Biochemical and chemical controls on sedimentation, sequence stratigraphy, and diagenesis, in the Phosphoria rock complex (Permian), Rocky Mountain region, USA

BIOCHEMICAL AND CHEMICAL CONTROLS ON SEDIMENTATION, SEQUENCE STRATIGRAPHY, AND DIAGENESIS, IN THE PHOSPHORIA ROCK COMPLEX

(PERMIAN), ROCKY MOUNTAIN REGION, USA

by

Copyright by Maxwell Pommer 2018 All Rights Reserved

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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 Doctor of Philosophy (Geology).

Golden, Colorado Date: _______________________ Signed: _________________________ Maxwell Pommer Signed: _________________________ Dr. J. Frederick Sarg Thesis Advisor Signed: _________________________ Dr. M. Stephen Enders Professor and Department Head Department of Geology and Geological Engineering

iii ABSTRACT

Biochemical sedimentation, near-surface diagenesis, stable isotopes, and porosity vary systematically stratigraphically and regionally in the Phosphoria Rock Complex (PRC), Rocky Mountain region, USA, in response to dynamic paleo-environmental conditions spanning the Middle Permian. Environmental, biochemical, and isotopic trends mimic diagnostic trends of the End-Permian Mass Extinction (EPME), occurring through Kungurian-Wordian time (~274Ma to 265Ma), ~13MY before the EPME and ~5MY before the end-Guadalupian crisis. These indicate PRC trends are of a similar genesis to the EPME, and EPME dynamics were driven by locally modified global processes spanning the Middle to Late Permian. Biochemical, isotopic, and environmental trends are heterogeneous across the PRC, a second-order (~9MY) cycle, and the third-order (2-5 MY) Franson (latest Kungurian - Wordian) and Ervay (Wordian) cycles.

During transgressions, influx of cool, acidic, low-oxygen, nutrient-rich waters warmed and interacted with hot, oxygenated marine and evaporitic waters. Flourishing sapropelic algal and anaerobic microbial communities resulted in phosphorites and sulfidic-OM-rich mudrocks seaward of calcitic biota and micritic carbonates, redbeds, evaporites and microbialites. Values of δ18_{O and δ}13_{C in carbonates and silica are depleted in distal settings due to microbial decay of} OM and increase landwards due to evaporative fractionation. Values of δ18_{O in carbonate} fluorapatite are depleted in distal environments, increase landwards and towards maximum transgression, indicating warming. Porosity in transgressions is low due to near-surface cementation and recrystallization, as well as compaction and infill of pore space by secondary OM (bitumen) in OM-rich mudrocks. S-rich OM catalyzed early secondary-OM generation and inhibited OM-hosted porosity generation through burial.

During highstands warm, oxygenated, alkaline marine waters dominated in and became increasingly hot, shelf-confined, and evaporitic. With limited nutrient influx, and input of eolian-sourced silica, resulted in widespread spiculites and calcitic-biota carbonates at maximum transgression and in distal highstands. Increasingly restricted and evaporitic conditions through highstands resulted in dolomitized bioturbated muds and sandstones, aragonitic molluscs, ooids, and peritidal microbialites. Values of δ18_{O and δ}13_{C became increasingly enriched throughout} highstands in marine carbonates and widespread authigenic silica. This and moganite-bearing

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chalcedony suggest evaporitic reflux drove silicification and dolomitization. Porosity is most abundant in dolomites deposited in restricted, evaporitic highstand conditions.

v TABLE OF CONTENTS ABSTRACT...…....iii LIST OF FIGURES...vii LIST OF TABLES...ix ACKNOWLEDGEMENTS...x

CHAPTER 1: GENERAL INTRODUCTION...1

CHAPTER 2: BIOCHEMICAL SEDIMENTATION AND DIAGENESIS IN RESPONSE TO MID-PERMIAN PALEO-ENVIRONMENTAL DYNAMICS IN A RESTRICTED SEAWAY, PHOSPHORIA ROCK COMPLEX (PERMIAN, KUNGURIAN-WORDIAN, ROCKY MOUNTAIN REGION, USA...2

2.1: Abstract...2 2.2: Introduction...4 2.3: Methodology...6 2.4: Results...13 2.5: Discussion...57 2.6: Conclusions...76 2.7: References...78

CHAPTER 3: BIOCHEMICAL AND STRATIGRAPHIC CONTROLS ON PORE-NETWORK EVOLUTION, PHOSPHORIA ROCK COMPLEX (PERMIAN), ROCKY MOUNTAIN REGION, USA...89

3.1: Abstract……...89

3.2: Introduction……...91

3.3: Methods…...98

3.4: Results: Sequence Stratigraphy, Sedimentation, Diagenesis and Porosity...99

3.5: Discussion: Pore Network Evolution in the Phosphoria Rock Complex...127

3.6: Conclusions...136

3.7 References...138

CHAPTER 4: FORECASTING THE END-PERMIAN MASS EXTINCTION: PALEO-ENVIORNMENTAL AND BIOCHEMICAL DYNAMICS IN THE MIDDLE PERMIAN PHOSPHORIA SEAWAY, ROCKY MOUNTAIN REGION, USA ...145

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4.2: Introduction...145

4.3: Dataset...148

4.4: Age of the Phosphoria Rock Complex...150

4.5: Paleo-Environmental, Biogeochemica, and Isotopic Trends across the Phosphoria Rock Complex……….………..151

4.6: Implications...158

4.8: References……...159

CHAPTER 5: GENERAL CONCLUSIONS...166

CHAPTER 6: SUGGESTIONS FOR FUTURE WORK...171

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LIST OF FIGURES

Figure 2.1: A) Schematic distribution of lithologies, cycles, and commonly referred to...4

Figure 2.2: Map of study area indicating location of measured sections, stable isotope data …...7

Figure 2.3: Schematic model of regional ramp environment terminology. Modified from …...15

Figure 2.4: Cross-section A-A'. Location in Figure 2. G = glauconite...19

Figure 2.5: Cross-section B-B'. Location in Figure 2, key in Figure 3...21

Figure 2.6: Cross-section C-C'. Location in Figure 2, key in Figure 3.21………..…….23

Figure 2.7: Photographs of basinal and ramp-margin exposures of the PRC. Staff is 5ft …...25

Figure 2.8: Photomicrographs of samples from the distal transgression. A) Daly's Spur ...28

Figure 2.9: Photographs of outcrops and core on the outer and middle ramp. A) ...31

Figure 2.10: Photomicrographs from transgressions on the carbonate platform. ...33

Figure 2.11: Photomicrographs from the distal highstand (basin, ramp-margin, and ...36

Figure 2.12: Photographs of outcrops and core deposited on the inner ramp and ramp...41

Figure 2.13: Photomicrographs from carbonates deposited in shallow environments...43

Figure 2.14: Stable isotope data from the PRC normalized by systems tracts. 542 samples…...45

Figure 2.15: Cross section D-D' plotted with corresponding δ18_{O (A), and δ}13_{C. Key...47}

Figure 2.16: SIMS data of δ18_{O in calcite (blue dots) and silica (yellow dots) from the...50}

Figure 2.17: SIMS data of δ18_{O in calcite (blue dots), dolomite (pink dots), and silica...51}

Figure 2.18: SIMS data of δ18_{O in calcite (blue dots), dolomite (pink dots), and silica...52}

Figure 2.19: SIMS data of δ18_{O in dolomite (pink dots), and silica (yellow dots) from the...53}

Figure 2.20: Schematic distribution of environmental conditions, resulting facies, and...68

Figure 2.21: Schematic distribution of environmental conditions, resulting facies, and...79

Figure 3.1: A) Schematic distribution of lithologies, cycles, and commonly referred to...92

Figure 3.2: Map of study area indicating location of measured sections, porosity data...94

Figure 3.3: A) BSE mosaic of thin-section R147-6198.5 overlain with extracted porosity…...99

Figure 3.4: Cross section from A - A' (Figure 2.1) illustrating distribution of facies...102

Figure 3.5: Plots of core-plug measurements of porosity and permeability, point count...105

Figure 3.6: Plots of pore size distribution separated by core and color-coded by facies...105

Figure 3.7: Photomicrographs and SIMS δ18_{O data in phosphorite grainstones. Dots...110}

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Figure 3.9: Photomicrographs and SIMS δ18_{O data of transgressive calcitic biota...115}

