Facies and Diagenesis of the Park City Formation: Sheep Mountain Anticline, Wind River Basin, Fremont County, Wyoming

FACIES AND DIAGENESIS OF THE PARK CITY FORMATION: SHEEP MOUNTAIN ANTICLINE, WIND RIVER BASIN, FREMONT COUNTY, WYOMING

By Daniel Griffin Hallau A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial fulfillment of the requirements for the degree of Master of Science (Geology).

Golden, Colorado

Date

Signed: Daniel G. Hallau

Signed: Dr. J. Frederick Sarg Thesis Advisor

Golden, Colorado

Date

Signed: Dr. Paul Santi Professor and Head Department of Geology and Geological Engineering

ii ABSTRACT The Phosphoria Rock Complex (PRC) includes: cherts, organic-rich mudrocks, and phosphorites of the Phosphoria Fm.; carbonates of the Park City Fm.; sandstones of the Shedhorn Fm.; and redbeds and evaporites of the Goose Egg Fm. The Permian succession at Sheep Mountain anticline near the southern margin of the Wind River basin in Fremont County, WY, is dominated by carbonates of the Park City Fm., but also includes phosphorites and mudrocks of the Phosphoria Fm. All three members of the Park City Fm. (i.e., Grandeur, Franson, and Ervay) crop out at Sheep Mountain. With potential source rocks to the west and potential sealing facies to the east, understanding the facies and facies changes in the carbonate members is crucial to exploring for stratigraphic traps in the Wind River basin. Carbonate facies and facies associations in the Ervay and Franson members indicate that deposition occurred along a very gently-dipping, westward-facing, carbonate ramp. Facies distribution between these two members is relatively similar, with the Ervay having a higher proportion of peloid packstones and ooid grainstones, and the underlying Franson having a higher proportion of bioclast packstones and intraclast packstones and wackestones. The position of Sheep Mountain along the carbonate ramp during Ervay time, therefore, was shallower than during Franson time, which may reflect the synchronous northwestward shift of the basin depocenter. The basal Grandeur Member is significantly more complicated, and a carbonate ramp may not be the most appropriate model for describing its depositional system. It is dominated by calcareous sandstones, silicified microbialites, and sandy carbonates. Sequence stratigraphic studies of the Park City Fm. to date have generally concluded that periods of dominant carbonate growth coincided with highstand systems tract deposition. Three main “cycles”, separated by regional sequence boundaries, have been described by previous workers in terms of their respective carbonate members (i.e., Ervay Cycle, Franson Cycle, and Grandeur Cycle). The findings of this study support the hypothesis of carbonate growth dominating during highstands but also show that significant carbonate growth occurred during transgressive systems tract deposition. Indeed, this interpretation is supported by facies association stacking patterns in outcrop, increase in phosphate content upward and basinward, hardground development as a result of transgression, and well log character in the surrounding subsurface wells. As such, most of the Franson carbonate at Sheep Mountain likely represents iii the transgressive systems tract deposition (and possibly lowstand systems tract deposition) of the Ervay Cycle. Based on the integration of X-ray fluorescence (XRF) data, phosphate accumulation generally occurred during transgressive and early highstand deposition. In this study, XRF-derived chemical signatures were only moderately successful at differentiating between depositional facies and between lithologies. The diagenetic history of the Park City Fm. at Sheep Mountain is complex. In outcrop, the Park City Fm. shows significant variability in dolomitization, silicification, and phosphogenesis. Phosphogenesis and dolomitization were likely the earliest events in the paragenetic sequence, where dolomitization may have helped to drive the Mg2+/Ca2+ ratio of porewaters low enough to encourage phosphate precipitation. As a feedback, precipitation of phosphate may have helped drive up the Mg2+/Ca2+ ratio. The presence of dolomite rhombs within collophane, however, indicates that phosphogenesis occurred prior to dolomitization. Marine cementation probably occurred next, followed by or synchronous with some silicification events. Later silicification, de-dolomitization, and calcite precipitation also occurred.

iv TABLE OF CONTENTS ABSTRACT...... iii TABLE OF CONTENTS...... v LIST OF FIGURES...... vii LIST OF TABLES...... xi LIST OF PLATES ...... xi ACKNOWLEDGEMENTS...... xii CHAPTER 1 INTRODUCTION...... 1 1.1 Location...... 1 1.2 Aims of study...... 2 1.3 Methods...... 3 1.3.1. . Measured sections ...... 3 1.3.2. . Thin section and hand sample analysis ...... 5 1.3.3. . Well log analysis...... 5 1.3.4. . X-ray fluorescence ...... 7 CHAPTER 2 GEOLOGICAL FRAMEWORK...... 8 2.1 Setting...... 8 2.2 Ages...... 10 2.3 The Permian Earth and tectonics...... 10 2.4 Basin configuration ...... 13 2.5 Sequence stratigraphy...... 15 2.6 Phosphate accumulation...... 17 CHAPTER 3 DEPOSITIONAL FACIES AND FACIES ASSOCIATIONS...... 20 3.1 Facies ...... 20 3.1.1. . Facies descriptions and interpretations...... 20 3.1.2. . Facies discussion...... 48 3.2 Facies associations...... 50 3.3 Depositional model ...... 55 CHAPTER 4 CHEMOFACIES...... 56 4.1 Chemofacies...... 56

v 4.1.1. . Compositional data analysis...... 56 CHAPTER 5 STRATIGRAPHIC CORRELATION AND SEQUENCE STRATIGRAPHY. . . .62 5.1 Pseudo gamma ray curve...... 62 5.2 Cross-section...... 63 5.3 Lithostratigraphic units...... 63 5.3.1. . Grandeur Mbr., Park City Fm...... 63 5.3.2. . Franson Mbr., Park City Fm...... 64 5.3.3. . Ervay Mbr., Park City Fm...... 68 5.4 Well log data ...... 69 5.5 Correlations and sequence stratigraphy ...... 72 CHAPTER 6 DIAGENESIS...... 78 6.1 Phosphogenesis ...... 78 6.2 Dolomitization ...... 79 6.3 Calcite cementation...... 82 6.4 Silicification ...... 84 6.4.1. . Early silicification...... 84 6.4.2. . Late silicification ...... 89 6.5 Late calcification events (dedolomite, fracture fill, etc.)...... 89 CHAPTER 7 DISCUSSION AND CONCLUSIONS...... 95 7.1 Discussion...... 95 7.2 Summary of conclusions...... 97 7.3 Suggestions for future work...... 98 REFERENCES...... 100 APPENDIX A MEASURED SECTIONS...... 107 APPENDIX B SUPPLEMENTAL ELECTRONIC FILES...... 135

vi LIST OF FIGURES Figure 1.1 Regional map. 1 Figure 1.2 Geologic map of Sheep Mountain (study area) ...... 4 Figure 2.1 Stratigraphic column...... 9 Figure 2.2 Map of major Paleozoic tectonic terranes and basins...... 12 Figure 2.3 Map showing basin depocenter shift based on thickness changes between the Meade Peak and Retort members...... 13 Figure 2.4 Late Permian paleogeographic map of the western United States. 14 Figure 2.5 Schematic stratigraphic column showing the prevailing sequence stratigraphic paradigm for the Phosphoria Rock Complex...... 16 Figure 2.6 Phosphogenesis and relative sea level. 18 Figure 2.7 Schematic diagram showing the process of phosphogenesis near the sediment-water interface...... 19 Figure 3.1 Hand-sample photo of a crinkly-laminated mudstone (Mc facies)...... 22 Figure 3.2 Hand-sample photo of a wavy-laminated microbialite (Mc facies)...... 22 Figure 3.3 Outcrop photo of silicified crinkly laminated mudstone with small- scale tepee structures (Mc facies)...... 23 Figure 3.4 Thin-section photomicrograph of a silty carbonate mudstone (M facies). 24 Figure 3.5 Thin-section photomicrograph of a silicified, bioturbated mudstone (M facies) . 24 Figure 3.6 Hand-sample photo of a bioturbated carbonate mudstone (M facies)...... 25 Figure 3.7 Outcrop photo of a heavily bioturbated carbonate mudstone ...... 25 Figure 3.8 Thin-section photomicrograph of a laminated sandy siltstone (Fg facies). . . . 27 Figure 3.9 Hand-sample photo of a calcareous siltstone (Fg facies)...... 27 Figure 3.10 Hand-sample photo of a calcareous shale (Fg facies)...... 28 Figure 3.11 Thin-section photomicrograph of a peloid wackestone (Wp facies)...... 29 Figure 3.12 Thin-section photomicrograph of a peloid wackestone (Wp facies)...... 29 Figure 3.13 Hand-sample photo of a peloid wackestone (Wp facies). 30 Figure 3.14 Thin-section photomicrograph of a bioclast wackestone (Wb facies)...... 31 Figure 3.15 Thin-section photomicrograph of a brachiopod wackestone or floatstone (Wb facies) ...... 31 Figure 3.16 Hand-sample photo of a bioturbated bioclast wackestone (Wb facies) . . . . . 32 Figure 3.17 Hand-sample photo of a phosphatic bioclastic peloidal intraclast wackestone (Wi facies). 33 Figure 3.18 Outcrop photo of a phosphatic bioclast intraclast wackestone (Wi facies) . 33 Figure 3.19 Hand-sample photo of a phosphatic intraclast wackestone (Wi facies). . . . . 34

vii Figure 3.20 Thin-section photomicrograph of a silty intraclastic peloid packstone with isopachous dolomitic cement (Pp facies) . 35 Figure 3.21 Thin-section photomicrograph of a peloid packstone or grainstone (Pp facies)...... 36 Figure 3.22 Outcrop photo of thick package of cross-bedded peloidal packstone (Pp facies). 36 Figure 3.23 Thin-section photomicrograph of a silicified bioclast packstone (Pb facies). . . 37 Figure 3.24 Thin-section photomicrograph of a brachiopod packstone (Pb facies). 38 Figure 3.25 Outcrop photo of a bioclast packstone (Pb facies) . 38 Figure 3.26 Outcrop photos of two ramose bryozoans and one fenestrate bryozoan . . . . 39 Figure 3.27 Outcrop photo of a bioclast packstone that grades up into a bioclast wackestone...... 40 Figure 3.28 Thin-section photomicrograph of a silica-cemented phosphatic intraclast packstone (Pi facies) . 41 Figure 3.29 Thin-section photomicrograph of an intraclast packstone where intraclasts contain siliceous sponge spicules (Pi facies)...... 42 Figure 3.30 Outcrop photos of interbedded mudstones, intraclast wackestone, and intraclast packstones ...... 42 Figure 3.31 Outcrop photo of an intraclast packstone grading into an intraclast wackestone. 43 Figure 3.32 Hand-sample photo of a pervasively silicified bioclast grainstone (Gb facies)...... 44 Figure 3.33 Hand-sample photo of an intraclast sandy bioclast grainstone (Gb facies). . . 44 Figure 3.34 Thin-section photomicrograph of a pervasively dolomitized ooid grainstone with isopachous cement and compaction features (Go facies). 45 Figure 3.35 Thin-section photomicrograph of a brachiopod ooid grainstone (Go facies) . 46 Figure 3.36 Outcrop photo of a cross-bedded peloid packstone or ooid grainstone. . . . . 46 Figure 3.37 Hand-sample photo of a calcareous silty intraclastic sandstone with a minor bioclast component (Ss facies)...... 47 Figure 3.38 Hand-sample photo of a sandstone (Ss facies)...... 47 Figure 3.39 Pie chart displaying the relative abundances of facies in the Ervay and Franson members...... 48 Figure 3.40 Pie charts comparing the relative abundances of facies between the Ervay and Franson members. 49 Figure 3.41 Schematic carbonate ramp superimposed with facies associations in this study, defined by ramp position and water depth...... 50 Figure 3.42 Outcrop photo of the Intertidal-Supratidal facies association (interbedded dolomudstone, siltstone, and replaced evaporite) . 51 Figure 3.43 Outcrop photo of the OR facies association, where intraclast and bioclast packstone lags punctuate overall Fg deposition. 53

viii Figure 3.44 Outcrop photo of the MR facies association...... 54 Figure 3.45 Schematic block-diagram of a carbonate ramp for Ervay and Fran- son deposition...... 55 Figure 4.1 Ternary diagrams of the U-K-Th element suite that demonstrate the value of data centering, and the relative ineffectiveness of the U-K-Th for differentiating the depositional facies defined in this study . 58 Figure 4.2 Centered ternary diagram of the Mg-Al-P element suite with data points colored by lithostratigraphic unit ...... 59 Figure 4.3 Centered ternary plot showing the Mg-Sr-Ba element suite with data points colored by lithostratigraphic unit...... 61 Figure 5.1 Sharp rugose contact near the base of the Franson bench interpreted to be a transgressive hardground. 65 Figure 5.2 Bioturbated marine hardground surface in the Franson bench. 66 Figure 5.3 Outcrop photo of the Franson at Schlichting Gulch overlaid with a schematic facies section...... 67 Figure 5.4 Outcrop photo of a heavily bioturbated unit overlaid by a cross- bedded peloid packstone or ooid grainstone . 69 Figure 5.5 Neutron-Density crossplot for the Dishpan Federal 12-29 well demonstrating the presence of anhydrite in wells east of the study area . . . . 70 Figure 5.6 Neutron-Density crossplot for the Carmody 34 well demonstrating the absence of anhydrite in wells west of the study area. 71 Figure 5.7 Color-filled gamma ray profile showing fining upwards and cleaning upwards patterns...... 73 Figure 5.8 Cross-section of measured sections along with the Mg, P, and Al XRF data in depth plot view...... 75 Figure 5.9 Centered ternary diagram of the Mg-Al-P element suite with data points color-coded by systems tract...... 77 Figure 6.1 Schematic visual representation of the paragenetic sequence. 78 Figure 6.2 Thin-section photomicrograph of a pervasively silicified bryozoan with phosphatic zooecia...... 80 Figure 6.3 Thin-section photomicrograph of a bryozoan fragment with phosphate-filled zooecia. 80 Figure 6.4 Thin-section photomicrograph of a pervasively silicified sample where phosphate has precipitated in echinoderm primary intraclast porosity. . 81 Figure 6.5 Thin-section photomicrograph of a pervasively silicified sample where phosphate has precipitated in echinoderm primary intraclast porosity. . 81 Figure 6.6 Thin-section photomicrograph of a sucrosic dolomite with high interparticle porosity and some poikilotopic calcite growing in the pore spaces ...... 82 Figure 6.7 Thin-section photomicrograph of a dolomite rhomb growth in a phosphate substrate in a Franson carbonate ...... 83

ix Figure 6.8 Thin-section photomicrograph of a dolomite rhomb growth on a calcite substrate (brachiopod)...... 83 Figure 6.9 Thin-section photomicrograph isopachous cement, interpreted to be marine phreatic, coating various allochems. 84 Figure 6.10 Thin-section photomicrograph of a bryozoan showing non-isopachous cement in its zooecia...... 85 Figure 6.11 Thin-section photomicrograph of a bryozoan zooecia filled with phosphate and lined with non-isopachous cement. 85 Figure 6.12 Thin-section photomicrograph of a dolomite rhomb that has been replaced by silica, within a phosphate-filled brachiopod spine . 86 Figure 6.13 Thin-section photomicrograph under cross-nicols showing length- slow fibrous quartz (chalcedony) . 86 Figure 6.14 Thin-section photomicrograph showing dolomite rhombs and silica...... 87 Figure 6.15 Thin-section photomicrograph demonstrating the excellent preservation of bioclasts as a result of silicification...... 88 Figure 6.16 Outcrop photo of a massive silicified unit. 88 Figure 6.17 Hand-sample photo of a silicicryptstone with apparent cross laminations (originally Go or Pp facies). 89 Figure 6.18 Thin-section photomicrograph of silica textures in an occluded pore space showing 3 phases of silica growth...... 90 Figure 6.19 Thin-section photomicrograph of dedolomite rhombs in a pervasively silicified sample...... 91 Figure 6.20 Thin-section photomicrograph of a dedolomite rhomb in a pervasively silicified sample...... 91 Figure 6.21 Thin-section photomicrograph of calcite degradation of a dolomite rhomb . . . 92 Figure 6.22 Thin-section photomicrograph of calcite degradation of a dolomite rhomb . . . 92 Figure 6.23 Thin-section photomicrograph of a calcite-filled fracture through a pervasively silicified sample...... 93 Figure 6.24 Thin-section photomicrograph of calcite-filled fractures cross-cutting phosphatic bioclasts and a siliceous matrix...... 93

x LIST OF TABLES Table 1.1 Locations of measured sections. . 5 Table 1.2 Well names and locations for the wells used in this study. Well logs that were digitized for this study are also noted...... 6 Table 3.1 Summary of facies and facies associations in this study...... 20

LIST OF PLATES Plate 1 Cross-section that integrates measured sections on Sheep Moun- tain with well logs from nearby wells...... P-1

xi ACKNOWLEDGEMENTS First and foremost, I’d like to thank Bob and Sue Cluff of the Discovery Group, Inc. (Den- ver, CO) for their unfaltering and continued support in this research. I’d also like to thank my advisor Rick Sarg and committee members Mark Longman and John Humphrey for their patient guidance and sage advice throughout the course of this project. Betsy and John Spence of Lander, WY graciously allowed access to the outcrops by way of their land, and generously invited us to stay in a wonderful cabin on their property during the field season. Thank you. Chuck Erickson allowed access to the Beaver Creek outcrops. Mitch Sigler and Brittany Oetter helped with the fieldwork. Thanks for hanging in there when my Jeep didn’t! Rick Wendlandt provided the use of his microscope cameras. Mike Batzle allowed me to use his rock saw.

xii CHAPTER 1 1 INTRODUCTION

1.1 Location This study examines Permian strata on the Sheep Mountain anticline, located in Fre- mont County, Wyoming, near the southern margin of the Wind River basin (Figure 1.1). Situ- ated about 35 kilometers southeast of Lander, WY, the approximately 10-square-mile study area spans Townships 97 & 98W and Ranges 30 & 31N. Sheep Mountain is a Laramide-age, NW-plunging, asymmetric anticline. It is part of a series of en echelon folds along the eastern front of the Wind River Mountains (Abercrombie, 1989). Structures along this trend are controlled by a SW-vergent thrust fault. As a result, anticlines at the surface exhibit southwest asymmetry (Abercrombie, 1989). Oil fields are commonly associated with many of these anticlines including Derby Dome, Dallas Dome, and Lander Field (Willis and Groshong, 1996). Outcrops are best exposed on the western flank of Sheep

110° W 109° W 108° W 107° W 44° N Park

Hot Springs Washakie MT Johnson Teton Wind River Basin l River Thermopolis Dubois der w WY o ID P

26 W ind n 287 e Riv 25 e e r r G R iver

Natrona Fremont 26 Sublette Riverton 20 43° N

Casper Pinedale Lander e 189 Platt

351 N Jeffrey City 0 15 30 Miles r te 287 River twa ee Sw

WYOMING Carbon Modified from Kirchbaum et al. (2007) Figure 1.1 The study area is located at the southwestern limit of the Wind River basin, about 35 km southeast of Lander, WY. The Wind River basin is a Laramide-age depositional basin in west-central Wyoming.

1 Mountain, where beds locally dip from 20 to 35° W, and on the northern flank of southeastern arm near Beaver Creek, where beds locally dip about 10° N.

1.2 Aims of study The Permian section on Sheep Mountain represents a critical position between the landward Goose Egg shales and evaporites and the outboard Phosphoria cherts and organic-rich mudrocks. A known reservoir facies, the Park City Formation is an attractive target in light of the updip trap potential and the high quality downdip source rock. Indeed, Claypool et al. (1978) estimated that the Phosphoria source rocks may have generated as much as 225 billion barrels of oil, and the Cottonwood Creek stratigraphic trap in the southeast Bighorn basin, for example, has an estimated ultimate recovery of 60 million barrels from the Permian carbonates (Coalson and Inden, 1990). As such, this study of facies changes and of depositional and diagenetic histories of the Phosphoria Rock Complex (PRC) should be useful in hydrocarbon exploration in the Wind River basin. Most PRC production to date in the basin is from anticlinal structures and is almost exclusively associated with Tensleep production. In light of that fact, there is a possibility that the basin is largely under-explored with respect to Permian stratigraphic traps. Un- derstanding facies variation in that shelfal position will be important in any exploration for those subtle stratigraphic traps. The goal of this study is to describe and interpret the Permian carbonate, chert, and mudrock stratigraphy in the Sheep Mountain anticline area using modern stratigraphic and sedi- mentologic concepts and modern elemental analytical tools. The study area, while relatively small, offers a good opportunity to examine the Permian section in great detail in an area with a wide variety of depositional facies. The main objectives of this study are to:

• Identify the lithofacies present in the study area, describe facies variability and distribution, and develop a depositional model based on this facies analysis.

