Analysis of lacustrine deltaic sedimentation in the Green River Formation, southern Uinta Basin, Utah

Detailed lithofacies analysis of over 4,500 m of measured sections of most of the Eocene portion of the fluvial and lacustrine Green River Formation in the south-central Uinta Basin documents twelve lithofacies: Sa (nonsinuous trunk streams), Sb (meandering delta distributary channels), Sc (amalgamated delta mouth bars), Sd (regressive deltaic sandsheets), Se (overbank and shallow-lacustrine sandsheets), Sf (crevasse channels and splays), C (passively-filled abandoned channels), Mg (subaqueous mudflats), Mr (subaerial mudflats), L (lake-margin carbonate flats), and la and lb (openlacustrine deposits). The lower half of the study section consists of the carbonate marker unit (130 m) and the overlying Sunnyside delta interval (375 m), which record marginal-lacustrine sedimentation along the southern shore of Lake Uinta within and adjacent to a large, fluvially-dominated lacustrine delta informally named the Sunnyside delta. Meandering delta distributary channels on the delta plain cannibalized most delta mouth bars. Shallow water depths in the southern half of Lake Uinta attenuated waves and wave-generated currents, thereby preventing the development of shoreface ravinement, beaches, barriers, or significant siliciclastic bars. Evaporative pumping on subaeriallyexposed mudflats produced brines which altered detrital clay minerals to analcime. The combination of moderately high local subsidence and variations in lake volume produced low amplitude (less than 12 m) fluctuations in relative lake level which, due to the gentle gradient of the delta plain, produced shifts in shoreline position on the order of 40-50 km. During periods of rapid relative lake level rise most siliciclastic sediment was trapped upstream, resulting in iv lake level which, due to the gentle gradient of the delta plain, produced shifts in shoreline position on the order of 40-50 km. During periods of rapid relative lake level rise most siliciclastic sediment was trapped upstream, resulting in the development of extensive, but thin, transgressive shallow-lacustrine carbonates. The regressive portion of each depositional cycle consists of upper and lower delta plain, shallow-nearshore lacustrine, and relatively rare delta front deposits. The upper half of the study section consists of the transitional interval (200 m), which records a major, but gradual, expansion and deepening of the lake, and the overlying upper member (300 m), which consists of dark mudstone and dolostone and relatively rare hummocky cross-stratified storm deposits produced by combined flows and nearshore-lacustrine sandbodies that accumulated in a generally quiet, but not necessarily very deep, relatively siliciclastic-poor, open-lacustrine setting.

ANALYSIS OF LACUSTRINE DEL TAIC SEDIMENTATION IN THE GREEN RIVER FORMATION, SOUTHERN UINTA BASIN, UTAH A Dissertation Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Doctor of Philosophy in The Department of Geology and Geophysics by Robert Reginald Remy B.A. Providence College, 1978 M.S. University of Colorado, 1984 May 1991 TABLE OF CONTENTS Page TABLE OF CONTENTS ii ABSTRACT iv CHAPTER I. INTRODUCTION 1 CHAPTER II. STRATIGRAPHY OF THE EOCENE PART OF THE 9 GREEN RIVER FORMATION IN THE SOUTH-CEN-TRAL UINTA BASIN, UTAH CHAPTER Ill. DEPOSITIONAL PROCESSES OF A FLUVIALL Y- 59 DOMINATED LACUSTRINE DELTA AND OF TRANSGRESSIVE DEPOSITS IN THE GREEN RIVER FORMATION, SOUTH-CENTRAL UINTA BASIN, UTAH CHAPTER IV. LACUSTRINE HUMMOCKY CROSS-STRAT- 214 IFICATION PRODUCED BY COMBINED FLOWS, GREEN RIVER FORMATION, UTAH CHAPTERV. DISTRIBUTION AND ORIGIN OF ANALCIME IN 234 MARGINAL LACUSTRINE MUDSTONES OF THE GREEN RIVER FORMATION, SOUTH-CEN-TRAL UINTA BASIN, UTAH CHAPTER VI. {FIELD GUIDE TO) DEL TAIC AND LACUSTRINE 272 FACIES OF THE GREEN RIVER FORMATION, SOUTHERN UINTA BASIN, UTAH CHAPTER VII. CONCLUSIONS 301 COMBINED REFERENCES 309 ,, ! ~· APPENDICES 340 Appendix 1. Thickness, Location, and Stratigraphic Markers 341 of Measured Stratigraphic sections Appendix 2. Maps Showing Locations of Measured Sections 342 Appendix 3. Explanation for Symbols Used in Measured 349 Stratigraphic Sections Appendix 4. Measured Sections 350 ii VITA CHART 1. CHART 2. CHART3. STRATIGRAPHIC NOMENCLATURE OF THE GREEN RIVER FORMATION, SOUTH-CEN­TRAL UINTA BASIN, UTAH STRATIGRAPHIC CROSS-SECTION A-A' SHOWING THE STRATIGRAPHY, LITH­OLOGY, AND INTERPRETED DEPOSITIONAL ASSEMBLAGES OF THE GREEN RIVER FORMATION, SOUTH-CENTRAL UINTA BASIN, UTAH STRATIGRAPHIC CROSS-SECTION B-B' SHOWING THE STRATIGRAPHY, LITH­OLOGY, AND INTERPRETED DEPOSITIONAL ASSEMBLAGES OF THE GREEN RIVER FORMATION, SOUTH-CENTRAL UINTA BASIN, UTAH iii 394 in pocket in pocket in pocket Remy, Robert Reginald, B.A., Providence College, 1978 M.S., University of Colorado, 1984 Doctor of Philosophy, Spring Commencement, 1991 Major: Geology Analysis Q.f Lacustrine Deltaic Sedimentation in til.e. Green River Formation. Southern l.!lrJ.1.g Basin. U1ab. Dissertation directed by Professor Dag Nummedal Pages in Dissertation, 399. Words in Abstract 345. Detailed lithofacies analysis of over 4,500 m of measured sections of most of the Eocene portion of the fluvial and lacustrine Green River Formation in the south-central Uinta Basin documents twelve lithofacies: Sa (nonsinuous trunk streams), Sb (meandering delta distributary channels), Sc (amalgamated delta mouth bars), Sd (regressive deltaic sandsheets), Se (overbank and shallow-lacustrine sandsheets), Sf (crevasse channels and splays), C (passively-filled abandoned channels), Mg (subaqueous mudflats), Mr (subaerial mudflats), L (lake-margin carbonate flats), and la and lb {open­lacustrine deposits). The lower half of the study section consists of the carbonate marker unit (130 m) and the overlying Sunnyside delta interval (375 m), which record marginal-lacustrine sedimentation along the southern shore of Lake Uinta within and adjacent to a large, fluvially-dominated lacustrine delta informally named the Sunnyside delta. Meandering delta distributary channels on the delta plain cannibalized most delta mouth bars. Shallow water depths in the southern half of Lake Uinta atttenuated waves and wave-generated currents, thereby preventing the development of shoreface ravinement, beaches, barriers, or significant siliciclastic bars. Evaporative pumping on subaerially­exposed mudflats produced brines which altered detrital clay minerals to analcime. The combination of moderately high local subsidence and variations in lake volume produced low amplitude (less than 12 m) fluctuations in relative ABSTRACT Detailed lithofacies analysis of over 4,500 m of measured sections of most of the Eocene portion of the fluvial and lacustrine Green River Formation in the south-central Uinta Basin documents twelve lithofacies: Sa (nonsinuous trunk streams), Sb (meandering delta distributary channels), Sc (amalgamated delta mouth bars), Sd (regressive deltaic sandsheets), Se (overbank and shallow-lacustrine sandsheets), Sf (crevasse channels and splays), C (passively-filled abandoned channels), Mg (subaqueous mudflats), Mr (subaerial mudflats), L (lake-margin carbonate flats), and la and lb (open­lacustrine deposits). The lower half of the study section consists of the carbonate marker unit (130 m) and the overlying Sunnyside delta interval (375 m), which record marginal-lacustrine sedimentation along the southern shore of Lake Uinta within and adjacent to a large, fluvially-dominated lacustrine delta informally named the Sunnyside delta. Meandering delta distributary channels on the delta plain cannibalized most delta mouth bars. Shallow water depths in the southern half of Lake Uinta atttenuated waves and wave-generated currents, thereby preventing the development of shoreface ravinement, beaches, barriers, or significant siliciclastic bars. Evaporative pumping on subaerially­exposed mudflats produced brines which altered detrital clay minerals to analcime. The combination of moderately high local subsidence and variations in lake volume produced low amplitude (less than 12 m) fluctuations in relative lake level which, due to the gentle gradient of the delta plain, produced shifts in shoreline position on the order of 40-50 km. During periods of rapid relative lake level rise most siliciclastic sediment was trapped upstream, resulting in iv lake level which, due to the gentle gradient of the delta plain, produced shifts in shoreline position on the order of 40-50 km. During periods of rapid relative lake level rise most siliciclastic sediment was trapped upstream, resulting in the development of extensive, but thin, transgressive shallow-lacustrine carbonates. The regressive portion of each depositional cycle consists of upper and lower delta plain, shallow-nearshore lacustrine, and relatively rare delta front deposits. The upper half of the study section consists of the transitional interval (200 m), which records a major, but gradual, expansion and deepening of the lake, and the overlying upper member (300 m), which consists of dark mudstone and dolostone and relatively rare hummocky cross-stratified storm deposits produced by combined flows and nearshore-lacustrine sandbodies that accumulated in a generally quiet. but not necessarily very deep, relatively siliciclastic-poor, open-lacustrine setting. the development of extensive, but thin, transgressive shailow-lacustrine carbonates. The regressive portion of each depositional cycle consists of upper and lower delta plain, sha!!ow-nearshore !acustrine, and relatively rare delta front deposits. The upper half of the study section consists of the transitional interval (200 m), which records a major, but gradual, expansion and deepening of the lake, and the overlying upper member (300 m), which consists of dark mudstone and dolostone and relatively rare hummocky cross-stratified storm deposits produced by combined flows and nearshore-lacustrine sandbodies that accumulated in a generally quiet, but not necessarily very deep, relatively siliciclastic-poor, open-lacustrine setting. v CHAPTER I INTRODUCTION 1 Basement deformation during the Laramide orogeny (Late Cretaceous­Eocene) broke the Late Cretaceous marine foreland basin into a number of separate non-marine intermontane basins (Dickinson and others, 1988). Blockage of fluvial drainages within basins in the core of the Laramide province produced large fresh to saline lakes (ponded basins of Dickinson and others, 1988). The Green River Formation (Paleocene-Eocene) accumulated in two such large lakes: Lake Uinta in the Uinta and Piceance Basins of northeastern Utah and northwestern Colorado, respectively, and Lake Gosiute in southwestern Wyoming (Fig. 1-1 ). Following an initial fresh water stage, the salinity of Lake Uinta increased steady throughout most of its history, resulting in the early elimination of saline sensitive molluscs and ultimately in the precipitation of nahcolite and halite (Johnson, 1985). According to the model proposed by Ryder and others (1976), the lower Green River Formation in the Uinta Basin can be divided into a central core of organic-rich open-lacustrine claystone and mud-supported carbonate surrounded by marginal-lacustrine facies consisting of claystone, sandstone, and carbonate deposited in the deltaic, interdeltaic, and lake-margin carbonate flat environments (Fig. 1-2). The formation is enveloped by alluvial claystone, conglomerate, and sandstone of the Paleocene and Eocene Colton and Wasatch Formations and the Eocene Uinta Formation that were deposited peripheral to the lake. Studies by a number of researchers (Cashion, 1967; Picard and High, 1970; Fouch, 1975; Ryder and others, 1976; Pitman and others, 1982, Dickinson and others, 1986) demonstrate that one of the largest of several fluvial/deltaic complexes in the basin accumulated along the southern shore of Lake Uinta and was centered around or east of the Green River (Fig. 1-3). This delta, which was informally named the Sunnyside delta by Remy (1989a 2 44° 40° 36° 112° 108° HIGH RELIEF LOW RELIEF Ll LAKES & RIVERS - DELTAS & ALLUVIAL FANS Figure 1-1. Paleogeography of the central Rocky Mountain region during the late early to middle Eocene showing the location of Lakes Gosiute and Uinta and the study area. Modified from McDonald (1972). 