Figure 3.10: Photomicrographs and SIMS δ18_{O data of spiculitic cherts and siltstones from...119}

Figure 3.11: Photomicrographs and SIMS δ18_{O data of calcitic biotic debris packstones...121}

Figure 3.12: Photomicrographs and SIMS δ18_{O data of bioturbated dolo-micrite and peloid…...123}

Figure 3.13: Photomicrographs and SIMS δ18_{O data of ooid dolo-grainstone and fenestral…...126}

Figure 3.14: Schematic distribution of facies, major chemical diagenetic processes in...129

Figure 4.1: A) Schematic distribution of lithologies, cycles, and commonly referred to...148

Figure 4.2: Plot of Sr-curves through the Permian with Phosphoria 87Sr/86Sr and U/Pb...152

Figure 4.3: Cross section A-A' plotted with corresponding δ13_{C values. Facies are color...155}

Figure 4.4: Stable isotope data from the PRC normalized by systems tracts. 542 samples...156

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LIST OF TABLES

Table 2.1: Measured section locations from core and outcrop. Cores are reported by their...8

Table 2.2: Facies, characteristic near-surface diagenetic overprints, interpreted...17

Table 2.3: Moganite content calculated by Raman spectra 501/464cm-1 peak integral ………...37

Table 2.4: SIMS values of δ18_{O in carbonates...54}

Table 2.5: SIMS and bulk SIRMS measurements of δ18O and δ17O in authigenic...55

Table 2.6: Values of δ18_{O in phosphate and paleotemperatures calculated from Longinelli ...56}

Table 3.1: Depositional facies, dominant diagenetic overprints, pore types, mean porosity...106

Table 3.2: Porosity, permeability, and pore type abundances. HST = highstand systems...107

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ACKNOWLEDGEMENTS

This study was supported financially by grants and scholarships from Devon Energy, GSA, SEPM, RMS-SEPM, The Colorado Scientific Society, Edward Coalson, and Richard Inden.

Technical assistance was provided by the USGS Core Research Center, Mihai Ducea (University of Arizona), Viorel Autudori (Center for Stable Isotopes, University of New Mexico), Katharina Pfaff, Thomas Monecke, Jae Ericson, Rania Eldam Pommer (Colorado School of Mines), Céline Defouilloy, Noriko Kita, John Valley (WiscSIMS, University of Wisconsin–Madison), Julien Allaz, Eric Ellison (University of Colorado Boulder), Heather Lowers (USGS), David Carpenter (Monsanto), Marshall Deacon, Vanessa O'Brien, Eric Pommer, Bailey Corson, Richard Geesaman, Patrick Patton, and land owners who allowed access to outcrops. A portion of equipment used was funded by NSF-EAR grants 1355590 and 1427626.

Thanks to Rick Sarg, who served as PhD advisor and encouraged me to see the big

picture through all of the detail. Marsha French, Wendy Harrison, and John Spear are thanked for serving as PhD committee members and their scientific contributions to this project. Kitty

Milliken is thanked for her helpful comments as well.

All of this would not have been possible without the love and support of my family and friends. A special thank you goes out to my brilliant, kind, and beautiful wife Rania Eldam Pommer. Lastly, my parents (Beth and Eric Pommer), and my sister Laura Fidler, are thanked for their lifelong encouragement, support, and love.

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1 CHAPTER 1

GENERAL INTRODUCTION

This study investigates biochemical sedimentation, diagenesis, and isotope geochemistry across the Phosphoria Rock Complex (PRC) in the Rocky Mountain Region, USA. Integrated stratigraphic, petrologic, and isotope geochemical datasets allow assessment of biotic, chemical, and environmental trends through deposition of the PRC from a microscopic to regional scale, illustrating how the system evolved spatially and through time.

From this integrated dataset the following are interpreted: 1) evolution of environmental conditions and resultant biochemical responses across deposition of the PRC; 2) environmental, near-surface biochemical, and burial controls on pore-network evolution in the PRC; and 3) significance of environmental conditions, biochemical processes, and isotopic signatures of PRC to global processes preceding the End-Permian Mass Extinction and end-Guadalupian Crisis. Methods, datasets, and interpretations are presented in three chapters:

1. Biochemical Sedimentation and Diagenesis in Response to Mid-Permian

Paleo-Environmental Dynamics in a Restricted Seaway, Phosphoria Rock Complex (Permian, Kungurian-Wordian), Rocky Mountain Region, USA

2. Biochemical and Stratigraphic Controls on Pore-Network Evolution, Phosphoria Rock Complex (Permian), Rocky Mountain Region, USA

3. Forecasting the End-Permian Mass Extinction: Paleoenvironmental and Biochemical Dynamics in the Middle Permian Phosphoria Seaway, Rocky Mountain Region, USA

In addition, appendices include spatially resolved measurements of δ18_{O from carbonate} and silica measured with secondary ion mass spectrometry (SIMS) in Appendix A, as well as stable isotope values obtained with stable isotope ratio mass spectrometry and 87/86Sr isotopes in Appendix B as supplemental electronic files. Detailed measured sections are available by request from the author.

2 CHAPTER 2

BIOCHEMICAL SEDIMENTATION AND DIAGENESIS IN RESPONSE TO MID-PERMIAN PALEO-ENVIRONMENTAL DYNAMICS IN A RESTRICTED

SEAWAY, PHOSPHORIA ROCK COMPLEX (PERMIAN, KUNGURIAN-WORDIAN, ROCKY

MOUNTAIN REGION, USA 2.1: ABSTRACT

Biochemical sedimentation, near-surface diagenesis, and stable isotopic signals vary systematically both stratigraphically and regionally in the Phosphoria Rock Complex (PRC), Rocky Mountain region, USA, in response to dynamic paleo-environmental conditions spanning the Middle Permian. The PRC's paleogeographic setting in a tropical, restricted, epicontinental seaway on the western margin of Pangea amplified impacts of dynamic long-term global

processes. Biochemical, isotopic, and environmental trends are heterogeneous across the PRC, a second-order (~9MY) cycle, and across the third-order (2-5 MY) Franson (latest Kungurian - Wordian) and Ervay (Wordian) cycles.

During transgressions, influx of cool, acidic, low-oxygen, nutrient-rich waters warmed and interacted with hot, oxygenated marine and evaporitic waters across the ramp profile causing sapropelic algal and anaerobic microbial communities to flourish in distal settings. This resulted in widespread accumulation of phosphorites, sulfidic-OM-rich mudrocks in basinal environments seaward of calcitic biota and micritic carbonates on the outer and mid ramp, and redbeds,

evaporites and microbialites on the inner ramp. Values of δ18_{O and δ}13_{C in carbonates and silica} are depleted in distal settings due to microbial decay of OM and increase landwards due to evaporative fractionation. Values of δ18_{O in carbonate fluorapatite are depleted in distal} environments, increase landwards and towards maximum transgression, indicating warming. Values of δ18_{O in phosphorites, brachiopods, and marine silica suggest temperatures ranged from} 14 to 47°C (mean = 29°C) in basinal transgressions and as from 30 to 48°C (mean = 36°C) on the outer ramp.

Warm, oxygenated, alkaline marine waters dominated in highstand settings and became increasingly hot, shelf-confined, and evaporitic. Coupled with limited nutrient influx, widespread

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input of windblown silica, and open, oxic marine conditions resulted in widespread silicified spiculites and calcitic-biota carbonates at maximum transgression and in distal highstands. Abundance of well-sorted detrital quartz, intimate association of detrital silica and spiculitic cherts, and no evidence of fluvial or gravitational transport suggest that dissolved windblown quartz was a primary source of aqueous silica into the PRC. Increasingly restricted and evaporitic conditions during highstands resulted in increasingly abundant dolomitized bioturbated muds and sandstones, aragonitic molluscs, ooids, and peritidal microbial

communities. Values of δ18_{O and δ}13_{C became increasingly enriched throughout highstands in} marine carbonates and silica. Coupled with abundant moganite-bearing chalcedony, this suggests evaporitic reflux drove coupled silica and dolomite diagenesis in alkaline, oxygenated, and saline environments buffered by carbonate solubility. Arid lithofacies, depleted δ18_{O in basinal silica} and in brachiopods, and values of depleted δ18_{O in phosphorites suggest highstands were hot,} ranging from 28 to 41°C in basinal settings and likely higher in shallow marine and inner ramp environments.