• Examine the strata within the large-scale sequence stratigraphic framework that has

already been defined by previous workers.

2 • Develop a paragenetic sequence that describes the varied diagenetic events that occurred in the succession.

• Examine to what extent handheld X-ray fluorescence (XRF) data is useful in discriminating between facies, lithology, and stratigraphic position.

1.3 Methods The approach to meeting these objectives is fourfold, including outcrop description (i.e., measured sections), thin section and hand sample analysis, subsurface ties using well logs, and X-ray fluorescence (XRF).

1.3.1 Measured sections Four detailed measured sections, three along the western flank and one on the eastern flank, help to assess lateral and vertical variability of the Phosphoria Rock Complex (PRC) on Sheep Mountain. None of these outcrops displays the complete Permian succession, but the carbonates typically crop out such that variation in the carbonate facies can be adequately as- sessed. In addition, these measured sections provide a context for the petrographic work and provide a tie to subsurface log data. The complete measured section descriptions can be found in Appendix A. The measured sections are named based on nearby geographic features from the Del Monte Ridge and Schoettlin Mountain quadrangles. In this study, from north to south, they are called Red Bluff (RB), Schlichting Gulch (SG), Wilson Draw (WD), and Beaver Creek (BC) (Figure 1.2; for specific location data, see Table 1.1). On the west side of the anticline, where beds dip westward at 20-35°, outcrops are best exposed along dry gulches. The underlying Pennsylvanian Tensleep Formation crops out at the center of the anticline, so its contact with the Permian succession is generally at the high part of the western slope. The contact between the Permian succession and the overlying Trias- sic Dinwoody Formation is down near the base of the mountain (Figure 1.2). A full stratigraphic section, therefore, may represent a transect of up to three-quarters of a mile. A Jacob staff was used to measure vertical heights where the section was covered, but because the covered

3 sections were commonly dip slopes, the distances involved were large, hence it is possible that some unavoidable error was introduced where there was significant covered section. Outcrop photos were used to verify covered section heights where possible. Facies were described in the field, to the extent that outcrop quality allowed, and were refined based on thin section and hand sample descriptions.

RB Measured sections

Triassic

RB Cretaceous

SG Jurassic

WD BC

Perm. Penn.

~1 mile

Modified from Johnson & Sutherland (2008) Figure 1.2 Geologic map of the study area. This figure approximately corresponds to the red box on Figure 1.1. Stars indicate the measured sections used in this study. Measured sections include Red Bluff (RB), Schlichting Gulch (SG), Wilson Draw (WD), and Beaver Creek (BC), all named for nearby geographic features.

4 Table 1.1 Locations of measured sections.

Measured Section Abbrev. Latitude Longitude Township, Range, Section 1 1 Red Bluff RB 42°37'42.67"N 108°29'11.73"W T31N R98W Sec. 25, S2 SE4 1 1 Schlichting Gulch SG 42°36'51.63"N 108°29'18.02"W T31N R98W Sec. 36, S2 SE4 1 1 Wilson Draw WD 42°35'27.15"N 108°28'27.03"W T30N R97W Sec. 7, SE4 NW4 1 1 Beaver Creek BC 42°35'17.12"N 108°24'15.68"W T30N R97W Sec. 10, W2 SE4

1.3.2 Thin section and hand sample analysis Sixty thin sections, made from samples collected from the measured sections, were described in detail with respect to carbonate texture and depositional and diagenetic fabric. Thin sections were prepared from cut billets by Spectrum Petrographics in Vancouver, WA. Thin sections were vacuum-impregnated with UV-sensitive blue-colored Epotek 301 epoxy and stained with alizarin-red and potassium-ferricyanide. Approximately 200 hand samples were cut perpendicular to bedding, photographed at high resolution, and described in detail with the aid of a stereo binocular microscope. Hand sample and thin section localities are indicated on the measured sections in Appendix A.

1.3.3 Well log analysis To tie the outcrop observations to a subsurface dataset, eight nearby modern (post- 1980) well logs in the vicinity of Sheep Mountain were digitized. Basic Neutron-Density crossplots were made to define several crucial lithologic differences between the succession to the west of the study area and the succession to the east. Wells were chosen based on their proximity to Sheep Mountain as well as their logging suite, but only wells with density logs were used. Logs for each of these wells were hand- digitized in IHS Petra software. The digitized logs include gamma ray (GR), deep resistivity

(ILD), neutron porosity (NPHI), bulk density (RHOB), photoelectric factor (PEF), and acoustic slowness (DT), where available. The well locations and logging suites are listed in Table 1.2. A cross-section that includes these wells is found in Plate 1, which also includes a map of the

5 Table 1.2 Well names and locations for the wells used in this study. Well logs that were digitized for this study are also noted.

Surface locations (°)

Completion API number Operator Well label Latitude Longitude Logging suite date Sonic, bulk density, gamma ray, 49013210360000 John A. March BULL CANYON STATE 1 9/15/1980 42.483 -108.1991 neutron porosity, deep resistivity

Bulk density, density correction, Kimbark 49013211160000 FEDERAL-JOHNSON 1-12 9/1/1981 42.6696 -108.6084 gamma ray, Operating Co. neutron porosity, deep resistivity

Sonic, bulk density, gamma ray, 49013213320000 John A. March UNIT 1 1/25/1983 42.485 -108.2691 neutron porosity, deep resistivity

Bulk density, photoelectric Union Oil of factor, gamma 49013215480000 CARMODY 34 10/17/1988 42.6912 -108.5549 California ray, neutron porosity, deep resistivity

Bulk density, photoelectric factor, spectral Union Oil of 49013215540000 DUNNE 37 8/15/1989 42.6844 -108.5501 gamma ray, California neutron porosity, deep resistivity

Bulk density, gamma ray, Gilmore Oil & 49013215590000 FEDERAL 2-4 9/4/1990 42.5982 -108.1995 neutron Gas Co. porosity, deep resistivity

Sonic, bulk density, Pacific gamma ray, 49013216330000 Enterprises Oil DISHPAN FEDERAL 12-29 3/9/1991 42.635 -108.2229 neutron Co. porosity, deep resistivity Sonic, bulk density, BHP photoelectric Petroleum 49013216510000 DISHPAN-FEDERAL 34-15 12/11/1991 42.6562 -108.2908 factor, gamma (Americas) ray, neutron Inc. porosity, deep resistivity

6 well locations. The gamma-ray curve has been color-filled to highlight “clean” versus “hot” formations and to facilitate visual comparison to each other and to the XRF-derived elemental gamma-ray profiles.

1.3.4 X-ray fluorescence X-ray fluorescence (XRF) data were acquired on nearly all collected hand samples (n=200) using a Niton XL3t GOLDD+ XRF Analyzer, which uses energy-dispersive X-ray fluorescence technology to measure elemental abundances. Samples were slabbed using a dia- mond bit rock saw, and measurements were taken on the slabbed surface, where possible, with assay times set at 3 minutes. In most cases, the sample was placed in a ThermoFisher test stand for the analysis. While this method is inferior to powdered homogenization of the sample, it has provided a semi-quantitative dataset that describes the rock assemblage with some degree of accuracy. The XRF data have been tied to subsurface well log data by using the uranium, thorium, and potassium abundances to create synthetic gamma ray curves for comparison to wireline gamma ray logs.

7 CHAPTER 2 2 GEOLOGICAL FRAMEWORK

2.1 Setting Permian stratigraphy in western Wyoming comprises four formations (Figure 2.1): (1) the Phosphoria (cherts, organic rich mudrocks, and phosphorites), (2) the Park City (marine carbonates), (3) the Shedhorn (sandstone) and (4) the Goose Egg (red beds and evaporites) (McK- elvey et al., 1959; Burk and Thomas, 1956). McKelvey et al. (1959) outlined this nomenclature, wherein the carbonate facies were defined as Park City and the chert and mudrock facies as Phosphoria. However, the complicated intertonguing relationship between the Phosphoria and Park City formations (Figure 2.1) and a lack of diagnostic fossils has made detailed correlation difficult for past workers, and as a consequence, oil field terminology typically does not differen- tiate the two, designating both carbonates and deeper water facies as “Phosphoria” (Ahlstrand and Peterson, 1978). The differentiation of the Phosphoria mud and chert facies from the Park City carbonates of McKelvey et al. (1959) seems to be arbitrary and largely lithostratigraphically driven, which early workers have admitted, such as Yochelson (1968). Moreover, the differentiation needlessly complicates the nomenclature, since the carbonate and deeper water facies are genetically related, as evidenced by the high phosphorite concentrations in both. Therefore, this study adopts the system used by Hiatt and Budd (2001) (modified fromYochelson, 1968) to refer to the Phosphoria, Park City, and Goose Egg formations, as well as the Shedhorn Sand- stone, together as the Phosphoria Rock Complex (PRC). The Park City and Phosphoria formations are further subdivided into 7 members (Figure 2.1). From oldest to youngest, the Park City Formation is comprised of the Grandeur, the Fran- son, and the Ervay members. The Phosphoria Formation is comprised of the Meade Peak and Retort organic-rich shale and phosphorite members, as well as the Rex and Tosi chert members. For most of the Permian, the Sheep Mountain anticline area was situated just west of the paleo-shoreline (Lane 1973) that marks the transition from continental evaporite and red-bed fa-

8 SE Idaho Central Wyoming Tr. “Cycles” “Ervay” Guadalupian “Franson” Permian

Leonardian “Grandeur” Penn. to Wolfcamp.

PARK CITY FM. OTHER UNITS Ervay Mbr Shedhorn Fm. Franson Mbr Wells / Tensleep Fms. Grandeur Mbr Goose Egg Fm. PHOSPHORIA FM. Minnelusa Fm. Rex / Tosi Mbrs. Dinwoody Fm. Meade Peak / Mackentire Mbr. Retort Mbrs. Cherty Shales Hiatus

Figure 2.1 Stratigraphic column, modified from Clark (1994) and Whalen (1996). The PRC is comprised of three informal “Cycles”, named for their equivalent Park City Fm. members (i.e., the “Ervay Cycle”, “Franson Cycle”, and “Grandeur Cycle”.

9 cies (Goose Egg) to the east, and marine carbonates (Park City), cherts, and mudrocks (Phos- phoria) to the west. The paleo-shoreline ran roughly north-south (Lane, 1973; Merschat, 1984).

2.2 Ages Detailed conodont-brachiopod biostratigraphic work by Wardlaw and Collinson (1986) has constrained the age of the succession to late Early Permian to Late Permian (Figure 2.1). While early workers lumped all of the PRC deposition into the undifferentiated “Middle Permian”, Yochelson (1968) suggested a relatively narrow time slice for deposition. Basing his conclusions on extensive biostratigraphic work, he viewed the Park City Formation as equivalent to parts of the Leonard and Word formations of west Texas. Franson and Ervay deposition occurred during the Guadalupian epoch, with some Ervay deposition in the earliest Capitanian epoch (Wardlaw and Collinson, 1986). For the most part, Grandeur deposition was likely Leon- ardian in age, the topmost portion perhaps being equivalent to the lowest part of the Meade Peak Member (Wardlaw and Collinson, 1986). Yochelson (1968) does suggest that at least part of the Grandeur is pre-Leonardian based on fossil assemblages in several localities, including southwestern Montana.

2.3 The Permian Earth and tectonics The Permian period was a time of enormous climatic changes. The amalgamation of the Pangaean super-continent appears to have had a profound effect on global climate (Hein 2004). The continental configuration may have led to an increase in the size and aridity of deserts, along with greater seasonal variations (e.g., Parrish, 1995). On a global scale, these trends manifest as extensive deposits of red beds and evaporites, as well as intense storm deposits (Hein, 2004). In addition, while the South Pole was extensively glaciated at the outset of the Permian, by the start of the Triassic the ice caps appear to have completely melted. Lastly, production of oceanic crust was near an all-time Phanerozoic low (Gaffin, 1987). Generally speaking, geologists invoke three separate orogenies when discussing Pa- leozoic tectonics of the U.S. western cordillera: the Antler (Devonian to Early Mississippian), Ouachita-Marathon orogeny (Pennsylvanian), and the Sonoma (latest Permian to Triassic).

10 However, this may be overly simplistic. In a general sense, the Phosphoria depositional basin was situated between the relic Antler highlands to the west, the Ancestral Rocky Mountains to the southeast, and the Milk River uplift (Maughan, 1979) to the northeast. While the Middle Mississippian to Late Permian has largely been considered a time of tectonic quiescence in the western cordillera, a number of tectonic phases, apparently incompatible with Antler/Sonoma/ Ouachita timing, have been documented (Trexler et al., 1991). Whether these represent separate tectonic events or simply intraplate effects of the Antler, Ouachita, and Sonoma orogenic events is still actively debated. Trexler et al. (1991) document several other tectonic phases that are relevant to sedimentation at the continental margin; namely the Dry Mountain (Wolfcampian to Leonardian) and Ishbel (Leonardian to Guadalupian) events (Figure 2.2). For example, Permian strata rest disconformably on Pennsylvanian strata in Colorado and Wyoming, but moving westwards to the Antler highlands, the unconformity becomes angular, implying late Pennsylvanian and Early Permian tectonism (at least some tilting). Most of the literature suggests relative quiescence through most of the Permian in the region of the Phosphoria Sea (e.g., Peterson, 1980). However, the Phosphoria basin depocenter shifted northward during the Permian, which suggests some tectonic control on basin configuration (Figure 2.3). Some workers (Hendrix and Byers, 2000; Walling, 2000) suggest that this shift of the basin may have been a result of movement on thrusts associated with the earliest pulses of the Sonoma orogeny (i.e., emplacement of the Golconda allochthon). Hendrix and Byers (2000) also describe an angular unconformity between the Grandeur and the overlying Meade Peak in the Uinta Mountains, which might also suggest some local Leonardian tectonism (e.g., Ishbel event of Trexler et al., 1991), though it is unclear whether the relationship is actually angular or simply apparently angular due to the large facies variation in the Grandeur. In actu- ality, the shift of the basin depocenter may be related to the Dry Mountain and/or Ishbel events described by Trexler et al. (1991).

11 ?

0 100 km

CASSIAR ISHBEL TERRANE TROUGH

KOOTENAY TERRANE

WOOD RIVER ANTLER BASIN BELT PHOSPHORIA BASIN GOLCONDA CASSIA TERRANE BASIN OQUIRRH BASIN DEEP CREEK- DEATH TINCTIC UPLIFT VALLEY DRY MOUNTAIN AND FERGU- SON TROUGHS

MOJAVE

Allochthonous terranes Sedimentary basins

Figure 2.2 Major Paleozoic tectonic terranes and basins of the North American Western Cordil- lera. Of particular interest to Permian tectonism are the Ishbel and Dry Mountain events, which may explain the shift in depocenter in the Phosphoria basin. Modified fromTrexler et al. (1991)

12 114° 112° 110° 108° 106° 104°

600 kg/mile2 (Extent of black shale facies) 46° Butte 0 Thrust belt 30 60 0 1,00 0 Approximate 3,000 0 Dillon Billings Retort 0 5,000 Montana

depocenter 7,00 Wyoming

44°

Jackson Wind

0 0 0 Lander 0 Pocatello 5,00 2,00 0 River 9,00 3,00 0 100 0 7,00 60 0 0 Idaho 30 Basin 42° Approximate Utah Meade Peak depocenter Cheyenne Salt Colorado Lake City 0 100 40° Miles Denver

Figure 2.3 Red contour lines in this figure represent a measure of organic richness (kilograms of black shale per square mile), as calculated by Claypool et al. (1978). The shift in organic richness through time is interpreted to reflect a shift in basin depocenters from Meade Peak to Retort times. Modified from Kirschbaum et al. (2007), after Claypool et al. (1978).

2.4 Basin configuration Irrespective of intra-Permian tectonic events, it appears that the pre-Permian orogenies largely set the stage for Permian sedimentation in the Phosphoria depositional basin. Indeed, relative tectonic quiescence, one reason for such minor siliciclastic influx into the Phosphoria sea, dominated during this time.

The PRC depositional setting was unique in that there was an apparent juxtaposition of shallow water carbonates with an oceanic upwelling center, something that is absent from modern marine depositional systems and rare in the rock record (Whalen, 1996). Some work-

13 ers have concluded that deposition occurred along a distally steepened carbonate ramp (e.g., Brittenham, 1976; Whalen, 1996). Others suggest that the shelf geometry was homoclinal and that the apparent shelf break in eastern Idaho is actually just a result of poor palinspastic restorations and a manifestation of differential compaction and faster subsidence rates in the basin (Peterson, 1984). To the east, the basin was bounded by a broad continental evaporative basin (Lane, 1973). Westward, the ramp dips gently into the Sublett basin (Phosphoria Sea), a paleo-depocenter defined by the continent to the east and the outboard exoticAntler terrane to the west (Whalen, 1996; Figure 2.4). Farther to the west, sediments reportedly shed from the

~30°N OIAT

AH ~equator

Figure 2.4 Late Permian paleogeography, modified from Blakey (2012). The study area has been demarcated by a star. Other features to note are the Phosphoria Sea (PS), Antler highlands (AH), and the outboard island arc terrane (OIAT)

14 incoming island-arc terrane intertongue with the PRC, but distributions of clastics and volcanics would indicate a relatively narrow orogenic belt (Brittenham,1976). Parts of the craton in present-day Montana and Colorado were paleotopographic highs, and consequently were areas of non-deposition during the Permian (Figure 2.4). In western Wyoming, the PRC strata were deposited disconformably on the eroded surface of the Pennsylvanian Tensleep Formation (McKelvey et al., 1959), with paleotopographic relief estimated to be around 6.1 meters (20 ft) in the area (King, 1957). By contrast, at the south end of the Bighorn basin, local paleotopographic relief is estimated to have been closer to 46 meters (150 feet) (King, 1957). While the topographic relief had apparently been significant in the Early Permian, by the Late Permian most of the highlands had been eroded and basins filled in (Miller et al., 1992). This is evident from the large continuous facies belts that character- ize Late Permian stratigraphy, in contrast to the lower part of the section where facies can be discontinuous.

2.5 Sequence stratigraphy Local stratigraphic work to date includes theses by Weichman (1958) and Ahlstrand (1972). Weichman (1958) was mainly concerned with the Permian stratigraphy along the southern portion of the Wind River basin, and looked at eight surface locations and thirteen wells over an area of about 7000 km2. Two of his control points were on Sheep Mountain anticline. His study resulted in a local refining of the lithostratigraphy first outlined by USGS workers (i.e., Klepper, 1950). Ahlstrand (1972) also included one stratigraphic section from the Sheep Moun- tain anticline in his study of the Permian lithostratigraphy in the western Wind River basin. As Hein et al. (2004) noted in their survey of the status of sequence stratigraphic understanding of the PRC, there is consensus that the Permian succession of western Wyoming and eastern Idaho comprises 3 disconformity-bound sequences (Figure 2.5). These sequences are referred to by their respective carbonate members: the Grandeur Cycle, the Franson Cycle, and the Ervay Cycle (Figure 3). There is general agreement that carbonate deposition in the Fran- son and Ervay record highstand systems tract (HST) sedimentation (e.g., Whalen, 1996; Inden and Coalson, 1996). Carbonate sedimentation in the PRC has been described as shoaling

15 Eastern SE Idaho Wyoming SERIES SB Ervay Carbonates HST Tosi Chert Di culty Shale MFS Retort Member LST/TST Franson Carbonates SB

Glendo Guadalupian Rex HST Upper Permian Chert Shale

Minnekahta Carbonates MFS Meade Peak Opeche Shale Member LST/TST SB Grandeur Carbonates

Lower SB Permian Leonardian

Modi ed from Hiatt & Budd (2001), after Maughan (1984) Figure 2.5 Schematic stratigraphic column showing the prevailing sequence stratigraphic paradigm. There are three cycles, named for their respective carbonate members. Sequence boundaries (SB) separate each cycle, and maximum flooding surfaces (MFS), here shown at the contact between the shale and chert members, separate the lowstand and transgressive systems tracts (LST, TST) from the highstand systems tracts (HST). upwards (e.g., Clark, 1994; Whalen, 1996; Inden and Coalson, 1996; Hendrix and Byers, 2000). Most workers recognize that the lower parts of the Meade Peak and Retort members are part of the transgressive systems tract (TST) (Hein et al., 2004). There is less agreement, however, on the position of the maximum flooding surface (MFS). Some workers have put the MFS at the contact between the phosphatic shale members (i.e., Meade Peak and Retort) and the chert members (i.e., Rex and Tosi) (e.g., Hiatt and Budd, 2001); others place the MFS in the middle of the phosphatic shales (e.g., Clark, 1994; Hendrix and Byers, 2000). Hein et al. (2004) attributes some of this confusion to the abundance of higher order (4th and 5th order) cycles. Indeed, Hendrix and Byers (2000) describe 29 cycles in their Sheep Creek canyon section on the northern flank of the Uinta Mountains. Hendrix and Byers (2000)

16 credit Milankovich cyclicity: 2-6 Ma time period for deposition of the Franson Member (Filippelli and Delaney, 1992) and 29 cycles would give cyclicity of 69ka to 207ka, which is within the Mila- nkovich framework.