3 4 D rm Oil/Gas field in Feldspathic ~ Sandstone of SunnysideDelta Position of Numbered • Measured Section Oil/Gas Field in Quartzose Sand­stone Derived from Uinta Mountains A-A' Position of Cross-Section Figure 1-3. Map showing the location of the Green River Formation outcrop in the south-central Uinta Basin and the study area in Nine Mile Canyon and its tributaries and along the Roan Cliffs. Geologic base map from Hintze (1980). Positions of all oil and gas fields except Peters Point from Grugel and others (1983). Position of Peters Point field from Hendel (1957). 5 and Chapter 6), was at least 100 km wide and prograded at least 40 km into Lake Uinta at times of maximum regression. The Sunnyside delta was a large fluvially-dominated shallow-water delta that accumulated in a region of low relief in a large, but shallow, saline lake. The sedimentology and stratigraphy of this type of lacustrine delta has seldom been investigated. Most previous studies on lacustrine deltas have focused on high-relief tectonic basins (link and Osborn, 1978; Link, 1984; Hentz, 1985; Demico and Gierlowski Kordesch, 1986; Scholz and others, 1990), glacial lakes (Gustavson and others, 1975; Shaw, 1975), and on relatively small delta systems in small alluvial valley lakes (Tye and Coleman, 1989). The western part of the Sunnyside delta is very well-exposed in Nine Mile Canyon and its tributaries and along the Roan Cliffs in the south-central Uinta Basin (Fig. 1-3). The fluvial-deltaic rocks are underlain by a 130-m-thick carbonate-rich interval which records marginal-lacustrine sedimentation before the major influx of elastic sediment of the Sunnyside delta and is overlain by a 500-m-thick interval of marginal- to open-lacustrine rocks which record a major transgression of Lake Uinta. The study area thereby provides a complete, and very well-exposed, record of the initiation, evolution, and eventual drowning of a type of lacustrine delta system which has not been adequately investigated. Despite several studies of the Green River Formation in the vicinity of Nine Mile Canyon and the Roan Cliffs (Jacob, 1969; Fouch and others, 1976; Ryder and others, 1976; Banks, 1981 ), a detailed lithofacies analyses of the Sunnyside delta and overlying transgressive deposits has not been conducted. Therefore, the primary purpose of this dissertation is to develop a lithofacies model for fluvial-deltaic and lacustrine sedimentation in shallow, saline southern Lake Uinta. Related goals of the dissertation include a 6 description and analysis of the stratigraphy of the Green River and Colton Formations in the study area, an examination of the origin of analcime-rich mudstone, and an examination of hummocky cross-stratification in the transgressive deposits that overlie the Sunnyside delta. The primary data base for this study consists of 17 measured stratigraphic sections with a total length of over 4,500 m, supplemented by x-ray diffraction, thin-section, and electron microprobe analyses. Most of the stratigraphic and lithologic data which form the basis of this study are presented in 4 appendices and 3 charts in the back of the dissertation. The body of the dissertation consists of five papers (chapters 2-6), each of which is a stand-alone paper with its own abstract, introduction, methods section, body, conclusions, and tables and figures. However, in order to avoid duplication and save space the references for all dissertation chapters are in a combined reference list. The original versions of the two dissertation chapters which have been published (chapters 5 and 6) have been slightly modified in order to make the stratigraphic terminology used in the papers consistent with current terminology and interpretations (as described in chapter 2). Moreover, minor errors made in the original version of chapter 6 have also been corrected and several figures have been redrafted. The first paper "Stratigraphy of the Eocene part of the Green River Formation in the south-central Uinta Basin, Utah" (in review, U.S. Geological Survey Bulletin) provides a detailed description and analysis of the stratigraphy of the Green River Formation and related Colton Formation. Chapter 3 is entitled "Depositional processes of a f!uvially-dominated lacustrine delta and of transgressive deposits in the Green River Formation, south-central Uinta Basin, Utah" and is a detailed lithofacies analysis of the rocks. A lithofacies model for lacustrine deltaic sedimentation is developed, 7 the effects of lake-level fluctuations on sedimentation are analyzed, and the geological history of south-central Lake Uinta is described. Chapter 4 is entitled "Lacustrine hummocky cross-stratification produced by combined flows, Green River Formation, Utah". The paper provides a description of hummocky cross-stratification (HCS) and related sedimentary structures in a thin tabular sandstone in the open-lacustrine sequence which overlies the Sunnyside delta and presents an argument that the HCS was produced by combined-flows. Chapter 5 is entitled "Distribution and origin of analcime in marginal lacustrine mudstones of the Green River Formation, south-central Uinta Basin, Utah" (Clays and Clay Minerals, v. 37, p. 419-432, 1989). The paper provides an analysis of the bulk mineralogy of sandstone and limestone, the bulk and clay mineralogy of mudstone, and of the distribution and composition of analcime (a sodium-rich zeolite) in marginal-lacustrine red and green mudstone. The paper refutes the popular concept that analcime in the Green River Formation formed from precursor zeolites derived from volcanic glass and argues that analcime formed from detrital clay minerals that underwent alteration in a moderately saline and alkaline environment. The last paper in the dissertation is entitled "(Field guide to) deltaic and lacustrine facies of the Green River Formation, southern Uinta Basin, Utah" (in Nummedal, D. and Remy, R. A., editors, Cretaceous shelf sandstones and shelf depositional sequences, Western Interior Basin, Utah, Colorado, and New Mexico: copyright by the American Geophysical Union, Washington, D.C., 28th International Geological Congress Field Trip T-119, p. 1-11, 1989). This chapter is a field guide to the formation in Nine Mile Canyon. Chapter 7 provides a brief summary of the major conclusions of the dissertation. 8 CHAPTER II STRATIGRAPHY OF THE EOCENE PART OF THE GREEN RIVER FORMATION IN THE SOUTH-CENTRAL UINTA BASIN, UTAH 9 ABSTRACT Seventeen stratigraphic sections totalling 4514.3 m were investigated and previous reports studied in order to clarify and illustrate the stratigraphy of most of the Eocene portion of the fluvial and lacustrine Green River Formation in the south-central Uinta Basin. In the study area the carbonate marker unit marks the base of the main body of the formation and consists of approximately 130 meters of micrite, carbonate grainstone, dolostone, green mudstone, siltstone, and sandstone that accumulated in shallow water along the fluctuating southern shore of Lake Uinta. The overlying delta facies is herein divided into two informal units: (1) a lower 375-m-thick sequence named the Sunnyside delta interval, and (2) an upper 200-m-thick sequence named the transitional interval. In the Nine Mile Canyon region the Sunnyside delta interval consists of sandstone, red and green mudstone, and shallow-water limestone deposited in a large fluvially­dominated delta complex. The transitional interval is characterized by an upward increase from the base of the unit in the amount of open-lacustrine dolostone, kerogenous laminated dolostone (oil shale), and dark-colored mudstone and a decrease in the amount of marginal-Iacustrine green mudstone, fluvial/deltaic sandstone, and shallow-water limestone. These lithologic changes record a major, but gradual, expansion of Lake Uinta. Several transgressive limestones in the Sunnyside delta interval and transitional interval serve as local stratigraphic markers. The top of the transitional interval is placed at the top of the S1 marker unit. The rocks of the Sunnyside delta interval and transitional interval in Nine Mile Canyon interfinger updip (southward) with lower delta plain to alluvial plain sandstone, 10 mudstone, and minor limestone of the interfingering Green River and Colton Formations exposed along the upper Roan Cliffs. In the region of Nine Mile Canyon the informal upper member of the Green River Formation overlies the transitional interval and consists of approximately 300 m of dark-colored mudstone, dolostone, and kerogenous laminated dolostone (oil shale), and minor sandstone and siltstone. The generally fine-grained rocks of the upper member were deposited in a low­energy open-lacustrine setting in Lake Uinta. The Mahogany oil-shale bed, 82 marker unit, Horse Bench Sandstone Bed, and an unnamed tuff serve as local to regional stratigraphic markers. The presence of the Mahogany oil­shale bed near the top of the Roan Cliffs demonstrates that the top 0-25 m of the Roan Cliffs is stratigraphically equivalent to the lower part of the upper member in Nine Mile Canyon. Analyses of published paleontological data and 40Ar/39Ar, K/Ar, and fission-track dates suggest ages of approximately 54 Ma, 47.5 Ma, and 43 Ma for the base of the carbonate marker unit, the top of the transitional interval, and the top of the upper member, respectively, in the study area. INTRODUCTION The Green River Formation in the Uinta Basin of northeastern Utah (Fig. 2-1) accumulated in and adjacent to a large lake basin (Lake Uinta) during Paleocene and Eocene time (Fig. 2-2). According to the model proposed by Ryder and others (1976), the lower part of the formation can be divided into a central core of organic-rich open-lacustrine claystone and mud-supported car­bonate surrounded by marginal-lacustrine facies consisting of claystone, 11 UTAH 10 MILES 10KM f@ Oil/Gas field in Feldspathic ~ Sandstone of SunnysideDelta • Position of Numbered Measured Section Oil/Gas Field in Quartzose Sand­stone Derived from Uinta Mountains A-A, Position of Cross-Section Figure 2-1. Map showing the location of the Green River Formation outcrop in the south-central Uinta Basin and the study area in Nine Mile Canyon and its tributaries and along the Roan Cliffs. Geologic base map from Hintze (1980). Positions of all oil and gas fields except Peters Point from Grugel and others (1983). Position of Peters Point field from Hendel (1957). 12 44° 40° 36° 112° 108° HIGH RELIEF LOW RELIEF ~ LAKES & RIVERS - DELTAS & ALLUVIAL FANS Figure 2-2. Paleogeography of the central Rocky Mountain region during the late early to middle Eocene showing the location of Lakes Gosiute and Uinta and the study area. Modified from McDonald (1972). 