Biochemical and isotopic heterogeneity across the Franson and Ervay resulted from long-term global forcings, and basin and ramp geometries. The Franson distally-steepened profile, combined with global Roadian transgression that raised relative sea-level by about 270ft (~80m), resulted in thick accumulations of basinal OM-rich mudrocks and phosphorites. In contrast, the Ervay was deposited across an irregular homoclinal ramp profile, and saw a lower sea-level rise than the Franson, resulting in a transgression of about 140ft (~45m). Ervay OM-rich mudrocks and phosphorites are thinner, more depleted in δ18_{O, enriched in δ}34_{S, more elevated in}

gammacerane and homophane biomarkers, and occur seaward to more widespread open marine environments with similar isotopic signatures on the outer ramp. This suggest warmer, lower-oxygen, and more saline environments in the distal Ervay transgression and more open marine environments influenced by basinal waters across the Ervay cycle. Temperatures were elevated in the Ervay cycle (16 - 48°C, mean = 35°C) relative to the Franson cycle (14 - 45°C, mean = 32°C).

4 2.2: INTRODUCTION

The Phosphoria Rock Complex

This study focuses on environmental and biochemical dynamics that drove sedimentation and near-surface diagenesis in the Phosphoria Rock Complex (PRC) – a Middle Permian

(Kungurian - Wordian) biochemical sedimentary system comprised of OM-rich mudrocks, phosphorites, cherts, dolomitic sandstone, carbonates, evaporites, and redbeds deposited across much of what is now the Rocky Mountain region (Figure 2.1) (Hiatt and Budd, 2001, 2003). Deposition spans major global environmental changes including: warming and deglaciation, increasing CO2 abundance, changes in oceanic circulation patterns, changes in sea-level, changes in nutrient cycles, and continental aridification. These dynamics and biogeochemical responses to them characterized the end of the Paleozoic (Chapter 3).

Figure 2.1: A) Schematic distribution of lithologies, cycles, and commonly referred to members of the PRC. Modified after Maughan (1984), Hiatt and Budd (2001), and Wardlaw (2015). B) Global sea-level trends compiled from relative location of coastal onlap on the North American

and Eastern Russian platforms. After Ross and Ross (1987). C) Paleogeographic map of North America in the Middle Permian (260Ma) illustrating major features, latitude, and north direction.

Modified from Blakey (2012). Paleolatitude and north-direction from Sheldon (1964), Scotese and Langford (1995), and Walker et al. (1995).

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PRC deposition occurred under restricted, stressed, and dynamic environmental

conditions on a shallow westward facing ramp, in a restricted epicontinental embayment on the western margin of a fully assembled Pangea (Figure 2.1B) (McKelvey et al., 1959; Sheldon, 1963; Peterson, 1980, 1984; Maughan, 1994; Whalen, 1996; Hein, 2004). Ramp geometry was low angle (<0.04 - 0.22°) and topographically complex, especially in the northern portion of the study area (Whalen, 1996; Inden and Coalson, 1996; Hiatt and Budd, 2003). Accommodation space generated by tectonic loading via the Antler orogeny on the western margin of the Sublett foreland basin heavily influenced basin geometry and long-term cyclicity. This resulted in heterogeneous ramp geometries and a shift in second-order maximum trangression from the Franson maximum transgression (earliest Wordian – the culmination of a global transgression through the Roadian), to the Ervay maximum transgression (middle Wordian) in most of

Wyoming and Southwest Montana (Maughan 1979, 1984, 1994; Arthur and Jenkyns, 1981; Ross and Ross, 1988; Sarg, 1987; Wardlaw, 2015; Chapter 3). Higher-order sea-level cyclicity

overprints this signal, and is influenced by global eustatic cycles (Inden and Coalson, 1996; Whalen, 1996; Hendrix and Byers, 2000).

Previous workers have constrained deposition of the PRC to span a second-order sea-level cycle (~ 9MY) comprised of three tectonically influenced third-order sea-sea-level cycles (2 - 5 MY): the Grandeur cycle (Kungurian), which is eroded and not present in much of the study area; the Franson cycle (Kungurian - Wordian), comprised of the Meade Peak, Rex Chert and Franson members and their equivalents in the Goose Egg Formation (Opeche, Minnekahta, Glendo, and Forelle); and the Ervay cycle (Wordian), comprised of the Retort, Tosi Chert, and Ervay members and their equivalents in the Goose Egg Formation (Figure 2.1A) (Wardlaw and Collinson, 1979; Peterson, 1980; Inden and Coalson, 1996; Wardlaw, 2015).

The upper two third-order cycles (Franson and Ervay cycles) of the PRC are comprised of phosphorites, OM-rich phosphatic mudrocks, spiculitic chert, subtidal and peritidal

carbonates, bioturbated dolomitic sandstone, siltstone, and evaporites. Facies distribution, and ramp geometry is heavily influenced by complex and evolving paleo-topographic features (Peterson 1980, 1984; Inden and Coalson 1996).

6 2.3: METHODOLOGY

This study integrates stratigraphy, petrology, and stable isotope geochemistry to assess biotic, chemical, and environmental trends through deposition of the PRC from a microscopic to regional scale, illustrating how the system evolved spatially and through time.

Stratigraphy

Stratigraphic description and interpretation of more than 11,000ft (~3350m) of measured section from 31 cores, and 18 outcrops, integrated with more than 60 published measured sections and over 200 wireline logs provide the framework for petrographic and geochemical observations and data (Figure 2, Table 1). A majority of the cores described and their

corresponding thin sections are publically available and stored at the USGS Core Research Center in Lakewood, Colorado, USA. In this study, core data is reported by the USGS CRC core library number and depth (in feet).

Facies were interpreted based on detrital grain assemblages and rock fabric and related to commonly interpreted depositional environments in ramp systems (Ahr, 1973; Burchette and Wright, 1992; Read, 1985; Kerans et al., 1994; Kerans and Fitchen, 1995). Terminology used here for the ramp profile is a modified version of Read (1980), Burchette and Wright (1992), Kerans et al. (1994), Kerans and Fitchen (1995).

Sea-level cyclicity and depositional sequence systems tracts are interpreted primarily by facies stacking patterns, patterns in near-surface chemical diagenesis, and to a lesser degree, stratigraphic surfaces (e.g. erosional surfaces). Isotopes are used to corroborate stratigraphic interpretations after comparisons and independent interpretation of stratigraphy and the isotope signal. Cycles in the PRC commonly deepen from subaerial exposure surfaces and shallow to peritidal and shallow marine facies. Magnitudes of relative changes in sea level are interpreted based on thicknesses between erosional and karst surfaces, maximum transgressive surfaces, and shallow marine to peritidal facies.

In this study, depositional cycles are defined as a genetically related package of rocks with indicators suggesting cycles of deepening, then shallowing depositional environments. Cycles are bound by sequence boundaries – subaerial unconformities and their basinal

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Figure 2.2: Map of study area indicating location of measured sections, stable isotope data and location of cross section A-A', B- B', and C-C'(Figures 2.3 - 2.5). Background image courtesy of

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Table 2.1: Measured section locations from core and outcrop. Cores are reported by their USGS Core Library Number or names where Core Library Numbers are unavailable.

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expressions, separating packages of rocks deposited in overall shallowing environmental conditions (i.e. increasingly landward environments) from rocks deposited in overall deepening environmental conditions (i.e. increasingly basinal environments). Sequence boundaries are erosional surfaces, karst surfaces, and sharp contacts. Lowstands are defined as packages of rocks deposited over sequence boundaries deposited when sea level was significantly lower than previously or after. PRC lowstands are interpreted where thick lags and sediments deposited in shallow environments overlie erosional sequence boundaries. Transgressions are defined here as packages of rocks deposited through overall deepening in paleoenvironments. Transgressions overlie a sequence boundaries and commonly lowstands. Similarly, highstands are defined here as packages of rocks deposited through overall shallowing, and capped by sequence boundaries. (Sarg, 1988; Van Wagoner et al., 1988; Kerans, 1995).

With good stratigraphic control, interpretation of systems tracts is generally

straightforward, however ambiguity arises where depositional environments do not change significantly across sequence boundaries where sedimentation is conformable, and where erosional surfaces show minimal character.

