconformity underlying the middle Turonian Tununk Shale Member of the Mancos Group (Molenaar and Wilson, 1990). In the southern Uinta Basin, the upper Cenomanian/Turonian Tununk Member of the Mancos Shale overlies the Dakota Formation (Molenaar and Cobban, 1991; Currie et al., 2008a). The Tununk Member is in turn capped by the middle Turonian Coon Springs Sandstone (Dakota Silt) (Currie et al., 2008a). The general lithologic characteristics and stratigraphic relationships of the Dakota Formation and Mowry Shale in both the northern and southern Uinta Basin, as well as bounding stratigraphic units, are discussed in more detail below.

Northern Uinta Basin First Dakota Sequence In the northern parts of the Uinta Basin, the first Dakota sequence is up to 35 m (~115 ft) thick and consists fluvial-channel sandstones and conglomerates, as well as overbank sandstones, siltstones, and mudstones (Vaughn and Picard, 1976; Currie, 2002). The first Dakota was

8 deposited above a regional erosion surface incised as much as 15 m (~50 ft) into the underlying Cedar Mountain Formation (Vaughn and Picard 1976). Relief at the base of first sequence is primarily defined by thickness changes in both the first Dakota sequence and Cedar Mountain Formation Ruby Ranch Member between outcrop localities (Figure 3). Fluvial channel deposits of the lower sequence consist of upward-fining beds of pebble- granule conglomerate and very coarse- to very fine-grained sandstone. Conglomerates in the lower Dakota sequence are found at the base of individual channel-form deposits. Clasts consist of chert, sandstone, and quartzite, as well as rip-up clasts of underlying lithologies. Dakota Formation sandstones in the Uinta Basin are dominated by quartz (83%), with subsidiary chert (13%) and feldspar (4%) grains (B.S. Currie, unpublished data). Observed sedimentary structures in both sandstones and conglomerates include trough-cross stratification, horizontal bedding, and ripple-cross lamination. Some beds are structureless. Individual channel-form sandstones are between 3 m and 15 m (~10-50 ft) thick with lateral dimensions between 75 m and 300 m (~250-1000 ft) when measured perpendicular to paleoflow direction. In some cases, vertically amalgamated channel bodies form sandstone/conglomerate intervals that are up to 20 m (~65 ft) thick. Paleocurrent orientations from the first Dakota sequence indicate primarily north-directed paleoflow (Vaughn and Picard, 1976; Currie, 2002). Overbank deposits in the first Dakota sequence consist of beds of structureless to laminated, dark gray, smectitic, floodplain/paludal mudstone, and thin bedded (< 0.5 m (1.6 ft) thick), horizontally-stratified/ripple cross-laminated crevasse splay sandstones and siltstones. In some instances, these Dakota overbank deposits have been overprinted by pedogenic modification in the form of root traces, hydroximorphic gley mottling, and authigenic siderite/iron oxide accumulations.

Second Dakota Sequence In the northern Uinta Basin, rocks of the second Dakota sequence were deposited above a surface that is incised up to 18 m (~60 ft) into underlying Dakota 1 strata (Figure 3) (Currie, 2002). Internally, the second Dakota sequence is between 15 m and 23 m (~50-75 ft) thick and consists of lithologies similar to the first Dakota sequence. Although compositionally indistinguishable, channel sandstones in the second Dakota make up higher overall percentage of

9 A. Steinaker B. Steinaker C. Split Mountain D. Cliff Creek/ E. Bull Canyon F. Monument W 1.5 km 15 km 24 km 16 km 10 km E Reservoir Reservoir/RT 191 Anticline RT 40 Headquarters meters meters Kt meters meters Kt 100 meters Kmy Kmy 120 Kmy

60 100 N. americanus 60

80

100 meters Kd2 40 Kd2 Kd2 80 40

60 60 Kd1 80 Kd1 20 Kd1 60 20

40 40 Kcr 60 Kcr 0 40 Mud Fine Medium Coarse Very Gravel Kcr 0 Sand Sand Sand Coarse Sand Mud Fine Medium Coarse Very Gravel Coarse 20 Sand Sand Sand 20 Sand 40

20

0 0 Fine Medium Coarse Gravel 20 Mud Fine Medium Coarse Very Gravel Mud Very Kcb Kcb Sand Sand Sand Sand Sand Sand Coarse Coarse Sand Sand Jm 0 Explanation Covered interval Carbonate nodules Mud Fine Medium Coarse Very Gravel Mottled horizons Sand Sand Sand Coarse Ripple lamination Altered volcanic ash Sand Early Cenomanian Palynomorphs Jm 0 Trough cross stratification Burrows Mud Fine Medium Coarse Very Gravel Albian Palynomorphs Sand Sand Sand Coarse Ammonites Sand Horizontal lamination

Figure 3. Measured sections of the Dakota Formation and Mowry Shale along the north flank of the Uinta Basin. Stratigraphic cross section illustrates the incised nature of the basal unconformities of both the First and Second Dakota Sequences. Formation abbreviations: Jm: Morrison Formation, Kcr: Ruby Ranch Member of the Cedar Mountain Formation, Kd1: First Dakota Sequence, Kd2: Second Dakota Sequence, Kmy: Mowry Shale, and Kmt: Tununk Member of the Mancos Shale. See Figure 1 and Table 1 for outcrop localities.

10 the unit than they do in the first Dakota sequence. Mudstones of the second Dakota sequence, however, appear more carbonaceous than those of the first Dakota. Fluvial channel sandstones of the second Dakota sequence range from 3 m to 15 m (10-50 ft) in thickness, with lateral dimensions of up to 500 m (~1650 ft) when measured perpendicular to paleoflow. Paleocurrent orientations from trough-cross stratified lower Dakota sequence sandstones indicate primarily north-directed paleoflow (Vaughn and Picard, 1976; Currie, 2002). Throughout the northern Uinta basin, Mowry Shale marine deposits overlie the Dakota Formation. A gravelly transgressive lag and/or shoreface deposits commonly marks the base of the Mowry in this area (see below). Sandstones immediately beneath these commonly contain invertebrate trace fossils including Skolithos, Thalassonoides, Ophiomorpha, and Arenicolites. This suggests that the uppermost parts of the second Dakota sequence may have had a marine influence on deposition. Alternatively, marine organisms may have burrowed into unconsolidated upper Dakota sands during transgression of the Mowry seaway.

Mowry Shale In the northern Uinta Basin, the Mowry Shale is 25-35 m thick and is composed of black, grey, and silver colored, marine shale, mudstone, and siltstone with multiple interbedded bentonite beds. The Mowry Shale is interpreted as being deposited in a marine shelf environment at or below storm wave base (Byers and Larson, 1979; Davis and Byers, 1989). The lower 10-15 m (~32-50 ft) of the Mowry Shale in the study area consists of black, fissile shale and siltstone with rare beds of coarse- to very fine-grained, trough and hummocky cross- stratified sandstone. The upper parts of the unit consist of hard, silver-gray weathering, siliceous shale and siltstone (Sharp, 1963). Both the lower and upper parts of the Mowry Shale contain abundant disseminated plant material, fossil fish scales and bone fragments, and rare ammonite fossils (Sharp, 1963; Molenaar and Wilson, 1990). In the northern Uinta Basin, the top Mowry Shale is placed at the sharp contact between the grey-silver siliceous shale of the upper Mowry and black, fissile, marine shales of the lower Tununk Shale Member (Molenaar and Wilson, 1990). The Mowry-Tununk Shale contact is interpreted as a regional unconformity (the “Middle Cretaceous Unconformity” of Molenaar and Cobban (1991)) based on the age of mollusk fossils in both units (see below). In the field area,

11 the Tununk Shale Member coarsens upward into shoreface and nonmarine deposits of the Frontier Formation (Molenaar and Wilson, 1990).

Southern Uinta Basin First Dakota Sequence In the southern Uinta Basin, the first Dakota sequence consists of up to 20 m (~65 ft) of fluvial-channel sandstones and conglomerates, and overbank mudstones. In study area outcrops, fluvial channel deposits of the first Dakota sequence are incised as much as 9 m (~30 ft) into the underlying Ruby Ranch Member of the Cedar Mountain Formation (Figure 4) (Currie et al., 2008b). First Dakota sequence channel deposits consist of an overall upward-fining sequence of conglomerates and coarse- to fine-grained sandstones. Sedimentary structures in the first Dakota include trough- and planar-cross stratification, horizontal stratification and ripple-cross lamination. Paleocurrent orientations, measured from the orientation of trough axes and foresets, indicate an overall east-northeast direction of paleo-flow (Currie et al., 2008a). Individual channel sandstones are up to 12 m (~40 ft) thick with lateral dimensions of up to 900 m (~3000 ft) when measured perpendicular to paleoflow direction (Currie et al., 2008b). First Dakota channel deposits are commonly conglomeratic near their bases. Clasts consist of granules and pebbles of chert, sandstone, and quartzite, as well as rip-up clasts of underlying lithologies. The framework mineralogy of first Dakota sequence sandstones is dominated by quartz (88%), with subsidiary chert (6%), rock fragment (4%), and feldspar (2%) grains (Dark et al., 2008). While first Dakota sandstones are primarily cemented by silica, in some localities they are pervasively cemented by kaolinite and smectite. In outcrop, these sandstones are white and appear bleached. The abundant clay cement in some first Dakota sandstones results in poor outcrop exposures, especially where overlying second Dakota Formation sandstones are absent. As in the north, overbank deposits in the lower Dakota of the southern Uinta Basin sequence consist of beds of structureless to laminated, dark gray, smectitic mudstone, and thin- bedded, crevasse-splay sandstones and siltstones.

12 K. Cottonwood J. Green I. Yellow H. Agate G. Westwater W E Wash 30 km River East 48 km Cat 29 km Wash 14 km Creek meters 100

C. woollgari Dakota

80 Silt

meters meters meters meters P. newberryi 5 60 Kmt P. newberryi 5 P. newberryi P. newberryi Kmt MCU 0 MCU Kcr M VF F M C VC G 0 Kd2 Kd3 Kcr M VF F M C VC G Kd2 60 Explanation 60 Ripple lamination 40 Trough cross stratification Carbonate nodules Horizontal lamination Rhizocretions Kd1 Covered interval Mottled zones 40 40 Altered volcanic ash Limestones Kcr 20 Kd1 Burrows Coal Silica-replaced carbonate nodules Grain-Size Scale Cenomanian/Turonian Palynomorphs M VF F M C VC G Middle Cenomanian Palynomorphs M: mud; VF: very-fine 20 Kcr 20 Early Cenomanian Palynomorphs sand; F: fine sand; M: Albian Palynomorphs 0 medium sand; C: coarse M VF F M C VC G Bivalves sand; VC: very-coarse Ammonites sand; G: gravel

0 M VF F M C VC G Jm 0 Jm M VF F M C VC G Figure 4. Measured sections of the Dakota Formation along the south flank of the Uinta Basin. Stratigraphic correlation shows the westward thinning of the formation and the incision along the base of three interpreted Dakota depositional sequences. Formation abbreviations: Jm: Morrison Formation, Kcr: Ruby Ranch Member of the Cedar Mountain Formation, Kd1: First Dakota Sequence, Kd2: Second Dakota Sequence, MCU: Middle Cretaceous Unconformtiy, Kd3: Third Dakota Sequence, and Kmt: Tununk Member of the Mancos Shale. See Figure 1 and Table 1 for outcrop localities.