13 sandstone, and carbonate deposited in the deltaic, interdeltaic, and lake­margin carbonate flat environments. The formation is enveloped by alluvial claystone, conglomerate, and sandstone of the Paleocene and Eocene Colton or Wasatch Formation and Eocene Uinta Formation that were deposited pe­ripheral to the lake. Ryder and others (1976), McDonald (1972), Fouch and Cashion (1979), Picard (1957, 1959), Johnson (1985), Fouch and others (1987), Fouch (1976, 1981 ), and Bryant and others (1990) illustrate and/or describe the overall stratigraphy of the Green River Formation in the Uinta Basin. Studies by a number of researchers (Cashion, 1967; Picard and High, 1970; Fouch, 1975; Ryder and others, 1976; Pitman and others, 1982, Dickinson and others, 1986) demonstrate that one of the largest of several fluvial/deltaic complexes in the basin accumulated along the southern shore of Lake Uinta (Fig. 2-2) and was centered around or east of the Green River (Fig. 2-1 ). This delta received feldspathic sand from basement rocks then exposed in the Laramide-age San Luis uplift in southwestern Colorado (Dickinson and others, 1986). The presence of marginal-lacustrine feldspathic sandstone in Pariette Bench (Pitman and others, 1982), Duck Creek (Osmond, 1985), Pleasant Valley (Colburn and others, 1985), and Monument Butte and other (Oleson, 1986) oil and gas fields indicates that the delta extended into the center of the basin, where it interfingered with quartzose sediment derived from the Uinta Mountains to the north (Sanborn and Goodwin, 1965; Koesoemadinata, 1970; Castle, in press) (Fig. 2-1 ). The western edge of the delta occurred west of Willow Creek/Indian Canyon (Ryder and others, 1976, their Figs. 15 and 16) and the eastern edge of the delta is poorly constrained. In the Nine Mile Canyon region of the south-central Uinta Basin (Fig. 2-1 ), the western margin of the delta that was centered around the Green River is 1 4 well-exposed. This portion of the delta was informally named the Sunnyside delta by Remy (1989a} and consists of approximately 375 m of fluvial/deltaic sandstone and mudstone and carbonate (Remy, 1989a and Chapter 6, 1989b). Similar marginal-lacustrine rocks serve as the reservoirs for many of the oil and gas fields in the basin subsurface (Fouch, 1975; Franczyk and others, 1989), and their updip equivalents serve as the host for the Sunnyside tar sand deposit on the Roan Cliffs (see below}. The fluvial/deltaic rocks are underlain by a 130-m-thick carbonate-rich sequence which accumulated along the fluctuating southern shore of Lake Uinta before the major influx of sand deposited in the Sunnyside delta. The fluvial/deltaic deposits are overlain by about 500 m of generally fine-grained, carbonate-rich, marginal- to open-lacustrine rocks that accumulated during a major expansion of the lake. The stratigraphy and depositional environments of the Green River Formation in the south-central Uinta Basin were first described by Bradley (1931) (Chart 1, Sections A and D). Subsequent workers (Hendel, 1957; Dane, 1955; Ray and others, 1956; Jacob, 1969, Ryder and others, 1976; Fouch and Cashion, 1979; Remy, 1989a, Weiss and others, 1990} provided additional information on the stratigraphy and depositional environments of the rocks and suggested a number of changes and additions to Bradley's (1931} stratigraphic nomenclature. Unfortunately, the variations in stratigraphic terminology used by different researchers and occasionally vague descriptions of criteria used to identify boundaries between strat­igraphic units make precise comparison of the results of these studies difficult. To date, no one has attempted a comprehensive review of this literature or conducted the detailed field work necessary to test the various stratigraphic schemes and produce an up-to-date composite stratigraphic section for the Green River Formation in the south-central Uinta Basin. Moreover, little 15 detailed information on the stratigraphy and lithology of the Green River Formation in the south-central Uinta Basin has been published and the age of the rocks is poorly constrained, particularly in the lower part of the formation. The purpose of this dissertation chapter is to provide a detailed analysis of the stratigraphy of most of the Eocene portion of the Green River Formation in the region of Nine Mile Canyon and the Roan Cliffs near the Sunnyside tar sand deposit (Fig. 2-1 ). Specifically, it is designed to: (1) summarize and evaluate reports on the surface stratigraphy of most of the Eocene portion of the Green River Formation in the south-central Uinta Basin, (2) describe and illustrate the stratigraphy of the rocks and briefly describe their lithology, depositional environments, and age, (3) illustrate the stratigraphic relation between the rocks exposed in Nine Mile Canyon and those exposed updip in the upper Roan Cliffs, and (4) present 15 detailed measured sections and 2 cross-sections of the formation. STUDY AREA AND METHODS The study area in the south-central Uinta Basin is bounded on the north by Nine Mile Canyon and the lower 5 km of Gate Canyon, on the south by the Roan Cliffs near Sunnyside, Utah, on the west by the junction of Minnie Maude Creek and Nine Mile Creek, and on the east by the junction of Nine Mile Canyon and North Franks Canyon (Fig. 2-1 ). The study section includes all but the basal 30 m of the Eocene carbonate marker unit of Ryder and others (1976, p. 497), the delta facies of Bradley (1931 ), and the upper member of Weiss and others (1990) (equivalent to a part of the Parachute Creek Member of the Green River Formation of Cashion and Donnell (1974)). 16 Seventeen stratigraphic sections (Fig. 2-1) totalling 4514.3 m were investigated in order to determine the lithology, color, bedding thickness, grain size, nature of bounding surfaces, sedimentary structures, geometry, and fossil content of the rocks and to determine the position of stratigraphic markers. The location of the measured sections are described in Appendix 1 and shown on topographic maps in Appendix 2. Symbols used in the sections are shown in Appendix 3, and fifteen of the seventeen sections which form the basis for the work are illustrated in Appendix 4. In order to facilitate description of the measured sections, 12 lithofacies were established (Chapter 3). The primary lithologic and sedimentologic characteristics and interpreted depositional environments of the lithofacies are summarized in Table 2-1 and their geographic and stratigraphic distribution are shown in Table 2-2. The lithofacies are grouped into five depositional assemblages which are described and illustrated in Charts 2 and 3. Photomosaics of the walls of Nine Mile Canyon and its tributaries and the Roan Cliffs were used to analyze the geometry of the rocks and to trace stratigraphic markers. Limestones, tuffs, distinctive sandstone units, and other types of lithologic markers were used to correlate the sections (Appendix 1 ). The stratigraphic position of the stratigraphic markers employed in this study are listed in Appendix 1 and correlations of the measured sections are shown in Charts 2 and 3. 17 TABLE 2-1. Summary of major lithologic and sedimentologic characteristics and intepretation of lithofacies lltholacies Definiuon Code lithology and Grain Size Sedimentary Structures Goome11Y and Thickness Other Charactertsncs Associated llthofacies Interpretation Thick (> 15 m), Sa SiltslDne and sandstone Trough crossbeds, current Thinner sandbodies are Bases sharp and nat to Common: Mr, Mg. Se, SI Non-sinuous streams scour-enclosed (62-280 μ,mean. 150 μ), and less common dimbing lenUcular to labular, thicker scoured, basal IFC Less common: Sb, L, c on upper delta to sandstone some coatsen or fine ripples, planar laminatlons, sandbodies are tabular, abundant, scours and IFC Rare: la alluvial plaln upward, most have much is structureless, no 57% of sandbodies are within sandbodies Never: Sc, Sd, lb multiple venical grain Size consistent verdcaJ amalgamated, 15-4 1 m abundant trends arrangement of structures thick (mean - 232 m) 3-15-m-thick, Sb SlltslDne and sandstone Trough crossbeds, current Lentlcular to tabular geo- Bases sharp and nat to Common: Mr, Mg. Se, Sf, L Meandering delta laterally-discontinuous (62-300 μ,mean. 125 μ), and wave ripples, planar me11Y. sloping channel scoured, lateral accretion Less common: Sa, Sc, C, distrlbu tary channels sandstone 30% fine upward, 7% lamlnaUons, much is edges common. about bedding and basal IFC are Rare: la, lb(?) on delta plain and coarsen upward, 43% structureless. many sand- 25% consist of slaeked abundant, scours and IFC Never: Sd stacked crevasse have multiple trends, 20% bodies have upward de- sandbodies, mean within sanctbodies are splays and overbank have uniform grain size crease In size or structures thickness: 5.8 m common sand sheets Thick (> 15 m). Sc SiltslDne and sandstone Current and wave ripples, Lenticular goome11Y with Bases generally sharp and Common: Mr, Mg. Se, Sf, Stacked and amal-lateratl y-lnterfingerlng (62-275 μ,most less than planar and wavy planar Irregular edges that Inter· Hat, basal IFC rare, L,Sb gamated lentk:ular sandstone 150 μ), uniform grain size laminations, HCS (?),rare finger laterally with other Internal scours and IFC Rare:C delta mouth bars or multiple nning· and trough crossbeds and rocks, thick sandbodies common, rare downstream Never: Sa, Sd, la, lb coarsening-upward cydes convolute bedding. consist of amalgamated accretion bedding wave-generated structures lentlcular sandbodles, more common In lower amalgamated sandbodies halves of sandbodies are 15-40+ m thick 3-15-m-thlck, Sd Sandstone (62-350 μ), Trough crossbeds and Tabular goome11Y (can be Base always sharp, basal Common: Se, Mg, la, lb Delta (front?) deposits laterally-continuous most sandbodles have planar laminatlons com- traced for over 20 km). S<X>Ur with IF C common. Never: all other lithofacies that accumulated in sandstone multiple tining- and rnon, ripples. convolute consists or slaeked lake Uinta during a coarsening-up cycles, bedding and structureless sandbodles, 4.5-11.5 m regional regression some line upward, some zones occur locally, no thick sandbodles oontain green consistent vertical and gray mudstone arrangement of structures Thin (<3 m) Se SlltslDne and One-grained Current ripples, planar Tabular goome11Y (lateral lndlllldual beds commonly Common: Sa, Sb, Sc, Sd, Fluvlal overbank and sandstone without sandstone (generally lamlnatlons, small-scale continuity commonly >few have sharp and flat bases Sf. Mg, Mr, L, la, C deltaic sandsheets !hat basal or Internal under 125 μ),most trough crossbeds, and 100 m), llthofacles is and tops, litholacies Rare: lb accumulated in nuvial, scour, coarsening sandbodies have uniform mudcracks common, 0.5-3.0 m thick, individual generally encased in lower delta plain, and upward grain size, or grain size, few fine locally abundant wave beds are a rew an to 3.0 m mudstone shallow lacustrine accretion bedding upward ripples and wavy planar thick (but most are less settings laminations than 1 .5 m thick) Thin (<3 m) Sf Siltstone and fine-grained same as lithofacies Se Tabular to lentlcular Basal scour and amal- Common: Sa, Sb, Sd, Crevasse splays, sandstone with t>asal sandstone (generally less except trough crossbeds goome11Y. lithofacles is gamallon of sandstone Se, Mg, Mr, L, la, crevasse splay or Internal scour, than 175 μ),most have more common 0.5-3.0 m thick, Individual beds are common, Rare: lb channels, and small, coarsening upward uniform grain slze, some beds are as much as 3.0 m downstream accretion delta d1stributary grain size. or fine or coarsen upward thick locally abundant, channels that accum-accrellon bedding lltholades generally ulated In ftuvial, lower encased In mudstones delta plain, and shal-low lacustrine settings _. en TABLE 2-1. Summary of major lithologic and sedimentologic characteristics and intepretation of lithofacies, continued Llthofades Definition Code Lithology and Grain Size Sedimentary Structures Geometry and Thickness Other Characteristics Associated Llthofacies Interpretation Sand- and/or c Red and green mudstone, Mudstone Is generally Mudstone-, sandstone-, Srours generally cut Common: Mg, Mr, Se, Sf, Passively-filled mud-filled channel siltstone, and fine-grained structureless, sandstone and siltstone-filled dlan- lnterbedded sandstone L, Sa, Sb, Sc(?) abandoned channels sandstone (generally less