Petrography

More than 400 thin sections were described with conventional petrographic microscopy and integrated into outcrop and core descriptions. Thin sections were impregnated with blue epoxy, polished, and stained with Alizarin red S and potassium ferricyanide. Petrographic analysis was performed with transmitted and reflected light, cathodoluminescence (CL), scanning electron microscopy (SEM), and confocal Raman microscopy. A thin conductive carbon coating was applied to thin sections to reduce charging and increase quality of SEM and CL images.

Ar-ion cross-section polished (XSP) surfaces were prepared on a JEOL IB-0910CP Cross-Section Polisher, generating pristine 2D surfaces for imaging softer organic components and nanopores (Reed and Loucks, 2007; Loucks et al., 2009, 2012). Samples were polished using accelerating voltages of 5.0-5.5kV for 8 - 12 hours. Polished surfaces are oriented perpendicular to bedding. A thin, conductive gold coating was applied to ion-polished surfaces to reduce charging and increase quality of SEM images.

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CL microscopy was performed on 26 representative thin sections with a Lumic Special Microscopes HC5-LM hot-cathode microscope to investigate heterogeneity and genesis of crystalline mineral phases. This instrument provides adequate energy to luminesce and image both silica and carbonate phases. CL imaging was performed at 5x magnification, with field of views of 2.7mm, ideal for image quality on this machine. Image mosaics were made in samples with relatively large components.

SEM imaging was used to characterize components, pores, and petrogenesis on 40 thin sections and the 11 ion-polished surfaces. Imaging was performed on a TESCAN MIRA3 LMH field emission-scanning electron microscope. Detectors utilized in this study include back-scattered electron (BSE), secondary electron (SE), and energy-dispersive X-ray spectroscopy (EDS). Images were acquired at accelerating voltages of 10-15 kV and at beam intensities of 8 and 11, approximating lower and midrange of the available beam current. Working distances ranged from 5 to 10 mm.

Raman spectra were collected on in-situ chalcedony, microquartz, and megaquartz (171 spots from 23 samples) with a Horiba LabRAM HR Evolution Spectrometer at the University of Colorado Boulder. A 532nm laser was focused through a 50x objective lens, resulting in a spatial resolution of ~1µm and power at the sample surface of 15mW. A 100µm confocal pinhole and 1800lines/mm grating were used to give a spectral resolution of 4.5cm-1_{. Spectra were collected} by averaging three iterations with 20s counting intervals at 100% power. Corrections for

instrumental artifacts were performed with LabSpec 6 (Horiba Scientific). Relevant Raman spectra peaks were carefully peak fitted. Moganite content of these phases was quantified with 501/464cm-1 _{integral ratios and the calibration curve reported in Schmidt et al. (2013). Samples} were not heat treated, and were simply stored in a desiccator, resulting in some uncertainty in the relative contribution of silanol (SiOH), which has a Raman peak at 503cm-1 _{and can overlap with} the 501cm-1 moganite peak (Schmidt et al., 2012, 2013). The difference between these peaks is difficult to distinguish, however absence of these peaks in many spots suggest these methods provide an adequate proxy to interpret chemical environments of silica genesis. Heaney (1995) concluded elevated moganite contents are indicative of evaporitic settings with elevated

11 Stable Isotope Geochemistry

Stable isotopes of δ18_{O and δ}13_{C in 377 samples of carbonates, δ}34_{S in 38 samples of} anhydrite, δ18_{O in 20 samples of phosphate, and δ}18_{O and δ}17_{in three samples of authigenic silica} were measured with stable isotope ratio mass spectrometry (SIRMS). Additionally, δ18_{O was} measured in carbonate and silica phases on 16 samples with secondary ion mass

spectrometry (SIMS). Samples were obtained from core and outcrop and span as much of the depositional profile and stratigraphy as possible given spatial distribution of

components, outcrops, and core. Additional data for 24 samples of carbonate with δ18_{O and} δ13_{C analyses, 83 samples of phosphate with δ}18_{O, 13 samples of phosphate with δ}34_{S in}

phosphate-hosted sulfate were obtained from published sources (Nathan and Nielsen, 1980; Kuniyoshi and Sakai, 1987; Piper and Kolodny, 1987; Hiatt, 1996; and Hiatt and Budd, 2001).

Coupled SIRMS and SIMS isotope geochemistry; and plain-light, SEM, and CL petrography integrated into stratigraphic context helps to clarify the origin of stable isotope signatures and exclude as much burial and meteoric signal as possible from interpretation, and clarifying the marine stable isotope signal in carbonates and authigenic silica. In this dataset, samples are excluded from interpretation of marine environmental conditions where influence of laboratory error (e.g. sampling, machine error), or influence of burial or meteoric diagenesis is suggested by petrographic or isotopic datasets.

Subsampling for Stable Isotope Ratio Mass Spectrometry

Slabbed core and outcrop samples were subsampled to measure δ18_{O and δ}13_{C in}

carbonates, δ18_{O and δO}17_{in authigenic silica, δ}18_{O in phosphate, and δ}34_{S in anhydrite. Samples} were slabbed, examined under binocular microscope, and tested with dilute HCl and Alizarin Red-S to assess mineralogy. Thin sections were prepared and examined for many samples analyzed for stable isotopes to aid accurate characterization. Carbonate and anhydrite were subsampled with a dental drill fixed with 0.3 - 2mm diameter burrs to measure bulk sample and distinct phases. Between 4 and 400mg of each sample was analyzed. Anhydrite was sampled only from cores to avoid alteration associated with meteoric weathering. Only unaltered samples of anhydrite precipitated as nodules and beds in near-surface environments were analyzed to avoid possible influence of thermochemical sulfate reduction. Phosphorite peloids, and one

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skeletal fragment were subsampled by disaggregating bulk samples, sifting out sand-size

fraction, and manually picking carbonate fluorapatite grains. Rock chips of pure authigenic silica (agates) were selected and prepared with a small rock saw, for bulk δ18_{O and δ}17_{O analyses.} Stable Isotope Ratio Mass Spectrometry

SIRMS was performed at the Center for Stable Isotopes, University of New Mexico, measuring δ18_{O and δ}13_{C in carbonates, δ}34_{S in anhydrite, δ}18_{O phosphate, and δ}18_{O and δ}17_in three samples of authigenic silica

Values of δ18_{O and δ}13_{C in carbonates were measured using the method described by} Spotl, and Vennemann, (2003). The samples were loaded in 12 mL borosilicate exetainers, then the exetainers were flushed with He and the samples were reacted for 12 hours with H3PO4 at 50ºC. The evolved CO2 was measured by continuous flow Isotope Ratio Mass Spectrometry using a Gasbench device coupled to a Thermo Fisher Scientific Delta V Plus Isotope Ratio Mass Spectrometer. The results are reported using the delta notation, versus Pee Dee Belemnite (PDB). Reproducibility was better than 0.1‰ for both δ13_{C and δ}18_{O based on repeats of a laboratory} standard (Carrara Marble). The laboratory standard were calibrated versus NBS 19, for which the δ13_{C is 1.95‰ and δ}18_{O is -2.2‰.}

Values of δ18_{O and δ}17_{O in silica were measured using the laser based fluorination} method (Sharp, 1990; and Sharp et al., 2016). Measurements were performed on a Thermo Fisher Scientific MAT 253 mass spectrometer. A comprehensive description of the methods can be found in Sharp et al. (2016).

Phosphatic peloids (carbonate fluorapatite) were converted to Ag3PO4 using a modified method after O’Neil et al., (1994). Silver phosphate crystals were analyzed using a high

temperature conversion Elemental Analyzer at a 1450C temperature. Delta V Plus mass

spectrometer. Isotope ratios of δ18_{O in the resultant CO were measured in continuous flow via a} ConfloIV interface on a Thermo Fisher Scientific Delta V Plus mass spectrometer. The precision of analyses based on long term measurements of internal standards is better than 0.3‰ (1 sigma). Internal standards are calibrated using TU-1, TU-2 standards (Venneman et al, 2002).

Values Sulfur isotope measurements were conducted by Continuous Flow Isotope Ratio Mass Spectrometry using a Costech Elemental Analyzer coupled to a Delta Plus XL Thermo Finnigan mass spectrometer via a Conflo II interface. Ag2S or BaSO4 (0.09 - 0.19 mg) is

13

combusted in a quartz tube packed with ultra-high purity copper wires and quartz chips (Fry et al., 2002) at 1020ºC in the presence of pure O2 gas. The resulting SO2 gas is passed through a GC column and measured in the mass spectrometer. International standards (NBS122, NBS123 and NBS127) and a laboratory standard (CP1), covering a range of δ34_{S values from –4.6‰ to} 20.3‰ VSMOW, were run at the beginning, at intervals between samples and at the end of analytical sessions. Analytical precision calculated from the standards is ± 0.3 ‰ (standard deviation). Analyses were normalized to the standards listed above.