2.6 Phosphate accumulation The concurrence of cherts, black shales, and phosphorites is generally considered to be indicative of upwelling. That facies assemblage is exactly what is present in the PRC. It appears, though, that upwelling alone is not enough to explain large phosphate accumulations. Indeed, all Permian phosphorite deposits occurred under upwelling regimes, but not all loci of upwelling during the Permian resulted in phosphorite deposits (Herring, 1995). So upwelling is necessary but not in itself sufficient to account for the accumulation of phosphate. Hendrix and Byers (2000) proposed three main allogenic controls on the accumulation of phosphate-rich sediments: upwelling, sea level, and siliciclastic dilution. In epeiric sea settings (best model for the Phosphoria sea), phosphorite packages extend across the shelf because water circulation transports dissolved phosphate from the locus of upwelling to the shallower shelf; accumulations can be quite thick because of continuous wave reworking of pristine phosphate (Pufahl, 2010). Phosphogenesis is typically highest near the maximum flooding surface (MFS) because siliciclastics get trapped in nearshore environments (Pufahl, 2010), though phosphogenesis can occur in most systems tracts (Figure 2.6). While small ephemeral streams may have drained into the Phosphoria Sea, there is no direct evidence for any large fluvial input (Hiatt and Budd, 2001). This aridity and lack of a major fluvial system led to low siliciclastic input into the Phos- phoria Sea, causing severely sediment-starved conditions (Piper and Link, 2002). Dilution could have been further intensified by high atmospheric CO2 of the Late Permian, which might have increased the acidity of the Phosphoria sea such that carbonate production may have been moderated. Conclusions about conditions necessary for phosphate accumulation have been de- duced from those phosphate accumulations that have been studied the most; namely, ore deposits. Less commonly studied are non-economic phosphate deposits like the Park City Forma- tion.

Time

S T

F T

tiv

e T

S L

Sequence Phosphorite

Modified from Pufahl, 2010 formation Figure 2.6 Phosphorite formation in an epeiric sea setting can occur during most of the sea level cycle. LST is lowstand systems tract; TST is transgressive systems tract; HST is highstand systems tract; and FSST is falling stage systems tract (modifed from Pufahl, 2010).

Phosphorus is a limiting nutrient for biologic activity. Upwelling and phosphorus fluxing ensures ample supply for marine productivity. Complexed with organic material, it drops to the seafloor, dissociates, and re-precipitates as phosphorite (e.g., francolite) in pore spaces below

2+ the sediment-water interface when concentrations of HPO4 are high enough (Figure 2.7; Pu- fahl, 2010). Phosphate precipitation also appears to be a biologically mediated process. De- cay of organic matter by bacteria can release phosphorus into pore waters, thereby increasing concentrations; alternatively, microbes can catalyze syndepositional phosphate precipitation via biogeochemical pathways (Glenn et al., 1994). Baturin (1982) reports that pH ranges from 7.0-7.5 in pore spaces where apatite

[Ca5(PO4)3(F,Cl,OH)] is precipitating off the west coast of Africa. Incidentally, when pH is less than 7.5, calcite is relatively unstable. This might encourage pristine phosphate (i.e., collophane) precipitation by driving down the Mg2+/Ca2- ratio. Incidentally, carbon dioxide levels in the late Permian may have been high enough to increase ocean acidity. Alternatively, dolomitization could decrease the Mg2+/Ca2- ratio by decreasing the amount of free Mg2+ ions thereby encouraging the precipitation of phosphate (Kastner et al., 1984).

18 O O O OXIC

F-

2- HPO4 SUBOXIC F- Francolite

HPO 2- 2- 4 HPO4

- 2- F HPO4 Francolite

ANOXIC 2- HPO4 2- HPO4 Pufahl, 2010 Figure 2.7 Francolite (i.e., carbonate fluorapatite) precipitation occurs at or below the sediment water interface where conditions are suboxic to anoxic. Phosphorus complexed with organic matter (green circles in above figure) accumulates on the sea floor; degradation of that organic 2- matter releases the P as hydrogen phosphate (HPO4 ). As concentration of the ion increases, precipitation of francolite occurs, given a sufficient supply of fluorine ions (F-) from the water column (from Pufahl, 2010).

19 CHAPTER 3 3 DEPOSITIONAL FACIES AND FACIES ASSOCIATIONS

3.1 Facies Detailed thin section, hand sample, and outcrop descriptions have led to the classification of the succession at Sheep Mountain into 12 facies, which in turn comprise 6 facies associations. Facies and facies associations are summarized in Table 3.1. The classification system established by Dunham (1962) is used. In these descriptions, diagenetic modifiers (e.g., “dolo”-mudstone) have been omitted because each facies can exhibit a range of lithologies (e.g., calcareous dolomudstone to dolomitic lime mudstone). In the descriptions that follow, sections are labeled by the facies name followed by the facies abbreviation (case sensitive). In this study, the terms “mudstone” and “mud” are used sensu Dunham (1962), i.e., a carbonate rock or fine-grained carbonate constituent. Fine-grained siliciclastic rocks, therefore, are not called “mudstones” in this study but rather are referred to generically as “fine-grained siliciclastics” or more specifically (e.g., siltstone, sandstone, etc.) Throughout the facies suite, there are a few commonalities. First, silt or locally very fine sand is a common component and is present in virtually all facies types at a low percentage (estimated at 1-5%). The silt is probably eolian in origin (e.g., Carroll et al., 1998; Walling, 2000). Next, common bioclasts include echinoderms (i.e., echinoids and crinoids), bryozoans, and brachiopods. The biodiversity as well as the specific fauna types would appear to indicate water salinities to be predominantly normal marine (Scholle and Ulmer-Scholle, 2003). Thin-section photomicrographs were taken in either plane polarized (PPL) or cross-polarized light (XPL).

3.1.1 Facies descriptions and interpretations Crinkly laminated mudstone (Mc)

Description: Silty, crinkly laminated carbonate mudstones comprise a volumetrically small part of the succession at Sheep Mountain. This facies locally displays convex up, discontinuous interbedded light and dark lamina (Figure 3.1). Dark lamina probably contain bitumen in pore spaces. In other examples, laminations

20 Table 3.1 Summary of facies and facies associations in this study.

Facies name Abbreviation Interpretation crinkly laminated dolomudstone Mc intertidal microbial mat mudstone M lagoonal muds or muds below storm wave base supratidal, lagoonal, or distal siliciclastic and siltstone and shale Fg carbonate factory shutdown deposition peloid wackestone Wp marginal lagoonal shoals bioclast wackestone Wb distal subtidal bioclastic sands intraclast wackestone Wi distal reworked phosphorite peloid packstone Pp lagoonal and ooidic shoals bioclast packstone Pb proximal subtidal bioclastic sands bioclastic intraclast packstone Pi proximal reworked phosphorite sandy bioclast grainstone Gb bioclastic sand bank ooid grainstone Go local pro-lagoonal ooid shoal sandstone Ss shallow marine, reworked eolian sediments

Facies Facies association Abbreviation assemblage Depositional position

Peritidal-Intertidal- PIS Wp, Pp, M, Mc, Fg Above mean low tide Supratidal

Upper Shallow Subtidal USS Go, Pp, Gb Mean low tide to fair weather wave base

Fair weather wave base to storm wave Lower Shallow Subtidal LSS Pb, Wb, M base Well below fair weather wave base and Deep Subtidal DS Pi, Wi, Pb, Wb, M above storm wave base Outer Ramp OR Fg, Pb, Pi Below storm wave base Marine Reworked MR Fg, Ss Shallow marine

are laterally continuous as linked hemispheroid features (Figure 3.2). Small- scale teepee structures locally disrupt the lamina (Figure 3.3). Geometries are always biostromal rather than biohermal. The lithology of this facies ranges from dolomite to calcareous dolomite.

Interpretation: Wavy and crinkly laminations commonly form from microbial growth during night-day or tidal cycles. Tepee structures imply periodic wetting

21 Figure 3.1 Example of the Mc facies from the Ervay Member at the Schlichting Gulch section. Crinkly interbeds of light and dark, mainly defined by bitumen in the pores of the darker zones; light layers are discontinuous, slightly convex up, contain silt, and are crinkly. Sample is largely silicified. (Hand-sample photo, cm-scale ruler at top, up is stratigraphic up)

Figure 3.2 Wavy-laminated microbialite (Mc) near the base of the Franson outcrop at the Schli- chting Gulch section. Laminations are continuous. (Hand-sample photo, 15-cm ruler for scale, up is stratigraphic up)

22 Figure 3.3 Largely silicified crinkly laminated mudstone (Mc) from the Grandeur Member at the Beaver Creek section. Note the tepee structures (shown with arrows) that probably indicate periodic wetting and drying in a peritidal setting. (Outcrop photo, field of view ~12cm)

and drying. Based on these observations, the Mc facies is interpreted to represent an intertidal microbial mat (microbialite).

Carbonate mudstone (M)

Description: Dominated by carbonate mud, this facies is typically silty, can be cross-laminated (Figure 3.4), and in some cases is sandy. Bioclasts are a minor component, with rare echinoderm and brachiopod fragments. Bioturbation is very common (Figure 3.5), and cm-scale tubes are commonly silicified (Figure 3.6). In some cases, what appear to be Thalassinoides burrows are well preserved due to silicification (Figure 3.7) The lithology of this facies ranges from dolomite to calcareous dolomite.

Interpretation: The abundance of carbonate mud implies a low energy setting. The modest bioclast component would indicate a marine setting. Bioturbation indicates an oxygenated environment. This facies is interpreted to have been deposited in two environments: 1) deep subtidal where sedimentation is periodically

23 Figure 3.4 Silty carbonate mudstone (M) in the Franson Member at the Wilson Draw section. Laminations are defined by higher concentrations of silt. (Thin-section photomicrograph, PPL, scale bar at upper left corner)

Figure 3.5 Bioturbated, silt to vF-sand carbonate mudstone (M) of the Ervay Member at the Red Bluff section. This example has been silicified primarily in the mottled portion of the slide (top half). (Thin-section photomicrograph, PPL on left, XPL on right, scale bar at upper left corner)

24 Figure 3.6 Slabbed face of a bioturbated carbonate mudstone (M) in the Franson Member at Wilson Draw section. This example also has grey-colored silicified burrows (one such example is marked by an arrow). (Horizontal field of view is ~12cm, up is stratigraphic up)

Figure 3.7 Burrowed M facies in the Ervay bench at the Wilson Draw section. Burrows are almost completely silicified, which has led to good preservation of the original Thalassinoides network. View is of the underside of an overhanging ledge. (Outcrop photo, ~30 cm hammer at bottom-left for scale)

25 punctuated by bioclast packstone and wackestone storm lags and 2) near shore lagoonal (non-restricted) subtidal, where energies are low due to wave and tide energy attenuation. Deep subtidal and lagoonal muds are very similar but there are minor differences. Lagoonal mudstones commonly have minor silt-defined cross laminations and a higher component of peloids. In addition, bioturbation is generally more intense in lagoonal mudstones than in the deep subtidal mudstones, though it is present in both environments. Deep subtidal mudstones tend to have a higher proportion of bioclasts and phosphatic intraclasts than the lagoonal mudstones. Lastly, lagoonal mudstones are locally associated with replaced anhydrite (white siliceous nodules, bedded chert interbeds, etc.).

Siltstone and shale (Fg)

Description: Due to poor outcrop quality and difficulty in collecting samples of this facies, it has been under-sampled as compared to its abundance on Sheep Mountain. This facies is highly variable. The lithologies range from siltstone to silty mudrock to clayey siltstone. Calcareous cement is generally present, and this facies is locally cross-laminated (Figure 3.8). It can be bioturbated, but bioclasts are uncommon (Figure 3.9). Clay is sometimes present and can make it slightly fissile (Figure 3.10). Calcareous siltstones are locally interbedded with replaced evaporites.

Interpretation: The abundance of silt and clay in this facies is indicative of low energy. The cross-laminations imply relatively low energy hydraulic reworking of the sediment. The juxtaposition of calcareous siltstone and replaced evaporites implies a shallow evaporative setting. Calcareous shale is commonly associated with deeper water facies (i.e., bioclast or intraclast packstones and wackestones). This facies is interpreted to record deposition in one of two environments: 1) High intertidal, supratidal evaporative, to low energy lagoonal or 2)

distal siliciclastic (below storm wave base). No sub-facies were defined.

26 D

Figure 3.8 Laminated sandy siltstone (Fg) with large component of dolomite mud (tan and brown matrix, labeled D). Silt is concentrated into lamina but also occurs sporadically in the dolomite matrix. (Thin-section photomicrograph, PPL, scale bar at upper left corner)

Figure 3.9 Slabbed face of a calcareous siltstone (Fg) that was apparently bioturbated (mottled appearance). (Hand-sample photo, cm-scale ruler at top, horizontal field of view is ~10.5cm, up is stratigraphic up)

27 Figure 3.10 Calcareous shale (Fg) with occasional cryptic bioclast from the Retort Member at the Schlichting Gulch section. (Hand-sample photo, cm-scale ruler at top, horizontal field of view is ~10cm, view is of top bedding surface)

Peloidal wackestone (Wp)

Description: Peloids are the dominant grain type in a muddy matrix but are commonly dissolved to form molds (Figure 3.11 and Figure 3.12). Silt is also present, but bioclasts are uncommon. Bioturbation is rare, as is fenestral fabric. Textures are cryptic in hand sample (Figure 3.13). The lithology of this facies ranges from dolomitic limestone to calcareous dolomite to dolomite.

Interpretation: No genetic origin is implied with by the term “peloid”. They can form as fecal pellets or coated grains (i.e., micritized or incipient ooids). The occurrence of this facies adjacent to peloid packstones implies that the peloids in those facies share a common origin. The abundance of mud implies a relatively low energy setting, either subtidal or far enough inboard that dampening of wave energy is sufficiently low. The concurrence of peloids and carbonate mud indi-

cates poor sorting. This facies is interpreted to represent marginal ooid/peloid bank deposition in a position that was protected from wave action.

28 Figure 3.11 Silty, pervasively dolomitized pelmoldic wackestone (Wp) from the lower Ervay at Wilson Draw (sample #070). The matrix has been dolomitized and the peloids have been leached away, leaving moldic porosity. Minor poikilotopic calcite is present. (Thin-section photomicrograph, PPL, scale bar at upper left corner)

Figure 3.12 Closer view of the same slide (Wp) seen in Figure 3.10. (Thin-section photomicrograph, PPL, scale bar at upper left corner)

29 Figure 3.13 Slabbed face of a peloidal wackestone (Wp) from the Ervay bench at the Wilson Draw measured section. (Hand-sample photo, cm-scale ruler at top, horizontal field of view is ~10cm, up is stratigraphic up)

Bioclast wackestone (Wb)

Description: Bioclasts, including echinoderms, bryozoans, and brachiopods are the main grain constituents, with silt also being a common constituent. The matrix is mud, though admittedly the presence of mud is sometimes inferred, as dolomitization has often recrystallized the matrix (Figure 3.14). In some cases, this facies could be described as “floatstone” (Figure 3.15) but here these two fabrics have been grouped because they likely represent similar depositional energies. Bioturbation is a common characteristic and can lead to a “mottled” appearance (Figure 3.16). The lithology of this facies ranges from dolomitic limestone to calcareous dolomite to dolomite.

Interpretation: The faunal assemblage implies normal marine salinities. The presence of bioturbation indicates oxygenated waters. Allochems that occur in

this facies are typically poorly sorted. The abundance of carbonate mud indicates that deposition occurred in a relatively low energy setting. However, ener-

30 Figure 3.14 Pervasively dolomitized bioclastic wackestone (Wb) from the Ervay Member at the Beaver Creek section. Dolomite rhombs associated with the cryptic clast (possibly a bryozoan) are larger than those in the surrounding dolomitized matrix. Poikilotopic calcite occludes some porosity. (Thin-section photomicrograph, PPL, scale bar at upper left corner)

Figure 3.15 Silty, dolomitic brachiopod wackestone or floatstone (Wb) from the base of the Franson carbonate bench at the Beaver Creek section. Mud has largely been dolomitized, leaving the bioclasts as calcite. (Outcrop photo, cm-scale ruler at base of photo for scale, up is stratigraphic up)

Figure 3.16 Bioturbated bioclastic wackestone (Wb) from the Franson bench at the Wilson Draw section. Echinoderm and brachiopod fragments are the main bioclasts. Bioturbation trac- es are wispy sub-horizontal zones which in this case are muddier than the substrate. (Hand- sample photo, cm-scale ruler at top, horizontal field of view is ~12cm, up is stratigraphic up) gies were high enough to also deposit bioclasts, sometimes as small lags. This facies is interpreted to have been deposited below fair weather wave base with periodic storm deposition.

Intraclast wackestone (Wi)

Description: Phosphatic intraclasts are the dominant grain type in this facies, with ubiquitous silt and occasional bioclasts (Figure 3.17). Peloids are also observed, but their size variability suggests they are on the intraclast continuum rather than a separate grain type. In outcrop, the facies commonly weathers in a manner that suggests laminations, and commonly appears as black allochems in an off-white matrix (Figure 3.18). Intraclasts can occur as small discontinuous lags or agglomerations in a dominantly muddy substrate (Figure 3.19). The

32 Figure 3.17 Phosphatic, bioclastic peloidal intraclast wackestone (Wi) from the Franson bench at the Red Bluff section. Brachiopods are productid and are commonly silicified. (Hand-sample photo, cm-scale ruler at top, horizontal field of view if ~9.5cm, up is stratigraphic up)

Figure 3.18 Phosphatic intraclasts (black) in a muddy matrix (Wi) near the top of the Franson carbonate bench at the Beaver Creek section. (Outcrop photo, mm-scale ruler at bottom, up is stratigraphic up)

33 Figure 3.19 Slabbed face of a phosphatic intraclast wackestone (Wi) from the Franson bench of the Schlichting Gulch section (sample # 218.5). Intraclasts (black) tend to concentrate in lags, but can also be dispersed in the muddy matrix. (Hand-sample photo, cm-scale ruler at top, horizontal field of view is ~6cm, up is stratigraphic up)

lithology of this facies ranges from dolomitic limestone to calcareous dolomite to dolomite.

Interpretation: While intraclasts are commonly inferred to represent intertidal depositional environments, the high phosphate content of these intraclasts indicates deposition near a setting where pristine phosphate (Pufahl, 2010) had precipitated (i.e., middle ramp). The facies is poorly sorted with carbonate mud, intraclasts, and bioclasts occurring together. Where bioclasts occur, they are a normal marine faunal assemblage. Based on these observations, this facies is interpreted to have been deposited near or above storm wave base.

Peloidal packstone or grainstone (Pp)

Description: Peloids are the dominant component in this facies. Silt and bioclasts are also very common components. Intraclasts are also present in some samples (Figure 3.20). The mud content is typically very low. Due to diagenesis, it can be difficult to tell whether the precursor to microcrystalline dolomite was

34 Figure 3.20 Pervasively dolomitized, silty intraclastic peloidal packstone (Pp) or grainstone with isopachous (interpreted to be marine phreatic) dolomitic cement. Sample is from the Fran- son bench at the Wilson Draw section (Thin-section photomicrograph, PPL, scale bar in upper left corner) mud or cement. This facies can be very well sorted (Figure 3.21) and is commonly cross-bedded (Figure 3.22), with some indication of bi-directionality of cross-bed sets. The lithology of this facies ranges from dolomite to calcareous dolomite. In the Beaver Creek section, this facies has been pervasively silicified.

Interpretation: This facies is typically well sorted. The cross-beds imply wave or tidal reworking of the sediment. This facies is interpreted to represent peloid/ ooid banks that were deposited above fair weather wave base, with some tidal influence. This could indicate two possible depositional locations: 1) outboard shoals or banks that occasionally grew high enough to see intertidal deposition or 2) beach deposits, inboard from a low energy lagoonal (non-restricted) environment and outboard from intertidal environments.

Bioclast packstone (Pb)

Description: Bioclast types in the bioclastic packstone facies include echinoderms, bryozoans, and brachiopods which are commonly silicified (Figure 3.23).