13 Second Dakota Sequence In the southern Uinta Basin the second Dakota sequence is up to 55 m (~180 ft) thick and consists of fluvial-channel and floodplain deposits that are similar to the first Dakota sequence (Currie et al., 2008b). Second Dakota fluvial channels are incised as much as 65 ft into the first Dakota sequence. In some places, the first Dakota interval has been completely eroded and second Dakota channel deposits rest directly on the Cedar Mountain Formation (Currie et al., 2008a). Fluvial channel sandstones of the second Dakota sequence are up to 14 m (~45 ft) thick, with flow-perpendicular widths ranging between 175 m and 900 m (~600-3000 ft) (Currie et al., 2008b). Paleocurrent orientations from trough-cross stratified lower Dakota sequence sandstones indicate primarily north-directed paleoflow (Vaughn and Picard, 1976; Currie, 2002). In some locations, stacked second Dakota channel complexes can be up to 30 m (~100 ft) thick with lateral dimensions of up to 1500 m (~5000 ft) wide. Most of these thick, amalgamated channel complexes are located at the base of the second Dakota sequence. However, occasionally, thick fluvial channel complexes are situated at the vary top of the interval (see Agate Wash Section, Figure 4). Overbank lithologies of the second Dakota sequence consist primarily of grey-black smectitic mudstones and siltstones, fine-grained sandstones, altered ash horizons, and thin coals (< 0.5 m (1.6 ft) thick). Like in the northern Uinta Basin, mudstones of the second Dakota sequence in the south are more carbonaceous than those of the first Dakota sequence. The second Dakota sequence also contains abundant fine- to very fine-grained, ripple cross-laminated, crevasse-splay sandstones and siltstones. In the southern Uinta Basin, marine deposits of the Tununk Member of the Mancos Shale overlie the Dakota Formation. Molenaar and Cobban (1991) proposed that the “Middle Cretaceous Unconformity” (MCU) is situated at the base of the Dakota in the southern Uinta basin. However, in their subsurface correlation of the Albian-Cenomanian interval, these authors positioned strata equivalent to the Dakota Formation and Mowry Shale in the northern part of the basin as being below the MCU in the south. This apparent discrepancy is attributed primarily to differences in stratigraphic terminology. In the southern part of the Uinta Basin Molenaar and Cobban (1991) used the term “Dakota Sandstone” to apply to fluvial channel sandstone and conglomerate beds that are

14 immediately overlain by the Mancos Shale Tununk Member. This designation would be analogous to fluvial channel sandstones that are situated at the very top of the Dakota Formation in the Agate Wash Section (Figure 4). In the southwestern parts of the study area near Green River, Utah (Figure 6), similar sandstones bodies rest unconformably on the Cedar Mountain Formation. Molenaar and Cobban (1991) speculated that the conglomerates, sandstones, and carbonaceous mudstones of the Dakota east of the Green River area rested above the MCU and that their “Dakota Sandstone” interval thickened to the east. However, Currie et al. (2008a) demonstrated that while the Dakota Formation does thicken to the east along the southern part of the basin, the interval is part of the first and second Dakota sequences as defined above. The uppermost fluvial channel complexes in the Dakota Formation that Molenaar and Cobban (1991) classified as “Dakota Sandstone” have thickness < 15 m (~50 ft) and are laterally discontinuous. It is likely that the MCU is situated at the base of these channel complexes and suggests that the Dakota Formation in the southern part of the Uinta Basin contains a third, unconformity-bound, depositional sequence. However in most locations, the MCU is situated between the top of the second Dakota sequence and the overlying Tununk Member of the Mancos Shale. In both instances a gravelly transgressive lag at the base of the Tununk Member commonly overlies the Dakota in this area (see below) (Currie et al., 2008a).

Mancos Shale Tununk Member The Tununk Member of the Mancos Shale overlies the Dakota Formation in the southern Uinta Basin (Molenaar and Cobban, 1991) (Figure 4). The base of the Tununk Member commonly contains a thin bed (< 0.3 m (~1 ft) thick) of poorly sorted, pebbly sandstone. This bed, which is interpreted as a transgressive lag deposit, is comprised of chert and quartzite granules and pebbles, mud rip-up clasts, plant fragments, disarticulated bivalve shells and rare ammonite molds. Above the transgressive lag, the Tununk Member consists of black and dark grey shale, and slightly calcareous, gray, glauconitic mudstone. Portions of this interval are thoroughly bioturbated and contain abundant fossils of the Gryphaeid oyster Pycnodonte newberryi often preserved in life position. The lower parts of the Tununk Member coarsen upward into siltstones and very-fine grained sandstones of the Coon Springs Sandstone Bed (Figure 4). The thickness of lower Tununk-Coon Springs Sandstone interval in the southern

15 Uinta Basin ranges from ~25 m to 60 m (~80-200 ft) (Molenaar and Cobban, 1991; Currie et al., 2008a).

16 DEPOSITIONAL AGE The Dakota Formation and Mowry Shale in the Uinta Basin are considered Albian- Cenomanian in age. Previous investigations on the depositional age of the Dakota Formation and Mowry Shale in eastern Utah have relied exclusively on biostratigraphic data. The palynological content of the Dakota Formation has been the primary tool used to define the age of the lower non-marine part of the interval (Carroll, 1992; Cushman, 1994). The stratigraphic range of marine mollusks from the Mowry and Mancos shales has been utilized to estimate a minimum age for deposition (Young, 1960; Molenaar and Wilson, 1990; Molenaar and Cobban, 1991). Details regarding previous age determinations of the Dakota and Mowry in the northern and southern Uinta Basin, and new palynological data collected as part of this study, are discussed below.

Previous Age Determinations Northern Uinta Basin Dakota Formation In the northern part of the Uinta Basin, few biostratigraphic studies have targeted the Dakota Formation. Carroll (1992) reported a palynomorph assemblage from the upper-most part of the Cedar Mountain Formation in northeastern Utah that indicated a late-middle- or early-late Albian age of deposition. Currie (2002), however, determined that Carroll’s Cedar Mountain sample was taken from the upper part of the first Dakota sequence, and posited a middle/late Albian age of deposition for the lower part of the formation. Currie (2002) postulated that the second Dakota sequence is latest Albian in age based on regional stratigraphic correlations, as well as the early Cenomanian age of the overlying Mowry Shale (See below).

Mowry Shale Ammonites and palynomorphs collected from the Mowry Shale in the northern part of the Uinta Basin indicate an early Cenomanian age of deposition (Molenaar and Wilson, 1990; Carroll, 1992). The ammonite Neogastroplites cornutus was collected from the base of the Mowry Shale in outcrops along the northern flank of the Uinta Mountains, while Neogastroplites americanus was collected near the middle part of the unit on the northern margin of the Uinta Basin near Steinaker Reservoir (Figure 3) (Molenaar and Wilson, 1990). These Neogastroplites

17 taxa are restricted to the early Cenomanian and indicate a depositional age of ~98 Ma (Gradstein et al., 2005). This is supported by palynomorphs collected from the unit in the northern part of the Uinta Basin. Carroll (1992) identified the early Cenomanian dinoflagellate cysts Ascostomocystis giganteus, Balmula pentaradiata, Thalassiphora microcysta, and Wigginsiella canadense in samples from the middle part of the Mowry Shale near Steinaker Reservoir.

Tununk Shale Member Mollusk fossils from the Tununk Shale Member and overlying Frontier Formation indicate a middle Turonian age of deposition. Molenaar and Wilson (1990) reported the ammonite Prionocyclus hyatti from the basal part of the Tununk Shale along the northeast flank of the Uinta Mountains in northwestern Colorado, as well as from the lower-most Frontier Formation sandstones near Steinaker Reservoir. Prionocyclus hyatti is restricted to the uppermost middle Turonian and indicates a depositional age of ~91 Ma (Gradstein et al., 2005). This age from the Tununk Shale and the ~98 Ma age of the Mowry Shale indicates that the unconformity separating the two units spans ~7 million years.

Southern Uinta Basin Dakota Formation Carroll (1992) investigated the palynological content of the Dakota Formation in the southern Uinta Basin in western Colorado, in outcrops of the formation near the Utah state line. Carroll (1992) interpreted a middle Cenomanian age for Dakota Formation deposition in this area based on the stratigraphic ranges of four species: Crybelosporites brenneri, Appendicisporities insignis, A. auritus, and Bacutrilites greenlandicus. Cushman (1994) also interpreted a middle Cenomanian age for the Dakota Formation exposed southeast of the present study area. This age determination was based on the presence of the trilete spore Cicatricosisporites crassiterminatus and dinoflagellate cyst Ovoidnium verrucosum sampled from tidally influenced Dakota deposits outcropping west of present-day Delta, Colorado.

Mancos Shale Tununk Member In the southern Uinta Basin the Tununk Member of the Mancos Shale is interpreted as late Cenomanian to early middle Turonian in age. These ages are based on molluscan taxa found

18 near the base of the Tununk Member and in the overlying Coon Springs Sandstone Bed. The late Cenomanian age is based on the marine bivalve Pycnodonte newberryi, identified in the lower parts of the Tununk Member (Young, 1960; Molenaar and Cobban, 1991). Pycnodonte newberryi is restricted to the Sciponoceras gracile ammonite zone (Molenaar and Cobban, 1991), and indicates a depositional age of ~94 Ma (Gradstein et al., 2005). The early middle Turonian age (~92 Ma) for the overlying Coon Springs Sandstone is based on the occurrence of the ammonite Collignoniceras woollgari in the unit (Molenaar and Cobban, 1991; Gradstein et al., 2005). Both Carroll (1992) and Cushman (1994) extensively sampled the lower parts of the Mancos Shale for palynological analysis. Carroll (1992) interpreted a late Cenomanian age for the lower Tununk in the southern Uinta Basin based its stratigraphic position above Dakota Formation (which he interpreted as middle Cenomanian) and the presence of the dinoflagellate cysts, Apteodinium maculatum, Kikansiiium polypes, Fromea fragilis, and Tanyosphaeridium salpinx. The presence of Pycnodonte newberryi in this same interval supports this interpretation. Cushman (1994), however, interpreted a middle Cenomanian age of the lower Mancos Shale southeast of the study area near Delta, Colorado. This interpretation is based on the presence of Cicatricosisporites crassiterminatus in marine shelf and shoreface deposits overlying the Dakota Formation at in the sample locality (Sharp, 1963; Cushman, 1994). Supporting this age are the middle Cenomanian ammonites Acanthoceras amphibolum and Calycoceras gilberti that were collected ~15-20 m (~50-65 ft) above the top of the Dakota Formation in the sample locality (Sharp, 1963). These taxa indicate a depositional age of ~96 Ma (Gradstein et al., 2005). The late Cenomanian bivalve Pycnodonte newberryi and the early middle Turonian ammonite Collignoniceras woollgari were also identified in the Delta section ~50-60 m (~160-200 ft) above the top of the Dakota Formation (Sharp, 1963; Cushman, 1994). Cushman (1994) also reported the dinoflagellate cyst Isabelidinium magnum (Alterbia sp.) from ~24 m to >60 m (~80- 200 ft) above the top of the Dakota Formation in the Mancos section at Delta. In the western interior Cretaceous, this species ranges in age from early middle Cenomanian to late Turonian (Nichols et al., 1982; Cushman, 1994).