and siltstone have ripples nels, size of channels and mudstone, basal IFC Never: la. lb, Sd (most appear to be than 150 μ) and planar laminations, varies from few meters common crevasse channels) and are commonly Wide to about 100 m wide structureless by 10 m deep Green mudstone Mg Green, greenish gray, and Most mudstone Is Tabular geometry, Base and top of Individual Common: all iltholacies Shallow water sub-light gray mudstone, structureless, rare planar lltholades Is 0.5 to 25 m beds are sharp to except lb aqueous mudftats In minor sandstone, laminations, ripples, small thick, Individual beds are a gradatlonal, ostracodes Rare: lb lnterdlstrlbutary bays, In siltstone, limestone, and burrrCMs, rootlets (?), few cm to 5 m thick common In mudstone shallow nearshore red and purple mudstone mudaacks, and syneresls portions of the lake, and aacks pertiaps In delra plain ponds and lakes Red mudstone Mr Red and purple Same as litholacles Mg Same as ll!holacles Mg Base and top of Individual Common: all iltholacies In term lnently mudstone. minor beds sharp to gradational, except L, la, lb subaerially-exposed sandstone, siltstone, ostracodes rare Rare: L mudflats limestone, and green, Never: la, lb greenish gray, and light gray mudstone Limestone L Ostracode ,ooid, lntradast, Rlpples, small-scale Tabular geometry for both Bases of beds generally Common: all litholacies and pellet gralnstone, trough aossbeds, planar llthofades and individual ftat and unscoured, except Mr, la, lb Limestones deposited in mlaite, and stromatollte, and WfNY planar beds, litholades Is 0.5-25 complex lnterbedding and Rare: Mr, lb, lb shallow, quiet to minor thin beds of laminations, and HCS (?) m thick, Individual beds are interlaminations of wave-agitated water in sandstone, siltstone, occur In grain stones, some a few cm to a few m thick ditterent limestone types lnterdistributary bays, in green mudstone, and mlcrite has planar common nearshore regions of the dolostone (induding oil laminations but most Is lake, and perhaps In shale) structureless, stromatolite delta plain ponds and has algal laminations lakes Brown and gray la Gray to brown mudstone t.\Jch dolostone and Both ilthofacies and beds Some coarsening and Common: lb, Mg, Se, Sd, mudstone, dolostone and dolostone (induding mudstone is structureless, are tabular In geometry, fining upward trends, Sf Proximal open-lacus- (<30%), and minor oil shale), minor green some has planar llthofades Is 0.5 to over Individual beds commonly Less common: Sb, L trlne environment: car-sandstone and mudstone, limestone, laminations In places, 100 m thick, individual have sharp ftat bases and Rare: Sa, C, Sc bonate and siliciclastic siltstone sandstone, and siltstone sandstones have a variety beds are as much as 10 m tops and are laterally Never: Mr mud deposited in low structures including thick continuous, ostracodes energy nearshore to ott-ripples, planar and wavy abundant In places shore regions of lake, planar laminations, HCS, occasional storm trans-and trough crossbeds port of sand into lake Brown and gray lb Similar to lithofacies la Same as lithofacies la Same as lithofacies la Same as llthofacies la Common: la, Sd Disral open-lacustrine mudstone, dolostone except more dolostone Less common: Mg, Se, Sf, environment; same as (>30%), and minor and less gray to brown L lithofades la except sandstone and mudstone, siltstone, Rare: Sa, Sb, Sc, generally deeper water siltstone sandstone, and green Never: Mr,C (?) and lower energy mud stone ....... tD TABLE 2-2. Stratigraphic and geographic distribution of lithofacies Nine Mile Canyon and tributaries 1 Roan Cliffs 2 ~c carbonate Sunnyside transitional interval3 upper lnterfingering Green upper member of I marker unit delta interval lower upper member River and Colton Fms. Green River Fm. Sa - - - - - 37.7% - Sb 12.5% 23.6% 9.5% 10.7% 4.4% 14.8% - Sc - 4.0% - - - - Sd - - - 7.8% - - - Se 9.9% 12.8% 12.4% 9.4% 0.5% 8.8% 4.4% Sf 5.7% 2.8% 2.3% 1.8% - 0.4% - c - - - - - - - Mr - 7.8% 0.4% - . 9.7% - Mg 14.2% 19.0% 33.2% 19.8% . 9.7% 24.3% L 16.3% 6.2% 13.7% 4.7% 0.1% 2.9% 15.7% la 25.3% 0.5% 0.6% 6.7% 53.5% 0.6% 7.8% lb 5.4% - 7.5% 8.6% - 47.8% Covered interval 10.7% 23.3% 27.9% 31.6% 32.9% 15.4% - 1 includes measured sections 4, 6, 7, 8, 9, 10, 11, 13, 14, 15, 16, and 17. 2 . Includes measured sections 1 and 2. 3 soundary between upper and lower parts of transitional interval placed at the B marker. N 0 LITHOSTRATIGRAPHY OF THE GREEN RIVER FORMATION: NINE MILE CANYON Units Underlying the Main Body of the Green River Formation The Green River Formation can be visualized as a jagged-edged lens of open and marginaHacustrine rocks enveloped by alluvial rocks of the Paleocene and Eocene Colton or Wasatch Formation and the Eocene Uinta Formation (Cashion, 1967, p. 8). West of the Green River the Colton Formation is separated from the underlying similar-appearing North Horn Formation by the Flagstaff Member of the Green River Formation (as defined by Fouch, 1976) (Weiss and others, 1990). In areas where the Flagstaff Member is absent or thin, as it is east of the Green River, it is common practice to group all of the rocks between the top of the Cretaceous and the base of the Green River Formation with the Wasatch Formation (McDonald, 1972, p. 249; Weiss and others, 1990). In the region of Nine Mile Canyon, the Flagstaff Member is approximately 91 m thick and is overlain by more than 725 m of mainly alluvial rocks of the Colton Formation (Fouch and others, 1976, p. 365) (Chart 1, Section C). The Colton Formation thins northward toward the center of the basin where the thickened Flagstaff Member and the main body of the Green River Formation merge and form a continuous lacustrine sequence (Fouch, 1976; Ryder and others, 1976). The interfingering contact between the Wasatch Formation of Bradley (1931) and overlying Green River Formation in the south central Uinta Basin was first described by Bradley (1931 ). In Willow Creek/Indian Canyon (Fig. 2- 1) he divided the rocks beneath his delta facies into (from base to top): (1) a 21 tongue or phase of the Green River Formation, consisting of about 60 m of paper shale, marlstone, limestone, and minor carbonaceous shale and coal, (2) a tongue of the Wasatch Formation, consisting of 115 m of sandstone and drab, buff, greenish, and red mudstone, and (3) a second lacustrine phase or facies of the Green River Formation, consisting of 230 m of light gray and brown shale, limestones, and minor sandstones (Chart 1, Section A). In Gate Canyon (Fig. 2-1 ), Bradley (1931) identified what he believed to be the basal member of the Green River Formation that he correlated with basal units in Willow Creel/Indian Canyon (Chart 1, Section D). Results of this investigation, however, indicate that the base of the surface section at Gate Canyon is several hundred meters stratigraphically above the top of the second lacustrine phase in Willow Creek/Indian Canyon (see below). Picard (1955, p. 83) designated the term "black shale facies" for dark gray to black shale, limestone, grayish-green shale, sandstone, and minor oil shale which he placed at the base of the Green River Formation in the basin subsurface. He correlated the black shale facies with Bradley's (1931) tongue of the Green River Formation and the tongue of the Wasatch Formation. Abbott (1957) extended the black shale facies to surface exposures and recommended that the terms "upper black shale facies", "Colton tongue", and "lower black shale facies" be substituted for Bradley's (1931) second lacustrine facies, tongue of the Wasatch, and basal tongue of the Green River Formation, respectively. Picard and others (1973) divided the black shale facies into 4 lacustrine units designated A through D and one fluvial unit designated the "Wasatch tongue" of the black shale facies. Recently, Weiss and others (1990) mapped the lower units of the Green River Formation as the lower member (Chart 1, Section B). They observed that the lower member of the Green River Formation is composed of three 22 lithologic units (base to top): (1) a lower lacustrine shale unit, which they cor­relate with the basal tongue of the Green River Formation of Bradley (1931 ), (2) an alluvial unit, which they correlate with Bradley's tongue of the Wasatch Formation, and (3) an upper lacustrine shale unit, which they correlate with Bradley's second lacustrine facies (Chart 1, compare Sections A and B). The interfingering Colton-Green River contact is well-exposed in western Nine Mile Canyon. Fouch and others (1976, p. 365) described an "unnamed tongue of the Green River Formation" as a 96-m-thick interval of ostracode grainstone, thin, mud-supported organic-rich carbonate, grayish green claystone, and sandstone. The thickness and lithology of this unit and its stratigraphic position above the main body of the Colton Formation suggest that it is equivalent to Bradley's (1931) basal tongue of the Green River Formation and Abbott's (1957) lower black shale facies. Little (1988) described the depositional environments, petrology, and diagenesis of limestones in this unit. In western Nine Mile Canyon the stratigraphic interval equivalent to the lower black shale facies of Abbott (1957) is overlain by a red claystone, silt­stone, and lenticular sandstone assemblage (Fouch and others, 1976, p. 365). These rocks, which were described as "an unnamed tongue of the Colton" by Fouch and others (1976), are presumably stratigraphically equivalent to the Bradley's (1931) tongue of the Wasatch and Abbott's (1957) Colton tongue. In his study of the subsurface stratigraphy and lithology of the lower part of the Green River Formation in the Peters Point Gas Field (Fig. 2-1 ), Hendel (1957) identified and briefly described the lower black shale, the "Wasatch tongue", and the upper black shale (Chart 1, Section E). Hendel (1957) placed the Colton-lower black shale contact at the base of the lowest typical lake bed. His lower black shale consists of approximately 11 0 m of 23 calcareous greenish-gray mudstone and shale, red mudstone, limestone, and sandstone. The lenticular sandstone in the lower part of this interval serves as the main producing interval for the Peters Point Field. The overlying Wasatch tongue of Hendel (1957) is approximately 11 O m thick and consists of fluvial deposits with minor lacustrine units. The stratigraphic positions and composi­tions of these units strongly suggest that the lower black shale is equivalent to Bradley's (1931) tongue of the Green River Formation and Abbott's (1957) lower black shale facies, and the Wasatch tongue is equivalent to Bradley's (1931) tongue of the Wasatch and Abbott's (1957) Colton tongue. The upper black shale is equivalent to the carbonate marker unit of this report (see below) and to Bradley's (1931) second lacustrine facies (Chart 1 ). Carbonate Marker Unit The carbonate marker unit of Ryder and others {1976) marks the base of the main body of the Green River Formation in the region of Nine Mile Can­yon. In eastern Nine Mile Canyon the unit is approximately 130 meters thick, the basal 25-30 m of which is poorly exposed. The upper 105 m of the unit is well exposed and consists of ostracode and ooid grainstone and micrite of the L lithofacies (16.3%), green mudstone of the Mg lithofacies (14.2%), sand­stone of the Sb (12.5%), Se (9.9%), and Sf (5. 