35 Figure 3.21 Pervasively dolomitized, silty, pelmoldic and peloidal packstone (Pp) with dolomitic cement from the Ervay bench at the Red Bluff section. (Thin-section photomicrograph, PPL, scale bar in upper left corner)

Figure 3.22 A thick package of peloidal packstone to grainstone (Pp) caps the Ervay bench. This photo comes from the Wilson Draw section. At the base, some decimeter-scale cross bedding is present. There is a possibility that the peloids may be ooids. (Outcrop photo, ~1m tall shovel at bottom right for scale)

36 R

B E

Figure 3.23 Bryozoan (B) brachiopod (R) echinoderm (E) silicipackstone (facies Pb). This example is pervasively silicified which has led to excellent preservation of clast textures. Bra- chiopod punctae, echinoderm “honeycomb”, and bryozoan zooecia are commonly occluded by collophane (i.e., phosphate). At least two types of silicification are present (light blue chalcedony and off-white chert in PPL). (Thin-section photomicrograph, PPL on left, XPL on right, scale bar in upper left corner) Silt and peloids are also common constituents. Bioclasts are commonly abraded (for example, spines of productid brachiopods or fragments of bioclasts; Figure 3.24). Large intact brachiopods are common, especially in the upper Franson bench (Figure 3.25). Large, intact, silicified fenestrate and ramose bryozoans are also present in the Franson. They tend to grow on a mud and bioclast-rich

substrate (Figure 3.26). This facies is commonly associated with bioclast wackestones, and the contact between the two facies is generally gradational (Figure 3.26). The lithology of this facies ranges from dolomitic limestone to calcareous dolomite to dolomite. In some cases this facies can be pervasively silicified, especially where it occurs as a lag.

Interpretation: It is likely that the Pb facies faced constant wave reworking, possibly being worked into banks. This would help to explain why landward from these deposits there are sometimes muddier units. It appears that only

37 R

Figure 3.24 Productid brachiopod (R) packstone (facies Pb). At center is transverse cut of a brachiopod spine (S). Low-angle fibrous texture is well preserved in the shell fragments. Ap - parently largely calcitic (Alizarin-red stain), probably both primary and secondary. Dolomite rhombs often occur in muddier zones and can be de-dolomitic. (Thin-section photomicrograph, PPL, scale bar in upper left corner)

Figure 3.25 Brachiopod packstone (facies Pb) in outcrop. Bioclasts are typically silicified in this sample from the Franson bench of the Beaver Creek section. Large brachiopods (R) are present, probably of the Dictyoclostid variety. (Outcrop photo, mm-scale ruler at bottom for scale)

38 A

Figure 3.26 Three examples of intact (i.e., not abraded) silicified bryozoans in the bioclast packstone (Pb) facies. Photos A and B show examples of ramose bryozoans. Photo C shows an example of a fenestrate bryozoan. The matrix in which the bryozoans are growing contains mud and bioclasts, and bioclasts are commonly replaced by silica. Beds where these occur are universally biostromal and do not show reef-like geometries; it is therefore inferred that they were not reef features. These photos are of the Franson carbonate at the Red Bluff section. (Outcrop photos, mm ruler at base of photos for scale, up is stratigraphic up)

39 Wb

Figure 3.27 Bioclastic packstone (Pb) grading up into a bioclastic wackestone (Wb). Reddish bioclasts are echinoderms (occasional crinoid). (Outcrop photo, cm ruler at base of photo for scale, up is stratigraphic up)

large bryozoans were able to survive without being broken or removed by wave agitation. In outcrop, bank or shoal geometries are not observed, but the relief on these features could have been low. The faunal assemblage is heterozoan (James and Lukasik, 2010), which might imply a cool water setting. Despite the low latitude of the Phosphoria basin (Figure 2.4), upwelling of cool waters may have provided conditions for development of this heterozoan assemblage (Ward- law and Collinson, 1986). This facies is interpreted to be subtidal bioclastic sand deposits, nearby to fair weather wave base. When it occurs as a lag in a muddier facies, this facies probably represents storm deposition.

Intraclast packstone to grainstone (Pi)

Description: Intraclasts are the dominant grain type, but this facies also includes peloid-sized particles (Figure 3.28) and a minor bioclast constituency.

This facies is commonly very phosphatic. The intraclasts can include silts or what appear to be siliceous sponge spicules (Figure 3.29). In outcrop, this fa-

40 Figure 3.28 Silica-cemented phosphatic peloid and intraclast packstone to grainstone (facies Pi). This sample is from the top of the Franson bench or low part of the Retort Member at the Red Bluff section. Intraclasts apparently include silicic sponge spicules, a possible source for the large volumes of silica in the PRC. Clast size variability is large. Occasional brachiomolds are observed. (Thin-section photomicrograph, PPL, scale bar in upper left corner)

cies is typically interbedded with Wi and M facies, and commonly occurs as a lag (Figure 3.30, Figure 3.31). The lithology of this facies ranges from phosphatic dolostone to calcareous phosphatic dolostone.

Interpretation: The existence of the lags of phosphatic intraclasts implies that pristine phosphate had previously precipitated in a low energy environment.

Subsequently, those laminated phosphates would have been reworked into the intraclast lags. Because no pristine phosphate facies is observed in outcrop, it is assumed that it was deposited in a place where it was occasionally calm enough for the pristine phosphate to precipitate but would ultimately be reworked. Sedi- mentation rates must have been low enough that the pristine phosphate was never buried before it was reworked. For these reasons, this facies was probably deposited above storm wave base but probably below fair weather wave base.

41 Figure 3.29 Close-up of same slide as above (facies Pi). This sample is from the top of the Franson bench or low part of the Retort Member at the Red Bluff section. Round and needle- like siliceous components within the intraclasts are apparently siliceous sponge spicules. At least two silicification events: cementation (off-white) and occlusion of porosity (bluish-black color). In some cases, silica isopachously coats grains, suggesting replacement of an earlier marine cement. (Thin-section photomicrograph, PPL, scale bar in upper left corner)

Figure 3.30 Interbedded mudstones, intraclast wackestones, and intraclast packstones (facies Pi). The Pi facies zones are indicated by the white arrows. This outcrop photo was taken near the top of the Franson carbonate bench at the Red Bluff section. (Outcrop photo, ~30cm hammer at bottom right for scale) 42 Figure 3.31 Intraclast packstone grading into intraclast wackestone. Black grains are phosphatic intraclasts. This photo was taken near the top of the Franson bench at the Wilson Draw section. (Outcrop photo, 15 cm ruler for scale, up is stratigraphic up)

Sandy bioclast grainstone (Gb)

Description: Volumetrically, this facies represents a very small proportion of the facies types on Sheep Mountain. This facies is dominated by bioclasts, normally echinoderms and bryozoans, typically abraded to uniform sizes and shapes (Fig- ure 3.32). The facies can have a large component of quartz sand, especially in the Grandeur bench and also intraclasts (Figure 3.33).

Interpretation: The lack of carbonate mud implies that the fines were winnowed away. The faunal assemblage implies normal marine conditions. This facies is interpreted to have been deposited as bioclastic sand banks in a high energy setting.

Ooid grainstone (Go)

Description: Ooids are the dominant component of this facies (Figure 3.34), but it can also include a small number of bioclasts or intraclasts (Figure 3.35). Silt is locally the nucleus of the ooid, but other times the nucleus is cryptic. Pervasive

43 Figure 3.32 Slabbed face of a pervasively silicified echinoderm bryozoan grainstone (Gb) with minor glauconite and phosphate components, Ervay bench at the Red Bluff section. (Hand- sample photo, cm-scale ruler at top, up is stratigraphic up)

Figure 3.33 Slabbed face of a dolomitic, intraclast vF-sand bioclastic grainstone (Gb), from the Grandeur Member at the Beaver Creek section. Sand component is large enough that the sample could almost be considered a sandstone. (Hand-sample photo, cm-scale ruler at top, up is stratigraphic up)

44 Figure 3.34 Pervasively dolomitized ooid grainstone (Go), Ervay bench at the Red Bluff section. Isopachous dolomitized cement coats all the grains. Most primary porosity has been occluded but oomoldic porosity has partially developed. Moldic porosity differentially leaches the concentric laminations of the ooids. Minor components include intraclasts, brachiopods, and echinoderms (crinoid in lower left, for example). Compaction features are also present (see white arrow). (Thin-section photomicrograph, PPL, scale bar at upper left corner) dolomitization has made it difficult to interpret the original textures, but concentric laminae appear to be dominantly tangentially oriented. In outcrop, where sedimentary structures have not been diagenetically obliterated, this facies is cross- bedded. The cross-beds can be bi-directional (Figure 3.36), possibly implying a tidal influence in those cases.

Interpretation: Ooids typically form in tropical environments where grains are kept in almost continual motion; the abundance of ooids in the upper Ervay contrasts sharply with the cool-water heterozoan assemblage of the Pb facies in the lower Ervay and Franson benches. This facies is interpreted to represent deposition in ooid banks or shoals above fair weather wave base. In some cases, the shoals probably built into the tidal range.

45 Figure 3.35 Same slide as Figure 3.34, showing brachiopod fragment within the pervasively dolomitized ooid grainstone (Go). (Thin-section photomicrograph, PPL, scale bar at upper left corner)

Figure 3.36 Facies Go or Pp in the upper portion of the Ervay carbonate bench at the Wilson Draw section. The preservation of sedimentary structures in the Ervay is relatively poor on Sheep Mountain, though this outcrop appears to show cross-bedding which may be bi-directional in places. This could imply a tidal influence. (Outcrop photo, fifteen cm ruler for scale).

46 Sandstone (Ss)

Description: This facies is unique to the Grandeur Member of the Park City Formation. Very fine sand dominates with cryptic bioclasts, intraclasts and silt as accessory grain types (Figure 3.37). In some cases, this facies has a mottled appearance. Fenestral-like vugs are also present in one sample (Figure 3.38). Calcite cement is common. Sedimentary structures have not been observed.

Figure 3.37 Calcareous, silty intraclast sandstone (facies Ss) with minor bioclast component from the Grandeur Member at the Beaver Creek section. Arrow in the photo points to an example of an intraclast(Hand-sample photo, cm-scale ruler at top, up is stratigraphic up)

Figure 3.38 Silica cemented sandstone with vF grains (facies Ss) from the Grandeur Member of the Wilson Draw section. Vugs are common, and white siliceous nodules occur, which probably are replaced evaporite nodules. (Hand-sample photo, cm-scale ruler at top, up is stratigraphic up)

47 Interpretation: Because there was not a major input of sediment into the Phos- phoria Sea from the continent during the Permian, it is likely that Pennsylvanian eolian sands of the Tensleep Fm. were reworked. The occurrence of carbonate intraclasts and bioclasts implies a shallow marine environment. The lack of sedimentary structures could be a result of intense bioturbation. This facies is interpreted to represent shallow marine deposition and reworking of Pennsylva- nian sediments.

3.1.2 Facies discussion The pie charts in Figure 3.39 and Figure 3.40 give a sense of the relative abundance of each facies. These charts are biased toward facies that actually crop out rather than facies that tend to be covered, so the pie charts have been normalized to only include carbonate facies of the Ervay and Franson benches. The pie charts were compiled by totalling the footages of each facies in the measured sections. In Figure 3.40 the facies in the Franson and Ervay benches have been separated to facilitate comparison.

Ervay and Franson facies

Mc M Wp Wb Wi Pp Pb Pi Gb Go

Figure 3.39 Pie chart displaying the relative abundances of facies in the Ervay and Franson members (combined) based on the 4 measured sections in this study.

48 Ervay Franson

Mc M Wp Wb Wi Pp Pb Pi Gb Go

Figure 3.40 Pie charts displaying the relative abundances of facies in the Ervay and Franson members (separated) based on the four measured sections in this study. The major differences in facies between the two benches is the relative abundance of Pp and Pb. Pp dominates in the Ervay and Pb in the Franson. In addition, the Ervay has a higher percentage of Mc, Go, and C, which may indicate that the Ervay was deposited in an overall shallower depositional environment than the Franson. In addition, the abundance of ooids (Go and Pp) in the Ervay indicates warm water deposition, whereas the heterozoan assemblage common in the Franson may indicate cooler water (farther basinward along the ramp setting).

In general, the Ervay and Franson benches have similar amounts of M and Wp, but virtually every other facies occurs in significantly different abundances when comparing the benches. The most significant difference is the relative abundances of Pp and Pb; the Ervay has significantly more Pp and less Pb than the Franson. This probably indicates that the depositional setting of the Ervay was shallower than that of the Franson. The Franson also has a high percentage of the Pi facies, indicating that the setting of the Franson was more conducive to phosphogenesis than that of the Ervay. Lastly, the abundance of warm water sediments in the Ervay (e.g., microbialites, ooids) versus the cool water assemblage of the Franson (e.g., heterozoan fauna, sponge spicules, etc.) might indicate that location on the ramp is related to water temperature, which is probably related to water depth.

49 3.2 Facies associations The 12 facies described above have been grouped into 6 facies associations. Facies associations are inherently genetic; that is, they are defined by their inferred positions and relative water depths on the ramp. Figure 3.41 shows their positions and the water depths that define those positions. Intertidal-Supratidal (Peritidal/marginal lagoonal) PIS

Facies assemblage: Wp, Pp, M, Mc, Fg

Description: Based on the abundance of muddy facies in this facies assemblage, this is a low energy environment. Periodic wetting and drying is indicated by some small scale tepee structures (Figure 3.3) and interbedded evaporite and silty mudstone units (Figure 3.42). This may reflect a tidal influence. Tidal energy is likely low due to ramp attenuation (e.g., Irwin, 1965; Whalen, 1996). Depositional environments range from pelletal mudstones to peloid banks to silty tidal flat microbial laminites. This facies assemblage is interpreted to be situated above mean low tide (MLT) in the peritidal position.

Outer Ramp Deep Subtidal Shallow Subtidal Intertidal Supratidal lower upper MHT MLT FWWB

SWB

Figure 3.41 Facies associations have been placed along a carbonate ramp. Placements are based on inferred energy of deposition, which is a largely a function of water depth (e.g., Burchette and Wright, 1992). Supratidal deposition occurs above the mean high tide (MHT). Intertidal environments are defined as being between MHT and mean low tide (MLT). Subtidal deposition is defined here as that which occurs between MLT and storm wave base (SWB); subtidal depositional style is further controlled by wave reworking, which is relatively constant above the fair weather wave base (FWWB). Below SWB is the Outer Ramp domain.

50 Figure 3.42 Interbedded muddy siltstones, crinkly laminated dolomudstones, and cherts (replaced evaporite) in the Franson Member near the base of the Schlichting Gulch section. These facies are part of the Intertidal-Supratidal facies assemblage. (Outcrop photo, ~30cm hammer at bottom left for scale, up is stratigraphic up)

Upper Shallow Subtidal (Banks/shoals) USS

Facies assemblage: Go, Pp, Gb

Description: Cross-beds are common and are locally bi-directional (Figure 3.36), which may imply a tidal influence on this facies association. This facies assemblage could accumulate outboard from the shoreline as a low relief barrier

system or at the shoreline if energies are high enough. Shoal flanks are muddier as they transition into Lower Shallow Subtidal facies (either basinward on the ramp or more likely landward to a more protected setting. The top of these features can grade into thin successions of Peritidal-Intertidal-Supratidal facies. Ooids, peloids, and bioclasts probably accumulated to form low-relief shoals or sand banks. This facies is interpreted to have been deposited in an environment

situated near or below mean low tide (MLT) and above fair weather wave base (FWWB), where depositional energies are relatively high and hydraulic reworking

51 is constant. The lateral continuity of this facies assemblage between measured sections suggests that the ooid or peloid banks were wide features, perhaps on the scale of kilometers.

Lower Shallow Subtidal (Subtidal wackestones and packstones) LSS

Facies assemblage: Pb, Wb, M

Description: In the lower energy portion of this facies association, muds can be heavily bioturbated with what appear to be, based on burrow shape and size and burrow network geometry, Thalassinoides burrows (Figure 3.7). In most cases, bioclasts do not show signs of continual reworking but can be broken or abraded (Figure 3.24). Bioclast-rich beds commonlky occur as lags and commonly fine upwards (Figure 3.27). Some constituents are intact; for example bryozoans can occur in growth positions among mud and partially abraded bioclasts (Figure 3.26). The bioclast diversity and fauna would seem to indicate normal marine salinities. This facies assemblage is interpreted to have been situated above storm wave base (SWB) and near and below FWWB. In part, it probably represents deposition by periodic storms with varying degrees of frequency and strength.

Deep Subtidal (Intraclastic wackestones and packstones) DS

Facies assemblage: Pi, Wi, Pb, Wb, M

Description: Phosphate precipitation would have primarily occurred in this zone, but reworking by storms has apparently destroyed any pristine phosphate. Bio- diversity and fauna types (echinoderms, brachiopods, and bryozoans) indicate normal marine salinities. This facies association comprises phosphatic intraclast lags with varying amounts of mud (Figure 3.18, Figure 3.31). The lags may record storm deposition. The occurrence of mud indicates that the fines were not winnowed away by wave agitation, so it is likely that this facies assemblage was

deeper than fair weather wave base. This facies assemblage is interpreted to have been situated above SWB and well below fair weather wave base.

52 Outer Ramp (Storm interrupted distal fine-grained siliciclastics ) OR

Facies assemblage: Fg, Pb, Pi

Description: This facies association is dominated by fine-grained siliciclastic material (silt and clay-sized particles), which implies a low energy setting. In places the siliciclastic deposition is punctuated by thin bioclastic and intraclastic lags (Figure 3.43). This facies association is interpreted to represent deposition below storm wave base (SWB) where active carbonate deposition apparently did not occur. The bioclast and intraclast lags probably represent uncommon storm events that effected depths below SWB.

Figure 3.43 Outcrop scale example of the OR facies association. The Fg facies dominates but is punctuated by intraclastic and bioclastic lags. This is a photo of the Schlichting Gulch section (white arrows point to several of these bioclastic and intraclastic benches). (Outcrop photo, Jacob staff at bottom left is 1.5m)

53 Marine Reworked (Nearshore reworked eolian sediments) MR

Facies assemblage: Fg, Ss

Description: No genetic definition is implied here; sedimentary structures are cryptic and facies changes, from clastic-dominated rocks to carbonate-dominated rocks, are unpredictable and abrupt, so no attempt is made to define the depositional environment in terms of hydraulics (Figure 3.44). The occurrence of marine fauna (e.g., brachiopods) implies a marine setting, so it is inferred that these sands and various allochems were deposited and reworked in a shallow marine environment. This vF-grained sand dominated facies assemblage probably represents reworked Pennsylvanian sands.

Figure 3.44 Outcrop of Marine Reworked (MR) facies association in the Grandeur Member at the Beaver Creek section. Preservation of sedimentary structures in this facies association is very poor and it is thus difficult to tell much about the depositional conditions. (Outcrop photo, ~30cm hammer at bottom left corner for scale)

54 3.3 Depositional model The findings of this study indicate that the Franson and Ervay facies assemblages repre- sented on Sheep Mountain best fit the model of a homoclinal carbonate ramp (Figure 3.45; e.g., Burchette and Wright, 1992), as previous workers have suggested (e.g., Clark, 1994; Whalen, 1996). Grandeur deposition appears to be significantly more complicated and without clear facies trends. Early Permian paleotopography in this area appears to have been quite variable, and consequently facies changes are abrupt and frequent in the Grandeur sediments. By the time of Franson and Ervay deposition, topographic features were more subdued (due to erosion and infill deposition), and consequently gently dipping, geometrically uncomplicated carbonate ramp deposition took over, where wide facies belts are common. Moreover, the Grandeur appears to be a largely mixed siliciclastic-carbonate system, with significant reworking ofTensleep sands and silts, which adds complexity. Therefore, the dominant facies association present in the Grandeur has not been incorporated into this carbonate ramp model.

PIS Intertidal & supratidal USS Upper shallow subtidal LSS Lower shallow subtidal DS Deep subtidal OR Outer ramp PIS MR Marine reworked LSS USS

MHT MLT FWWB LSS SWB DS OR ~100 km

Figure 3.45 A schematic block diagram for Park City deposition has been made based on findings of this study. The facies have been placed into facies associations based on inferred ramp setting, water depth, and depositional energy.