19 New Biostratigraphic Data As part of this study, 77 samples were collected from outcrops of the Dakota Formation, Mowry Shale, and Tununk Shale from seven outcrop sections along the north and south flanks of the Uinta Basin, and from one industry core from the southern part of the basin (Figure 1, Table 1). Of these samples, 66 yielded identifiable fossil pollen, spores, and dinoflagellate cysts. Age- diagnostic marine mollusks were also identified at several different outcrop locations. The following section outlines the diagnostic taxa, interpreted depositional environment, and depositional age for each sampled interval. Palynomorph taxa diversity charts, kerogen content, and visual Thermal Alteration Index values for the samples colleted at each locality are displayed in Plate 1-6 in Appendix A.

Northern Uinta Basin Steinaker Outcrop Location Mowry Shale A sample collected from directly above the transgressive lag at the base of the Mowry Shale at the Steinaker Reservoir section (Figure 3, Figure 5) contained both marine microplankton and land-derived spores and pollen. Age-diagnostic palynomorphs in the sample consisted of the dinoflagellate cysts Chichaoudinium vestitum and Subtilisphaera perlucida (Appendix A, Plate 1). Both taxa have been identified in deposits of the western interior that also contain the early Cenomanian ammonites Neogastroplites cornutus and Neogastroplites americanus (Reeside and Cobban, 1960; Molenaar and Wilson, 1990; Oboh-Ikuenobe et al., 2007). Given that these same ammonites occur in the Mowry Shale in the Uinta Mountain region, the presence of Chichaoudinium vestitum and Subtilisphaera perlucida in the sample supports the previously determined early Cenomanian age of the unit in the northern Uinta Basin (Molenaar and Wilson, 1990).

Southern Uinta Basin Westwater Outcrop Location At two Westwater outcrop locations (Figure 1, Table 1, Figure 6), seventeen samples were collected for palynological analysis from the second Dakota sequence and the overlying Mancos Shale Tununk Member. Age-diagnostic marine mollusks were also identified at two

20 Steinaker Reservoir Kt meters Kmy120

N. americanus

100

Kd2

80 Kd1

60 Kcr Explanation Ripple lamination Trough cross stratification Carbonate nodules Horizontal lamination Rhizocretions 40 Covered interval Mottled zones Altered volcanic ash Limestones Burrows Coal Silica-replaced carbonate nodules Grain-Size Scale Cenomanian/Turonian Palynomorphs M VF F M C VC G Middle Cenomanian Palynomorphs M: mud; VF: very-fine Early Cenomanian Palynomorphs 20 sand; F: fine sand; M: Albian Palynomorphs medium sand; C: coarse Bivalves sand; VC: very-coarse Ammonites sand; G: gravel

Jm 0 Mud Fine Medium Coarse Very Gravel Sand Sand Sand Coarse Sand Figure 5. Measured section of the Steinaker Reservoir outcrop location with palynological sample horizon and stratigraphic positioin of ammonite sample from Molenaar and Cobban (1991). Formation abbreviations: Jm: Morrison Formation, Kcr: Ruby Ranch Member of the Cedar Mountain Formation, Kd1: First Dakota Sequence, Kd2: Second Dakota Sequence, Kmy: Mowry Shale, and Kt: Tununk Shale Member. See Figure 1 and Table 1 for outcrop location.

21 NW Westwater ~1 km Westwater SE Creek Creek East meters 100

Dakota C. woollgari Silt 80 P. newberryi Kmt Kd2

meters 60 60

40 40 Kd1

Kcr 20 20

0 0 Jm M VF F M C VC G M VF F M C VC G

Figure 6. Measured sections of the Westwater Explanation Ripple lamination Creek and Westwater Creek East outcrop locations Trough cross stratification Carbonate nodules showing palynological and molluscan samples. Horizontal lamination Rhizocretions Formation abbreviations: Jm: Morrison Formation, Covered interval Mottled zones Kcr: Ruby Ranch Member of the Cedar Mountain Altered volcanic ash Limestones Burrows Coal Formation, Kd1: First Dakota Sequence, Kd2: Silica-replaced carbonate nodules Grain-Size Scale Second Dakota Sequence, Kmt: Tununk Member Cenomanian/Turonian Palynomorphs M VF F M C VC G of the Mancos Shale. Dakota Silt in the figure is Middle Cenomanian Palynomorphs Early Cenomanian Palynomorphs M: mud; VF: very-fine equivalent to the Coon Springs Sandstone Bed of Albian Palynomorphs sand; F: fine sand; M: Bivalves medium sand; C: coarse Molenaar and Cobban (1991). See Figure 1 and sand; VC: very-coarse Ammonites Table 1 for outcrop location. sand; G: gravel

22 stratigraphic horizons. Palynomorphs recovered from the Dakota Formation were all land- derived indicating deltaic or swamp paleoenvironments. Palynomorph from the Mancos Shale samples consisted of both marine microplankton and land-derived spores and pollen suggesting nearshore/shallow marine paleoenvironments. The Dakota Formation yielded late Albian and early Cenomanian taxa while Tununk Member samples yielded middle Cenomanian-late Cenomanian/Turonian palynomorphs (Appendix A, Plate 2). Further information on the stratigraphic-age determinations on each sample is listed in more detail below.

Dakota Formation The two stratigraphically lowest samples (WWC 46.5 and WWC 50, Plate 2) in the Dakota Formation at Westwater Creek contained the age-diagnostic trilete spores Klukisporites pseudoreticulatus, K. areolatus, Rouseisporites spp., Neoraistrickia robusta, Pilosisporites trichopapillosus, Trilobosporites apiverrucatus, T. crassus and T. trioreticulosus. These taxa indicate a late Albian age of deposition for the lower parts of the second Dakota sequence in the study area (G. Waanders, personal communication, 2007). Nine samples from the upper ~20 m (~65 ft) of the Dakota Formation at Westwater Creek contained palynomorphs that are long ranging throughout the Cretaceous (Figure 6, Plate 2). In this interval, however, there is a decrease in overall taxa diversity and an absence of the definitive Albian-aged assemblage identified in the lower part of the formation (Plate 2). As there are no apparent lithological or interpreted paleoenvironmental changes that might account for theses differences, an early Cenomanian age is interpreted for the upper part of the second Dakota sequence.

Mancos Shale Tununk Member Seven samples were collected from the Tununk Member and the overlying Coon Springs Sandstone Bed at the Westwater Creek outcrop locality. The stratigraphically oldest sample from this interval (WWC 70.5, Plate 2) was taken from just above a thin transgressive lag at the top of the Dakota Formation (Figure 6). Sample WWC 70.5 contained the age-diagnostic dinoflagellate cysts Cribroperidinium edwardsi and Palaeohystrichophora infusorioides, as well as the trilete spore Cicatricosisporites crassiterminatus. Given previous palynological interpretations in the study area (Cushman, 1994; McPherson et al., 2006), this assemblage

23 indicates a middle Cenomanian age of deposition. These same taxa, however, have also been reported from throughout Cenomanian in Utah and Wyoming (Carroll, 1992; Oboh-Ikuenobe, et al., 2007), indicating the lower parts of the Tununk Member in the southern part of the Uinta Basin may be as old as early Cenomanian or as young as late Cenomanian. Stratigraphically situated ~3.5 m (~11 ft) above the top of the Dakota Formation, Sample WWC 77.5 contained the dinoflagellate cyst Palaeohystrichophora infusorioides as well as abundant Pycnodonte newberryi fossils preserved in life position (Figure 6, Plate 2). Pycnodonte newberryi is restricted to the late Cenomanian Sciponoceras gracile ammonite zone (Molenaar and Cobban, 1991) and indicates a depositional age of ~94 Ma (Gradstein et al., 2005). Four additional samples colleted above the Pycnodonte newberryi-bearing interval (WWC 80.5 through WWC 86.5; Figure 6, Plate 2) contained the dinoflagellate cysts Palaeohystrichophora infusorioides and Isabelidinium acuminatum (Alterbia sp. A), and the trilete spore Cingulatisporites distaverrucosus. These taxa range from the Cenomanian through the Turonian. The stratigraphically youngest sample (WWC 86.5) was taken from the same horizon in the Coon Springs Sandstone that contained the early middle Turonian ammonite Collignoniceras woollgari. The presence of this ammonite indicates a depositional age ~92 Ma (Molenaar and Cobban, 1991; Gradstein et al., 2005). Given that the four youngest palynomorph samples in the Westwater Creek section are situated between the beds containing Pycnodonte newberryi and Collignoniceras woollgari, the age of this interval is interpreted as being late Cenomanian-middle Turonian in age (Figure 6, Plate 2).

Agate Wash Outcrop Location Eight samples from the Dakota Formation were collected from the Agate Wash section (Figure 1, Table 1, Figure 7). The organic recoveries were good to very good and consisted mostly of mixed woody and cuticular kerogens. The palynomorph recoveries were all land- derived indicating deltaic or swamp paleoenvironments (Appendix A, Plate 3). Two samples from the upper part of the Dakota Formation yielded possible early Cenomanian palynomorphs, while six samples from the lower Dakota Formation yielded late Albian palynomorphs (Plate 3). Further information on the stratigraphic-age determinations for each sample is listed in more detail below.

24 Agate Wash meters Kmt 60 P. newberryi Kd3 MCU Explanation Ripple lamination Trough cross stratification Carbonate nodules Horizontal lamination Rhizocretions Covered interval Mottled zones Kd2 Altered volcanic ash Limestones Burrows Coal 40 Silica-replaced carbonate nodules Grain-Size Scale Cenomanian/Turonian Palynomorphs M VF F M C VC G Middle Cenomanian Palynomorphs M: mud; VF: very-fine Early Cenomanian Palynomorphs sand; F: fine sand; M: Albian Palynomorphs medium sand; C: coarse Bivalves sand; VC: very-coarse Ammonites sand; G: gravel

Kd1 20

Kcr

0 Jm M VF F M C VC G Figure 7. Measured section of the Agate Wash outcrop location showing lithology, sedimentary features, and the position of palynological and molluscan samples collected for age determinations. Formation abbreviations: Jm: Morrison Formation, Kcr: Ruby Ranch Member of the Cedar Mountain Formation, Kd1: First Dakota Sequence, Kd2: Second Dakota Sequence, MCU: Middle Cretaceous Unconformtiy, Kd3: Third Dakota Sequence, and Kmt: Tununk Member of the Mancos Shale. See Figure 1 and Table 1 for outcrop location.