Secondary Ion Mass Spectrometry and Electron Microprobe

In situ measurements of δ18_{O in carbonates and silica were performed with secondary ion} mass spectrometry (SIMS) on 16 samples with characteristic facies and diagenesis spanning the depositional profile and stratigraphy. Here, data for silica is presented as well as carbonates where relevant to paleoenvironmental conditions and calibrating marine isotope signals. More of the dataset is presented in (Chapter 3). Values of δ18_{O are reported in per mil notation (‰)} standardized to Vienna Standard Mean Ocean Water (VSMOW) for silica, and PDB for carbonates. In conjunction with a suite of other petrographic analyses, this data allows for the characterization of δ18_{O in petrographically distinct carbonate and silica phases at an}

approximately 10µm scale. Values that are interpreted to be influenced by machine error, either due to irregular instrument settings, contamination, spot location, and anomalous values are excluded from the dataset. See Chapter 2 for detailed discussion of SIMS methodology. 2.4: RESULTS

Biochemical sedimentation, near-surface diagenesis, and stable isotope signatures are systematically covariant regionally as well as within and between interpreted systems tracts at second- (~ 9MY) and third-order (2 - 5 MY) scales. Changes are most pronounced in the Franson (Latest Kungurian - Wordian) and Ervay (Wordian) cycles (Figures 2.3 - 2.14) (Wardlaw, 2015; Chapter 3), which are the focus of this study.

14 Systems Tracts, Facies, and Near-Surface Diagenesis

Sedimentation and near-surface biochemical diagenesis are heterogeneous in the

Phosphoria regionally, across cycles, and systems tracts interpreted from facies stacking patterns and erosional surfaces. Facies, facies characteristics, and interpreted depositional environments are summarized in Table 2.2. Distribution of ramp sub-environments is presented in Figure 2.3. Distribution of facies, composition, and interpreted systems tracts are presented in Figures 2.4 - 2.6. Images of facies and stratigraphy at outcrop, core, thin-section, and ion-polished surface scale are presented in Figures 2.6 - 2.12. Moganite content in authigenic silica is presented in Table 2.3.

Regional Ramp Environments

The PRC ramp profile shows clearly differentiated sub-environments at a regional scale, but in many cases lack clear indicators used in previous ramp models based carbonate systems dominated by physical sedimentation (e.g. Burchette and Wright, 1992; Kerans and Fitchen, 1994). Fair weather wave base, storm wave base, and pycnoclines are not always distinguishable, and are transient at high-frequency orbital time-scales.

Correspondingly, a practical terminology modified from Burchette and Wright (1992) and Kerans and Fitchen (1994) for ramp sub-environments at regional and long-term scales in the PRC is used as follows (Figure 2.3). "Inner ramp" refers to peritidal and supratidal

environments dominated by micritic dolomites, evaporites, and redbeds deposited in sabkhas, salinas, and tidal pools. The inner ramp is behind the grain-dominated ramp crest where it occurs and includes all of the peritidal in low-energy settings where the ramp crest is not

distinguishable. "Ramp crest" refers to grain-dominated sediments that accumulate in beach, peritidal, and high-energy shallow subtidal environments that form a barrier to the inner ramp. Ramp crest sedimentation is dominated by dolomitized fenestral microbialites, ooid grainstones, and associated peritidal facies. "Middle ramp" refers to shallow subtidal and restricted marine environments seaward of the ramp crest where sedimentation is heavily impacted by evaporitic processes and is dominated by dolomitized and bioturbated peloidal micrites, peloidal molluscan and other skeletal packstones, bioturbated sandstones, and sparse cherts. "Outer ramp" refers to open marine environments where sedimentation is impacted by basinal and oceanic processes

15

and is dominated by spiculitic cherts, calcitic biota carbonates, bioturbated micrites and sandstones. Evidence of storm reworking is abundant in outer ramp deposits, but rudstones, floatstones, and bindstones are more abundant than on the middle ramp. "Ramp margin" refers to transitional environment between open marine and basinal environments, which can span the relatively abrupt thickening deepening to basinal facies seaward (Figure 2.3 - 2.6) and is where basinal and outer ramp facies commonly interfinger (Read, 1980). Lastly "basin" or "basinal environments" refers to distal environments strongly influenced by oceanic waters, seaward of significant carbonate sedimentation where sedimentation is dominated by OM-rich muds, phosphorites, spiculites, micritic carbonates, and micritic siltstones. Basinal environments are overall low energy, but show periodic influence of storms and even waves where sea level dropped at a high-frequency during transgression as sea level was low and rising, resulting in phosphorite phosphatic grainstones, rudstones, and floatstones deposited in high-energy settings.

Figure 2.3: Schematic model of regional ramp environment terminology. Modified from Burchette and Wright (1992), and Kerans and Fitchen (1994). MSL = mean sea level, FWWB =

fair-weather wave base, SWB = storm wave base.

Criteria for Defining Sequences in the Phosphoria Rock Complex

Second- and third-order cycles show heterogeneous expression across the ramp profile but are defined based primarily on facies stacking patterns and stratigraphic surfaces that suggest overall cycles of deepening and shallowing bound by subaerial unconformities (Figures 2.4 - 2.6) (Van Wagoner et al, 1988; Kerans, 1995). Characterization of higher-frequency cycles overprint long-term trends and follow a similar framework at a smaller scale typically with smaller, more

16

abbreviated changes in depositional environments and biochemical sedimentation and less subaerial exposure, except in landward environments.

Sequence boundaries at the top of the Grandeur, Franson, and Ervay cycles show heterogeneous expression as the result of subaerial exposure and its basinal expression.

Pronounced erosional surfaces and conglomerates are common, but not ubiquitous at third-order sequence boundaries, which are commonly sharp contacts and interpreted from stacking patterns (transition from shallowing to deepening facies) (Figures 2.4 - 2.6). Pronounced karst, thick calcretes and silcretes are rare throughout much of the study area, however a karst surface caps the Grandeur in the basinal portion of the study area, which is eroded in most of the study area.

Lowstands are interpreted in basinal settings where abundant grain-dominated phosphorites were deposited in shallow high-energy environments overlying an erosional or karsted sequence boundary. Basinal lowstands are interpreted to have been deposited following pronounced shallowing of sea-level into the basin, but are the shallowest expression of

transgression, and referred to as such. Little or no sedimentation occurs on the platform during lowstand, and is characterized by isolated intraclast lags and subaerial exposure surfaces (Figures 2.4 - 2.6).

Transgressions in the Franson and Evay cycles are interpreted as overall deepening shifts in facies and depositional environment at a basinal scale overlying a sequence boundary and rocks deposited in shallow environments of the previous highstand. Transgressive sediments can be shallow, restricted, open marine, and heavily influenced by low oxygen and nutrient rich oceanic waters, but overall they deepen up-section into widespread spiculitic cherts that occur across marine environments at maximum transgression, landward of salinas in the inner ramp (Figures 2.4 - 2.6).

Highstands in the Grandeur, Franson, and Ervay cycles are interpreted as overall shallowing upwards facies and depositional environments. Widespread open marine spiculites and equivalent facies shallow upwards into open and restricted marine environments and eventually peritidal environments, across the middle and outer ramp. An increase in

dolomitization, decrease in calcite, and an eventual decrease in silica accompany this transition. In basinal sections, chert and silicified bioturbated sandstones cap cycles (Figures 2.4 - 2.6).

17

Table 2.2: Facies, characteristic near-surface diagenetic overprints, interpreted depositional environments, and interpreted systems tracts.

18

Figure 2.4: Cross-section A-A' illustrating distribution of facies, compositions, and interpreted third-order systems tracts (Grandeur, Franson, and Ervay). Location in Figure 2.2. G = glauconite. Interpretations of systems tracts are based on facies stacking patterns,

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22

24

Sedimentation and Near-Surface Diagenesis in Lowstands and Transgressions

Sedimentation during lowstands and transgressions was dominated by phosphorites, OM-rich mudrocks, and micritic sediments in distal settings seaward of calcitic biotic debris

(bryozoans, brachiopods, and crinoids), micritic, and peritidal carbonates as well as evaporitic redbeds and evaporites.