55 CHAPTER 4 4 CHEMOFACIES

4.1 Chemofacies A Niton XL3t GOLDD+ XRF Analyzer was used to assess elemental signatures of each of the hand samples collected for this study. Using the “Test-All-Geo” mode, the tool is config- ured to estimate the abundances of 39 elements: Mg, Al, Si, P, S, Cl, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Zr, Nb, Mo, Pd, Ag, Cd, Sn, Sb, Te, Cs, Ba, W, Au, Hg, Pb, Bi, Th, and U. The elemental signature can be used to tie the measured sections to the subsurface. To a very limited extent, elemental signatures can also be used to distinguish facies and systems tracts at Sheep Mountain. Broadly speaking, elemental abundances in sediments and sedimentary rocks have been used to describe provenance of the detrital material (e.g., Taylor and McClennan, 1985), paleoredox conditions (e.g., Tribovillard et al., 2006), or diagenetic conditions (e.g., Berner, 1971). To a much lesser extent, attempts have been made to tie elemental abundances to sequence stratigraphic boundaries and systems tracts (e.g., Thyberg et al., 2000; Jarvis et al., 2001), to varying degrees of success.

4.1.1 Compositional data analysis Compositional data require special treatment because compositional datasets only convey relative information (Pawlowsky-Glahn and Egozcue, 2006). Indeed, compositional datasets are confined, usually between 0 and 100 or 0 and 1 (i.e., the simplex). Necessarily, as the value of one datum increases, the value of another decreases in a compositional dataset. Traditional statistical analysis techniques, however, assume unconfined (i.e., Euclidean) geometries that allow data to vary from -∞ to +∞. As a consequence, traditional techniques (e.g., cluster analysis, ANOVA, etc.) applied to compositional datasets can lead to spurious results. A whole science meant to deal with this problem has developed behind the pioneering work of Aitchison (1986). The solution for dealing with this problem is log-ratio transformation. Recognizing that relative (rather than absolute) magnitudes and variations are central to compositional datasets,

56 log-ratio transformations serve to convert compositional data to vectors, or coordinates, for ease and accuracy of analysis (Pawlowsky-Glahn and Egozcue, 2006). Pawlowsky-Glahn and Egozcue (2006) summarize several approaches, including the additive log-ratio transform (alr), the isometric log-ratio transform (ilr), and the centered log-ratio transform (clr). One tool in the log-ratio transform toolbox is called data centering, after Martín-Fernán- dez et al. (1999), which involves data perturbation by the inverse of the datasets’ geometric means. In other words, the coordinate that represents a 3-part composition is essentially re- scaled based on the relative magnitude of each part’s geometric mean. This method allows for the visualization of relative abundances of elements on a traditional ternary plot. Centering is accomplished by implementing the following transform:

(4.1) where D is the sample size and N is the number of variables (Thió-Henestrosa & Martín-Fernán- dez, 2005). In plain terms, the geometric mean of each variable is calculated; next, the geometric means are scaled to 100 to find the barycenter of the dataset; last, the inverses of the scaled geometric means are used to perturb each composition in the dataset. Once each composition in the dataset has been perturbed in this way, the data can be plotted on a ternary diagram. The process is greatly simplified by analysis in CoDaPack software (Thió-Henestrosa & Martín- Fernández, 2005). A demonstration of the utility of the centering process can be seen in Figure 4.1, where the U, Th, and K abundances are plotted on two ternary diagrams (one prior to centering, and one after centering). In that figure, data points are colored based on the facies assigned to each sample in the course of this work. Prior to centering, data points cluster in the K corner because of the abundance of K is so much larger than the abundances of U and Th. After the centering transform has been implemented, the ternary diagram is much more useful in visually distinguishing facies. In exploratory data analysis of a compositional dataset, three variables is a good number to work with because of ease of visualization on ternary diagrams. In data analysis for 57 Figure 4.1 Demonstration of geometric data centering transform. Data points are colored based on their facies. A) U, Th, and K on a ternary plot whose center point is defined as [33.33, 33.33, 33.33]. Data points all cluster in the K corner because the relative abundances of K versus Th and U. The plot is not useful because one cannot distinguish the facies visually. B) Data after the data centering transformation, where c(x) is the transformed data. Unsurprisingly, the U-Th-K suite is useful for discriminating Fg facies from the carbonate facies (Pp, Pb, Wb, etc.). Indeed, the green Fg data points cluster towards the c(K) corner. This probably reflects either potassium in clay and/or feldspar silt. The U-Th-K suite is not, however, useful for distinguishing between carbonate facies since those facies tend to cluster indistinguishably near the center of the ternary plot.

58 this study, there was very little success in distinguishing facies based on 3-part sub-compositions. However, the Mg-Al-P suite appears to explain a small degree of variability in terms of lithostratigraphy. In general terms, Mg is probably a proxy for dolomitization, Al for siliciclastic input, and P for phosphate accumulation. The Mg-Al-P subcomposition is plotted on a centered ternary plot where data points are colored by lithostratigraphic unit (Figure 4.2). The Ervay unit has Mg-Al-P compositions that encompass basically the entire ternary plot. This would indicate that the Mg-Al-P suite is not useful for distinguishing the Ervay from the other members. The

Figure 4.2 Ternary plot showing centered compositions of the Mg-Al-P suite. To a minor extent, the Mg-Al-P subcomposition can distinguish lithostratigraphic units. On this plot, rough polygons have been drawn around clouds of datapoints for several of the lithostratigraphic units. The Ervay Member (blue) subcompositions vary greatly, so this suite of elements is probably not useful in distinguishing it from the other members. The Grandeur Member (yellow) and the Franson Member, on the other hand, appear to be quite different from one another in terms of their Mg-Al-P compositions.

59 Grandeur and Franson, on the other hand, appear to be readily distinguishable based on the Mg-Al-P suite. When 3 of the alkaline earth metals (Mg, Sr, and Ba) are centered and plotted on a ternary diagram (Figure 4.3), many of the Ervay and Grandeur points plot in two separate clusters. The Mg-Sr-Ba signature of most dolomitic (i.e., the points closest to the Mg corner of the ternary plot) samples of the Ervay and Grandeur dolomites are subtly yet distinctly different. The less dolomitized Ervay and Grandeur samples (i.e., points that are farther from the Mg corner of the ternary plot), on the contrary, are not distinguishable based on the Mg-Sr-Ba suite. This suggests that conditions during dolomitization of each of the units were different. Whether that means a difference in water chemistry, dolomitization mechanism, or chemistry of the dolomite substrate is unknown. One goal of this study was to assess whether or not U, Th, and K abundances can be used to distinguish the facies at Sheep Mountain, as defined by detailed thin section, hand sample, and outcrop analysis. If so, it could be possible to distinguish facies in well logs based on spectral gamma ray logs. In the case of the U-Th-K suite, the usefulness in distinguishing between the carbonate facies at Sheep Mountain is limited; indeed, the centered ternary plot shows that the facies have approximately equal distributions of U, Th, and K (Figure 4.1). The U-Th-K suite is, however, useful in distinguishing between the Fg facies and the carbonate facies as a whole. The Fg data points cluster in the c(K) corner of the centered plot. This probably reflects a component of K-rich clay and/or feldspar in the Fg facies that is not present in the carbonate facies. Though the U-Th-K suite is not useful in this case to distinguish facies, it has proven useful in tying measured sections with subsurface data (well logs), which is described in the following chapter.

60 Figure 4.3 As another example of a centered ternary plot, plotted here are 3 alkali earth metals. Noteworthy are the tight clusters where many of the Ervay (blue) and Grandeur (yellow) dolomites plot. Those dolomites appear to have a subtle yet distinct geochemical signature in terms of their Mg-Sr-Ba compositions. Franson (red) samples are scattered across the diagram, indicating the incomplete and variable dolomitization character of that unit.

61 CHAPTER 5 5 STRATIGRAPHIC CORRELATION AND SEQUENCE STRATIGRAPHY

5.1 Pseudo gamma ray curve In this study, measured sections were tied to the subsurface by comparing X-ray fluorescence (XRF) derived “pseudo” gamma-ray curves to gamma-ray well logs. Natural gamma radiation has been routinely measured in well logging since at least the 1950s (Bassiouni, 1994). Radioactive isotopes of K, Th, and U release gamma radiation as they randomly decay to their more stable daughter elements. A typical gamma ray tool measures total radiation by essentially counting the number of those incident gamma rays that interact with a sodium iodide crystal. Some gamma-ray tools are also designed to measure the energy levels of the incident gamma rays, which correspond to one of the elements with naturally occurring radioactive isotopes (i.e., K, Th, U). The result is a spectral gamma ray log suite, where U and Th are measured in ppm and K in wt%. The relationship between total radiation and natural gamma can be approximated by the following equation:

EGR=(8·U)+(4·Th)+(K) (5.1) where EGR is the “elemental gamma ray” in API units, U is the uranium content in ppm, Th is the thorium content in ppm, and K is the potassium content in % (Bassiouni, 1994). Likewise, the handheld XRF tool outputs the U, Th, and K abundances in the same units. From this simple equation, therefore, it is possible to calculate an elemental gamma ray curve to facilitate comparison of the measured sections to well logs. This is exactly what has been done in the cross section in Plate 1. On that diagram, the 4 measured sections have been plotted in cross- section view along with well logs from 8 surrounding well logs. Despite being on slightly different scales than the well log GR curves, the XRF-derived elemental gamma ray (EGR) does a good job of approximating a gamma-ray response.

62 5.2 Cross-section Measured sections and well logs from neighboring wells have been combined in a cross-section (Plate 1). When comparing the measured sections with those well logs, the Permian succession at Sheep Mountain appears to be ~20 m thinner than the succession in the surrounding wells. The Tensleep top was picked on well logs from the obvious shift in bulk density, marking an upward change from sandstone to limestone; for example, this shift can be observed in the Federal Johnson 1-12 well on Plate 1 at a depth of 3390 ft. In the measured sections, the very top of the Tensleep has been described. In the Beaver Creek section, for example, the measured section begins just above the cross-bedded sandstone of the Tensleep Fm. This all suggests that Permian section is actually thinner on Sheep Mountain than in the surrounding wells rather than it being error associated with the measured sections. One possible explanation for this could be that the fault that controls the Sheep Mountain anticline (i.e., the Beaver Creek thrust, Willis and Groshong, 1993) may hint at the existence of an even earlier fault, which could have caused shortening during the Permian. Workers such as Maughan (1983) have suggested the existence of basement lineaments in the vicinity of Sheep Mountain.

5.3 Lithostratigraphic units This discussion admittedly favors the carbonate members of the PRC because those are the units that crop out consistently at Sheep Mountain. The paragraphs that follow address the stratigraphy in terms of the USGS defined members (i.e., Grandeur, Franson, and Ervay). This will help with the later discussion where I compare and contrast the lithostratigraphic and sequence stratigraphic paradigms of the succession.

5.3.1 Grandeur Mbr., Park City Fm. The Grandeur Member was measured in the Wilson Draw and Beaver Creek sections. Nine of the twelve facies are present in this member. Their stacking patterns and lateral changes, however, make it difficult to place these facies assemblages into meaningful facies associations. In contrast to the relatively well-behaved facies assemblages (both vertically and laterally) of the Ervay and Franson members, the Grandeur facies assemblages are variable and unpredictable. For example, the Grandeur at Wilson Draw is dominated by the Marine

63 Reworked facies association (MR). In contrast, the Grandeur at Beaver Creek has only thin MR benches and is instead dominated by interbedded facies of the Lower Shallow Subtidal facies association (LSS). This rapid facies shift suggests that the carbonate ramp model does not sufficiently describe sedimentation of the Grandeur at Sheep Mountain and contrasts with the wide facies belts in the Ervay and Franson that would be expected on a very shallowly dipping carbonate ramp. Because only two measured sections from this study extend into the Grandeur, no alternative model for Grandeur deposition is offered here. After King (1957), it is suggested, though, that paleotopography on the top of the Tensleep is a main control on the facies variability. On the other hand, it is possible that a portion of the succession is part of the “Nowood complex”, a slightly older Permian unit which was described by Todd (1996) in the Big Horn and Owl Creek mountains. However, his conclusions were based on biostratigraphic control; the lack of biostratigraphic data in this study makes it difficult to compare the successions.

5.3.2 Franson Mbr., Park City Fm. The Franson carbonate bench represents approximately 10-12 m of section in each of the measured sections. Overall, the Franson at Sheep Mountain appears to be a transgressive package, with facies associations representing progressively deeper depositional settings upward through the succession. Previous workers have described Franson deposition as a series of shoaling cycles (e.g., Whalen, 1996), so it is surprising that the Franson carbonates on Sheep Mountain are transgressive in nature. In the context of the well control to the west of Sheep Mountain, it appears that the Franson carbonate member is thinner on Sheep Mountain than in the wells to the west (Plate 1), with only the top several meters of Franson carbonate deposition cropping out at Sheep Mountain. It is likely that the thicker Franson carbonate bench at the well locations records shoaling, as described by, for example, Whalen (1996), but at Sheep Mountain only the bottom several meters appear to show any shallowing upward character. At the base of the Franson are a couple meters of the Peritidal-Intertidal-Supratidal (PIS) facies association. Facies include Fg interbedded with silica-replaced evaporite, Mc, M, and Wp. These facies suggest a low energy setting with periodic wetting and drying and shallow near-shore marine deposition. That facies assemblage is punctuated at the top by a sharp yet rugose contact (Figure 5.1). Relief on the contact does not exceed a few centimeters and in

64 Figure 5.1 Sharp rugose contact near the base of the Franson bench at the Wilson Draw section. The facies below the contact is Pp and above is Wp, which suggests a transgression and development of a hardground. Isopachous marine phreatic cement coats the grains below the contact, which suggests marine settings during lithification. The contact geometry, however, is suggestive of microkarst, which could indicate subaerial exposure. (Outcrop photo, 15-cm ruler at top for scale) fact is quite flat in places. The shift in facies above and below the contact is not large enough to be sure that the surface represents a sequence boundary; on the contrary, the facies contrast above (Wp) and below (Pp) might indicate a landward shift in facies rather than a basinward shift in facies. Therefore, the contact could simply be a hardground, recording a depositional hiatus due to transgression and drowning of the carbonate factory. In any case, it appears to represent a turnaround from overall regression to overall transgression. Above that rugose contact, there are several bed boundaries interpreted here to be marine hardgrounds (Figure 5.2). These hardgrounds exhibit sharp upper contacts and diffuse lower contacts. Borings can extend down from the hardgrounds. The borings appear to have been filled with the same sediment that occurs above the hardground. The hardground can have a rust-discoloration, which may indicate an iron encrustation on the hardground surface.

65 Figure 5.2 Marine hardground in the Franson Bench at the Beaver Creek section. The hardground contact with the above unit is sharp. Burrows extend down from the surface and appear to be filled with the same material that is above the contact. Rusty discoloration appears to concentrate at the surface as well. (Outcrop photo, cm-scale ruler at top for scale)

Overlying the Peritidal-Intertidal-Supratidal facies is a succession of Lower Shallow Subtidal (LSS) and Upper Shallow Subtidal (USS). Dominantly muddy, this likely represents a shallow ramp, low energy, subtidal depositional setting, where ramp geometry attenuation has dissipated the tidal and wave energies. In the Wilson Draw section, there is a thin Pp unit before deposition in the more basinward LSS dominates. The Pb and Wb facies that dominate the LSS in this location are somewhat cyclic in their depositional style: ±5 fining-upward cycles stack. Overall, the mud content in those cycles remains approximately constant, though in some cases it appears to fine upward overall. Overlying the Lower Shallow Subtidal succession is a Deep Subtidal unit, characterized by Pi, Wi, Pb, and M facies. The Deep Subtidal unit is thickest (~4m) in the Red Bluff section (northwesternmost and most basinward) and thinnest (<1m) in the Beaver Creek section (easternmost and most landward). The increase in the abundance of this more basinal facies association both vertically and laterally (moving east to west) is evidence for transgression. An outcrop photo of the Franson at the Schlichting Gulch section has been overlain with a facies and facies association schematic in Figure 5.3.

66 Mc Facies M Facies Assoc. Fg Wp DS Pp Wi Pi Wb LSS Pb Franson Gb Go SS

PIS Schlichting Gulch section

Figure 5.3 Outcrop photo of the Franson carbonate at the Schlichting Gulch section with a schematic facies overlay. The PIS facies association gives way to LSS then to DS at the top. Above the DS is covered section, which is presumably the OR facies association. Also of note are the biostromal geometries rather than any reef-like buildups. (Outcrop photo, seated person near base of outcrop for scale)

67 Deep Subtidal deposition gradually gives way to the even more basinal Outer Ramp facies association. Outer Ramp deposition is characterized by fine-grained siliciclastics, which may be punctuated by storm lags and can be calcareous. Lithostratigraphic nomenclature would label this unit as the Retort Member, as it appears to be a phosphatic mudrock.

5.3.3 Ervay Mbr., Park City Fm. The Ervay represents approximately 15 meters of section in each of the measured sections. At Sheep Mountain, it is a shallowing-upward succession, which is consistent with conclusions of previous researchers working in the Bighorn basin (e.g., Clark, 1994; Whalen, 1996; Inden and Coalson, 1996). The Ervay rests on the Outer Ramp (OR) facies association. Above that, a relatively thick and muddy Lower Shallow Subtidal (LSS) succession eventually give ways to a package of Upper Shallow Subtidal (USS) ooid shoals and peloidal banks. The Schlichting Gulch measured section is the only section with a continuous section of the Retort Member cropping out beneath the Ervay. The succession moves from Fg with periodic inter- ruptions of Pb and Pi (storm lags) to thick packages of M and Wb with thin lags of pervasively silicified Pb. Facies M in the Ervay is typically heavily bioturbated, especially directly before the shift to Go and Pp deposition (Figure 3.7). The shift from M and Wb facies to Go and Pp facies is abrupt (Figure 5.4). In the two northernmost sections (Red Bluff and Schlichting Gulch), the Go/Pp package is over 9 m thick; in the other two sections (depositionally landward), the Go/Pp thins to as little as 3 m; however, silicification makes it difficult to discern original texture in the equivalent strata at the Beaver Creek section. Notably absent from the Ervay succession at Sheep Mountain is the Pb facies that the carbonate ramp model (Figure 3.45) would predict. Its absence and the sharpness of the contact is suggestive of a forced regression. The contact between the Ervay and the overlying Triassic Dinwoody Formation is not well exposed at this location. An unconformable relationship is inferred based on previous work on the succession (e.g., McKelvey et al., 1959)

68 Figure 5.4 The shift from heavily bioturbated, largely silicified M and Wb to cross-bedded Go and Pp is abrupt. This is a photo of the Ervay bench at the Red Bluff section. (Outcrop photo, ~30cm hammer for scale at right)

5.4 Well log data As a demonstration of location of the study area being along the paleoshelf, Neutron- Density (N-D) crossplots have been made from wells to the east and west of the study area. In a N-D crossplot, anhydrites appear in the southwest corner of the plot due to that lithology’s low density porosity (i.e., high electron density) and low neutron porosity (i.e., low neutron capture). If anhydrite content is used as a proxy for distance from the paleo-shoreline, the assumption being that anhydrites were primarily forming in the supratidal setting or in the Goose Egg basin, it can be seen that the study area is located where the anhydrite content goes to zero from east to west. This is evident in the N-D crossplots in Figure 5.5 and Figure 5.6. Figure 5.5 shows an example well (Dishpan Federal 12-29) to the east of the study area; Figure 5.6 shows an example well (Carmody 34) to the west of the study area. A purple rectangle has been drawn on both cross-plots, and the data points that fall within that rectangle are highlighted on the correspond- ing log curves. Anhydrite is present in the Dishpan Federal 12-29 well but is notably absent from the Carmody 34 well.

69 Depth (ft) Depth 6380 6400 6420 6440 6460 6480 6500 6520 6260 6280 6300 6360 6320 6340 ERVAY FRANSON GRANDEUR DPHI (-20-50) NPHI (-5-50) 50

4 5

4 0

5 35

3 E

T I

0 O

2 D

5 25

N POLYHALITE

5 T

1 S

E M

S 2

1 O

NPHI - Neutron Porosity (%) R

P 0

5 15

WELL: 49013216330000, Dishpan Federal 12-29 (569 samples)

0 1

E T A

N X 0

O O S I 1

R A T 5

P G C E

E T P I

A R R

R 0

O Y

C H N

SALT 5 SULFUR

0 0 LANGBEINITE -5

50 30 40 20 10 y (%) y P o r t y o s i e n s i D I - t H P D -10 -20

Figure 5.5 Dishpan Federal 12-29 well is approximately 12 miles east of Sheep Mountain. A Neutron-Density crossplot of the Permian section reveals the presence of anhydrite in all three carbonate members, where the Grandeur appears to have the most. The data points that fall within the purple rectangle on the crossplot are highlighted in their respective positions on the accompanying log plots.