25 Dakota Formation At the Agate Wash outcrop locality, nine samples were collected from the Dakota Formation (Figure 7, Plate 3). Six of the samples (AW 17, AW 17.5, AW 20.3, AW 21, AW 22, and AW 24) from the lower part of the Dakota Formation are interpreted as late Albian based on the presence of the trilete spores Trilobosporites marylandensis, Trilobosporites apiverrucatus, Trilobosporites crassus, Neoraistrickia robusta and Pilosisporites trichopapillosus. A probable age no older than late Albian is based on the presence of the monosulcate pollen Liliacidites peroreticulatus, Liliacidites inaequalis and the tricolpate pollen Fraxinoipollenites inaequalis (Singh, 1971 and G. Waanders, personal communication, 2006). Three samples (AW 25.5, AW 41.5, AW 44.5) from the upper ~35 m (~115 ft) of the Dakota Formation yielded no diagnostic species (Figure 7, Plate 3). The palynomorphs recovered from these samples are all long ranging throughout the Cretaceous. An early Cenomanian age for this interval is suggested by a decrease in overall taxa diversity as compared to the definitive Albian-aged assemblage recovered lower in the section. As with the Westwater Creek palynology samples, there does not appear to be any lithological or paleoenvironmental changes within the sampled interval that might account for the observed decrease in taxa diversity. The basal fluvial channel sandstone of the second Dakota sequence is absent from the Agate Wash outcrop locality, making the placement of the sequence boundary approximate (Figure 4, Figure 7). Given the palynological content of the Agate Wash section and comparing it with the results of the palynological study at Westwater Creek, the boundary between the second and first Dakota sequences is interpreted as being located at the stratigraphic position of the upper-most Albian-aged assemblage in the Agate Wash section (AW 24; Figure 7, Plate 3).

Mancos Shale Tununk Member At the Agate Wash section, the upper Cenomanian mollusk Pycnodonte newberryi was identified in the lower part of the Tununk Member, ~3 m (10 ft) above the top of the Dakota Formation (Figure 7). Pycnodonte newberryi is restricted to the late Cenomanian Sciponoceras gracile ammonite zone (Molenaar and Cobban, 1991) and indicates a depositional age of ~94 Ma (Gradstein et al., 2005).

26 Yellow Cat Outcrop Location Dakota Formation At the Yellow Cat section, three palynomorph samples were collected from near the top of the first Dakota sequence (Figure 1, Table 1, Figure 8). The organic recoveries were very good and consisted of mostly woody kerogens. Palynomorphs were all land-derived indicating deltaic or swamp depositional environments (Appendix A, Plate 4). All samples yielded identifiable late Albian palynomorphs. An age no younger than late Albian is indicated for this interval by occurrences of the trilete spores Concavissimisporites punctatus, Ischyosporites disjunctus, I. punctatus, Klukisporites pseudoreticulatus, Pilosisporites trichopapillosus, and Trilobosporites trioreticulosus. The stratigraphically lowest sample (YC 43.5; Plate 4) contained the bisaccate gymnosperm pollen Rugubivesiculites rugosus. This taxon suggests a depositional age no older than late Albian (G. Waanders, personal communication, 2006).

Green River East At the Green River East section, samples were collected from both the Dakota Formation and the lower part of the Tununk Member (Figure 1, Table 1, Figure 9). The Dakota Formation is <4 m (~13 ft) thick at this location and is separated from the overlying Tununk Member by a transgressive lag containing chert/quartzite pebbles and Pycnodonte newberryi fossils (Figure 9). Palynomorphs recovered from the Dakota Formation were all land-derived indicating deltaic or swamp/paludal paleoenvironments. Palynomorphs from the Tununk Member sample consisted of both marine microplankton and land-derived spores and pollen suggesting nearshore/shallow marine paleoenvironments (Appendix A, Plate 5). The Dakota Formation yielded Cenomanian taxa while Tununk Member samples yielded Cenomanian/Turonian palynomorphs (Plate 5). Further information on the stratigraphic-age determinations on each sample is listed in more detail below.

Dakota Formation The Dakota Formation sample was taken from ~10 cm (4 in) below the transgressive lag at the base of the overlying Tununk Member (Figure 9). Taxa identified from this sample range throughout the middle Cretaceous, but lack the definitive late Albian palynomorphs identified in the Dakota Formation at other localities in the study area (e.g. Westwater Creek, Agate Wash,

27 Yellow Cat Kmt meters P. newberryi Kd2

60

Kd1 Kcr 40 Explanation Ripple lamination Trough cross stratification Carbonate nodules Horizontal lamination Rhizocretions Covered interval Mottled zones Altered volcanic ash Limestones Burrows Coal Silica-replaced carbonate nodules Grain-Size Scale Cenomanian/Turonian Palynomorphs M VF F M C VC G 20 Middle Cenomanian Palynomorphs M: mud; VF: very-fine Early Cenomanian Palynomorphs sand; F: fine sand; M: Albian Palynomorphs medium sand; C: coarse Bivalves sand; VC: very-coarse Ammonites sand; G: gravel

0 Jm M VF F M C VC G Figure 8. Measured section showing lithology and palynological sample locations at the Yellow Cat outcrop location. Formation abbreviations: Jm: Morrison Formation, Kcr: Ruby Ranch Member of the Cedar Mountain Formation, Kd1: First Dakota Sequence, Kd2: Second Dakota Sequence, Kmt: Tununk Member of the Mancos Shale. See Figure 1 and Table 1 for outcrop location.

28 Green River East meters Kmt 5 P. newberryi Kd2 Kcr 0 M VF F M C VC G

Cottonwood Wash meters 5 Kmt P. newberryi

Kcr 0 M VF F M C VC G Explanation Ripple lamination Trough cross stratification Carbonate nodules Horizontal lamination Rhizocretions Covered interval Mottled zones Altered volcanic ash Limestones Burrows Coal Silica-replaced carbonate nodules Grain-Size Scale Cenomanian/Turonian Palynomorphs M VF F M C VC G Middle Cenomanian Palynomorphs M: mud; VF: very-fine Early Cenomanian Palynomorphs sand; F: fine sand; M: Albian Palynomorphs medium sand; C: coarse Bivalves sand; VC: very-coarse Ammonites sand; G: gravel

Figure 9. Measured section of the Green River East outcrop location (top) and Cottonwood Wash outcrop location (bottom). Formation abbreviations: Kcr: Ruby Ranch Member of the Cedar Mountain Formation, Kd2: Second Dakota Sequence, and Kmt: Tununk Member of the Mancos Shale. Both measured sections show the Dakota Formation thinning to the west. At the Green River East location the Dakota Formation is only a few meters thick and at the Cottonwood Wash location, near the San Rafael Swell, the Dakota Formation is absent. See Figure 1 and Table 1 for outcrop location.

29 Yellow Cat). This observation, as well as the presence of three angiosperm species (Liliacidites inaequalis, Retitricolpites vulgaris, and Tricolpites crassimurus) indicates a Cenomanian age for the sample (G. Waanders, personal communication, 2006). Collectively, the identified taxa indicate that the Dakota at this location is part of the second Dakota sequence (Plate 5).

Mancos Shale Tununk Member The Tununk Member sample was taken from ~0.5 m (1.6 ft) above the transgressive lag at the base of the unit (Figure 9). The sample contained the dinoflagellate cysts Isabelidinium acuminatum (Alterbia sp. A) and Palaeohystrichophora infusorioides, which as in the Westwater Creek Tununk samples, indicate a Cenomanian/Turonian age of deposition (Plate 2, Plate 5). The close proximity of the sample to the lag containing the Pycnodonte newberryi fossils suggests a late Cenomanian or younger age for the Tununk Member at this location (Figure 9).

Cottonwood Wash Mancos Shale Tununk Member At the Cottonwood Wash section location (Figure 1, Table 1, Figure 9) the Dakota Formation is not present and the Tununk Member of the Mancos Shale directly overlies the Cedar Mountain Formation. The base of the Tununk Member at this location is marked by a transgressive lag containing ammonite fragments and abundant Pycnodonte newberryi fossils (Figure 9). The one sampled horizon from the Cottonwood Wash was situated directly above the transgressive lag and contained both marine microplankton and land-derived spores and pollen suggesting a shallow marine environment of deposition (Plate 5). The sample contained the dinoflagellate cyst Isabelidinium acuminatum (Alterbia sp. A) (Plate 5). As in the Westwater Creek and Green River East sections, this taxa indicates a Cenomanian/Turonian age of deposition. The close proximity of the sample to the Pycnodonte newberryi-bearing lag suggests a late Cenomanian or younger age for the Tununk Member at this location.

Trapp Spring Core Twenty-four samples of core from the Coseka Trapp Spring 13-25 (API 4304730978) well in the southern part of the Uinta Basin (Figure 1, Table 1, Figure 10) yielded identifiable palynomorphs (Plate 6). The core, which is archived at the Utah Geological Survey Core

30 Trapp Springs Core

70

60 Kmt

50

40 Kd

30

20

10

C S VF F M C VC G P C Kcm

Explanation Grain-Size Scale

M VF F M C VC G Early-Middle M: mud; VF: very-fine Vertical scale on Cenomanian sand; F: fine sand; M: core description Palynomprphs medium sand; C: coarse is in meters and Late Albian sand; VC: very-coarse in feet on log. Palynomprphs sand; G: gravel

Figure 10. Lithologic description and palynological sample locations from the Trapp Spring core matched with geophysical log data (core scale in meters from base, well log scale in feet from surface). Formation abbreviations: Kcm: Cedar Mountain Formation, Kd: Dakota Formation, Kmt: Tununk Member of the Mancos Shale. See Figure 1 and Table 1 for well location.

31 Research Center, was taken from the lower part of the Mancos Shale (above the Coon Springs Sandstone) to near the base of the Dakota Formation (Figure 10) (Currie et al., 2008a). Palynomorphs recovered from the Dakota Formation were all land-derived indicating deltaic or swamp paleoenvironments. Palynomorphs from the Mancos Shale also consisted of land-derived spores and pollen suggesting restricted marine paleoenvironments or significant reworking of underlying nonmarine strata (Plate 6). The Dakota Formation yielded late Albian and early Cenomanian taxa while samples from the lower part of the Tununk Member yielded palynomorphs that may be as young as middle Cenomanian (Plate 6). Further information on the stratigraphic-age determinations on each sample is listed in more detail below.

Dakota Formation Nine samples from the Trapp Spring core were collected from the Dakota Formation (Figure 10, Plate 6). The eight oldest samples (TS 8758-TS 8856) contained the age-diagnostic trilete spores Concavissimisporites punctatus, Klukisporites pseudoreticulatus, Neoraistrickia robusta, Pilosisporites trichopapillosus, Rouseisporites spp., and Trilobosporites trioreticulosus, as well as the angiosperm pollen Retitricolpites georgensis and R. vulgaris. These taxa indicate a late Albian age of deposition (Singh, 1971; G. Waanders, personal communication, 2007). The upper-most Dakota Formation sample in the Trapp Spring core (TS 8752) was taken from ~3 m (10 ft) below the base of the overlying Tununk Member (Figure 10, Plate 6). Taxa identified from this sample range in age throughout the middle Cretaceous, but lack the definitive late Albian palynomorphs identified lower in the section and in the Dakota Formation at other localities in the study area. An early Cenomanian age for the upper 3-5 m (~10-16 ft) of the Dakota Formation in Trapp Spring core is suggested by a decrease in overall taxa diversity as compared to the definitive Albian-aged assemblage recovered in the underlying samples (Figure 10, Plate 6). As with the early Cenomanian age determinations in the Westwater Creek and Agate Wash locations, there does not seem to be a change in lithology or depositional environments between the interpreted Albian and Cenomanian sample intervals that may have contributed to the observed diversity decrease. While the boundary between the first and second Dakota sequences is difficult to resolve in both outcrops and the subsurface of the southern Uinta basin (Dark et al., 2008), the upper-most part of the Dakota Formation in the Trapp Springs core

32 contains both Albian and Cenomanian-age taxa and is correlated with the second Dakota depositional sequence.