7%) lithofacies, dark lamin-ated mudstone and kerogenous laminated dolostone (oil shale) of the la (25.3%) and lb (5.4%) lithofacies, and covered intervals (10.7%) probably underlain by mudstone (Table 2-2; Appendix 4, Units 1-66 of Measured Section 11 ). These rocks accumulated along the fluctuating southern shore of Lake Uinta (Fouch and others, 1976; Remy, 1989a and Chapter 6, 1989b; Chapter 3) in lake- 24 margin carbonate flat, subaqueous mudflat, crevasse splay, overbank sand­sheet, delta distributary channel, and proximal open-lacustrine environments. In the subsurface, the top of the carbonate marker unit is placed at the carbonate marker, a well log response that can be recognized in most of the subsurface part of the basin (Ryder and others, 1976). In his study of the subsurface stratigraphy and lithology of the lower part of the Green River Formation in the Peters Point Gas Field, Hendel (1957) placed the boundary between the delta facies of Bradley (1931) (see below) and the upper black shale facies of Abbott (1957) at the Green River marker bed, which he described as a "persistent limestone" (Chart 1, Section E). Handel's upper black shale facies is a 90 m thick interval of limestone, black and gray shale, and sandstone (Figure 3 of Hendel (1957)). Similarities in stratigraphic position, lithology, and thickness suggest that the upper black shale facies is stratigraphically equivalent to the carbonate marker unit and that the Green River marker bed of Hendel (1957) is equivalent to the carbonate marker of Ryder and others (1976) (Chart 1, compare Sections C and E). In this report the top of the carbonate marker unit is placed at a sharp distinctive change in the weathered color of the rocks (Chart 1, Section C). The carbonate-rich carbonate marker unit weathers light gray whereas the overlying carbonate-poor Sunnyside delta interval weathers light brown. Jacob (1969) used the same criteria to place the boundary between the black shale facies (carbonate marker unit of this report) and the delta facies of Bradley (1931) (Chart 1, Section F). 25 Delta Facies (Sunnyside Delta Interval and Transitional Interval) The interval between the carbonate marker unit and the mudstone- and dolostone-rich upper member consists of approximately 575 m of mainly fluvial and shallow-lacustrine sandstone and mudstone, shallow-water limestone, and some dolostone and dark mudstone near the top of the sequence. Bradley (1931) examined this interval near the Duchesne-Uintah County line, which occurs approximately 9 kilometers east of the easternmost measured section (Measured Section 13) of this report (Fig. 2-1 ), and at Gate Canyon. Because of the similarity of the sections, only the Gate Canyon section is shown in Chart 1 (Section D). Bradley (1931) divided the interval below his shaly facies (upper member of this report) into (from base to top): (1) the basal member, consisting of approximately 76 m (250 ft) of greenish gray shale and subordinate sandstone, limestone, and low-grade oil shale, and (2) the delta facies, which consists of 152-183 m (500-600 ft) of sandstone (which constitutes 75-80% of the interval) and greenish gray mudstone. However, because the basal 80 m of the surface section at Gate Canyon is not significantly different from overlying rocks (Fig. 2-3; Appendix 4, Measured Section 7), subsequent researchers (Hendel, 1957; Jacob, 1969; Remy, 1989a and Chapter 6) dropped the term "basal member" and refer to all of the rocks beneath Bradley's (1931) shaly facies as the "delta facies of Bradley (1931 )". According to McDonald (1972), the delta facies is equivalent to the Douglas Creek Member of the Green River Formation in the eastern part of the Uinta Basin (Chart 1, Section H). Picard (1957) recommended that the term "green shale facies" be substituted for the delta facies in the western part of the basin in order to avoid environmental interpretation in a stratigraphic term and because the term is 26 Figure 2-3. Sunnyside delta and transitional intervals at the junction of Gate and Nine Mile Canyons. The thick sandstones of the Sb lithofacies and associated thin sandstones of the Se and Sf lithofacies, red and green mudstones of the Mr and Mg lithofacies (covered intervals), and limestone of the L lithofacies were deposited in and adjacent to a large fluvially-dominated delta. At this location the C marker of this report is approximately 15 m above a pair of prominent yellow-weathering limestones (arrows) which are the C2 and C3 markers of Jacob (1969). The C marker separates the Sunnyside delta interval from the overlying transitional interval. The interval from the base of the photograph to the C marker is approximately 170 m thick. 27 more indicative of the sediment type. The middle member of the Green River Formation of Weiss and others (1990) is equivalent to most of the delta facies of Bradley (1931 ). Bradley (1931, p. 15) states that "in Gate Canyon, the writer estimates that about 300 feet at the base is not exposed". It is unclear whether Bradley was referring to the base of the main body of the Green River Formation (i.e. base of the delta facies) or the contact between his tongue of the Green River Formation and the underlying main body of the Colton Formation. Detailed correlations of the rocks (Charts 2 and 3) indicate that Bradley was incorrect in either case. The base of the delta facies, as defined to include Bradley's (1931) basal member, is actually 160 m below the floor of Gate Canyon (see Measured Section 7 on Chart 2) and the contact between the tongue of the Green River and the main body of the Green River Formation is about 500 m below the floor of the canyon. Moreover, Bradley erroneously correlated his basal member at Gate Canyon with his basal lacustrine tongue, tongue of the Wasatch Formation, and second lacustrine phase in the Willow Creek/Indian Canyon region (his Plate 3). This mis-correlation, plus the fact that Bradley underestimated the thickness of the basal member and delta facies by approx­imately 100 m, led to the erroneous conclusion that the delta facies thickens dramatically westward toward Willow Creek/Indian Canyon. Results of this study indicate that the delta facies (Sunnyside delta interval and transitional interval of this report) is about the same thickness (575 m) in the Nine Mile Canyon region and at Indian Canyon (Chart 1, compare Sections A and C). Several different approaches have been taken in defining the top of the delta facies. Bradley (1931, p. 16 and his plate 9B) noted that the top of the delta facies occurs at the top of the inner gorge of eastern Nine Mile Canyon (which he referred to as the "canyon of Minnie Maude Creek"). In the region of 28 central and western Nine Mile Canyon the inner gorge of the canyon and its tributaries are held up by two sandstone units (Fig. 2-4). The lower sandstone unit constitutes lithofacies Sd of this report (Table 2-1) and consists of 4.5- 10.5 m of trough cross-stratified sandstone (see, for example, Unit 29 of Measured Section 4 or Units 219-220 of Measured Section 9 in Appendix 4). This prominent rim-forming sandstone generally forms a relatively narrow plateau which underlies a broader plateau underlain by the S2 marker unit (see below) (Figs. 2-5, 2-6). The sandstone unit was subsequently mapped as the "1-bed" by Ray and others (1956) and informally named the "S1 marker unit" by Fouch and others (1976, p. 369). The upper rim-forming sandstone near the top of the inner gorge of Nine Mile Canyon occurs approximately 35-60 m above the S1 marker unit (Fig. 2- 4) and consists of about 1 m of very fine-grained, hummocky cross-stratified sandstone and, in places, mudstone (see, for example, Unit 25 of Measured Section 10 and Unit 17 of Measured Section 15 in Appendix 4). In central and eastern Nine Mile Canyon this thin but resistant unit underlies a broad plateau that underlies a higher plateau at the top of the Horse Bench Sandstone Bed of the upper member of the Green River Formation of this report. The unit was subsequently mapped as the "3-bed" by Ray and others {1956) and informally named the "S2 marker unit" by Fouch and others {1976). Chapter 4 provides a detailed description of the sedimentary structures, hydrodynamic origin, and depositional environment of the S2 marker unit. Bradley (1931) did not directly specify which of the two rim-forming sandstones at the top of the inner gorge of Nine Mile canyon define the top of his delta facies or publish his measured sections in Nine Mile Canyon. How­ever, Bradley (1931) states that a set of oil shales that occur below the top of his delta facies represent the upper oil-shale group of the Parachute Creek 29 Figure 2-4. Uppermost transitional interval and overlying open-lacustrine upper member in Gate Canyon. Note the S1 marker unit (S1 ), S2 marker unit (S2), and the Horse Bench Sandstone Bed (HS). The contact between the transitional interval and upper member is placed at the top of the S1 marker unit. See Measured Section 10 (Appendix 4) for a description of the rocks between the S1 and S2 marker units at this location. The interval from the base of the S1 to the top of the S2 is approximately 60 m thick. 30 Figure 2-5. Stratigraphy of the upper part of the Green River Formation in central Nine Mile Canyon. Note the upper Sunnyside delta interval (SD) and transitional interval (T) exposed in the inner gorge of Nine Mile Canyon, the S1 marker unit (S1) which marks the transitional interval-upper member contact, the S2 marker unit (S2) which underlies a broad plateau, the Horse Bench Sandstone Bed (HB) which underlies the upper plateau, and the top of the upper member (arrows). The view is from a small airplane at the approximate position of Measured Section 9 (Fig. 2-1) and looks eastward toward the Green River (not visible). Photograph provided by Xudong Ying. 31 Figure 2-6. Stratigraphy of the upper part of the Green River Formation in eastern Nine Mile Canyon. Note the transitional interval (T), 81 marker unit (S1), 82 marker unit (82), and the broad plateau held up by the Horse Bench Sandstone Bed (HB). The view is from a small airplane approximately half way between Measured Section 13 and the Green River (not visible) and looks eastward. Photograph provided by Xudong Ying. 32 Member (although he did not apply the term "Parachute Creek Member" to any beds west of the Green River). The Mahogany oil-shale bed occurs within the upper oil-shale group (Cashion, written communication, 1990), and, in Gate Canyon, the Mahogany oil-shale bed occurs between the S1 and the S2 marker units (Fouch and others, 1976). Therefore, the S1 marker unit must occur below the top of the delta facies, indicating that Bradley (1931) placed the contact between his delta facles and his overlying shaly facies at or near the S2 marker unit. Dane (1954, 1955) and Ray and others (1956), on the other hand, placed the top of the delta facies at the base of a set of oil shales which occur about 30 m below their 1-bed (S1 marker unit of this report) (Chart 1, Section G). These oil shales occur in several measured sections of this report (Appendix 4), including Measured Sections 4 and 9. Jacob (1969) placed the top of the delta facies at the top of a persistent sandstone that occurs below the main body of oil shale (Chart 1, Section F). In his Devils Canyon measured section this sandstone, which he called "marker A", occurs approximately 55 m below the top of the rim-forming sandstone picked by Bradley (1931) as the top of the delta facies and 25 m below the Mahogany oil-shale bed. The lithology and stratigraphic position of marker A relative to the Mahogany oil-shale bed and S2 marker unit (see Measured Section 10, Appendix 4) indicate that it is equivalent to the 1-bed of Ray and others (1956) and the S1 marker unit of Fouch and others (1976). Weiss and others (1990) placed the top of their middle member of the Green River Formation (delta facies of Bradley, 1931) at the base of the Ma­hogany ledge, a zone of several oil shale beds which includes the Mahogany oil-shale bed. The Mahogany ledge directly overlies the S1 marker unit. For ease of mapping, however, they drew the boundary between the upper and 33 middle members at the top of the Mahogany oil-shale bed, which occurs about 1 O m above the base of the