Phosphorites are common throughout distal transgressions and just below maximum transgression as thin phosphatic beds as far landward as the middle ramp (Figures 2.4 - 2.6, 2.7D, 2.8E, F). Phosphorites are commonly bioturbated and massive (Figure 2.7D). Phosphatic grains are peloids, intraclast, ooids, and phosphatized skeletal grain and are heavily bored and micritized. Dolomitic micrite, OM-rich muds, as well as detrital and authigenic silica are

common components of phosphorites (Figure 2.8E, F). Conodonts, and other phosphatic skeletal grains are also present throughout phosphorites. Helicoprion whorls were observed in Mead Peak phosphorites and associated micrite in Idaho. Phosphorites are cemented with silica, calcite, dolomite, and carbonate fluorapatite (Figure 2.8E, F) (Chapter 2). Microcrystalline silica in basinal phosphorites contains no moganite, however only one sample was analyzed (Table 2.3).

OM-rich mudrocks are abundant in transgressions of the Franson and Ervay cycles in basinal settings (Figures 2.4 - 2.7). OM-rich mudrocks are commonly laminated or bioturbated containing simple diminutive burrow forms and cryptic fabrics (Figure 2.7E, 2.8A). Grains in OM-rich mudrocks are dominated by sulfur-rich detrital OM (i.e. kerogen), phosphate peloids, clay, siliciclastic silt (quartz, K-feldspar, and mica), skeletal calcite, and dolomite. Argillaceous, siliceous, and OM-rich grains are commonly agglutinated as aggregates. Agglutinate

foraminifers and recrystallized planispiral benthic foraminifers, and brachiopods occur, but are sparse in OM-rich mudrocks. Dolomite, secondary OM (i.e. bitumen, pyrobitumen) euhedral pyrite, and calcite occur as diagenetic components in mudrocks (Figure 2.8A - C). Dolomite concretions are common in OM-rich mudrocks. Phosphorite nodules have been reported in the upper Meade Peak and cherty shale members (distal Franson and Ervay transgression) as well (Marshall, 2017; Tysdale, 2000).

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Figure 2.7: Photographs of basinal and ramp-margin exposures of the PRC. Staff is 5ft (1.52m) tall with 6in (15.2cm) markings. A) Exposed trench just north of Daly's Spur, blue arrow indicates maximum transgression separating OM-rich mudrocks phosphorites and micritic siltstones of the Ervay transgression (Retort Member) from spiculitic cherts and siltstones of the

Ervay highstand (Tosi Chert Member). B) Western exposure at Ballard Mine, blue arrow is maximum transgression of the Franson cycle separating OM-rich mudrocks phosphorites and

micritic siltstones of the transgression from spiculitic cherts and siltstones of the Franson highstand (Rex chert). approximately 200 feet of section exposed. C) Exposure at Crystal Creek,

blue arrows indicate the base of the PRC, the top Franson, and the top Ervay sequence boundaries (from the bottom up). Blue arrows are maximum transgressions. PRC is 192ft

(58.6m) thick. Transgressions are phosphorites, OM-rich muds, and micritic siltstones. Highstands are bioturbated sandstones, spiculitic cherts, and open marine carbonates in the Franson cycle. D) Phosphatic grainstone interbedded with OM-rich mudrocks at Ballard Mine in

Franson transgression. E) Close up of maximum transgression of the Ervay cycle at Crystal Creek (blue arrow), separating black laminated OM-rich mudrocks of the transgression from silty spiculitic cherts of the highstand. Note irregular nodular beds in the chert and inter-nodular siliceous siltstone. Tan bed above the maximum transgression is a dolomitic sandstone. F) Large columnar Skolithos grandis burrows in sandy spiculitic chert of the Ervay highstand (Tosi Chert

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Figure 2.8: Photomicrographs of samples from the distal transgression. A) Daly's Spur, sample DS-27, from the Ervay transgression (Retort Member), a laminated OM-rich phosphate peloid silty claystone. B) BSE image of an ion-polished surface on sample DS-27, showing abundant detrital OM-stringers, dolomite crystals, siliciclastic grains, and secondary OM filled phosphatic

peloids. C) Elemental map (EDS) of sample LR-18 from the Lakeridge core, a phoshate peloid dolomitic argillaceous siltstone. Aggregates of dolomite crystals (purple), and abundant detrital siliciclastics (green and red). Phosphate peloids are microcrystalline and bright green. OM is dark and commonly detrital stringers. D)Plain light image of sample BDM-106 from ballard mine, an OM-bearing bioturbated quartz-silt dolomite wackestone. E) Plain-light image of sample CC-29, from Crystal Creek, a quartz-sand phosphate peloid/intraclast rudstone with abundant chert cement and skeletal phosphate. From the basal bed of the Ervay transgression (Retort member). F) Plain-light image of sample BdM-67, a phosphate cemented phosphatic ooid grainstone from Ballard Mine. Note aggregate grains and isopachous cement. Top of the Franson

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Bioturbated micrites and grey-tan micritic siltstones are intimately associated with OM-rich mudrocks and phosphorites in distal environments during transgression (Figures 2.4 - 2.7). Micrites in distal transgressive deposits are pelloidal wackestones, and are commonly crystalline dolomite or calcite (Figures 2.8D). Macrofossils (e.g. gastropods, brachiopods, crinoids,

helicoprion whorls, conodonts, gastropods, etc) occur in distal micrites, but not in abundance. In the Ervay transgression, and to a small degree the Franson transgression, calcitic biotic sediments (bryozoans, brachiopods, and crinoids) accumulated on the outer ramp (Figures 2.4 - 2.6, 2.9F, G, 2.10C, D). These are clearly identifiable as part of a deepening facies stacking pattern where they overlie peritidal sediments of the Franson highstand and are capped by phosphorites and spiculites at the maximum transgression (e.g. Figure 2.4 sections T383, R147; Figure 2.5 section Anchor Dam). However, in several sections it is ambiguous if calcitic biotic debris below phosphorites is in the Ervay transgression or the Franson highstand, especially where they overlie other open marine facies (e.g. Figure 2.5 section Burroughs Creek, Figure 5 Bull Lake, Baldwin Creek). It is important to note that this sediment package is referred to as part of the "Franson Member" by previous workers (e.g. Sheldon, 1953; Cheyney, 1953; McKelvey et al, 1967; Ahlstrand and Peterson, 1978; Inden and Coalson, 1996; Ulmer-Scholle and Scholle, 1996; etc.) who did not distinguish shallow carbonates of the Franson highstand from the deepening open marine carbonates of the Ervay transgression. Stable isotopic signatures confirm this interpretation. A similar package occurs across much of the Wind River Mountains, however, based on data in this study, it is ambiguous if it is in the Franson highstand or Ervay transgression because it sits on dolomitized bioturbated sandstone in many cases, not peritidal dolomite (Figure 2.7) (Ahlstrand and Peterson, 1978). Calcitic biotic sediments range in texture from packstones and grainstones, to floatstones, rudstones, and bafflestones, however

floatstones, rudstones, and bafflestones are more common on the outer ramp. Calcitic sediments in transgressions commonly contain phosphatic and glauconitic grains, are partially dolomitized, calcite cemented, micritized and/or silicified (Figures 2.4 - 6, 2.9G, 2.10C - D). Accumulations of calcitic biota in the Ervay cycle are commonly capped with a drowning surface overlain with a thin bed of grainy phosphorite and spiculite (e.g. Figure 2.4 sections T383 and R147).