Mancos Shale Tununk Member Thirteen samples (TS 8743–TS 8654) from the Trapp Spring core were taken from the interval above the Dakota Formation that has been correlated with the Tununk Member and Coon Springs Sandstone (Dakota Silt) (Currie et al., 2008a). Taxa identified in the samples range in age throughout the middle Cretaceous. The presence of the trilete spores Cicatricosisporites crassiterminatus and Perotrilites allensis in the lower 6 m (~20 ft) of the interval indicate that the lower parts of the Tununk Member may be as young as middle Cenomanian (Figure 10, Plate 6) (Waanders personal communication, 2007). This is the same age that is interpreted for the lower-most Tununk Member at Westwater Creek (Figure 6, Plate 2).

Biostratigraphic Synthesis The new biostratigraphic data from the study area presented above generally supports the previous age determinations for the Dakota Formation, Mowry Shale, and lower Mancos Shale in the study area. In the northern Uinta basin, my interpreted early Cenomanian age of the Mowry Shale is in accord with previous investigations (Molenaar and Wilson, 1990; Carroll, 1992). The early Cenomanian age of the Mowry Shale supports the interpretation that the underlying Dakota Formation is Albian in age (Carroll, 1992; Currie, 2002). The primary discrepancy between the new palynological interpretations and those of previous workers is the age of the Dakota Formation in the southern part of the Uinta Basin. Carroll (1992) and Cushman (1994) both interpreted a middle Cenomanian age for Dakota Formation deposition in eastern Utah and western Colorado while my data suggests a late Albian-early Cenomanian age. Carroll (1992) interpreted a middle Cenomanian age for Dakota Formation deposition in this area based on the stratigraphic ranges of four taxa; Crybelosporites brenneri (middle Albian- middle Cenomanian), Appendicisporities insignis (early-middle Cenomanian), A. auritus (middle Cenomanian-Turonian), and Bacutrilites greenlandicus (middle Cenomanian-

33 Coniacian). Further research into the documented stratigraphic range of Appendicisporities auritus and Bacutrilites greenlandicus indicate these species extend into the early Cenomanian and Albian, respectively. Nichols and Jacobson (1982) reported Appendicisporities auritus from the early Cenomanian Aspen Shale of western Wyoming, while Sweet (1979) reported Bacutrilites greenlandicus from Albian rocks from the Canadian arctic. Cushman (1994) interpreted a middle Cenomanian age for the upper part of the Dakota Formation in western Colorado based on the identification of the trilete spore Cicatricosisporites crassiterminatus and dinoflagellate cyst Ovoidnium verrucosum. These taxa, however, have both been reported from the early Cenomanian aged Mowry Shale in the northern Uinta Basin. Given these considerations, the interpreted early Cenomanian age of the upper part of the second sequence of the Dakota Formation in the southern part is plausible. The interpreted late Albian age for the lower parts of the Dakota Formation (lower and basal upper Dakota sequences) outlined above remains unresolved with the results of previous workers. As presented above, the Tununk Member of the Mancos Shale in the southern part of the Uinta Basin is interpreted as middle-late Cenomanian in age. This age is in accord with the late Cenomanian age of the lower Tununk Member determined by Molenaar and Cobban (1991) and Carroll (1992) in the southern Uinta Basin, and the middle Cenomanian age interpreted by Cushman (1994) for the lower Mancos Shale in western Colorado.

34 STRATIGRAPHIC IMPLICATIONS

Dakota Formation and Mowry Shale The biostratigraphic data presented above indicate that in the southern Uinta Basin, the second sequence of the Dakota Formation is late Albian-early Cenomanian in age, while the first sequence is late Albian. This is significant as it indicates the unconformity between the first and second Dakota sequences is confined to the late Albian. A late Albian unconformity is also present between the first and second Dakota sequences in the northern part of the Uinta Basin, suggesting that both Dakota sequences are correlative across the basin. The early Cenomanian age of the upper parts of the second Dakota sequence in the south also implies the interval is correlative to the Mowry Shale in the northern part of the Uinta basin.

Mancos Shale Tununk Member The most significant indicator for the middle-late Cenomanian age of the lower Tununk/Mancos interval throughout the southern part of the Uinta Basin is in the occurrence of the late Cenomanian mollusk Pycnodonte newberryi. While this fossil occurs at the base of the Tununk Member in the western parts of the study area, it is found up to 6 m (~ 20 ft) above the Dakota Formation in eastern Utah (Figure 7). This trend continues into western Colorado where Pycnodonte newberryi has been identified at ~50 m (~165 ft) above the Dakota Formation near the town of Delta (Cushman, 1994). The lower Mancos Shale in this area also contains unequivocal middle Cenomanian ammonites (Cushman, 1994). This observation suggests that the lower Tununk Member/Mancos Shale in the southern part of the Uinta Basin is either time transgressive from east to west, and/or contains significant intraformational unconformities that merge towards the west. In either case, the marine deposits overlying the Dakota Formation in eastern Utah and western Colorado are undoubtedly highly condensed with ~3 million years of time (~95-92 Ma) represented by ~25 m (~80 ft) of stratigraphic section. A similar amount of time is missing between the middle-late Cenomanian lower Tununk Member and the underlying early Cenomanian second Dakota sequence along the MCU. This regional unconformity is situated between the two units throughout most of the southern part of the Uinta Basin (Molenaar and Cobban, 1991), or at the base of the laterally discontinuous fluvial channel complexes at top of the Dakota stratigraphic interval. Given the age of the strata above and below the unconformity, the MCU likely represents ~3 million years of early and

35 middle Cenomanian time (~98-95 Ma). Collectively the MCU, the condensed lower Tununk Member, and the overlying Coon Springs Sandstone, represents as much as 6 million years of early Cenomanian-middle Turonian time (~98-92 Ma). This same time interval is represented by the MCU between the Mowry Shale and the Tununk Member in the northern parts of the basin (Figure 2) that spans ~7 million years (~98-91 Ma).

36 UINTA BASIN CORRELATIONS In order to delineate the stratigraphic relationships between the Albian-Cenomanian rocks in the northern and southern parts of the Uinta Basin, geophysical logs from petroleum wells in the basin were used to construct a regional subsurface correlation. Stratigraphic picks identified in wells were anchored to outcrop measured sections of the Dakota Formation and Mowry Shale in the northern part of the basin and the Dakota Formation and lower parts of the Mancos Shale in the southern part of the basin (Figure 11). In the correlation, the top of the Mowry Shale was determined by comparing outcrop thicknesses with subsurface logs, in conjunction with log facies criteria described by Molenaar and Wilson (1990). The published log correlations and core descriptions of Kirschbaum (2003) further aided in designating between the Mowry Shale marine shelf and shoreface deposits and Dakota fluvial deposits in the southern part of the basin. The stratigraphic contacts of the lower Mancos Shale interval and the Dakota Formation were determined in subsurface geophysical logs using the correlation model described by McPherson et al. (2006) and McPherson et al. (2008). The base of the Cedar Mountain Formation was also correlated in order to demonstrate the incised nature of the lower Dakota Formation contact using the correlation model of McPherson et al. (2008). An outcrop gamma-ray log for the Westwater locality (Currie et al., 2008a) was utilized to aid correlations between the surface and subsurface in the southern part of the basin. A stratigraphic cross section of the resulting correlation is displayed in Figure 11. The datum used for the cross section is the MCU at top of the Mowry Shale in the northern part of the basin and the MCU at the top of the Dakota Formation in the southern part of the basin. The correlative nature of the MCU surface has been previously demonstrated by Molenaar and Cobban (1991). These authors correlated the MCU surface into the southern part of the Uinta Basin, placing it at the top of lithologies they classified as the undifferentiated, Albian-lower Cenomanian(?) Dakota and Cedar Mountain formations. In the stratigraphic cross section shown in Figure 11, the undifferentiated Dakota-Cedar Mountain formations of Molenaar and Cobban (1991) in the southern part of the basin (Wells 12-17, Section G) are made up primarily of the Dakota Formation, with a thin (<30 m (~100 ft)) interval of the Cedar Mountain Formation at the base.

37 A 10 miles 1 10 miles D 7.8 miles 2 9.3 miles 3 8.7 miles 4 6.9 miles 5 6.3 miles 6 1.4 miles 7 4.8 miles 8 G.R. G.R. G.R. G.R. Utah Colorado 1000 G.R. G.R. G.R. 13000 G.R. 12400 8100 Kmc 6900 6500 Kmy400 MCU 200 8600 Kd3 Kmy MCU mfs Kd2 1200 Kd2 13200 6800 Kd2 Unc 12600 8300 Kd1 7100 Kd1/Kd2 Unc 6700 Kc Kd1 Unc 200 8800 Kc Mud Fine Medium Coarse Very Gravel Jm Sand Sand Sand Coarse Sand TD=6800 Match Line 1400 13400 Kcb 7000 12800 TD=8494

TD=7070 7300 TD=10641 J/K Unc 9000 Mud Fine Medium Coarse Very Gravel Jm Sand Sand Sand Coarse Sand TD=13538

TD=4308 TD=13030 TD=18807

8 2.2 miles 9 3.1 miles 10 2.3 miles 11 6.6 miles 12 5.2 miles 13 11.7 miles 147 miles 151.4 miles 167.5 miles 17 8.2 miles G G.R. G.R. G.R. G.R. G.R. G.R.

Utah Colorado G.R. 9000 G.R. G.R. 3100 3000 900 8600 Westwater G.R. 6600 8100 8400 7000 G.R. 300 Kmc Kmc 6500 Kd3 Kd2 MCU 9200 3300 3200 1100 MCU Kmy 8800 mfs 6800 8300 Kd2 8600 7200 100 Kd1 Kd1/Kd2 Unc Kc Kc 6700

Mud Fine Medium Coarse Very Gravel Sand Sand Sand Coarse Jm Jm 3500 3400 Sand TD=6990 9400 1300 9000 TD=6800 8500 8800 TD=9068 TD=9472 TD=3640 TD=8840 TD=7780 TD=3692 TD=2793 TD=8562 Figure 11. Surface-to-subsurface cross section from north to south across the eastern side of the Uinta Basin with subsurface correlations anchored to outcrop locations. See Figure 1 and Table 1 for outcrop/well locations. The correlation model shows that the basal unconformities separating the Dakota and Cedar Mountain Formations can be correlated across the entire basin and that the Second Dakota Sequence in the south is correlative to the Second Dakota Sequence and Mowry Shale in the north. The correlation also shows the MCU situated at the top of the Mowry Shale in the north and at the top of the Second Dakota Sequence in the south. This model also shows the presence of the Third Dakota Sequence fluvial deposits (Wells 6-10) incised into marine shelf and shoreface deposits of the Mowry Shale.