Mahogany ledge (Chart 1, Section B). Several laterally-continuous, yellow-weathering limestones were employed by Jacob (1969), and are employed in this report, to correlate and subdivide Bradley's (1931) delta facies (Sunnyside delta interval and transitional interval of this report). The stratigraphic positions of these markers are shown in Appendix 1 and their correlation are illustrated in Charts 2 and 3. Jacob's (1969) D marker consists of approximately 2.0 m of carbonate mud­stone, ostracode grainstone, domal stromatolite, greenish gray mudstone, and a distinctive bed of oolite grainstone with ostracode nuclei (Fig. 2-7A; Appen­dix 4, Units 3-4 of Measured Section 8). This unit is equivalent to Remy's (1989a) ostracode oolite marker. In this report, however, Jacob· s original name for the marker is employed because it has precedence over Remy's name and because the marker does not everywhere contain oolites with ostracode nuclei. The D marker occurs approximately 160 m above the top of the carbonate marker unit (Chart 2) and can be traced from a position several kilometers west of Measured Section 16 through Measured Section 8 to a position 3 km west of Measured Section 7 (Fig. 2-1) where the marker goes into the subsurface. Jacob's (1969) C marker consists of three ostracode grainstones which he designated (from base to top) C3, C2, and C1. Markers C3 and C2 form a prominent yellow double band which can be traced visually in the upper walls of central and eastern Nine Mile Canyon (Fig. 2-3). Jacob's (1969) C3 marker is approximately 4-17 m above the C2 marker and consists of 2 to 8 meters of ostracode grainstone, domal stromatolites up to 1 m wide by 50 cm high (Fig. 2-78), micrite, and minor sandstone and mudstone (see, for example, Units 100-101 of Measured Section 8 and Units 83-85 of Measured Section 9 in 34 Figure 2-7. Limestone stratigraphic markers in the Green River Formation. A. Bed of ooids with ostracode nuclei in the D marker. The D marker occurs near the middle of the Sunnyside delta interval. Coin for scale. B. Large domal stromatolites in the C marker {Unit 78, Measured Section 7 of Appendix 4). The C marker marks the contact between the Sunnyside delta interval and overlying transitional interval. Ruler (15 cm) for scale. 35 Appendix 4). Both the thickness of the marker and the size of the domal stromatolites decrease westward. The C1 marker of Jacob (1969) is equivalent to the stromatolite marker of Remy (1989a) and the C marker of this report. The C marker occurs approximately 215 m above the D marker and can be traced 30 km along Nine Mile Canyon {Chart 1) and 15 km from the canyon southward toward the Roan Cliffs (Chart 2). In this report the C marker serves as the boundary between the Sunnyside delta interval and the overlying transitional interval. The C marker is roughly stratigraphically equivalent to the middle marker of Ryder and others (1976) {Fouch, personal communication, 1988). Jacob's (1969) B marker occurs approximately 85 m above the stromatolite marker and 115 m below the base of the upper member (as defined by the top of the S1 marker unit). The thickness of the unit varies from 0.5 m to 4.0 m. In most measured sections the B marker is composed of ostracode grainstone (see, for example, Unit 129 of Measured Section 8, Appendix 4). In other places, however, the unit consists of ooid grainstone (Unit 104, Measured Section 13 of Appendix 4), a mixture of ooid and ostracode grainstone and micrite (middle of Unit 61, Measured Section 2 of Appendix 4) , or micrite with ooids and ostracodes, and domal stromatolites (Unit 120, Measured Section 14 of Appendix 4). Like the C marker, the B marker can be traced throughout most of Nine Mile Canyon (Chart 2). Recently, Remy (1989a and Chapter 6) recognized that Bradley's (1931) delta facies in the Nine Mile Canyon region, as redefined to include his basal member, consists of two distinct suites of rocks: (1) a lower, 375-m-thick sequence of marginal-lacustrine rocks informally named the Sunnyside delta interval, and {2} an upper, 200-m-thick sequence of marginal- to open­lacustrine rocks informally named the transitional interval {Chart 1, Section C}. 36 The boundary between the units is placed at the C marker, and the B marker subdivides the transitional interval into informal upper and lower portions. In this report the contact between the transitional interval and the overlying upper member is placed at the top of the S1 marker unit. The S1 marker unit is employed for this purpose because the unit is the most prominent strati­graphic marker in this interval of the Green River Formation (Figs. 2-5, 2-6) and because the interval overlying the 81 consists mainly of dark colored mudstone and dolostone (including the Mahogany ledge), which are typical lithologies in the upper member. The Sunnyside delta interval was named for the Sunnyside tar sand deposit on the Roan Cliffs. Surface exposures of the unit consist of sandstone of the Sb (23.6%), Sc (4.0%), Se p 2.8%), and Sf (2.8 %) lithofacies, red and green mudstone of the Mr (7.8%) and Mg (19.0%) lithofacies, respectively, carbonate grainstone, micrite, and stromatolite of the L lithofacies (6.2%), very minor (0.5%) dark mudstone of the la lithofacies, and covered intervals (23.3%) probably underlain mainly by mudstone (Table 2-2). These rocks accumulated in meandering delta distributary channel (Fig. 2-8), delta mouth bar (Fig. 2-9), crevasse splay, overbank and shallow-lacustrine sandsheet, subaerial and subaqueous mudflat, lake-margin carbonate flat, and minor open-lacustrine settings in and adjacent to a large fluvially-dominated delta along the southern shore of Lake Uinta (Remy, 1989a and Chapter 6, 1989b; Chapter 3). In this report the term "Sunnyside delta interval" refers to the stratigraphic interval deposited in the Sunnyside delta in the Nine Mile Canyon region. The Sunnyside delta interval and transitional interval of this report are equivalent to Picard's (1957, 1959) green shale facies. As its name implies, the transitional interval is a zone of transition between the underlying sand-rich Sunnyside delta interval and the overlying 37 Figure 2-8. Sunnyside delta interval in western Nine Mile Canyon immedia­tely west of Measured Section 11. In this location the Sunnyside delta interval consists of tabular sandbodies of the Sb lithofacies (two indicated with arrows), which are interpreted as meandering delta distributary channels, separated by red and green mudstone, thin sandstone, and limestone that accumulated in subaqueous and subaerial mudflat, crevasse splay, overbank sandsheet, and lake-margin carbonate flat environments. The height of the cliff at the extreme right of the photograph is 265 meters. 38 Figure 2-9. Sunnyside delta interval in eastern Nine Mile Canyon opposite Measured Section 9. In this location the Sunnyside delta interval consists of thick amalgamated sandbodies of the Sc lithofacies, which are interpreted as stacked distributary mouth bars, and associated mudstone, thin sandstone, and limestone beds that accumulated in subaqueous and subaerial mudflat, crevasse splay,overbank sandsheet, and lake-margin carbonate flat environments. The cliff on the left side of the photograph is approximately 150 m high. 39 fine-grained, mudstone- and dolostone-rich upper member. The lower transitional interval contains less sandstone (24.2%vs 43.2%) and red mudstone (0.4% vs. 7.8%} and more green mudstone (33.2% vs 19.0%) and limestone (13.7% vs 6.2%} than the underlying Sunnyside delta interval. Measured sections of the lower half of the transitional interval consists of sandstone of the Sb (9.5%), Se {12.4%), and Sf (2.3%) lithofacies, green and very minor red mudstone of the Mg (33.2%) and Mr (0.4%) lithofacies, respectively, carbonate grainstone, micrite, and stromatolite of the L lithofacies (13.7%), dark mudstone and dolostone of the la lithofacies (0.6%), and covered intervals (27.9%} probably underlain mainly by mudstone (Table 2-2). The lower transitional interval is illustrated by Units 83-163 of Measured Section 9 (Appendix 4). The upper part of the transitional interval (i.e. above the B marker), on the other hand, contains less green mudstone (19.8% vs 33.2%), and limestone (4.7% vs. 13.7%), and more dark mudstone and dolostone of the la (6.7% vs 0.6%) and lb (7.5% vs 0%) lithofacies than the lower part of the transitional interval. The upper transitional interval is illustrated by Units 14-29 of Measured Section 4 (Appendix 4). The tran­sitional interval is interpreted to record a major, but gradual, expansion (trans­gression) of Lake Uinta (Remy, 1989a and Chapter 6, 1989b; Chapter 3). Upper Member In Nine Mile Canyon the transitional interval is overlain by approximately 300 m of predominantly fine-grained rocks which generally form light-gray covered slopes (Figs. 2-4, 2-6). Measured sections of this interval consist of dark colort1d mudstone, dolostone, kerogenous laminated dolostone (i.e. oil 40 shale), and minor sandstone, siltstone, and green mudstone of the la (53.5%) and lb (8.6%) lithofacies, minor sandstone of the Sb (4.4%) and Se (0.5%) lithofacies and limestone of the L lithofacies (0.1 %), and covered intervals (32.9%) presumably underlain by mudstone and dolostone (Table 2-2). Measured Section 17 (Appendix 4) illustrates these rocks. These generally fine-grained rocks are interpreted to have been deposited in generally low energy nearshore to offshore open-lacustrine settings (Table 2-1) during a period when Lake Uinta was at its maximum extent (Chapter 3). However, several intervals in the member, including the interval capped by the S2 marker unit and the Horse Bench Sandstone Bed (see below) contain significant amounts of sandstone and siltstone interbedded with green mudstone. The sandstone contains a variety of sedimentary structures, including hummocky cross-stratification (Remy, 1989c; Chapter 4), trough crossbeds, and ripples (wave, current, and combined-flow). The high content of sandstone and siltstone, sedimentary structures indicative of relatively high energy, and the absence of open-lacustrine dolostone suggest that these sandy intervals record major periods of siliciclastic sediment influx into Lake Uinta, perhaps due to decreases in lake level (Chapter 3). Bradley (1931) named these rocks the shaly facies (Chart 1, Section D). The shaly facies is, in part, equivalent to the upper part of the Bradley's (1931) Parachute Creek Member in the eastern Uinta Basin (Chart 1, Section H). Bradley (1931) did not apply the term "Parachute Creek Member" to the rocks overlying his delta facies because the Parachute Creek Member in the eastern Uinta Basin consists predominantly of kerogenous dolostone whereas the interval above the delta facies in the western Uinta Basin consists predominantly of mudstone, siltstone, and lesser dolostone. 