Sedimentation in transgression on the middle and inner ramp is dominated by bioturbated and peritidal carbonates as well as evaporitic redbeds, green siltstones, and sparse evaporites (Figures 2.4 - 2.6, 2.12A - B). Red and green siltstones are evaporitic and dolomitic. Red and

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Figure 2.9: Photographs of outcrops and core on the outer and middle ramp. A) Exposure at Wind River Canyon. Grey spiculitic chert shallows to calcitic biota dolomite, bioturbated micrites, molluscan dolomite, ooid grainstone, and eventually micritic microbialites. Exposure is 86ft (26.2m). B) Micritic microbial bindstone at the top of Wind River Canyon. Note desiccation

cracks. C) Core R147, 6227.5ft. Silicified thallassinoides burrow in a peloidal dolomite with calcite replaced evaporite nodules. D) Dolomitic mollusc floatstone at Wind River Canyon. E)

Silicified burrows in a siliceous silt matrix at Anchor Dam in the basal Ervay highstand (Tosi chert). F) Exposure at Anchor Dam. Red arrows indicate the base of the PRC, the top Franson,

and top Ervay sequence boundaries from the base up. Blue arrows indicate maximum transgression. Carbonates of the Ervay highstand comprise the upper cliff face below tan beds of the Dinwoody Formation. G) Ramose bryozoan rudstone (possibly bafflestone) with dolomitized

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Figure 2.10: Photomicrographs from transgressions on the carbonate platform. A) Plain light image of sample R147-6289.5, a dolomitized bioturbated peloidal wackestone from the Ervay transgression. B) Plain light image of sample NwR-2 from Nowood Road (Mahogany Butte), a peloidal microbial dolobindstone with sparse fenestral and interparticle pores from the Franson

trangression (Minnekahta member). C) Cross-polarized image of sample T383-6192.9, a partially dolomitized, calcitic biota (brachiopods, crinoids, and bryozoans) rudstone/packstone

from the Ervay transgression. Skeletal grains are calcite (stained red), and partially silicified. Matrix is dolomitized, dark grains are phosphatic peloids. D) Plain light image of sample D330-11667.2, a bioturbated dolomitic sandstone from the Ervay transgression. E) Plain light image of sample R147 sample 6285.5, a silicified quartz-sand phosphate peloid grainstone from the Ervay

transgression. Phosphatic intraclasts, phosphatized crinoid grains, phosphate peloids, and siliciclastic sand are abundant. F) Plain light image of sample T383-6131, a calcite-cemented phosphate peloid calcitic biota (crinoids, brachiopods, bryozoans) grain-dominated packstone.

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green siltstones are commonly evapoturbated, and host anhydrite nodules in addition to sparse axe-heads and halite hoppers.

Sedimentation and Near-Surface Diagenesis in Highstands

Sedimentation during highstands was dominated by silicisponge spicule cherts and siltstones and calcitic biota in distal settings that shallow to bioturbated sandstones, dolomitized micrites, mollusc debris, ooid grainstones, microbialites, and evaporites in more landward settings (Figures 2.4 - 2.6, 2.7, 2.8, 2.11 - 2.13).

Silicisponge-spicule cherts and siltstones are abundant across the depositional profile at maximum transgression and in distal environments throughout highstands (Figures 2.4 - 2.6, 2.7A - C, E, F, 2.9A, E, F, 2.11C - E, 2.12B, E). Spiculitic cherts are bioturbated, nodular, massive, bedded, and intimately associated with siliciclastic quartz (Figure 2.12E).

Thallassinoides and Skolithos grandis burrows are abundant in spiculites, especially on the outer ramp. Massive bedded, bioturbated, and irregular silicified nodules are abundant in distal

spiculites in the western portion of the study area, especially in the Franson cycle, often corresponding to coarser spicules, less dolomite and more silica cement and matrix (Figures 2.7A - C, E, F, 2.9F). At a petrographic scale, authigenic silica is abundant in spiculites as spicule replacements, cements, and evaporite replacements. Microcrystalline silica in spiculitic cherts average between 3 and 19% moganite (mean = 11%) in each sample (Table 2.3). Dolomite and calcite in some samples are dispersed throughout chert as microcrystals and micrite (Figure 2.11C, D, E) (Chapter 2). Silicified evaporite nodules are common in spiculites (Chapter 2.2). Sediment-filled neptunian fractures are common in silicified nodules (Figure 2.11C).

Bioturbated dolomitic and siliceous sandstones are abundant through highstands associated with the northern part of the study area (northwestern Wyoming and Southwest Montana), and isolated throughout the rest of the study area associated with paleotopographic highs (Figures 2.4 - 2.6, 2.7C, 2.11F). A diverse suite of shallow-marine burrows occur in PRC sandstones, including widespread and abundant Skolithos grandis and thallassinoides

(Thornburg, 1990; Anderson and Sauvagnat, 1998). Detrital grains are commonly well-rounded and very-fine-grained quartz mixed with phosphatic and dolomitic peloids and skeletal grains. Dolomite is abundant as microcrystalline cements and micrite. Sandstones can be fully or partially silicified (e.g. silicified burrows), especially where associated with spiculites and in the

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Figure 2.11: Photomicrographs from the distal highstand (basin, ramp-margin, and outer ramp). A) Plain light image of sample B933-13004.5, a silicified peloid skeletal bryozoan dolo-floatstone from the Ervay highstand. Dark grains are phosphatized. B) Plain light image of

sample LR-93a from the Lakeridge core, a dolomitized peloid bryozoan floatstone Ervay highstand. C) Plain light image of sample C073-1076.3 a fractured silty spiculitic chert in the Ervay highstand (Tosi Chert member). Sample shows abundant mineralized and sediment-filled fractures at the margin between a silica nodule and spiculitic dolomitic siltstone. White fractures are filled with silica. D) Plain light image of C073-1076.3, illustrating spiculitic dolomitic silt. E)

Plain light image of sample BdM-87 from Ballard Mine, a coarse pervasively silicified spiculitic chert. Note abundant spherulitic chalcedony cements. Sample is from the Franson highstand (Rex Chert member). F) Plain light image of StM-101 from Sawtooth Mountain, a bioturbated silicified sandstone from the Ervay Highstand (Shedhorn Member). Note abundant phosphatic

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Table 2.3: Moganite content calculated by Raman spectra 501/464cm-1 peak integral ratios. Data calculated with best fit curve from Schmidt et al., (2013). Data for macrocrystalline silica is reported as spot type (*), but excluded from the rest of the dataset. Measured

sections are roughly in order of their regional position descending from landward to seawards (east to west). n = number of analyzed spots. Italicized values are anomalously large and left out of interpretation.

38 northwestern portion of the study area (Figure 2.11F).

Calcitic biotic debris (bryozoans, brachiopods, and crinoids) is abundant across the outer ramp during early highstands and the ramp margin during late highstand. Shoals of silicified calcitic biota debris is intimately associated with spiculitic cherts in the distal highstand of the Franson in southeast Idaho, and landward onto the platform (Figures 2.4 - 6, 2.9G, 2.11A, B) (Brittenham, 1973, 1976; Ahlstrand and Peterson, 1978). Calcitic biotic debris is widespread in the Ervay highstand across the outer ramp, where carbonate sedimentation extended across much of the study area. Sedimentation of calcitic biotic debris continued throughout the highstand, progressively more isolated to the ramp margin with regression. Calcitic biotic debris occurs as wackestones, packstones, grainstones, floatstones, rudstones, and bryozoan bafflestones (Figures 2.4 - 2.6, 2.9G). Calcitic skeletal sediments in highstands are partially to fully dolomitized, silicified, or calcite cemented. Skeletal grains are commonly micritized and phosphatized

(Figures 2.11A, B). Silicified skeletal grains in calcitic biota carbonates contain microcrystalline silica averages between 0 and 19% (mean = 16%) moganite in each sample (Table 2.3).

Bioturbated micritic dolomites are widespread across much of the depositional profile throughout late highstands (Figures 2.4 - 2.6, 2.9A, C). These rocks are pervasively dolomitized and are commonly silicified. Nodular silica, evaporites, and silicified thallassinoides burrows are recurrent across lagoonal settings. Bioturbated micrites are dominantly peloidal wackestones comprised of microcrystalline dolomite. Phosphatic peloids and sparse skeletal grains are common in bioturbated micritic dolomites (Figures 2.9C, 2.13E). Microcrystalline silica in bioturbated micritic dolomite averages between 6 and 31% (mean = 17%) moganite in each sample (Table 2.3).

Peloidal aragonitic molluscan dolomite flourished across the outer ramp throughout highstands, especially in the Ervay cycle (Figures 2.4 - 2.6, 2.9A, D, 2.13F). Mollusc debris is bioturbated (often cryptic or massive) and comprised of scaphopods, pelecypods, gastropods, and peloids with packstone, floatstone, and rudstone textures. Peloidal mollusc debris is pervasively dolomitized and aragonitic components have all been either dissolved or replaced (Figure 2.9D, 2.13F). Aragonitic green algae (phylloid and calcispheres) have been described as abundant in previous work (Ahlstrand and Peterson, 1978; Peterson, 1984; Inden and Coalson, 1996) but clear examples of these are sparse throughout this dataset. Microcrystalline silica in molluscan dolomite averages between 0 and 24% (mean = 12%) moganite in each sample (Table 2.3).