38 In the northern part of the basin, deepwater shales and siltstones of the Mowry Shale below the MCU (Outcrops/Wells A-2) transition laterally into upward-coarsening shelf/shoreface deposits (Wells 3-10). This transition reflects the overall shoaling of the Mowry Shale along a paleoshoreline that trended NW-SE across the study area (Merewether and Cobban, 1986). The overall shallowing of the Mowry sea toward the southern part of the study area during the early Cenomanian produced the transition from the marine Mowry shoreface deposits to the nonmarine deposits of the second Dakota sequence observed between Wells 10 and 12 of the cross section (Figure 11). In the southern part of the basin, the base of the lower Mancos Tununk Member below the Coon Springs Sandstone corresponds with the MCU surface. A fluvial channel sandstone at the top of the Dakota interval (i.e. Well 11, Figure 11) likely represents fluvial incision during development of the MCU and deposition of the third Dakota sequence. This relationship is analogous to the fluvial channel complex situated at the top of the Agate Wash outcrop section (Figure 4, Figure 7). Additionally, in Wells 6-11 of the cross section, sandstones identified in core samples as fluvial deposits (Kirschbaum, 2003) are incised up to ~23 m (~75 ft) into marine shelf and shoreface deposits of the Mowry Shale. This relationship gives further credence to the interpreted presence of the MCU and third Dakota depositional sequence in the southern part of the basin. In wells that display this incision, the cross section datum is placed at the marine flooding surface between the fluvial channel deposits and the overlying Mancos Shale (Figure 11). In the correlation cross section, the Dakota Formation can be separated from the underlying Cedar Mountain Formation along the regional unconformity at the base of the first Dakota sequence (Figure 11). The unconformity at the base of the second Dakota sequence can also be traced with confidence in the subsurface in the northern half of the basin (Outcrops/Wells 1-7; Figure 11). However, south of Well 7, it is unclear whether the second Dakota unconformity merges with or erosionally truncates the first Dakota sequence-bounding unconformity. Therefore the first and second Dakota depositional sequences cannot be correlated with confidence in the subsurface of the southern part of the Uinta Basin. This observation is similar to that reported by Currie et al. (2008a) and Dark et al. (2008).

39 REGIONAL STRATIGRAPHIC EVOLUTION Combined, the biostratigraphic data and regional subsurface correlation presented above permits the reconstruction of the stratigraphic evolution of the Albian-Cenomanian strata of the Uinta Basin. First Dakota sequence fluvial incision began during late Albian time in both the northern and southern study areas. The development of the unconformity at the base of the first Dakota sequence likely occurred during a regional decrease in basin accommodation that is recorded throughout the Western Interior (Kauffman and Caldwell, 1993; Gale et al., 2008). The basal Dakota unconformity is likely correlative with the unconformity at the base of the Fall River Sandstone in Wyoming (Dolson et al., 1991), and the unconformity at the base of the Plainview Sandstone in eastern Colorado (Holbrook and Wright Dunbar, 1992; Scott et al., 2001). As relative sea level began to rise, the corresponding increase in accommodation resulted in filling of the incised paleovalleys at the base of the Dakota Formation (Figure 12, Time 1). Continued accommodation development resulted in fluvial channel and overbank deposition of the first Dakota sequence throughout the study area. First Dakota sequence nonmarine deposits in Utah are likely correlative with the marine deposits of the Skull Creek Shale in Wyoming and eastern Colorado (Dolson et al. 1991; Currie, 2002). Marine deposits that correlate with the first Dakota sequence have been identified in the subsurface of the Green River Basin ~100 km (~60 mi) north of the study area in southern Wyoming (Kirschbaum and Roberts, 2005). The base of the second Dakota sequence marks a second regional erosional unconformity that again was likely caused by a decrease in relative sea level in the basin. Age data presented above shows that this intra-formational unconformity developed during the late Albian. This age is similar in age to the unconformity separating the Skull Creek Shale and Muddy Sandstone in Wyoming, the Skull Creek Shale and the Horsetooth Member of the J Sandstone in the Denver Basin (Dolson et al., 1991). This unconformity can be traced northward into a correlative conformity represented by lower part of the Thermopolis Formation in northern Wyoming and southern Montana (Porter et al., 1997). A second late Albian increase in relative sea level initiated fluvial channel and overbank deposition of the second Dakota depositional sequence across the study area (Figure 12, Time 2). The lower parts of the Second Dakota sequence in Utah are likely correlative with the Muddy Sandstone in Wyoming, and the J Sandstone in the Denver Basin (Dolson et al. 1991; Currie, 2002). The increase in basin accommodation development accompanying the sea level rise continued into early Cenomanian time and resulted

40 S Time 4 N East - Central Utah Northeast Utah Non-Marine Mowry Shale Marine

Second Dakota Marine Flooding Surface Sequence First Dakota Sequence Cedar Mtn Formation

Time 3 S East - Central Utah Northeast Utah N Second Dakota Marine Flooding Surface Mowry Shale Sequence First Dakota Sequence Cedar Mtn Formation

S Time 2 N East - Central Utah Northeast Utah

Second Dakota First Dakota Sequence Sequence Cedar Mtn Formation

S Time 1 N East - Central Utah Northeast Utah First Dakota Sequence Cedar Mtn Formation

Explanation Channel Deposits Second Dakota Sequence Shoreface Deposits Overbank Deposits First Dakota Sequence Bounding Unconformity Prograding Sand Marine Deposits Second Dakota Sequence Bounding Unconformity First Dakota Sequence Overbank Deposits Coal Measures

Figure 12. Stratigraphic evolution of the Dakota Formation, Mowry Shale and Mancos Shale of eastern Utah (See text for explanation). Time 1: First Dakota Sequence fluvial incision and subsequent nonmarine aggradation; Time 2: Second Dakota Sequence fluvial deposition and aggradation; Time 3: Continued nonmarine deposition south of the basin and marine flooding of the Mowry Shale; Time 4: Continued nonmarine deposition in the south and marine deposition in the north.

41 S Time 6 N East - Central Utah Northeast Utah

Coon Springs Mancos Shale Sandstone Marine Marine Flooding Surface Third Dakota MCU MCU Sequence Non-Marine Mowry Shale Marine

Second Dakota Marine Flooding Surface Sequence First Dakota Sequence Cedar Mtn Formation

Time 5 S East - Central Utah Northeast Utah N

Third Dakota MCU MCU Sequence Non-Marine Mowry Shale Marine

Second Dakota Marine Flooding Surface Sequence First Dakota Sequence Cedar Mtn Formation

Explanation Channel Deposits Second Dakota Sequence First Dakota Sequence Shoreface Deposits Overbank Deposits Bounding Unconformity Second Dakota Sequence Prograding Sand Marine Deposits Bounding Unconformity First Dakota Sequence Middle Cretaceous Overbank Deposits Coal Measures Unconformity

Figure 12, continued. Time 5: Development of the Middle Cretaceous Unconformity at the top of the Mowry Shale in the north and at the top of the Second Dakota Sequence in the south. Time 5 also shows Third Dakota Sequence fluvial incision and aggradation. Time 6: Marine deposition of the Tununk Member of the Mancos Shale directly above the MCU followed by deposition of the marginal marine Coon Springs Sandstone.

42 in the encroachment of the Western Interior Mowry Seaway into the northern parts of the Uinta Basin. Mowry Shale deposition in the northern Uinta Basin was temporally equivalent with the coal-bearing, nonmarine deposits of the upper Second Dakota sequence in the southern part of the basin (Figure 12, Time 3). Stacked, progradational shoreface deposits identified in the subsurface of the Uinta Basin (Figure 11 and Figure 12, Time 4) mark the transition between the nonmarine Dakota Formation and the marine shelf deposits of the Mowry Shale. A regional decrease in relative sea level at the end of early Cenomanian time resulted in the development of the “Middle Cretaceous Unconformity” (MCU) throughout the study area (Figure 12, Time 5). Fluvial incision observed in logs of the Mowry shoreface deposits in the subsurface of the Uinta Basin (Figure 11 and Figure 12, Time 5) and interpreted in outcrops at the top of the Dakota interval in the southern Uinta basin (Figure 4 and Figure 7) are the most dramatic examples of the unconformity in the study area. In most parts of the Uinta Basin, however, the MCU is subtle. In the southern study area the unconformity is marked by the age difference between the underlying early Cenomanian second Dakota Sequence and the overlying middle-late Cenomanian Tununk Member of the Mancos Shale (Figure 4, Figure 11). The MCU is marked in the northern study area is by the difference in age between the early Cenomanian Mowry Shale and the middle Turonian Tununk Member of the Mancos Shale as identified by molluscan fossils (Figure 3, Figure 11) (Molenaar and Cobban, 1991). Regionally, the MCU transitions northeastward into a correlative conformity in Wyoming. Interpreted lowstand delta deposits in the early-middle Cenomanian Belle Fourche Member of the Frontier Formation in northeastern Wyoming (Bhattacharya and Willis, 2001) may be coeval with MCU development in Utah and Colorado. An accommodation increase following MCU development resulted in initial marine deposition of the Tununk Shale across the study area during middle-late Cenomanian time (Figure 12, Time 6). The development of a marine transgressive surface of erosion at the base of the Tununk Shale likely removed the majority of the nonmarine deposits associated with the third Dakota depositional sequence in the study area, preserving only the incised fluvial channel complexes observed in outcrop and the subsurface. Additional submarine erosion and/or intrabasin uplift in the northern parts of the study area may have produced the absence of middle Cenomanian-early Turonian strata in the northern parts of the study area (Molenaar and Cobban 1991). The overall coarsening upward nature of the highly condensed lower Tununk Shale/Coon Springs Sandstone Bed (Dakota Silt) in the southern part of the Uinta

43 Basin, suggests that a minor drop in sea level may have been coeval with the development of the MCU in the northern part of the basin (Molenaar and Cobban 1991).

44 CONCLUSIONS The biostratigraphic and regional correlation data presented in this study helps clarify the stratigraphic relationships between the Dakota Formation, Mowry Shale and Mancos Shale in eastern Utah and northwestern Colorado. The Dakota Formation contains three, unconformity- bound depositional sequences. The first Dakota sequence is late Albian in age and was deposited above a regional unconformity that can be traced throughout the Uinta Basin. The second Dakota sequence was deposited above a second regional unconformity that formed during latest Albian time. In the northern part of the Uinta Basin, nonmarine deposition of second Dakota sequence was confined to the late Albian. Early Cenomanian-aged marine deposits of the overlying Mowry Shale comprise the upper parts of the sequence in this part of the study area. In the southern part of the basin, however, the second Dakota sequence is entirely nonmarine. Stacked shoreface deposits identified in the subsurface of the Uinta Basin mark the transition between the nonmarine second Dakota sequence in the southern part of the basin and the correlative marine deposits of the Mowry Shale to the north. This interpreted stratigraphic framework of the majority of the Dakota Formation and the Mowry Shale in the northern and southern part of the Unite Basin is consistent with the regional stratigraphy proposed by Currie (2002). A regional decrease in relative sea level at the end of early Cenomanian time resulted in the development of the “Middle Cretaceous Unconformity” (MCU) throughout the study area. In the southern parts of the Unite Basin, the MCU is marked by the age difference between the underlying early Cenomanian second Dakota Sequence and the overlying middle-late Cenomanian Tununk Member of the Mancos Shale. The MCU is marked in the northern study area is by the difference in age between the early Cenomanian Mowry Shale and the middle Turonian Tununk Member of the Mancos Shale. Thin nonmarine deposits of the third Dakota sequence sporadically lie above the MCU in the southern parts of the study area. Incised fluvial channel complexes observed in well logs and outcrops of the southern Uinta Basin represent the only preserved deposits of the third Dakota sequence in the study area. Identification of the MCU and the third Dakota sequence in the southern part of the Uinta Basin is consistent with the stratigraphic interpretations of the uppermost parts of the Dakota interval postulated by Molenaar and Cobban (1991).