70 Depth (ft) Depth 650 800 850 900 950 750 700 GRANDEUR FRANSON ERVAY DPHI (-20-50) NPHI (-5-50) 50

4 5

4 0

5 35

3 E

T I

0 O

2 D

5 25

N POLYHALITE

5 T

1 S

E M

S 2

1 O

NPHI - Neutron Porosity (%) R

P 0

5 15 1

WELL: 49013215480000, Carmody 34 (656 samples)

0 1

E T A

N X 0

O O S I 1

R A T 5

P G C E

E T P I

A R R

R 0

O Y

C H N

SALT 5 SULFUR

0 0 LANGBEINITE -5

50 30 40 20 10 y (%) y P o r t y o s i e n s i D I - t H P D -10 -20

Figure 5.6 In contrast, the Permian section at the Carmody 34 well, located approximately 7 miles to the northwest of Sheep Mountain, has no anhydrite. No data points fall within the purple “anhydrite rectangle”. This is interpreted to mean that deposition at Carmody 34 was exclusively subtidal or intertidal whereas deposition at Dishpan Federal 12-29 was at times supratidal.

71 5.5 Correlations and sequence stratigraphy For this study, sequence stratigraphic features are defined as follows: lowstand systems tract is defined as the units between the sequence boundary (SB) and the transgressive surface (TS); transgressive systems tract as the units between the TS and the maximum flooding surface (MFS); and highstand systems tract (HST) as the units between the MFS and the SB. Plate 1 shows correlations made from well logs and measured sections for this study. The cross-section has been flattened on the MFS datum. Both lithostratigraphic and sequence stratigraphic tops have been picked on that cross-section. Lithostratigraphic tops include the Ervay, Franson, Grandeur and are corroborated by picks made by previous workers for this area of the Wind River basin (e.g., Ahlstrand, 1972); sequence stratigraphic tops have been picked only for the latest cycle (“Ervay Cycle” in the nomenclature of Whalen, 1996; Figure 2.1) because that is all that crops out sufficiently enough to assess at Sheep Mountain. The MFS of the Ervay Cycle has been picked in well logs at the maximum GR log inflec- tion (i.e., the “hottest” GR), which coincides with the middle of the Retort Member. Below the MFS, the gamma ray character of wells in the study area shows an overall “fining-upward” character (Figure 5.7), which is suggestive of transgression. Above the MFS, the gamma ray logs show a “cleaning upwards” character, which is expected during HST deposition. It has been pulled across the measured sections mainly based on the facies observed in the Schlichting Gulch section. In the Schlichting Gulch section, the exact location of the MFS is unknown, but it has been inferred to be in the middle of a package of Outer Ramp (Figure 3.45) facies. Above the MFS at the Schlichting Gulch section, facies grade from Outer Ramp to Deep Subtidal, then back to Outer Ramp with pulses of Lower Shallow Subtidal deposition. Eventually Lower Shal- low Subtidal deposition takes over. The surface has been approximated in the other measured sections where it is inferred to be beneath covered section. The TS has been picked at what appears to be the onset of transgression, manifest as a marine hardground at the Wilson Draw section (Figure 5.1). To reiterate, the facies above the contact is muddier than the facies below, suggesting a landward shift in facies, and the unit below the contact exhibits isopachous cement, which suggests lithification in the marine environment. In well logs, the TS apparently manifests as a sharp change from low GR character

72 NPHI 45 -15 GR ILD RHOB 0 200 0.2 2000 1.95 2.95

6 Top of Ervay

2 MFS

Top of Franson

5 SB

Figure 5.7 An example set of well logs from Dishpan Federal 12-29. Red arrows show overall “fining upward” pattern below the maximum flooding surface (MFS) and “cleaning upwards” pattern above the MFS. Also shown is the sequence boundary (SB), marked by an apparent basinward shift in facies, and the transgressive surface (TS), marked by an apparent landward shift in facies.

73 to high GR character (for example, see Figure 5.7 or see the Dishpan-Federal 34-15 well at a measured depth of 5254 ft; Plate 1). Lastly, the SB has been correlated at a sharp change from high GR character to low GR character (for example, see Disphan-Federal 12-29 at a measured depth of 6372 ft; Plate 1). That change in gamma ray character apparently represents a basinward shift in facies, which is common directly above sequence boundaries. This surface was not observed directly in outcrop, so it has been inferred to be in the covered section below the Franson outcrops. The Mg-Al-P XRF elemental suite has also been plotted in depth view in Figure 5.8. Mg, a proxy for dolomitization, is highest during the Ervay HST. Al, a proxy for the siliciclastic proportion, slowly increases through the TST, rapidly increases at and above the MFS, then drops again during the HST. Lastly, P increases through the TST then falls again to baseline readings during the HST. Of particular interest in these correlations is the superposition of the TST and the LST with the top several meters of the Franson Member. In fact, it appears that the entire Franson Member that crops out at Sheep Mountain is part of the TST (and possibly the LST) of the Ervay Cycle. This interpretation contrasts with the interpretations of previous workers (e.g., Whalen 1996; Clark, 1994; Inden and Coalson, 1996) who place all Franson carbonate growth into the HST of the Franson Cycle (see Figure 2.5). This study suggests that the Franson carbonates at Sheep Mountain are transgressive based on the following lines of evidence:

• The facies association stacking pattern points to an overall deepening during deposition of the Franson carbonates at Sheep Mountain.

• The overall log character of the equivalent succession in well logs displays a classic fining upward character, which often implies transgression in marine environments.

• In the PRC system as a whole, phosphate content increases toward the basin center. Since phosphate content in the Franson carbonates increases both upwards and in a basinward direction, it is presumed that the increase in phosphate represents a landward shift in facies (i.e., transgression).

• The occurrence of several hardgrounds throughout the Franson carbonate succession

74 Red Bluff Schlicting Gulch Wilson Draw Beaver Creek RB-12-03 SG-12-04 WD-12-01 BC-12-02 <5,152FT> <9,362FT> <18,775FT> XRF_Mg XRF_Mg XRF_Mg XRF_Mg 0 100000 0 100000 0 100000 0 100000 XRF_Al XRF_Al XRF_Al XRF_Al 0 60000 0 60000 0 60000 0 60000 XRF_P XRF_P XRF_P XRF_P 0 100000 0 100000 0 100000 0 100000

5 ERVAY

7 MFS

0 FRANSON

5 TS

Mc crinkly laminated dolomudstone Pp peloidal packstone Pb bioclast packstone

M mudstone Wi intraclast wackestone Gb sandy bioclast grainstone Fg fine-grained siliciclastics Pi bioclastic intraclast packstone Go ooid grainstone

Wp peloidal wackestone Wb bioclast wackestone Ss sandstone Figure 5.8 Measured sections along with the Mg, P, and Al XRF data. Units of the elemental curves are in ppm. Shapes represent data points and lines have been drawn in to connect the points to help display trends. Distance between sections is labeled. 75 suggests drowning of the carbonate factory, hence transgression during deposition of that unit.

Indeed, carbonate growth is not at all incompatible with TST deposition. According to Sarg (1988), carbonate factory production can continue during the transgression as long as the region is still in the photic zone despite a rising sea level. This suggests that the Sheep Moun- tain area was shallow enough on the carbonate ramp to remain in the photic zone even during transgression. In a rudimentary sense, the Mg-Al-P elemental suite may also be useful in differentiating systems tracts. A ternary plot of that element suite in the Franson and Ervay members is shown in Figure 5.9. The data have been color-coded by interpreted systems tract (HST or TST). When high-Al data samples are removed, data points from different systems tracts plot in different portions of the ternary plot. If we use Mg as a proxy for dolomitization, P as a proxy for phosphogenesis, and Al as a proxy for aluminosilicate input, the ternary plot suggests that the relative amounts of dolomitization, phosphogenesis, and detrital input can be used to differenti- ate systems tracts in the Park City Formation.

76 Figure 5.9 Centered ternary diagram of the Mg-Al-P element suite. Data points have been color-coded by interpreted systems tract and colored lines have been drawn around the two data clouds. In this plot, high-Al samples (>3% Al by weight), inferred to be siliciclastics, were removed. In addition, Grandeur samples were not plotted due to ambiguity of the sequence stratigraphy of that member. At least to some extent, TST carbonates can be distinguished from HST carbonates when viewed in the manner. Mg probably reflects dolomitization; P probably reflects phosphogenesis; and Al probably reflects siliciclastic input.

77 CHAPTER 6 6 DIAGENESIS The diagenetic history of the PRC at Sheep Mountain is complex. Pervasive dolomitization, phosphate precipitation, multiple calcification events, and multiple silicification events have altered these rocks. A paragenetic sequence has been constructed based on thin section observations (Figure 6.1).

Phosphate precipitation Paragenetic sequence Dolomitization

Calcite cementation Late-stage silicification Silicification to (solution cavity fill, etc.) Late-stage calcification (poikilotopic, fracture fill, and de-dolomitization)

Time

Early to shallow burial Moderate to maximum burial Uplift to subaerial exposure Figure 6.1 Visual representation of the paragenetic sequence. Time increases to the right, so events listed at the top left occurred first and the events listed at the bottom right occurred last. There is likely significant overlap between diagenetic events. There is also uncertainly about when events might have started or ended and how long those events lasted. No absolute time- line is implied; rather diagenetic events are listed as such to show relative order. Inferred burial depths or diagenetic setting are indicated at the base of the figure.

6.1 Phosphogenesis In an attempt to better understand the controls on phosphate formation in the Phospho- ria Sea, Hiatt and Budd (2001) used stable oxygen isotopes from the structural phosphate in francolite, a carbonate mineral rich in fluorapatite [Ca5(PO4)3F], to assess paleotemperatures. They found that phosphate formed at a wide range of temperatures (14-40°C) along the shelf and was not significantly altered by burial recrystallization. At Sheep Mountain, an important precursor to the paragenetic sequence appears to have been the authigenic precipitation of phosphate (collophane, pristine phosphorite of Pu- fahl, 2010), which was later reworked and consolidated into granular deposits (Figure 3.28). Early phosphogenesis also included precipitation of phosphate into primary pore structures: for

78 example bryozoan zooecia (Figure 6.2 and Figure 6.3), echinoderm “honeycombs” (Figure 6.4 & Figure 6.5), and brachiopod punctae and spines. This phenomenon is extremely common in the bioclasts, especially in the Pb facies of the Franson Member. In some cases, glauconite is present along with the phosphate.

6.2 Dolomitization There have been very few oxygen and carbon isotopic studies of Phosphoria limestones and dolostones. One such study by Murata et al. (1972), who apparently analyzed bulk samples rather than cements or specific grain types, concluded that Park City dolomites formed in well aerated waters and have isotopic signatures consistent with those of normal marine carbonates, with the exception of a few samples from the eastern part of the basin that imply salina-like environments. The lack of iron-bearing carbonates at Sheep Mountain is also suggestive of oxygenated waters, since reducing conditions are typically required for the formation of ferrous

13 carbonate. Murata et al. (1972) reported values of -6 to +5‰ δ CPDB and approximately 24 to

13 32 δ OSMOW for Park City dolostones. Their dolomite samples from the Phosphoria Fm. had a

13 more depleted δ CPDB signature, which Murata et al. (1972) attributed to uptake of light carbon sourced by bacterially degraded organic matter. In a more recent study, Whalen (1993) found

13 that δ CPDB values for the Phosphoria dolomites average about -1.16‰ and max out at 3.78‰. Dolomitization is pervasive and ubiquitous in the carbonates on Sheep Mountain. In some cases, depositional fabrics have been obliterated (Figure 6.6). In other cases, what appears to have previously been carbonate mud has been dolomitized, leaving the bioclasts relatively intact (Figure 3.15). Rhombic dolomite is common. Rhombs are typically about the same size throughout any given sample, but in some cases the distribution is bimodal (Figure 3.14). This may indicate two separate dolomitization events, such that dolomitization affected one type of rock constituent more than once (or for a longer time). Like phosphogenesis, it is possible that dolomitization commenced in tandem with or shortly after deposition, since precipitation of apatite is inhibited by high Mg2+/Ca2+ ratios (Kast- ner et al., 1984). Dolomitization, therefore, could drive phosphate precipitation as it consumes free Mg2+. On the other hand, when pH is less than 7.5, for example, calcite is relatively un-

79 Figure 6.2 Pervasively silicified bryozoan, with dominantly phosphatic zooecia. Glauconite (greenish) and silica (light blue and off-white colors) can locally occur in the zooecia as well. (Thin-section photomicrograph, scale bar at upper left corner)

Figure 6.3 Bryozoan fragment with phosphate-filled zooecia. This example also has calcareous zooecia walls, in contrast to the bryozoan in Figure 6.2. (Thin-section photomicrograph, scale bar at upper left corner)

80 Figure 6.4 Pervasively silicified sample with a phosphatic echinoderm. In the large specimen at the center of the slide, phosphate (brownish) precipitated in the “honeycomb” voids and the echinoderm “skeleton” was later silicified. (Thin-section photomicrograph, PPL, scale in upper left corner)

Figure 6.5 Another example of a silicified echinoderm where primary intraparticle porosity has been filled with precipitated phosphate. (Thin-section photomicrograph, PPL, scale in upper left corner)

81 Figure 6.6 Pervasively dolomitized carbonate from the Wilson Draw section. Original fabric has been obliterated by diagenesis and replaced by sucrosic dolomite. Poikilotopic calcite has formed in some pore spaces (Alizarin-red stained minerals). (Thin-section photomicrograph, PPL, scale in upper left corner) stable. Dissolution of calcite would drive down the Mg2+/Ca2+ ratio, which encourages pristine phosphate precipitation (Pufahl, 2010). In a few cases, intact dolomite rhombs are observed to be growing in a phosphate substrate (Figure 6.7), indicating that the dolomite grew after that pore space had already been occluded by phosphate. Dolomitization was apparently a continuous process, as there is evidence that dolomite rhombs grew at several different phases of in the paragenetic sequence. Dolomite is observed to be growing on calcite substrates (Figure 6.8) and obliterating depositional fabrics to sucrosic textures (Figure 6.6).

6.3 Calcite cementation Carbonate cement in these rocks is almost always dolomite. Because of the pervasive dolomitization of the rocks, it is assumed that the cement was originally calcite. Most commonly this is isopachous (Figure 3.20, Figure 3.34, and Figure 6.9), interpreted to be marine phreatic in origin. In fewer cases, non-isopachous cement is observed in biologic pore spaces (specifically bryozoan zooecia) (Figure 6.10 and Figure 6.11). Because of its tendency to be present

82 Figure 6.7 Dolomite rhomb growing in a phosphate substrate in a Franson carbonate (sample # 024B). This probably indicates that the dolomite grew after phosphate had already precipitated. (Thin-section photomicrograph, scale in upper left corner)

Figure 6.8 Dolomite rhomb at the center of the slide is growing in a calcite substrate, which in this case is a well-preserved brachiopod. (Thin-section photomicrograph, scale in upper left corner)

83 Figure 6.9 Isophachous (interpreted to be marine phreatic) cement coating various allochems. The cement likely was originally calcite and was later dolomitized. (Thin-section photomicrograph, PPL, scale in upper left corner) only in bryozoan zooecia, it is not clear whether this is indicative of vadose zone cementation, or if there is something specific to these bryozoans that encourages non-isopachous cement precipitation. In some cases, isopachous cement envelops bioclasts that have phosphate in their intraclast pore spaces; because there is commonly no cement internal to those pore spaces, it is inferred that cementation occurred after phosphatization.

6.4 Silicification

6.4.1 Early silicification Silicification probably occurred next, as there is evidence of dolomite rhombs being replaced by silica (Figure 6.12). This implies that dolomite rhombs would have been present prior to the silicification event that replaced them. Evaporites were replaced by length-slow chalcedony (Figure 6.13). On the other hand, some evidence for a continuum of dolomitization and silicification can be seen in Figure 6.14. Dolomite rhombs occur throughout that slide, but they are notably larger and more abundant in the lower-left half of the photomicrograph. The upper-

84 Figure 6.10 Bryozoan with non-isopachous cement in some of the zooecia (see arrow for example). (Thin-section photomicrograph, XPL, scale in upper left corner)

Figure 6.11 Bryozoan zooecia (?) filled with phosphate and lined non-isopachously by dolomite cement. The cement was likely originally calcite. (Thin-section photomicrograph, XPL, scale in upper left corner)

85 Figure 6.12 Dolomite rhomb that has been replaced by silica. The rhombs are in the void of a calcitic brachiopod spine and the rest of the pore space is filled with phosphate. (Thin-section photomicrograph, upper half is XPL, lower half is PPL, scale in upper left corner)

Figure 6.13 Length-slow chalcendony has replaced evaporite. Under cross-nicols, length-slow chalcedony exhibits greenish-blue coloration in the NE and SW quadrants of the mineral and yellow-orange-red coloration in the NW and SE quadrants. As Folk and Pittman (1971) detail, this feature usually indicates the precursor was an evaporite. (Thin-section photomicrograph, cross-nicols, scale bar in upper left corner)

86 right half is interpreted to have been bioturbated, which left an early migration pathway for silica- rich fluids. That effectively stopped dolomitization in that portion of the slide, while dolomitization continued in the un-bioturbated portion. Later, a more pervasive silicification event silicified the rest of the rock. The silica also replaced many bioclasts, leading to excellent preservation of original textures (Figure 6.15), and carbonate mud (e.g.,Figure 6.14). Silicification does not appear to have a preference for a specific type of calcium carbonate; indeed, it replaces HMC (e.g., echinoderms) as often as it replaces LMC (e.g., brachiopods). In hand sample, silicification can obliterate depositional fabric beyond recognition (Figure 6.16). In some cases, sedimentary structures are preserved but the allochem makeup is cryptic

(Figure 6.17). Silicicrypstone caps the Ervay bench at the Beaver Creek section (Figure 6.16), and may represent silicified Mc, Pp and Go facies, based on the equivalent units in the other measured sections.

Figure 6.14 This slide may demonstrate that dolomitization and silicification are occurring simultaneously. In the lower left half of the slide, dolomite rhombs are larger than those on the upper right half of the slide, which is mostly silica. Silica rich fluids may have moved through the upper right half first, shutting off dolomitization, yet dolomitization continued where the silica-rich fluids had not flushed. A later silicification event, more pervasive in nature, silicified the rest of the rock. (Thin-section photomicrograph, XPL, scale in upper left corner)

87 R

Figure 6.15 Pervasive silicification has led to excellent preservation of bioclasts. In this case, bryozoans (B), brachiopods (R), and echinoderms (E) are all excellently preserved. (Thin-section photomicrograph, XPL, scale bar in upper left corner)

Figure 6.16 Silicicryptstone (C). This massive silicified unit caps the Ervay bench at the Beaver Creek outcrop section. Original texture is cryptic, but stratiform units are observed, suggesting the original geometry was stratiform, and some of the porosity looks fenestral. Any mounding suggested by the photo is not real and is instead a result of outcrop weathering and the angle from which the photo was taken. (Outcrop photo, ~30cm tall hammer at left for scale, up is stratigraphic up) 88 Figure 6.17 Silicicryptstone (C) from the Ervay bench at the Beaver Creek section, sample #185. Colorations are vaguely reminiscent of cross-lamina. Stratigraphic position with respect to the other measured sections would indicate that this was probably an ooid grainstone or peloidal packstone. (Hand-sample photo, cm-scale ruler at top, horizontal field of view if ~11cm, up is stratigraphic up)

Silicification probably affected a wide range of depositional fabrics, especially those that were both permeable and porous. Although “primary” chert has been described in the Phospho- ria Fm., chert should not be used to classify a depositional environment on the carbonate shelf of the Phosphoria Sea (Wardlaw and Collinson, 1986). Indeed, it has a tendency to replace multiple facies types. Regionally, “primary” depositional chert is relatively uncommon; with the exception of some black chert beds in southeastern Idaho, most of the chert in the succession replaces carbonates or sandstones (Wardlaw and Collinson, 1986).

6.4.2 Late silicification At a later time, another phase of silicification apparently occurred that occluded some moldic pore spaces (Figure 6.18). Cement in that figure is microcrystalline quartz; what appears to have been a bioclast mold has been leached, and megaquartz grew into the pore space; last, a microporous silica filled in the rest of the mold.