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Ooid grainstones occur on the ramp crest in highstands, commonly marginal to

microbialite complexes and associated with paleotopographic highs (Figures 2.4 - 2.6). Peloidal and skeletal grains (mostly mollusc fragments) are abundant components of ooid grainstones. Ooids are pervasively dolomitized, micritized, cemented with dolomite and evaporites, and commonly dissolved (Figure 2.13C). Partially phosphatized and micritized ooids, and thin beds of silicified ooids are common. Microcrystalline silica in silicified ooid grainstones averages between 0 and 28% (mean = 12%) moganite in each sample (Table 2.3).

Microbial dolomite complexes flourished throughout late highstands in peritidal environments, particularly in the Ervay highstand on the ramp crest and inner ramp in what is now central Wyoming (Figure 2.4 - 2.6, 2.9A, B, 2.12A - D, G). PRC microbialites include both mud- and grain-dominated fabrics, including peloidal microbial bindstone, insipient "wispy" laminated wackestone, and fenestral peloid and/or coated grain bindstone (Table 2.2, Figures 2.9B, 2.12C, D, G, 2.13A, B). Subaerial exposure surfaces, tepee structures, flat-pebble

conglomerates, leached fractures, polycheate worm burrows, and pisoid rudstones are common in microbialite complexes, especially at the ramp crest, often open, are common in microbialites.

PRC microbialites are pervasively dolomitized and micritized. In fenestral microbialites, a large proportion of peloids are interpreted to be micritized coated grains with bridging micritic cements. Isopachous dolomite cements are ubiquitous in fenestral microbialites (Figure 2.13B). Anhydrite (usually hydrated to gypsum in outcrop) is common throughout microbialites as nodules, poikilotopic cements, and interbedded with in peloidal microbial bindstone (Figure 2.12G, 2.13B, D). Fibrous botryoidal calcite, interpreted as originally aragonite, is observed in outcrop samples associated with tepee structures. Pendant cements have been described in fenestral microbialites (Inden and Coalson, 1996) however clear of examples of these are rare in this dataset.

Anhydrite interbedded with microbialites and redbeds dominate sedimentation in salinas and sabkhas on the inner ramp during highstands (Figures 2.4 - 2.6, 2.12A, B, F - H). Anhydrite occurs as nodules (often replaced) in carbonates and siltstones as well as beds with laminated, massive, nodular, and palmate fabrics (Figures 2.12F - H, 2.13B, D, E). Anhydrite likely formed in these sediments as replacement of gypsum and to some primary precipitation as in modern sabkhas and salinas (Shinn, 1983; Warren ad Kendall, 1985), however the distinction is typically

40

Figure 2.12: Photographs of outcrops and core deposited on the inner ramp and ramp crest. A) Exposure at Nowood Road (Mahogany Butte), a sequence of interbedded redbeds, evaporites,

and microbial dolomites. Red arrows indicate interpreted sequence boundaries (Grandeur, Franson, and Ervay) from the base up. Blue arrows indicate maximum transgression. Phosphoria

is 298ft (90.8m) thick here. B) Exposure at Sheep Mountain (Bighorn Basin) looking west towards the crest of the anticline. Arrows indicate top Grandeur, Franson, and Ervay sequence

boundaries. Redbeds in the background are the Grandeur and Franson cycles. The Ervay sequence boundary is noted in the foreground at the top of the exposed bedding plane. PRC is 236ft (71.9m) thick here. Described canyon ("Canyon #3") is next canon to right of image. C) Three-dimensional exposure of Tepee structure at Sheep Mountain showing buckled polygonal plates. Staff is 5ft (1.52m) tall. D) Dolomitic fenestral microbialite at Sheep Mountain. Scale bar

in cm. E) Beds of irregular bedded nodules of spiculitic chert in a dolomitic siltstone at Sheep Mountain in the Ervay highstand (Tosi Chert member). Staff has 6in (15.2cm) markings. F) Chicken-wire nodules of anhydrite in core E669-10184 from the Ervay highstand. Scale bar in inches. G) Domal stromatolite deepening upwards into laminated anhydrite, Franson highstand. image is ~6in high (15.2cm) H) Core D678-4141, palmate anhydrite pseudomorphic to gypsum

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Figure 2.13: Photomicrographs from carbonates deposited in shallow environments during highstand. A) Plain light image of Sample D645-9374 from the Ervay highstand, a peloidal

dolo-wackestone with insipient microbial laminations. B) Plain light image of sample D645-9374, a fenestral peloidal coated-grain microbial bindstone with anhydrite and dolomite cements. Note abundance of prolific micritized grains. C) Cross polarized image of A669-4789.9, an anhydrite

cemented oomoldic dolo-grainstone. Note micritized ooids and preserved isopachous dolomite. D) Cross-polarized light image of sample A669-4856, a silicified evaporite nodule hosted in

peloidal wackestone. E) Plain light image of sample R147-6227.5, a peloidal dolo-wackestone with a silicified thallassinoides burrows and a calcite replaced evaporite nodule. F)

Plain light image of D330-11606, a peloidal mollusc dolo-floatstone/packstone. Mollusc are dominantly scaphopods. White-mold filling cement is fluorite, which coats secondary OM and is

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unclear except where palmate bottom-growth, or axe-head gypsum crystals are discerned (Figure 2.12H) (Hovorka, 1992).

Stable Isotope Geochemistry and Stratigraphy

Carbonates, silica, anhydrite, and carbonate fluorapatite have δ18_{O, δ}13_{C, δ}34_{S, and δ}17_O values that are systematically heterogeneous regionally, across systems tracts, facies, and within each sample between petrographically distinct phases (Figures 2.14 - 2.19; Tables 2.4, 2.5; Appendix A.1 - A.3). Values are discussed as "depleted" and "enriched" relative to the rest of the dataset and modern values in marine systems.

Values of δ18_{O and δ}13_{C and in Carbonates}

Detrital and diagenetic carbonate contains a wide heterogeneity of δ18_{O and δ}13_{C, ranging} from -22.1 - 5.6‰ and -23.1 - 7.3‰PDB respectively (mean values = -0.9‰ and -2.6‰). Values show systematic variation across systems tracts and across cycle hierarchies, regionally, within each stratigraphic section, and within each sample. Values of δ18_{O and δ}13_{C in carbonates} interpreted as marine vary by approximately 10‰ in highstands and 18‰ in transgressions across facies, near-surface diagenetic overprints, and regionally (Figures 2.14A, B, 2.15).

Marine carbonate in transgressions is characteristically depleted in δ18_{O and δ}13_{C in} distal environments. This is true in OM-bearing carbonate, dolomite concretions, micritic carbonates, brachiopods and dolomite in sandstones. Dolomites that are OM-bearing or

intimately associated with OM-rich mudrocks (e.g. dolomite concretions, bedded micrites) are depleted, especially in δ13_{C and show a broad range of values ( -12.1 to -0.52‰PDB).}

Carbonates, especially calcitic biotic debris, deposited during the Ervay transgression contain depleted δ18_{O and δ}13_{C values in dolo-micrite, lime-micrite, and skeletal calcite (Figure 2.14,} 2.15). Considerable heterogeneity occurs between and within marine carbonates deposited and precipitated during transgressions, even in the same sample (Figures 2.16 - 2.19). Values of δ13_C are increasingly depleted towards maximum transgressions in two of these successions (Figure 2.15: sections Burroughs Creek, T383), and generally enriched landward, especially in dolomites deposited in restricted settings.

Marine carbonate deposited in the PRC is characteristically and increasingly enriched in δ18_{O and δ}13_{C throughout highstands and landwards in dolomite, spiculitic cherts, dolomitic}

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Figure 2.14: Stable isotope data from the PRC normalized by systems tracts. 542 samples total, 107 of which are from Hiatt (1997), Piper and Kolodny (1984), and Hiatt and Budd (2001). Datasets include: A) δ18_{O in carbonates, B) δ}13_{C in carbonates, C) δ}18_{O in}

silica, sampled from SIMS analyses (sample icon describes host, all samples are silica), D) δ18_{O in phosphatic peloids, E) δ}34_{S in}

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Figure 2.15: Cross section D-D' plotted with corresponding δ18_{O (A), and δ}13_{C. Key for measured sections is in Figure 2.3. Data for}