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49 Oboh-Ikuenobe, F.E., Benson, D.G., Scott, R.W., Holbrook, J.M., Evetts, M.J., and Erbacher, J., 2007, Re-evaluation of the Albian-Cenomanian boundary in the U.S. Western Interior based on dinoflagellate cysts. Review of Paleobotany and Palynology, v. 144, p. 77-97.

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50

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51

APPENDIX A

Plate 1. Detailed palynology for the Steinaker Reservoir Location 53 Plate 2. Detailed palynology for the Westwater Creek and Westwater 54 Creek East Location Plate 3. Detailed palynology for the Agate Wash Location 55 Plate 4. Detailed palynology for the Yellow Cat Location 56 Plate 5. Detailed palynology for the Green River East and Cottonwood 57 Wash Locations Plate 6. Detailed palynology for the Trapp Springs Core Location 58

52 Plate 1. Taxa Occurance (Top) and kerogen content/taxa distribution (Bottom) charts for the Steinaker Reservoir outcrop location.

SPORES AND POLLEN MICROPLANKTON sp. sp. spp. sp.

Age Sample Alisporites microsaccus Annulispora Araucariacites australis Concavissimisporites punctatus Deltoidospora Gleicheniidites senonicus Lilliacidites crassatus austroclavatidites Lycopodiumsporites Podocarpidites epistratus Podocarpidites Taxodiaceae scurrandus Tigrisporites Bisaccates Undifferentiated rotundus Verrucosisporites Chichaoudinium vestitum Pterospermella Subtilisphaera perlucida Tasmanaceae SR 1-B R R A R F A R R R R R R F R A R R R Early Cenomanian R = Rare, less than 6 specimens/slide F = Frequent, 6-15 specimens/slide C = Common, 16-30 specimens/slide A = Abundant, over 30 specimens/slide

Kerogen Distribution Taxa Distribution

Kerogen Content Species Diversity (Amorphous/Cuticular/ (Spores/ Woody) Microplankton) Reaction Amorphous Cuticular Woody Organic HCl Recovery Age Depth T.A.I. Spores Microplankton Paleoenvironment Early 0% 20% 40% 60% 80% 100% 0 5 10 15 SR 1-B 0.3-0.4 10% 20% 70% Very Good None 14 4 Estuarine Cenomanian

53 Plate 2. Taxa Occurance (Top) and kerogen content/taxa distribution (Bottom) charts for theWestwater Creek and Westwater Creek East outcrop locations.

SPORES AND POLLEN MICROPLANKTON ) A sp. sp. spp.

Age Sample spp. sp. A sp. spp. spp. sp. sp. (Pz reworked) spp. sp. Spiniferites ramosus Alterbidium acutula Cleistosphaeridium Coronifera oceanica Dinopterygium cladoides Odontochitina costata Oligosphaeridium complex Operculodinium Spiniferites cingulatus Surculosphaeridium longifurcatum Impletosphaeridium whitei Subtilisphaera terrula Exochosphaeridium bifidum Hystrichosphaeridium recurvatum Kiokansium polypes Subtilisphaera terrula Crassosphaera ornata Pterospermella Canninginopsis colliveri Downiesphaeridium multispinosum Araucariacites australis Camarozonosporites insignis Bisaccates Undifferentiated Gleicheniidites senonicus Taxodiaceae Classopollis classoides Deltoidospora Cicatricosisporites australiensis Cicatricosisporites brevilaesuratus Exesipollenites tumulus Densosporites Rugubivesiculties reductus subrugulatus Trizonites Cingulatisporites distaverrucosus Lusatisporis circumundulatus Retitriletes cenomanianus Schizosporites reticulatus Lycopodiumsporites Schizosporis reticulatus Camarozonosporites Foveotriletes Cicatricosisporites crassiterminatus Rugubivesiculites rugosus spackmani Taurocusporites Costatoperforosporites foveolatus Cicatricosisporites hallei Cicatricosisporites venustus Foraminisporis dailyi Laevigatosporites Foraminisporis wonthaggiensis Rouseisporites radiatus Schizosporis parvus Appendicisporites potomacensis Concavissimisporites punctatus Rouseisporites triangularis triangularis Lycopodiaciditres Ornamentifera echinita Cicatricosisporites imbricatus Cicatricosisporites pseudotripartitus Klukisporites pseudoreticulatus Osmundacidites wellmanii Sphagnumsporites regium Rouseisporites reticulatus Klukisporites areolatus Apiculatisporites Appendicisporites bifurcatus Appendicisporites jansonii Callialasporites dampieri austroclavatidites Lycopodiumsporites Neoraistrickia robusta Pilosisporites trichopapillosus apiverrucatus Trilobosporites crassus Trilobosporites trioreticulosus Trilobosporites Circulodinium distinctum Cribroperidinium edwardsi Micrhystridium Microforaminifera linings castanea Trichodinium Hystrichodinium pulchrum Isabelidinium acuminatum (Alterbia Florentinia stellata Florentinia ferox Hystrichosphaeridium recurvatum Odontochitina operculata Palaeohystrichophora infusorioides WWC 86.5 R R R R F R RRR FF R A R Late Cenomanian- WWC 84.5 R R F R R R R R R R RRRRR Middle Turonian WWC 83.2 F R R R R F R R R R R F R A RRR A RRRRRR F RR WWC 80.5 R R R R R R FF RR FAF R F R F WWC 77.5 C R F F RR R RR A RRRR RRRRR Middle-Late WWC 71.5 R R R RR RR Cenomanian WWC 70.5 F R R A R F R R R RRRRRRFRRRRR RR C C R FR WWC 69.4 R R R RR WWC 65.6 R R FRC WWC 63.1 F R R RRF WWC 57 R F F R R R Early Cenomanian WWCE 51.7 RRFR RR R WWCE 51.1 R RR RR R WWCE 50.7 RR R R WWCE 49.5 RRRRRR R R WWC 50 R F R R F R R R R RRRRR RRRRRRR Late Albian WWC 46.5 R R R A A C R RAARA RRAFRRRRFRRR R = Rare, less than 6 specimens/slide F = Frequent, 6-15 specimens/slide C = Common, 16-30 specimens/slide A = Abundant, over 30 specimens/slide

Kerogen Distribution Taxa Distribution

Species Diversity Kerogen Content (Spores/ Spores Microplankton Amorphous Cuticular Woody Organic HCl Reaction Age Depth T.A.I. Recovery (Amorphous/Cuticular/Woody) 0 Microplankton) 10 20 30 Paleoenvironment

0% 20% 40% 60% 80% 100% WWC 86.5 0.3-0.4 30% 20% 50% Excellent None 6 8 Cenomanian/Turonian WWC 84.5 0.3-0.4 40% 30% 40% Excellent None 8 6 Open Marine (Frontier Equivalent) WWC 83.2 0.3-0.4 10% 10% 80% Good Weak 11 17 Shelf WWC 80.5 0.3-0.4 90% 5% 5% Very Good Weak 5 12 WWC 77.5 0.3-0.4 10% 30% 60% Excellent None 5 Middle-Late Cenomanian WWC 71.5 0.3-0.4 0% 10% 90% Fair None 3 3 Restricted Marine WWC 70.5 0.3-0.4 30% 30% 40% Excellent None 21 7 Nearshore Marine WWC 69.4 0.3-0.4 25% 40% 35% Excellent None 5 WWC 65.6 0.3-0.4 0% 10% 90% Excellent None 0 WWC 63.1 0.3-0.4 25% 45% 30% Excellent None 6 WWC 57.0 0.3-0.4 0% 10% 90% None 6 Early Cenomanian Very Good WWCE 51.7 0.3-0.4 5% 25% 70% Excellent None 7 Deltaic/Swamp WWCE 51.1 0.3-0.4 10% 20% 70% Excellent None 6 WWCE 50.7 0.3-0.4 15% 15% 70% Very Good None 3 WWCE 49.5 0.3-0.4 5% 20% 75% Very Good None 8 WWC 50.0 0.3-0.4 10% 60% 30% Excellent None 21 Late Albian WWC 46.5 0.3-0.4 15% 15% 70% Good None 24

54 Plate 3. Taxa Occurance (Top) and kerogen content/taxa distribution (Bottom) charts for the Agate Wash outcrop location.

SPORES AND POLLEN sp. sp. A sp. sp. sp. sp. A sp. sp. sp.

sp.

Age Sample Apiculatisporis sp. Deltoidospora Exesipollenites tumulus Foraminisporis dailyi Lusatisporis circumundulatus Retitriletes cenomanianus Taxodiaceae Laevigatosporites ovatus Araucariacites australis Concavissimisporites punctatus Foraminisporis wonthaggiensis Gleicheniidites senonicus Balmeisporites Callialasporites marylandensis Trilobosporites Bisaccates Undifferentiated Appendicisporites bifurcatus Appendicisporites potomacensis Cicatricosisporites australiensis Cicatricosisporites hallei Cicatricosisporites mahroides Lilliacidites peroreticulatus marginatus Lycopodiumsporites Ornamentifera echinata Rouseisporites reticulatus apivrrucatus Trilobosporites Appendicisporites jansonii Appendicisporites problematicus Cicatricosisporites imbricatus Cingulatisporites distaverrucosus Foveotriletes Fraxinoipollenites venustus Lilliacidites inaequalis Matonisporites excavatus Microreticulatisporites spackmani Taurocusporites crassus Trilobosporites Aequitriradites ornatus Camarozonosporites insignis Cicatricosisporites brevilaesuratus Cicatricosisporites potomacensis Lycopodiumsporites Matonisporites equiexinus Platysaccus Rouseisporites radiatus minor Trilobosporites Apiculatisporis babsae Apiculatisporis Arcelites disciformis Callistosporites graniferus Neoraistrickia robusta Perotrilites pannuceus Pilosisporites trichopapillosus Tasmanaceae segmentatus Taurocusporites humilis Trilobosporites AW 44.5 RRRRRRR Early Cenomanian AW 41.5 R AW 25.5 FRR CRRR AW 24 RRRARRCRRRF AW 22 C RCRF ARRRRRRRRRR AW 21 CR RARCRARRR RRRRRRRRRRRR Late Albian AW20.3 RRR CRCRARRFR RRRR RRRRRRRRRR AW 17.5 RR RRRR RA R R RRRFRRRRCRRRRR AW 17 FRRRRC RC RR R R RFRRRFRFRRR R = Rare, less than 6 specimens/slide F = Frequent, 6-15 specimens/slide C = Common, 16-30 specimens/slide A = Abundant, over 30 specimens/slide

Agate Wash Kerogen Distribution Taxa Distribution

Kerogen Content (Amorphous/Cuticular/W Species Diversity oody) (Spores) Reaction Amorphous Cuticular Woody Organic HCl Recovery Age Depth T.A.I. Spores Microplankton Paleoenvironment

0% 20% 40% 60% 80% 100% 0 10 20 30 AW 44.5 0.3-0.4 10% 50% 40% Very Good None 7 Early Cenomanian AW 41.5 0.3-0.4 0% 25% 50% Very Good None 1 AW 25.5 0.3-0.4 0% 15% 85% Good None 7 AW 24 0.3-0.4 0% 60% 40% Very Good None 11 AW 22 0.3-0.4 0% 15% 85% Very Good None 23 Deltaic/Swamp AW 21 0.3-0.4 0% 25% 75% Very Good None 23 Late Albian AW 20.3 0.3-0.4 0% 25% 75% Very Good None 26 AW 17.5 0.3-0.4 5% 10% 85% Good None 24 AW 17 0.3-0.4 0% 5% 90% Good None 23

55 Plate 4. Taxa Occurance (Top) and kerogen content/taxa distribution (Bottom) charts for the Yellow Cat outcrop location.