41 Dane (1954, 1955) and Ray and others (1956) divided Bradley's shaly facies into the Parachute Creek Member and the Evacuation Creek Member (Chart 1, Section G), which are stratigraphic terms for the upper part of the Green River Formation originally assigned by Bradley (1931) to the formation in eastern Uinta Basin. Cashion and Donnell (1974) later abandoned the term Evacuation Creek Member and reassigned the rocks to the Parachute Creek Member in the eastern Uinta Basin. Weiss and others (1990) did not use the terms "Parachute Creek Member" and "shaly facies" and assigned that part of the Green River Formation between the base of the Mahogany oil­shale zone and the base of the saline facies of Dane (1954, 1955) and Ray and others (1956) to the informal "upper member". This report employs the stratigraphic terminology of Weiss and others (1990) for this portion of the Green River Formation and places the base of the upper member at the top of the S1 marker unit, which is also the base of the Mahogany ledge. The most widespread outcrop and subsurface marker in the upper member is the Mahogany oil-shale bed (Cashion, 1967, Fouch and Cashion, 1979). In the study area this unit occurs 18-32 m above the base of the upper member (as defined by the top of the S1 marker unit) and consists of 1-2 m of black, highly kerogenous, laminated dolostone (see, for example, Units 12-15 of Measured Section 1 O of Appendix 4). The Mahogany bed is the richest and most prominent oil shale in the Mahogany ledge, which consists of several resistant rich oil-shale beds (Cashion, 1967). This interval was named the Mahogany ledge by Bradley (1931, p. 23) because polished surfaces of the rock resemble old mahogany. The S2 marker unit of Fouch and others (1976) occurs 35-60 m above the S1 marker unit. In the study area the S2 is a thin (1 m), ledge-forming, very fine-grained sandstone with ripples (wave, current, and combined-flow), 42 planar laminations, and hummocky cross-stratification (see, for example, Unit 17 of Measured Section 15, Appendix 4) and contains green mudstone in places. The unit consists of several stacked and amalgamated hummocky cross-stratified storm deposits that accumulated in the open-lacustrine environment (Remy, 1989c; Chapter 4). As noted above, the S2 marker unit is equivalent to the 3-bed of Ray and others (1956). The S2 can be traced regionally along the south flank of the basin (Fouch and others, 1976). In surface exposures of the study area the most prominent unit in the upper member is a plateau-forming interval of sandstone and mudstone (Figs. 2-5, 2-6, 2-10) that Bradley (1931, p. 16) named the Horse Bench Sandstone Lentil. Subsequent researchers (Dane, 1955; Cashion, 1967; Fouch, 1975) have referred to this unit as the "Horse Bench Sandstone Bed". In the study area (Fig. 2-1) the resistant Horse Bench Sandstone Bed forms a broad smooth plateau that is overlain and underlain by generally poorly-exposed, slope-forming, mudstone and dolostone (Figs. 2-5, 2-6). The base of the Horse Bench Sandstone Bed occurs approximately 150 m above the base of the upper member (i.e. top of S1 marker unit). It is a 10-20 m thick interval consisting of greenish gray to brown mudstone, siltstone, and sandstone (Fig. 2-10; Measured Sections 5 and 6, and Units 69-73 of Measured Section 17 of Appendix 4). Sedimentary structures in the rocks include wave and current ripples, trough crossbeds, syneresis cracks, and burrows. The top of the Horse Bench Sandstone Bed and equivalent horizons are equivalent to the upper marker of Fouch (1975), which can be traced throughout most of the basin subsurface (Fouch and Cashion, 1979; Fouch, 1981 }. Dane (1954, 1955) and Ray and others (1956) described two tuft zones above the Horse Bench Sandstone Bed. In the region of Gate Canyon, however, the only prominent stratigraphic marker encountered in this 43 Figure 2-10. Horse Bench Sandstone Bed of the upper member in Gate Canyon. See Measured Section 6 (Appendix 4) for a detailed description of the rocks. Jacob staff (1.5 m) for scale (arrow). 44 investigation in the upper part of the upper member is a tuft bed that occurs about 80 m below the top of the member. The tuft is approximately 20-35 cm thick, weathers yellow, and is characterized by abundant biotite crystals in the lower half of the bed (Unit 86, Measured Section 17 of Appendix 4). In this report the top of the upper member is placed approximately 150 m above the top of the Horse Bench Sandstone Bed at the first occurrence upwards of substantial sandstone beds above the Horse Bench Sandstone Bed. The contact is also marked by a change in the weathered color of the rocks. The upper member forms light gray slopes whereas overlying rocks weather light brown. In the region of Nine Mile Canyon the upper member of the Green River Formation is overlain by the saline facies of the Green River Formation of Weiss and others (1990) and by the sandstone and limestone facies of Bryant {in press). The saline facies of Weiss and others (1990) is equivalent to the saline facies of the Uinta Formation of Dane (1954, 1955) and Ray and others (1956). LITHOSTRATIGRAPHY OF THE GREEN RIVER FORMATION: ROAN CLIFFS The upper 500 m of the Roan Cliffs near the Sunnyside tar sand deposit consists of a 470-500-m-thick sequence containing abundant sandstone and mudstone and rare limestone overlain by a 0-30-m-thick sequence containing abundant dolostone and green mudstone (Fig. 2-11; Measured Sections 1 and 2 in Appendix 4; Chart 3). Measured sections of the lower sand-rich sequence consists of sandstone of the Sa (37.7%), Sb (14.8%), Se (8.8%), and Sf {0.4%) lithofacies, red and green mudstone of the Mr (9.7%) and Mg 45 Figure 2-11. Upper Roan Cliffs and Sunnyside tar sand quarry. The quarry and all but the top 0-30 m of the Roan Cliffs consists of interfingering alluvial to marginal-lacustrine deposits of the Colton and Green River Formations. Thick sandbodies of the Sa lithofacies are exposed in the quarry and over­lying interval (one sandbody indicated with an arrow) and are interpreted as non-sinuous channels on an upper delta to alluvial plain. The top 0-30 m of the Roan Cliffs at this location consists predominantly of dark mudstone and dolostone and is stratigraphically equivalent to the lower part of the upper member in Nine Mile Canyon. The portion of the Roan Cliffs shown is approximately 500 m high. 46 (9.7%) lithofacies, respectively, limestone of the L lithofacies (2.9%), dark mudstone of the la lithofacies (0.6%), and covered intervals (15.4%) that are probably underlain mainly by mudstone (Table 2-2). These rocks are interpreted to have been deposited in non-sinuous channels, meandering delta distributary channels, crevasse splays, overbank sandsheets, subaerial and subaqueous interchannel mudflats, and rare lake-margin carbonate flats in a lower delta plain to alluvial setting (Table 2-1, Chart 3, Chapter 3). A measured section of the dolostone-rich interval at the top of the Roan Cliffs (Measured Section 2, Units 81-95, Appendix 4) consists of sandstone of the Se lithofacies (4.4%), green mudstone of the Mg lithofacies (24.3%), carbonate grainstone and micrite of the L lithofacies (15.7 %), and laminated and structureless dolostone and dark mudstone of the la (7.8%) and lb (47.8%) lithofacies. These rocks are interpreted to have been deposited in overbank and shallow-lacustrine sandsheet, subaqueous mudflat, lake­margin carbonate flat, and proximal open-lacustrine environments (Table 2-1, Chapter 3). The lower green mudstone- and limestone-rich part of this sequence are interpreted to have accumulated in a shallow nearshore­lacustrine setting and the upper dolostone-rich part of the sequence is inter­preted to have accumulated in a proximal open-lacustrine setting (Chart 3). The stratigraphic sequence exposed in the upper Roan Cliffs near the Sunnyside tar sand deposit has been variously placed in the upper part of the Colton or Wasatch Formation and lower part of the Green River Formation (Holmes and others, 1948; Williams, 1950; Abbott and Liscomb, 1956; Covington, 1975; Banks, 1981 ), in the upper black shale facies of Picard (1955, 1959) {Hendel, 1957; Murany, 1964), and in the lower part of the main body of the Green River Formation (Campbell and Ritzma, 1979; Ryder and others, 1976; Jacob, 1969). Recently Weiss and others (1990) mapped the 47 uppermost fine-grained sequence at the top of the cliffs as the upper member of the Green River Formation, the 200-m-thick sequence underlying the upper member as the middle member of the Green River Formation, and the underlying rocks as the Colton Formation. Most researchers (Jacob, 1969; Fouch and others, 1976, their Fig. 2-2; Campbell, written communication, 1986; Weiss and others, 1990) agree that the Mahogany oil-shale bed occurs near the top of the Roan Cliffs. The same oil shale was also mapped by Winchester (1923, his plate XVI). In the Roan Cliffs above the Sunnyside tar sand quarry the Mahogany oil-shale bed is approximately 80 cm thick and consists of laminated, kerogenous dolostone (i.e. oil shale), structureless dolostone, and brown laminated dolostone or shale (basal 80 cm of Unit 83, Measured Section 2 in Appendix 4). The Mahogany is underlain by limestone and overlain by green mudstone. The presence of the Mahogany oil-shale bed at the top of the Roan Cliffs allow the stratigraphic section at the Roan Cliffs to be correlated with the Green River Formation in the region of Nine Mile Canyon (Chart 3). This correlation demonstrates that the dolostone- and green mudstone-rich interval at the top of the Roan Cliffs is stratigraphically equivalent to a portion of the lower part of the upper member of the Green River Formation in the Nine Mile Canyon region (Weiss and others, 1990). The underlying interfingering Green River and Colton Formations, in which the Sunnyside tar sand deposit occur, are stratigraphica!ly equivalent to the lowermost portion of the upper member, all of the transitional interval, and the upper half of the Sunnyside delta interval. The fact that lithofacies characteristic of the lower delta plain assemblage (i.e. lithofacies L, Mg, and Sb) are more abundant in the upper half of the interfingering Colton and Green River Formations interval than in the lower half and lithofacies characteristic of the upper delta/alluvial plain 48 assemblage (i.e. lithofacies Mr and Sa) are more abundant in the lower half of the interval than in the upper half (Chart 3) indicate that the expansion (transgression) of Lake Uinta indicated by the transitional interval in Nine Mile Canyon also affected sedimentation in the region that is now the Roan Cliffs. As noted above, Weiss and others (1990) mapped the rocks above the Mahogany oil-shale bed at the Roan cliffs near Sunnyside as the upper member of the Green River Formation and the sandstone-rich sequence below the Mahogany as the middle member of the Green River Formation underlain by the Colton Formation. The middle member as mapped by Weiss and others (1990) is approximately 200 m thick at this location. However, Measured Sections 1 and 2 of this report (Appendix 4) show that there is no easily identifiable consistent lithologic break in the stratigraphic section that can be employed to distinguish the middle member from the Colton Formation. Moreover, lithofacies Sa, which is typical of inferred upper delta plain to alluvial deposits of the Colton Formation, occur within 100 m of the top of the Roan Cliffs (see, for example, Unit 63 of Measured Section 2, Appendix 4). Rather than having a sharp break between the Green River and Colton Formations, the upper Roan Cliffs beneath the fine-grained upper member of the Green River Formation consists of extensive interfingering between rocks typical of the Green River Formation and those typical of the Colton Formation. Therefore, in this report no attempt has been made to differentiate the middle member of the Green River Formation from the Colton Formation. The entire 475-500-m-thick sequence beneath the upper member is simply referred to as the "interfingering Green River and Colton Formations" in Chart 3. The S1 and S2 marker units and limestone markers B and C pinch-out or lose their identity somewhere between the Roan Cliffs (Measured Sections 1 and 2) and Measured Section 14, which is approximately 11 km north of the 49 Roan Cliffs (Fig. 2-1; Chart 3). The carbonate marker unit could not be confidently identified in the Roan Cliffs beneath Measured Sections 1 and 2. The Mahogany oil-shale bed is. therefore, the only stratigraphic marker in the Green River Formation that can be confidently identified along the Roan Cliffs near the Sunnyside tar sand quarry. CHRONOSTRATIGRAPHY OF THE GREEN RIVER FORMATION Unlike the upper member, the lower part of the Green River Formation (carbonate maker unit, Sunnyside delta interval, and transitional interval) does not contain tuffs which may be radlometrically dated. However, paleontological data may be used to roughly constrain the age of these rocks (Fig. 2-12). Analyses of microfossils suggest that the Paleocene-Eocene boundary occurs in the upper third of the Colton Formation on the south flank of the basin (Ryder and others, 1976, p. 497). This interpretation is supported by the presence of late Paleocene nonmarine molluscs in the underlying Flagstaff Member of the Green River Formation in Price Canyon (Fouch and others, 1987). In the southern Uinta Basin the Paleocene-Eocene boundary occurs approximately 550 m below the top of the carbonate marker unit (Fouch, 1981 ). In the study area the interval between the top of the carbonate marker unit and the top of the transitional interval is approximately 550 m thick. The 1, 100 meters of rocks between the Paleocene-Eocene boundary, which Berggren and others (1985) place at approximately 58 Ma, and the top of the transitional interval, which radiometric dates on tuffs place at approximately 47.5 million years (see below) accumulated in about 10.5 million years. These data suggest a rock accumulation rate of approximately 50 CHRONOSTRATIGRAPHY OF PART OF THE GREEN RIVER FORMATION, SOUTH-CENTRAL UINTA BASIN PALEOCENE & EOCENE ~ ~ m TIME SCALE CHRONOSTRATIGRAPHIC DATA :..._ lJ Cll (from Berggren et al. 1985) c z-;-; f-!