6.5 Late calcification events (dedolomite, fracture fill, etc.) Dedolomitization by calcite occurred, as evidenced by dedolomite rhombs (Figure 6.19 and Figure 6.20) as well as dolomite rhombs that have been degraded by the incursion of

89 S

PPL XPL Figure 6.18 Silica textures in an occluded pore space of a Pi facies sample, PPL at left and XPL at right. Microcrystalline quartz (M) with “pinpoint” extinction appears to be the primary cement. The feature at the center of the slide appears to have been a void (possibly a bioclast mold) into which megaquartz has grown (Q). The center of the void has been filled with what appears to be another phase of silica (S). (Thin-section photomicrographs, PPL on left, XPL on right, scale bar in upper left corner) calcite precipitation (Figure 6.21 and Figure 6.22). This necessarily occurred after the dolomite rhombs had grown. It probably also occurred after silicification. This is because dedolomite is sometimes present in rocks that have been extensively silicified. Since it has been established that silicification occurred after dolomitization, and that it commonly replaces calcite and leaves dolomite intact, it is likely that the silica would have replaced the dedolomite if the dedolomite had been there prior to silicification. Therefore, it is reasonable to infer that de-dolomitization occurred after silicification. Moreover, most authors recognize dedolomite as a product of late- stage near-surface or weathering processes (Flügel, 2010), so it makes sense that it is one of the latest diagenetic events. Another calcification event is indicated by poikilotopic calcite precipitatation (Figure 6.6) and calcite-filled fractures, which cross-cut earlier diagenetic minerals (Figure 6.23 and Figure 6.24). Poikilotopic calcite may be an indicator of burial stage lithification (Scholle and Ulmer- Scholle, 2003). Because poikilotopic calcite is forming in a sucrosic dolomite substrate (Figure 6.6), it can be inferred that the poikilotopic calcite formed after dolomitization. This would ex-

90 Figure 6.19 Dedolomite rhombs in a pervasively silicified sample. The rhombic shape is evidence that these Alizarin-red etched calcite minerals were originally dolomite. Also noteworthy are the “grungy” edges of the dolomite rhombs. It appears that the silicification event probably degraded the integrity of the dolomite rhombs. This would imply that the dolomite had formed prior to the silicification of the matrix. (Thin-section photomicrograph, PPL, scale bar in upper left corner)

Figure 6.20 Another example of dedolomitization. The rhomb at the center of the slide has been dedolomitized incompletely in this pervasively silicified sample. (Thin-section photomicrograph, PPL, scale bar in upper left corner)

91 Figure 6.21 Dolomite rhomb at the center of the slide has degraded edges where calcite mineralization has taken place (as seen with the Alizarin-red staining). This implies that a calcification event occurred after the dolomite rhomb had grown. (Thin-section photomicrograph, PPL, scale bar in upper left corner)

Figure 6.22 Dolomite rhomb at the center of this slide is showing signs of degradation as a result of a late-stage calcification event. The bioclast (brachiopod) at the top of the slide is touching the calcite mineralization that is degrading the dolomite rhomb. (Thin-section photomicrograph, PPL, scale bar in upper left corner)

92 PPL XPL

Figure 6.23 Calcite-filled fracture cross-cutting a microcrystalline quartz sample. It may even be that the calcite-filled fracture exploited the trace of a preexisting fracture. (Thin-section photomicrograph, PPL on top, XPL on bottom, scale in upper left corner)

XPL PPL

Figure 6.24 Late-stage calcite-filled fractures cross-cut megaquartz matrix and phosphatic bioclasts (bryozoan and echinoderms). (Thin-section photomicrograph, XPL on top, PPL on bottom, scale in upper left corner)

93 clude the possibility of the poikilotopic calcite replacing poikilotopic gypsum or halite. In addition, since calcite-filled fractures cross-cut some samples, they occurred latest. The orogenic event that deformed and brought Sheep Mountain strata to the surface (i.e., Laramide orogeny) is probably responsible for the cross-cutting fractures, which were subsequently filled with calcite.

94 CHAPTER 7 DISCUSSION AND CONCLUSIONS

7.1 Discussion The depositional facies and diagenetic history at Sheep Mountain anticline has been investigated using measured sections, thin-section and hand sample analysis, and handheld X-ray fluorescence technology (XRF). Twelve facies and six facies associations were described in outcrop. The outcrops were successfully tied to nearby well logs using a synthetic (“pseudo”) gamma ray curve, calculated from the XRF U-Th-K elemental suite. Even though the XRF dataset was only moderately useful in distinguishing depositional facies, the ability to convert the U-Th-K elemental suite to a “pseudo” gamma ray curve is a valuable corollary of XRF data collection. This method could be used in other outcrop studies where tying outcrop data to well logs would be beneficial. In addition, calculating a “pseudo” gamma ray curve from XRF data may be superior to traditional handheld gamma ray spectroscopy, because other potentially useful elemental signatures are measured at the same time. The facies and facies associations described in this study are interpreted to have been deposited on a carbonate ramp with an updip lagoonal environment. Facies belts in the Ervay and Franson are broad. At outcrop scale, bed geometries are stratiform and do not suggest that features on the ramp had significant positive relief. For example, even where reef building fauna (e.g., large bryozoans) are present, beds are biostromal rather than biohermal. Facies changes in outcrop are predictable and well-behaved, and they appear to reflect depth-controlled hydrodynamic changes based on location on the homoclinal ramp. The ramp, situated on the western margin of Pangaea, would have dipped gently westward (much less than 0.5°) toward the basin depocenter. From west to east, organic-rich mudrocks, cherts, and phosphorites grade into subtidal carbonates, which in turn grade into intertidal and supratidal facies. That same facies succession is seen vertically in outcrop. Outer Ramp silty mudrocks are overlain by Deep Subtidal mudstones and phosphatic intraclast packstones and wackestones. Those facies are overlain by phosphatic bioclast packstones and wackestones of the Lower Shallow Subtidal facies association, which in turn give way to ooid/

95 peloid shoals and lagoonal bioclastic mudstones of the Upper Shallow Subtidal facies association. The succession culminates in facies from the Peritidal facies association, including crinkly laminated mudstones as well as interbedded siltstones and replaced evaporites. The entire succession from the base of the Franson carbonate through the Ervay member at Sheep Mountain appears to record deposition in the Ervay sequence stratigraphic cycle. This interpretation deviates from previous interpretations where Franson carbonate growth occurs only in the highstand systems tract of the Franson sequence stratigraphic cycle. At Sheep Mountain, Franson deposition probably records transgressive systems tract deposition in the Er- vay Cycle. Franson carbonates rest on the top of near-shore calcareous siltstones, mudstones, and replaced evaporites. The transgression is recorded as a deepening of facies, an increase in phosphate upwards, several marine hardgrounds, and a “fining up” pattern in well logs. The transgression culminates in an inferred maximum flooding surface (MFS) in the Retort Member above the phosphatic intraclast lags. Mudrocks and carbonates of the Retort and Ervay members appear to record highstand tract deposition in the Ervay Cycle. Above the MFS, facies changes through the Retort and Ervay suggest overall regression. Mudrocks with interbedded storm lags give way to bioclastic carbonate mudstone and wackestone deposition, which is eventually overlain by ooid or peloid shoal and intertidal crinkly dolomudstone. The diagenetic history of the Park City Formation at Sheep Mountain is complex and varied. In a general sense, it appears that the earliest diagenetic events were phosphatization and dolomitization. These two processes may have contributed to a feedback mechanism, where phosphatization could have encouraged dolomitization, and vice versa. While this study systematically examined neither porosity volumes and types nor perme- abilities, in general reservoir character tends to be best where dolomite textures are sucrosic and where moldic textures are observed. Silicification and late calcification tend to be detrimen- tal to porosity, but the brittle nature of the silicified rocks could mean that there is potential for fractured reservoirs in that rock type.

This study suggests on several fronts that there is potential for stratigraphic traps in the Park City carbonates of the Wind River basin. Sheep Mountain is located in a transition zone where anhydrite starts to appear, which could provide an updip seal for hydrocarbon accumula- 96 tion. In addition, it appears that just to the west of the field area and at a deeper interval than the units at Sheep Mountain, Franson highstand carbonates, which do not crop out at Sheep Mountain, pinch out into coastal siltstone and shale facies. This suggests stratigraphic reservoir potential in those carbonates. Highstand carbonates in the Ervay typically have well-developed porosity due to extensive dolomitization and moldic porosity development, which might suggest that Franson highstand carbonates could have favorable reservoir properties.

7.2 Summary of conclusions

• Twelve facies and six facies associations were described. The facies and facies associations suggest that the Ervay and Franson members of the Park City Fm. at Sheep Mountain anticline were deposited on a homoclinal carbonate ramp possibly with an updip lagoon. The Ervay Cycle represents a shallower position on the ramp, possibly because the basin depocenter shifted to a more distant position when compared with Franson deposition.

• Facies variability in the basal Grandeur Member would indicate a significantly more complicated depositional setting that a simple homoclinal carbonate ramp. Pre-existing topography was possibly a main control.

• Uppermost Franson carbonate deposition represents the transgressive systems tract for the overlying Ervay Cycle, in contrast to conclusions of previous workers.

• Phosphogenesis was likely the earliest event in the paragenetic sequence, followed by dolomitization, silicification, and late calcification. Dolomitization, however, was likely a very early event as well and could have helped drive phosphogenesis by decreasing the Mg2+/Ca2+ ratio of pore waters. Likewise, phosphogenesis may have helped to increase the Mg2+/Ca2+ ratio, thereby driving dolomitization.

• To a limited extent, XRF data can be used to distinguish lithologies in this succession.

The Mg-Al-P suite of elements shows systematic differences between carbonates of the Franson and Grandeur members, but the Ervay is compositionally indistinguishable. In

97 general, P increases through transgression and into the early highstand, but quickly drops off with continued highstand systems tract development. Mg is highest in the highstand systems tract, and Al relfects the siliciclastic input.

7.3 Suggestions for future work The limited scope of this project has left a number of unanswered questions that would benefit from further study:

• The sequence stratigraphic framework put forth in this study for the Ervay Cycle should be extended into the subsurface of the Wind River basin and extended up to the Bighorn basin to see how it compares with the framework that has been established for that basin (e.g., Clark, 1994; Inden and Coalson, 1996).

• The Grandeur Member of the Park City Fm. is among the least studied units of the PRC. It is also still unknown whether the “Nowood” unit of Todd (1996) extends to the southern Wind River basin. More work should be done to understand the facies and facies variability of this unit in the Wind River basin.

• Rather than replacing bioclasts, as some workers have observed in the Big Horn basin (e.g., Inden and Coalson, 1990), phosphate at Sheep Mountain appears to precipitate within primary intraparticle porosity in bioclasts. If indeed phosphate is replacing bioclasts, it would be interesting to examine whether it has any preference for particular calcium carbonate pseudomorphs. For example, it may be possible to constrain pore water acidity since phosphate likely precipitates at a pH range of 7.0-7.5. Relative stabilities of aragonite, low-magnesium calcite, and high-magnesium calcite might dictate what phosphate replaces. However, on Sheep Mountain phosphate rarely replaces bioclasts but instead commonly fills intraparticle pore spaces.

• The differences in dolomitization styles of the Grandeur, Franson, and Ervay should be

examined in more detail using stable oxygen and carbon isotope analysis. In addition, the use of strontium isotopes could elucidate whether any dolomite formed in the mixing

98 zone; if not, the strontium isotope ratio of the carbonate would mirror the ratio of Permian sea water.

99 REFERENCES

Abercrombie, S., 1989, Structural analysis of the Sheep Mountain-Beaver Creek thrust area: Master’s thesis, Baylor University, Waco, 71 pp.

Ahlstrand, D. C., 1972, Permian Carbonate Facies, Wind River Mountains and Western Wind River Basin, Wyoming: Master’s thesis, University of Montana, Missoula, 104 pp.

Ahlstrand, D. C., and J. A. Peterson, 1978, Permian carbonate facies, Wind River Basin, Wyo- ming, in R. G. Boyd, G. M. Olson, and W. W. Boberg (eds.), Wyoming Geological Association Guidebook, Thirtieth Annual Field Conference, pp. 89–99.

Aitchison, J., 1986, The statistical analysis of compositional data: Chapman & Hall Ltd., 440 pp.

Bassiouni, Z., 1994, Theory, measurement and interpretation of well logs: SPE Textbook Series v. 4, 372 pp.

Baturin, G. N., 1982, Phosphorites on the sea floor: origin, composition, and distribution: Else- vier Scientific, New York, 343 pp.

Berner, R. A., 1971, Principles of chemical sedimentology: McGraw-Hill, New York, 240 pp.

Blakey, R. C., 2012, Paleogeography of North America website, http://jan.ucc.nau.edu/rcb7/ nam.html.

Brittenham, M. D., 1976, Permian Phosphoria carbonate banks, Idaho-Wyoming thrust belt, in J. G. Hill (ed.), Symposium on geology of the Cordilleran hingeline: Rocky Mountain Association of Geologists, pp. 173–191.

Burchette, T. P., and V. P. Wright, 1992, Carbonate ramp depositional systems: Sedimentary Geology, v. 79, no. 1, pp. 3–57.

Burk, C. A., and H. D. Thomas, 1956, The Goose Egg Formation (Permo-Triassic) of eastern Wyoming: Wyoming Geological Survey Report of Investigations no. 6: University of Wyoming, Laramie, 11 pp.

100 Carroll, A. R., N. P. Stephens, M. S. Hendrix, and C. R. Glenn, 1998, Eolian-derived siltstone in the Upper Permian Phosphoria Formation: implications for marine upwelling: Geology, v. 26, no. 11, pp. 1023–1026.

Clark, W. J., 1994, The Ervay cycle of the Permian Phosphoria and Park City formations, Big- horn Basin, Wyoming: sequence stratigraphy, facies, and porosity trends: Doc- toral dissertation, University of Colorado, Boulder, 660 pp.

Claypool, G. E., A. H. Love, and E. K. Maughan, 1978, Organic geochemistry, incipient meta- morphism, and oil generation in black shale members of Phosphoria Formation, western interior, United States: AAPG Bulletin, v. 62, no. 1, pp. 98–120.

Coalson, E.B., and R.F. Inden, 1990, Geology and oil production of the Ervay (Phosphoria) reservoirs, eastern Big Horn Basin, Wyoming, Mountain Geologist, v. 27, no. 3, pp. 77-98.

Dunham, R. J., 1962, Classification of Carbonate Rocks According to Depositional Textures, in W.E. Ham (ed.), AAPG Memoir 1: Classification of carbonate rocks: a symposium, pp. 108–121.

Filippelli, G. M., and Delaney, M. L., 1992, Similar phospliorus fluxes in ancient phosphorites and a modern phosphogenic environment, Geology, v.20, pp. 709-712.

Flügel, E., 2010, Microfacies of carbonate rocks: analysis, interpretation and application, second edition, Springer, 984 pp.

Folk, R. L., and J. S. Pittman, 1971, Length-slow chalcedony; a new testament for vanished evaporites: Journal of Sedimentary Research, v. 41, no. 4, pp. 1045–1058.

Gaffin, S., 1987, Ridge volume dependence on seafloor generation rate and inversion using long term sea level change: American Journal of Science, v. 287, no. 6, pp. 596–611,

Glenn, C. R., K. B. Follmi, S. R. Riggs, G. N. Baturin, K. A. Grimm, J. Trappe, A. M. Abed, C. Galliolivier, R. E. Garrison, and A. V. Ilyin, 1994, Phosphorus and phosphorites- sedimentology and environments of formation: Eclogae Geologicae Helvetiae, v. 87, no. 3, pp. 747–788.

101 Hein, J. R., 2004, The Permian earth, in James R. Hein, ed., Handbook of Exploration and Environmental Geochemistry: Elsevier Science B.V., Life Cycle of the Phosphoria Formation From Deposition to the Post-Mining Environment, pp. 3–17.

Hein, J. R., R. B. Perkins, and B. R. McIntyre, 2004, Evolution of thought concerning the origin of the Phosphoria Formation, western US phosphate field, in James R. Hein (ed.), Handbook of Exploration and Environmental Geochemistry: Elsevier Sci- ence B.V., Life Cycle of the Phosphoria Formation From Deposition to the Post- Mining Environment, pp. 19–42.

Hendrix, M. S., and C. W. Byers, 2000, Stratigraphy and sedimentology of Permian strata, Uinta Mountains, Utah: Allostratigraphic controls on the accumulation of economic phosphate, in C.R. Glenn, L. Prévôt-Lucas, J. Lucas (eds.), SEPM Special Publi- cation, v. 66, pp. 349–368.

Herring, J. R., 1995, Permian phosphorites: a paradox of phosphogenesis, in P.A. Scholle, T.M. Peryt, and D.S. Ulmer-Scholle (eds.), The Permian of Northern Pangea: Springer Berlin Heidelberg, p. 292–312.

Hiatt, E. E., and D. A. Budd, 2001, Sedimentary phosphate formation in warm shallow waters: new insights into the palaeoceanography of the Permian Phosphoria Sea from analysis of phosphate oxygen isotopes: Sedimentary Geology, v. 145, no. 1–2, pp. 119–133.

Inden, R., and E. Coalson, 1996, Phosphoria Formation (Permian) cycles in the Bighorn basin, Wyoming, with emphasis on the Ervay Member, in M. W. Longman and M. D. Sonnenfeld (eds.), Paleozoic Systems of the Rocky Mountain Region: Rocky Mountain Section SEPM, pp. 379–404.

Irwin, M. L., 1965, General theory of epeiric clear water sedimentation: AAPG Bulletin, v. 49, no. 4, pp. 445–459.

James, N. P., and J. Lukasik, 2010, Cool-and cold-water neritic carbonates: in N. P. James and R. W. Dalrymple (eds.), Facies Models 4, v. 4, pp. 371–399.

Jarvis, I., A. M. Murphy, and A. S. Gale, 2001, Geochemistry of pelagic and hemipelagic carbonates: criteria for identifying systems tracts and sea-level change: Journal of the Geological Society, v. 158, no. 4, pp. 685–696.

102 Johnson, J. F., and W. M. Sutherland, 2008, Geologic map of the Lander 30’ X 60’ quadrangle, Fremont County, Wyoming: Wyoming Geological Survey, Map Series 87.

Kastner, M., K. Mertz, D. H. Zenger, and R. E. Garrison, 1984, The association of dolomite- phosphorite-chert: causes and possible diagenetic sequences, in R. E. Garrison, M. Kastner, and D. H. Zenger (eds.), Dolomites of the Monterey Formation and Other Organic-Rich Units: Pacific Section SEPM, pp. 75–86.

King, R. H., 1957, Stratigraphy of the Phosphoria Formation in the Wind River Mountains: in Wyoming Geological Association Guidebook, 12th Annual Field Conference, pp. 35–38.

Kirschbaum, M. A., P. G. Lillis, and L. N. R. Roberts, 2007, Geologic Assessment of Undis- covered Oil and Gas Resources in the Phosphoria Total Petroleum System of the Wind River Basin Province, Wyoming, in Petroleum Systems and Geologic Assessment of Oil and Gas in the Wind River Basin Province, Wyoming, U.S. Geological Survey Digital Data Series DDS-69-J, Chapter 3, 27 pp.

Klepper, M. R., 1950, A geologic reconnaissance of parts of Beaverhead and Madison Counties, Montana: U.S. Geol. Survey Bulletin 969-C, pp. 55–85.

Lane, D. W., 1973, Phosphoria and Goose Egg formations in Wyoming: Wyoming Geological Survey, Preliminary Report No. 12, 24 pp.

Martın-Fernández, J. A., M.Bren, C. Barceló-Vidal, and V. Pawlowsky-Glahn, 1999, A measure of difference for compositional data based on measures of divergence, in S. J. Lippard, A. Naess, and R. Sinding-Larsen (eds.), Proceedings of IAMG’99, The Fifth Annual Conference of the International Association for Mathematical geology, Trondheim, Norway, 211-216.

Maughan, E. K., 1979, Petroleum source rock evaluation of the Permian Park City Group in the northeastern Great Basin, Utah, Nevada, and Idaho, in G. W. Newman and H. D. Goode (eds.), Basin and Range Symposium: Rocky Mountain Association of Geologists and Utah Geological Association, pp. 523-530.

Maughan, E., 1983. Tectonic setting of the Rocky Mountain region during the Late paleozoic and the Early Mesozoic, in D. E. Walter (ed.), Proceedings of Symposium on the Genesis of Rocky Mountain Ore deposits: changes with time and tectonics: Den- ver Regional Exploration Geologists Society, pp. 39–50. 103 McKelvey, V.E., J.S. Williams, R.P. Sheldon, E.R. Cressman, T.M. Cheney, R.W. Swanson, 1959, The Phosphoria, Park City, and Shedhorn formations in the western Phos- phate Field: U.S. Geological Survey Professional Paper 313-A, 47 pp.

Merschat, W. R., 1984, Possible basal Phosphoria coquinite trend, Fremont and Sweetwater Counties, Wyoming, in J. Goolsby and D. Morton (eds.), The Permian and Penn- sylvanian Geology of Wyoming, WGA 35th Annual Field Conference Guidebook, pp. 119-125.