SPORES AND POLLEN sp. sp. sp.

Age Sample Alisporites microsaccus Annulispora sp. Araucariacites australis Concavissimisporites punctatus Deltoidospora spp. Gleicheniidites senonicus Lilliacidites crassatus austroclavatidites Lycopodiumsporites Podocarpidites epistratus Podocarpidites Taxodiaceae scurrandus Tigrisporites Bisaccates Undifferentiated rotundus Verrucosisporites Bennittiteaepollenites lucifer Appendicisporites potomacensis Callialasporites sp. Cicatricosisporites australiensis Foraminisporis Wonthaggiensis Ischyosporites punctatus Laevigatosporites spp. Laricoides gigantea Monosulcites scabratus Osmundacidites wellmanii Perinopollenites Perotrilites Pilosisporites trichopapillosus Punctatosporites scabratus Rouseisporites reticulatus Schizosporis parvus trioreticulosus Trilobosporites Appendicisporites tricornitatus Cingutriletes clavus Foraminisporis dailyi Foveotriletes subtriangularis Klukisporites pseudoreticulatus Camarozo nosporites insignis Cicatricosisporites hallei Ischyosporites disjunctus Matonisporites excavatus Parvisaccites radiatus Rugubivesiculites rugosus Undulatisporites undulosus YC-45.5 R C R R R R RRRRRRRRRRRRRRRRRR

Late Albian YC- 44.5 R R F R F RRRR RRRRR

YC-43.5 R F R R CRRRRRR RRRRRRR

R = Rare, less than 6 specimens/slide F = Frequent, 6-15 specimens/slide C = Common, 16-30 specimens/slide A = Abundant, over 30 specimens/slide

Kerogen Distribution Taxa Distribution

Kerogen Content (Amorphous/ Species Diversity Reaction Spores Microplankton Amorphous Cuticular Woody Organic HCl Age Depth T.A.I. Recovery Cuticular/ Woody) (Spores) Paleoenvironment

0% 20% 40% 60% 80% 100% 0 10 20 30

YC-45.5 0.3-0.4 5% 10% 85% Very Good None 24 0

Late Albian YC- 44.5 0.3-0.4 0% 15% 85% Very Good None 13 0 Swamp/Deltaic

YC-43.5 0.3-0.4 0% 20% 80% Very Good None 18 0

56 Plate 5. Taxa Occurance (Top) and kerogen content/taxa distribution (Bottom) charts for the Green River East and Cottonwood Wash outcrop locations.

SPORES AND POLLEN MICROPLANKTON A) Alterbia ( spp. sp. spp. sp. sp. spp. sp. spp.

Age Sample Araucariacites australis Camarozonosporites insignis Cicatricosisporites australiensis Cicatricosisporites brevilaesuratus Costatoperforosporites foveolatus Classopollis classoides Deltoidospora Distaltriangulisporites perplexus Exesipollenites tumulus Gleicheniidites senonicus Klukisporites Sphagnum Taxodiacee Bisaccates Undifferentiated Cicatricosisporites venustus Foraminisporis dailyi Liliacidites inaequalis sporites Lycopodium Retitricolpites vulgaris crassimurus Tricolpites minor Trilobosporites Matonisporites excavatus Rugubivesiculites reductus Stereisporites regium Canningia scabrosa Cleistosphaeridium Circulodinium distinctum Coronifera oceanica Hystrichosphaeridium recurvatum Isabelidinium acuminatum Florentinia ferox Immpletosphaeridium Micrhystridium Odontochitina operculata Oligosphaeridium complex Operculodinium Palaeohystrichophora infusorioides Spiniferites ramosus castanea Trichodinium Tasmanaceae GR East 5.0 F R R R F R R R R R R F RARRFARARRFRRAF Cenom./Turonian GR East 4.4 R R R R R RRRRRRRR R Cenomanian GR East 2.7 Indeterminate

Cenom./Turonian CW2.65 R R R R R R R R RRR FR R

Indeterminate CW1.9 R = Rare, less than 6 specimens/slide F = Frequent, 6-15 specimens/slide C = Common, 16-30 specimens/slide A = Abundant, over 30 specimens/slide

Kerogen Distribution Taxa Distribution

Kerogen Content (Amorphous/ Species Diversity Cuticular/ Woody) (Spores/ Microplankton) Reaction Amorphous Cuticular Woody Organic HCl Recovery Age Depth T.A.I. Spores Microplankton Paleoenvironment 0% 20% 40% 60% 80% 100% 0 5 10 15 20 Restricted Marine

Cenom./Turonian CW2.65 0.3-0.4 15% 15% 70% Very Good Weak 11 3 Estuarine/Lagoonal Indeterminate CW1.9 ? 0% 0% 100% Trace None 0 0 Fluvial/Floodplain

Cenom./Turonian GR East 5.0 0.3-0.4 30% 30% 40% Very Good Weak 12 15 Open Marine Shelf Cenomanian GR East 4.4 0.3-0.4 0% 15% 85% Very Good None 13 1 Swamp/Shallow Lacustr. Indeterminate GR East 2.7 0.3-0.4 0% 5% 95% Very Good None 0 0 Fluvial/Deltaic

57 Plate 6. Taxa Occurance (Top) and kerogen content/taxa distribution (Bottom) charts for the Trapp Springs well location.

SPORES AND POLLEN sp. A sp. spp. sp. (reworked Pz) sp. (reworked Pz) sp. (reworked Pz) spp. sp. sp. (reworked Pz) sp. sp. (reworked Pz)

Age Sample Araucaricites australis Classopollis classoides Deltoidospora Perotrilites Sphagnum Lycospora minor Trilobosporites Densosporites austroclavatidites Lycopodiumsporites Murospora Punctatisporites Cicatricosisporites australiensis Cingulatisporites distaverrucosus Exesipollenites tumulus Convolutispora Camarozonosporites insignis Cicatricosisporitres crassiterminatus Gleicheniidites senonicus Taxodiaceae Callialasporites dampieri Costatoperforosporites foveolatus Aequitriradites spinulosus sp. (reworked Pz) Tasmanites Cicatricosisporites hallei Foveosporites canalis Psilatricolpites parvulus Antulisporites baculatus Cicatricosisporites brevilaesuratus Matonisporites excavatus Peromolites allensis Cicatricosisporites hughesii Laevigatosporites spackmani Taurocusporites Leptolepidites verrucatus Neoraistrickia robusta Nevesisporites semiscalaris Osmundacidites wellmanii Reteitricolpites georgensis Rouseisporites reticulatus Rouseisporites triangularis scurrandus Tigrisporites trioreticulosus Trilobosporites Apiculatisporites babsae Cicatricosisporites potomacensis Cicatricosisporites venustus Concavissimisporites punctatus Cyathidites australis Foraminispooris wonthaggiensis Ischyosporites disjunctus Pilosisporites trichopapillosus Bisaccates Undifferentiated Klukisporites pseudoreticulatus Retitricolpites vulgaris Appendicisporites jansonii Appendicisporites problematicus Cicatricosisporites annulatus Cicatricosisporites imbricatus Lycopodiumsporites Cicatricosisporites pseudotripartitus Klukisporites variegatus Appendicisporites potomacensis Biretisporites potonei Foraminisporis wonthaggiensis Schizosporis parvus TS8654 R R R TS8667 R R R R R TS8670 R RR TS8680 TS8689 R R R R R R R R TS8702 R Early to Middle TS8708 R RRRR Cenomanian TS8715 R R R R R R TS8724 R R RRRRRRR TS 8731 R R RRR TS8735 R RR TS8739 R R R RRR TS8743 R R RR RRRRR TS 8752 R R F R RR RRR TS8758 R R R R RRRR RRRRRRRRRRRR TS8767 R R RRRRRRRRR RRRRRRRFRRR TS8775 R RRR R R TS8785 R R R RARAR C RRRR Late Albian TS8798 R R RRRR R TS8810 C F C RF R R RR RRRRRR TS 8834 R R R R RR R RR TS 8845 R R CR R C TS 8856 R A RRRRR F FRR ARRR Indeterminate TS 8871 R = Rare, less than 6 specimens/slide F = Frequent, 6-15 specimens/slide C = Common, 16-30 specimens/slide A = Abundant, over 30 specimens/slide

Kerogen Distribution Taxa Distribution

Kerogen Content (Amorphous/ Cuticular/ Species Diversity Amorphous Cuticular Woody Organic HCl Reaction Recovery Age Depth T.A.I. Woody) Spores Microplankton (Spores) Paleoenvironment

0% 20% 40% 60% 80% 100% 0 5 10 15 20 25 TS8654 0.6-0.7 40% 10% 50% Very Good None 3 0 TS8667 0.6-0.7 70% 10% 20% Very Good None 5 0 TS8670 0.6-0.7 60% 10% 30% Very Good None 3 0 TS8680 0.6-0.7 40% 20% 40% Fair None 0 0 TS8689 0.6-0.7 70% 10% 20% Good None 8 0 TS8702 0.6-0.7 60% 10% 30% Fair None 1 0 Early to Middle TS8708 0.6-0.7 70% 10% 20% Good None 5 0 Cenomanian TS8715 0.6-0.7 70% 10% 20% Very Good None 6 0 TS8724 0.6-0.7 60% 10% 30% Very Good None 9 0 TS 8731 0.6-0.7 70% 10% 20% Very Good None 5 0 TS8735 0.6-0.7 50% 10% 40% Very Good None 3 0 TS8739 0.6-0.7 30% 20% 50% Very Good None 6 0 Swamp/Lacustrine TS8743 0.6-0.7 60% 10% 30% Very Good None 9 0 TS 8752 0.6-0.7 30% 40% 30% Very Good None 9 0 TS8758 0.6-0.7 25% 25% 50% Very Good None 20 0 TS8767 0.6-0.7 25% 25% 50% Very Good None 22 0 TS8775 0.6-0.7 20% 20% 60% Very Good None 6 0 TS8785 0.6-0.7 60% 20% 20% Very Good None 13 0 Late Albian TS8798 0.6-0.7 40% 20% 40% Very Good None 7 0 TS8810 0.6-0.7 25% 25% 50% Very Good None 15 0 TS 8834 0.6-0.7 30% 20% 50% Very Good None 9 0 TS 8845 0.6-0.7 40% 20% 40% Very Good None 6 0 TS 8856 0.6-0.7 30% 10% 60% Fair None 15 0 Indeterminate TS 8871 0.6-0.7 20% 20% 60% Poor None 0 0 Fluvial/Floodplain

58