Miller, E. L., M. M. Miller, C. H. Stevens, J. E. Wright, and R. Madrid, 1992, Late Paleozoic paleogeographic and tectonic evolution of the western US Cordillera, in B. C. Burchfiel, P. W. Lipman, and M. L. Zoback (eds.), The Cordilleran Orogen: Con- terminous U.S.: Geological Society of America, The Geology of North America, v. G-3, pp. 57–106.

Murata, K. J., I. Friedman, and R. A. Gulbrandsen, 1972, Geochemistry of carbonate rocks in Phosphoria and related formations of the western Phosphate Field: US Geologi- cal Survey, Professional Paper, v. 800, pp. D103–D110.

Parrish, J. T., 1995, Geologic Evidence of Permian Climate, in P. A. Scholle, T. M. Peryt, and D. S. Ulmer-Scholle (eds.), The Permian of Northern Pangea: Springer Berlin Heidelberg, pp. 53–61.

Pawlowsky-Glahn, V., and J. J. Egozcue, 2006, Compositional data and their analysis: an introduction, in A. Buccianti, G. Mateu-Figueiras, V. Pawlowsky-Glahn (eds.), Compo- sitional Data Analysis in the Geosciences, Special Publication v. 264, Geological Society, pp. 1–10.

Peterson, J. A., 1980, Depositional history and petroleum geology of the Permian Phosphoria, Park City, and Shedhorn formations, Wyoming and southeastern Idaho, United States Geological Survey Open File Report 80-667, 29 pp.

Peterson, J. A., 1984, Permian stratigraphy, sedimentary facies, and petroleum geology, Wyo- ming and adjacent area, in J. Goolsby and D. Morton (eds.), The Permian and Pennsylvanian Geology of Wyoming: Wyoming Geological Association Guide- book 35, pp. 25–64.

104 Piper, D. Z., and P. K. Link, 2002, An upwelling model for the Phosphoria sea: a Permian, ocean-margin sea in the northwest United States: AAPG Bulletin, v. 86, no. 7, pp. 1217–1235.

Pufahl, P. K., 2010, Bioelemental sediments, in N. P. James and R. W. Dalrymple (eds.), Facies Models 4, v. 4, pp. 477–503.

Sarg, J. F., 1988, Carbonate Sequence Stratigraphy, in C.K. Wilgus, B.S. Hastings, C.A. Ross, H. Posamentier, J. Van Wagoner & C.G. St. C. Kendall (eds.), Sea-level changes: an integrated approach, SEPM Special Publications v.42, pp. 155-181.

Scholle, P., and D. S. Ulmer-Scholle, 2003, A color guide to the petrography of carbonate rocks: grains, textures, porosity, diagenesis: AAPG Memoir 77, 474 pp.

Taylor, S. R., and S. M. McLennan, 1985, The continental crust: its composition and evolution: Blackwell, Oxford, 312 pp.

Thió-Henestrosa, S., and J. A. Martín-Fernández, 2006, Detailed guide to CoDaPack: a free- ware compositional software, in A. Buccianti, G. Mateu-Figueiras, V. Pawlowsky- Glahn (eds.), Compositional Data Analysis in the Geosciences, Special Publica- tion v. 264, Geological Society, pp. 101–118.

Thyberg, B., H. Jordt, K. Bjorlykke, and J. Faleide, 2000, Relationships between sequence stratigraphy, mineralogy and geochemistry in Cenozoic sediments of the northern North Sea, in A. Nøttvedt, B.T. Larsen (eds.), Dynamics of the Norwegian Margin: The Geological Society of London Special Publication v. 167, pp. 245–272.

Todd, L. M., 1996, Stratigraphy at the Boundary of the Tensleep Sandstone and Park City/ Goose Egg formations in the Southern Big Horn Mountains and Eastern Owl Creek Mountains, Wyoming, in C.F. Bowen, S.C. Kirkwood, T.S. Miller (eds.), Wyoming Geological Association Guidebook, v. 47, pp. 159–178.

Trexler, J.H., Jr., Snyder, W.S., Cashman, P.H., Gallegos, D.M., and Spinosa, C., 1991, Missis- sippian through Permian orogenesis in eastern Nevada: Post-Antler, pre-Sonoma tectonics of the western Cordillera, in J. D. Cooper and C. H. Stevens (eds.), Paleozoic paleogeography of the western United States, Volume II: Los Angeles, Pacific Section SEPM, pp. 317–330.

105 Tribovillard, N., T. J. Algeo, T. Lyons, and A. Riboulleau, 2006, Trace metals as paleoredox and paleoproductivity proxies: an update: Chemical Geology, v. 232, no. 1-2, pp. 12–32.

Walling, C. T., 2000, Origin of quartz silt in the Permian Phosphoria Formation: isotopic and grain size evidence: Master’s thesis, University of Wisconsin–Madison, 97 pp.

Wardlaw, B. R., and J. W. Collinson, 1986, Paleontology and deposition of the Phosphoria Formation, Contributions to Geology, University of Wyoming, v. 24 no. 2, pp. 107- 142.

Weichman, B. E., 1958, Stratigraphy of the Phosphoria Formation in the southern portion of the Wind River Basin: Master’s thesis, University of Wyoming, Laramie, 68 pp.

Whalen, M. T., 1993, Depositional and diagenetic history of the Park City Formation carbonate ramp, northwestern USA: Implications for eastern ocean basin carbonate plat- form development: Doctoral dissertation, Syracuse University, Syracuse, 270 pp.

Whalen, M., 1996, Facies architecture of the Permian Park City Formation, Utah and Wyoming: implications for the paleogeography and oceanographic setting of western Pan- gea, in M. W. Longman and M. D. Sonnenfeld (eds.), Paleozoic Systems of the Rocky Mountain Region: Rocky Mountain Section SEPM, pp. 355–378.

Willis, J. J., and R. H. Groshong Jr, 1993, Deformational style of the Wind River uplift and associated flank structures, Wyoming, in W. R. Keefer, W. J. Matzger, and L. H. God- win (eds.), Oil and Gas and Other Resources of the Wind River Basin: Wyoming Geological Association Guidebook, pp. 337–375.

Yochelson, E. L., 1968, Biostratigraphy of the Phosphoria, Park City, and Shedhorn Formation: US Geological Survey Professional Paper 313-D, pp. D571–D660.

106 APPENDIX A MEASURED SECTIONS Appendix A consists of digitized versions of the four measured sections used in this study. The sections appear here in order from north to south. Red Bluff (RB) is on pages 96- 99; Schlichting Gulch (SG) is on pages 100-104; Wilson Draw (WD) is on pages 105-113; and Beaver Creek is on pages 114-122. The base of each measured section was set at 0.0m. The location (latitude and longitude) of the base of each section is indicated on the heading of the measured section template. The legend for symbols and colors used on the measured sections are below:

Symbols Facies

Mc cross-bedding crinkly laminated dolomudstone

M mudstone (carbonate) stylolite Fg fine-grained siliciclastic

chert bed Wp peloid wackestone

Pp peloid packstone burrows or bioturbation Wi intraclast wackestone

crinkly or wavy lamina Pi bioclastic intraclast packstone

Wb bioclast wackestone ripples Pb bioclast packstone sharp bed contact Gb sandy bioclast grainstone

massive chert Go ooid grainstone

Ss sandstone

Thin section Inferred facies or facies association 032B Example of sample locality

covered interval

107 Measured section: Base of measured section is at: Red Bluff (RB) 42°37'41.91"N, 108°29'8.31"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay) Facies Samples Height (m) B G P W M (cvrd)

10.0

Pi 113

112 Fg (M) 9.0

111 8.0 Pi 110

Wi 109 7.0 Pb 108 M 107 Wb Pi Wi 106 Pi 105 M

6.0

Pi 104

102 Wi 5.0 101 M/Slt 100 Wb

103

4.0

Pb M 099

3.0 098

Pb 097 096 095 Wb 094 Pb 093 2.0 M

092 M

1.0 Wb 091

M 090

0.0 B G P W M (cvrd)

108 Measured section: Base of measured section is at: Red Bluff (RB) 42°37'41.91"N, 108°29'8.31"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay) Facies Samples Height (m) B G P W M (cvrd)

21.0

20.0

19.0

18.0

17.0

16.0

15.0

14.0

13.0

12.0

11.0 B G P W M (cvrd)

109 Measured section: Base of measured section is at: Red Bluff (RB) 42°37'41.91"N, 108°29'8.31"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay) Facies Samples Height (m) B G P W M (cvrd)

132 Mc

Pp 131 32.0

130

Wp 129 31.0

128

Pp/Go 127 30.0

126

Pp/Go 125

29.0 124

M 123

28.0 122

121 Wb M 27.0 Wb 120 M

Pb M Pb M 119 26.0 Wb 118 Pb

M 117 25.0

Pb 116A 116B 115 Wb

24.0

114 M

Pb 23.0 Mc

22.0 B G P W M (cvrd)

110 Measured section: Base of measured section is at: Red Bluff (RB) 42°37'41.91"N, 108°29'8.31"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay) Facies Samples Height (m) B G P W M (cvrd)

143 Fg 43.0

42.0

41.0

40.0

39.0

Fg 142

141

38.0

140

139 37.0

Pp 138

137 36.0

136

35.0 135

34.0

Pp 134

Mc 133 33.0 B G P W M (cvrd)

111 Measured section: Base of measured section is at: Schlichting Gulch 42°36'53.54"N, 108°29'5.51"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay) Facies Samples Height (m) B G P W M (cvrd)

Pb 204

9.0

203 ~200? 8.0 Mc

7.0 Wp 202

6.0

5.0

4.0

3.0

2.0

201

1.0 M

0.0

-1.0 B G P W M (cvrd)

112 Measured section: Base of measured section is at: Schlichting Gulch 42°36'53.54"N, 108°29'5.51"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay) Facies Samples Height (m) B G P W M (cvrd) M 215 Pi/Wi

20.0

19.0

18.0

Pi 214 Fg

17.0

16.0 Wi Pb Wb Wi

15.0

Pi 14.0 213 Wb 212

13.0 211

210

12.0 209

Wb 208 207 Pb

11.0 M 206

Pb Wb Pb 205 Wb 10.0 Pb B G P W M (cvrd)

113 Measured section: Base of measured section is at: Schlichting Gulch 42°36'53.54"N, 108°29'5.51"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay) Facies Samples Height (m) B G P W M (cvrd)

31.0

30.0

29.0

M 28.0

27.0 233 Fg

Pb 232B Fg 26.0 Pb 232A

231 Fg

25.0 230 Pi 229 Wi 228

24.0 227 222

226 221 Fg 23.0 220 225

219

22.0 Pi 218 Wi 217.5 M 217 Pi 21.0 Fg 216 B G P W M (cvrd)

114 Measured section: Base of measured section is at: Schlichting Gulch 42°36'53.54"N, 108°29'5.51"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay) Facies Samples Height (m) B G P W M (cvrd) 243

Pp 42.0

242

41.0

241

40.0 240 Mc

239 39.0

Pp 238 38.0

237

37.0

236 36.0 Pp

235

35.0

34.0 234

M 33.0

Wb Pb Wb

32.0 Gb/Pb B G P W M (cvrd)

115 Measured section: Base of measured section is at: Schlichting Gulch 42°36'53.54"N, 108°29'5.51"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay) Facies Samples Height (m) B G P W M (cvrd)

46.0

45.0 Fg

44.0 Wp?

Mc 244 Wp

43.0 Pp B G P W M (cvrd)

116 Measured section: Base of measured section is at: Wilson Draw (WD) 42°35'34.42"N, 108°28'11.41"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay) Facies Samples Height (m) B G P W M (cvrd)

9.0

8.0

7.0

6.0 Ss

001

5.0

4.0

3.0

2.0

1.0 Ss

0.0

-1.0 B G P W M (cvrd)

117 Measured section: Base of measured section is at: Wilson Draw (WD) 42°35'34.42"N, 108°28'11.41"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay)

Facies Facies Samples Height (m) B G P W M (cvrd)

20.0

19.0

18.0

Wp? 007 17.0

006 Ss 16.0

005

Pp?

15.0

14.0

M 004

13.0

Ss 003

12.0

002

11.0 Ss

10.0 B G P W M (cvrd)

118 Measured section: Base of measured section is at: Wilson Draw (WD) 42°35'34.42"N, 108°28'11.41"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay) Facies Samples Height (m) B G P W M (cvrd)

31.0

30.0

29.0

28.0 011 Ss 010

009 008

27.0

26.0

25.0

24.0

23.0

22.0

21.0 B G P W M (cvrd)

119 Measured section: Base of measured section is at: Wilson Draw (WD) 42°35'34.42"N, 108°28'11.41"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay) Facies Samples Height (m) B G P W M (cvrd) Fg

Fg 019

42.0 M 016

Fg 015

014 41.0 018

Fg ~017

013 40.0

39.0

38.0

37.0

36.0

35.0

34.0

33.0

32.0 B G P W M (cvrd)

120 Measured section: Base of measured section is at: Wilson Draw (WD) 42°35'34.42"N, 108°28'11.41"W Texture, Fossils,

Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay) Facies Samples Height (m) B G P W M (cvrd)

53.0

52.0

51.0

50.0

49.0

48.0

47.0

46.0

45.0

Ss 012

44.0 Fg

Fg 43.0 B G P W M (cvrd)

121 Measured section: Base of measured section is at: Wilson Draw (WD) 42°35'34.42"N, 108°28'11.41"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay) Facies Samples Height (m) B G P W M (cvrd)

Pb 055

054 053 Wb 052 64.0 051 Pb 050 M 049 Wi 048 Pi 047 Wi Pb 046 Wi 63.0 045

/Wb Pb 044

62.0 Wb

043

61.0 Wb

Pb M 042 Wb 041 Pb 040 60.0 M 038 037? 036

Wb 035

Wb 034 59.0 033 Wb 039 Pb 032 031 Pp

58.0 030 029

57.0 Pb

028

027 M

56.0 026

Wp 025B 025A 024A Pp 55.0 024B 024D Mc 024C M 023

022 Fg 021 54.0 023A 023B B G P W M (cvrd)

122 Measured section: Base of measured section is at: Wilson Draw (WD) 42°35'34.42"N, 108°28'11.41"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay)

Facies Facies Samples Height (m) B G P W M (cvrd)

75.0

74.0

73.0

72.0

71.0

70.0

69.0

68.0

Pi 059 67.0

66.0

Pi/Wi 058 057 Pi Wi 65.0 Pb 056 B G P W M (cvrd)

123 Measured section: Base of measured section is at: Wilson Draw (WD) 42°35'34.42"N, 108°28'11.41"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay) Facies Samples Height (m) B G P W M (cvrd)

065

86.0

064

85.0 063

062

Wb 84.0 Pb 061

060

Wb 83.0

074

82.0 Pb

Wb 073 81.0 M Wb

Wb Wb

M 072 80.0 Pb 071 Wb

79.0 Wb 070

Wb 069

78.0

M 068

77.0

76.0 B G P W M (cvrd)

124 Measured section: Base of measured section is at: Wilson Draw (WD) 42°35'34.42"N, 108°28'11.41"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay) Facies Samples Height (m) B G P W M (cvrd)

97.0

96.0

95.0

94.0

93.0

92.0

91.0 Wp 067

90.0

89.0

066

88.0

87.0 B G P W M (cvrd)

125 Measured section: Base of measured section is at: Beaver Creek (BC) 42°35'5.41"N, 108°24'19.25"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay) Facies Samples

Height (m) B G P W M (cvrd) Ss Pb 148 Gb 147

9.0

146

Pb 8.0

145 7.0 M 144 M

Fg M Fg Pb Wb 6.0

M or Wp?

5.0

4.0

Fg M 3.0 Mc 076 M Fg

Ss 075 2.0

1.0

Ss M

Ss 0.0

-1.0 B G P W M (cvrd)

126 Measured section: Base of measured section is at: Beaver Creek (BC) 42°35'5.41"N, 108°24'19.25"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay) Facies Samples Height (m) B G P W M (cvrd)

20.0

19.0 Ss 157 Pi Ss Wi

Ss 156 18.0 Wi

17.0 155 Gb

153 Wb

16.0 M 152 Gb

151

Ss 154 15.0

Pp 150

14.0

13.0

12.0 M 149

11.0

10.0 B G P W M (cvrd)

127 Measured section: Base of measured section is at: Beaver Creek (BC) 42°35'5.41"N, 108°24'19.25"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay) Facies Samples

Height (m) B G P W M (cvrd)

31.0

30.0

29.0

28.0 Mc

27.0 160

Fg 26.0

159

25.0

24.0

Ss 158

Pb/Wb

23.0 Fg

22.0

21.0 B G P W M (cvrd)

128 Measured section: Base of measured section is at: Beaver Creek (BC) 42°35'5.41"N, 108°24'19.25"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay) Facies Samples

Height (m) B G P W M (cvrd)

42.0

41.0

40.0

39.0

38.0

37.0

36.0

35.0

34.0

33.0

32.0 B G P W M (cvrd)

129 Measured section: Base of measured section is at: Beaver Creek (BC) 42°35'5.41"N, 108°24'19.25"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay) Facies Samples Height (m) B G P W M (cvrd)

53.0

52.0 173

172 51.0 Fg

50.0

49.0

48.0

47.0

46.0

45.0

44.0

43.0 B G P W M (cvrd)

130 Measured section: Base of measured section is at: Beaver Creek (BC) 42°35'5.41"N, 108°24'19.25"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay) Facies Samples Height (m) B G P W M (cvrd)

64.0

Pb Wb 171 Pb 63.0 Pi Pb Pi

62.0

Pb Wb

61.0 170 Wb

169

Pb 168 60.0 Wb Pb Wb

59.0 Wb

167

58.0

Wb Pb Wb Pb Wb 57.0 166

165 Pb

56.0 Wb 164 Pb

Wb Pb Wb 163 162 55.0 Wb

161

54.0 B G P W M (cvrd)

131 Measured section: Base of measured section is at: Beaver Creek (BC) 42°35'5.41"N, 108°24'19.25"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay) Facies Samples Height (m) B G P W M (cvrd)

M 178

M 177 75.0 Wi Pi

176

74.0

M 175

73.0

174

72.0

71.0

70.0

69.0

68.0

67.0

66.0

65.0 B G P W M (cvrd)

132 Measured section: Base of measured section is at: Beaver Creek (BC) 42°35'5.41"N, 108°24'19.25"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay) Facies Samples Height (m) B G P W M (cvrd)

86.0 Pp

Fg/Pp 187 85.0 186A 186B

84.0 Pp

83.0

185 82.0 Mc

81.0

80.0 184

79.0

183

78.0 Pb

Wb 182 Pb M Pb M 181 Wb 77.0 M Wb Pb 180 M Wb M 179 Wb 76.0 M B G P W M (cvrd)

133 Measured section: Base of measured section is at: Beaver Creek (BC) 42°35'5.41"N, 108°24'19.25"W Texture, Fossils, Sedimentary Structures

(vC) (C) (M) (F) (Silt) (Clay) Facies Samples Height (m) B G P W M (cvrd)

97.0

96.0

95.0

94.0

93.0 188

92.0

91.0 M

90.0

89.0

88.0

87.0 B G P W M (cvrd)

134 APPENDIX B SUPPLEMENTAL ELECTRONIC FILES Included with this thesis are two datasets that were used in this study. First is the entire X-ray fluorescence (XRF) dataset that was collected for this study. XRF data were acquired on nearly all collected hand samples (n=200) using a handheld Niton XL3t GOLDD+ XRF Analyzer. The data are presented here in comma delimited files (.csv). Data are raw (not normalized) concentrations in parts per million (ppm). When the concentration of an element falls below the level of detection (LOD), a 0 value has been substituted. In addition, the data are also included as csv files separated by measured section. Measured sections start by definition at a height of zero feet and increase upwards. For ease of comparison with well logs, and arbitrary “depth” value (MD) has also been given for each sample (i.e., “depth-registered”), which is based on the section heights. Second are the well logs that were digitized for this study. Those are submitted in stan- dard log ASCII (.las) format as a data archive (.zip).

Comma delimited file with all the XRF data SheepMountain_XRFdata.csv that were collected for this study. Comma delimited file with depth-registered BC_XRFdata.csv XRF data for the Beaver Creek measured section Comma delimited file with depth-registered RB_XRFdata.csv XRF data for the Red Bluff measured section Comma delimited file with depth-registered SG_XRFdata.csv XRF data for the Schlichting Gulch measured section Comma delimited file with depth-registered WD_XRFdata.csv XRF data for the Wilson Draw measured section Archive including the digital well logs in log well_logs.zip ASCII format (.las).

135