--u~-,--=.;=--..-~-'--~....:+-~~~~~~~~~~~~~~~~~~-.-~~~~~~~~--1z~~~ - RADIOMETRIC PALEONTOLOGICAL -; 0 > ~E~ North DATING DATA !:§~m~ American - ...... ""' ~ ~ Epochs land Tuff 91 m Tuff 69 m Tuff 260 m ?!i ~ !:2 e1 13 0 iS mammal Curly under below top of above top of z !j ;!:! m w stages tuft Wavy tuft H.B. SS upper mbr. upper mbr. ;n < ~ C?l 1 1 2 2 3 2 2 2 3 4 5 6 7 ;!?:~ 34- 36- 38- OLIG. CHADRON IAN UJ 5r----- 40- 42- 44- r-- DUCHES· NEAN UJ _J UINTAN ______ I- _____ f __ -I -I- ___________ ~43 Ma . I I I upper ,_ 0 UzJ Q UJ ::.! (.) 0 BRIDGER- 46- 48- so- UJ IAN - ~ WASATCH cr: IAN 54- < UJ-- 56- 58 _ ,__ __, CLARK­i: ni::i1<1A"1 w w TIFFAN-jj 5 IAN u -- ?--- 0 - TORREJ- ~ ~ -<?NJf..N_ - a.. < 66 -r---UJ-r_P_U_E_R_C_A_N-t 60- 62- 64- LATE 68- CRET - - - - - --l - - - - - -.- base of carbonate marker unit LEGEND H B SS = Horse Bench Sandstone Bed Flagstaff Mbr/~ of Green : River Fm. , North • Horn : Fm. j I I member G = lower part of Green River Formation • carbonate marker unit, Sunnyside delta interval, and transitional interval BG basal Green River Formation = beneath carbonate marker unit Data sources used to construct chart: 1. 40Arl39Ar radiometric dates on tufts (O'Neill and others, 1981 ), 2. recalibration of K/Ar radiometric dates on tufts of Mauger (1977), as reported in Krishtalka and others (1987), 3. fission track ages of zircons in tufts (Bryant and others, 1990, their Table 1), 4 Bridgerian or possibly latest Graybullian (early Wasatchian) turtles in Sunnyside delta in Nine Mile Canyon (identified by J. H. Hutchison, written communication, 1989), 5. early Eocene palynomorphs in attrital coal in basal Green River Formation beneath carbonate marker unit, Indian Canyon (Fouch and others, 1976, p. 371 ), 6. analysis of palynomorphs, ostracodes, charophytes, and mollusks indicate age of basal part of North Hom Formation is Late Cretaceous (Maestrichtian), upper part of the North Horn Formation is middle to late Paleocene and Flagsstafl Member of the Green River Formation is late Paleocene in Price Canyon (Fouch and others, 1987), 7. Bridgerian fauna occurs in Green River Formation 82 m below Mahogany oil shale bed in eastern Uinta Basin (Krishtalka and others, 1987). Figure 2-12. Chronostratigraphy of the Green River Formation in the south­central Uinta Basin. 51 105 meters/million years. This estimate is supported by Bradley (1929), who estimated that fluvial rocks above and below the Green River Formation accumulated at a rate of about 1 foot/3,000 years (101.6 meters/million years). Assuming that the generally sand-rich lower part of the Green River Formation accumulated at about the same rate as the underlying rocks, the 700 meters of the lower part of the Green River Formation (base of carbonate marker unit to top of transitional interval) accumulated in about 6.5 million years, suggesting an age for the base of the main body of the Green River Formation in the region of Nine Mile Canyon of very roughly 54.0 Ma. The upper member contains several tufts which serve as regional stratigraphic markers. Some of these tuffs have been radiometrically dated (Mauger, 1977; O'Neill, 1980; O'Neill and others, 1981; Bryant and others, 1990), thereby providing chronstratigraphic control on the upper member. These data are shown on Figure 2-12 and are discussed below. The curly tuft occurs between the 81 marker unit and the Mahogany oil shale bed (O'Neill, 1980) (Chart 1, Section C). The tuft is 2.5 to 46 cm thick and characterized by undulatory upper and lower contacts and contorted bedding (Cashion, 1967, p. 16). A mean 40Ar/39Ar date on biotites from the tuft in Gate Canyon was initially reported by O'Neill {1980) as 46.2 +/- 0.7 Ma. O'Neill and others (1981) subsequently reported a 47.2 Ma date for the same tuff. The later date presumably represents a reevaluation of the data originally reported in O'Neill (1980) and is therefore the date use in this report. The Curly tuft lies a little above the 81 marker unit and is therefore a little younger than the base of the upper member, suggesting that the age of the base of the member is approximately 47.5 Ma in the Gate Canyon area. The wavy tuft occurs approximately 55 m above the Mahogany oil shale bed in Gate Canyon (O'Neill, 1980, his Fig. 32). The tuff averages 30 cm thick 52 (O'Neill, 1980) and is characterized by intercalated stringers of marlstone which accentuate the wavy bedding surfaces produced by plastic flowage or differential compaction (Cashion, 1967, p. 16). O'Neill (1980) obtained a mean 40Ar/39Ar date of 46.2 +/- 0.5 Ma from biotite separates from this tuff. O'Neill and others (1981) subsequently reported a date of 46.7 Ma for the same tuff. The later date is used in this report for the reason discussed above. Recalibration of Mauger's (1977) K/Ar dates on biotites from the wavy tuff in Gate Canyon (his sample RLM-7-70) and Indian Canyon (his sample RLM-2- 70) yielded dates of 46.0 +/- 0.9 and 44.7 +/- 1.0 Ma, respectively (reported in Krishtalka and others, 1987, their Table 4.1 ). Bryant and others (1990, their Table 1) obtained a zircon fission track age of 42.3 +/· 2.0 Ma for the wavy tuff in Indian Canyon (their locality 23). They noted, but did not offer an explanation for, the discrepancy between their results and those of Mauger (1977) and O'Neill and others {1981 ). Excluding the anomalous zircon fission track age of Bryant and others (1990), the wavy tuff has a mean age of approx­imately 46.2 Ma, which is in reasonable agreement with a presumed date of 47.5 Ma for the base of the upper member based on the curly tuft (see above). Recalibration of Mauger's (1977) K-Ar date for an unnamed tuff (his sample RLM-2-69) 91 m below the base of the Horse Bench Sandstone Bed in Dane's (1955) Indian Canyon section yielded an age of 45.9 +/- 0.9 Ma (recalibrated date reported in Krishtalka and others, 1987, their Table 4.1 ). This tuff occurs 7 m above the wavy tuff, which occurs 98 m below the Horse Bench Sandstone Bed in Dane's (1955) Indian Canyon section (Mauger, 1977, his Table 1 ). Recalibration of Mauger's (1977) K-Ar date for a tuff (his sample RLM-1-69) 69 m below the top of Dane's (1954, 1955) Evacuation Creek Member (upper part of upper member of this report} in Indian Canyon yielded a date of 43.1 +/- 1.3 Ma (Krishtalka and others, 1987, their Table 4.1 ). 53 Recalibration of Mauger's (1977) K-Ar date on a tuff in Indian Canyon (his sample RLM-8-70) which occurs about 19 m below the the top of Dane's (1954, 1955) limestone-sandstone facies of the Uinta Formation yielded a date of 42.8 +/-1.0 Ma (Krishtalka and others. 1987, their Table 4.1 ). This tuff is approximately 260 m above the top of the upper member as defined in this report. Bryant and others (1990, their Table 1) obtained a zircon fission track age of 42.8 +/- 2.2 Ma for the same tuff in Indian Canyon (their locality 22). The top of the upper member is thereby bracketed by ages of tuffs above the wavy tuff of 45.9 +/- 0.9 Ma and 43.1 +/- 1.3 Ma and by two age estimates of about 42.8 Ma for a tuff substantially above the top of the member. These data suggest an age of about 43 Ma for the top of the upper member in the study area. To summarize, analyses of published paleontological and radiometric age data from the Green River Formation suggest a date of about 54.0 Ma for the base of the carbonate marker unit, a date of about 47.5 Ma for the contact between the transitional interval and the upper member, and a date of about 43 Ma for the top of the upper member in the study area (Fig. 2-12). This interval extends from late early Eocene to the upper half of the middle Eocene and from the middle Wasatchian to the late Uintan North American land mammal stages (time scale of Berggren and others, 1985). The conclusion that the interval between the base of the carbonate marker unit and the top of the transitional interval spans the late Wasatchian, all of the Bridgerian, and a portion of the early part of the Uintan North American land mammal stages is supported by: (1) the presence of Bridgerian or latest Graybullian {early Wasatchian) turtles in the Sunnyside delta interval (J. H. Hutchison, written communication, 1989), (2) a Bridgerian mammal fauna collected 82 m below the Mahogany oil shale bed in eastern Uinta Basin (Krishtalka and others, 54 1987, p. 101 ), and (3) early Eocene palynomorphs in attrital coal beneath the carbonate marker unit in Indian Canyon {Fouch and others, 1976, p. 371 ). SUMMARY AND CONCLUSIONS 1. The carbonate marker unit (Fouch and others, 1976; Ryder and others, 1976) marks the base of the main body of the Eocene portion of the Green River Formation in the south-central Uinta Basin. It consists of approximately 130 meters of ostracode and ooid grainstone and micrite, green mudstone, sandstone and siltstone, and uncommon dark laminated mudstone and kerogenous laminated dolostone {oil shale). These rocks accumulated along the fluctuating southern shore of Lake Uinta in lake­margin carbonate flat, subaqueous mudflat, crevasse splay, overbank and shallow-lacustrine sandsheet, and delta distributary channel settings. Handel's {i 957) upper black shale of Peters Point Gas Field is equivalent to the carbonate marker unit, and the distinct change in the weathered color of the rocks from light gray below to light brown above which marks the top of the carbonate marker unit in surface exposures is equivalent to the carbonate marker of Ryder and others (1976) in the basin· s subsurface. 2. In the region of Nine Mile Canyon the delta facies of Bradley (1931 ), as redefined to include his basal member, consists of two distinct suites of rocks: (1) a lower, 375-m-thick sequence of marginal lacustrine and alluvial rocks informally named the Sunnyside deltaic interval, and (2) an upper, 200-m­thick sequence of marginal- to open-lacustrine rocks informally named the transitional interval. In the Nine Mile Canyon region the Sunnyside delta interval consists of sandstone, red and green mudstone, and shallow-water 55 carbonate deposited in a large fluvially-dominated delta system along the southern shore of Lake Uinta. The transitional interval is characterized by an upward increase from the base of the unit in the amount of open-lacustrine dolostone, kerogenous laminated dolostone (oil shales), and dark-colored mudstone and a decrease in the amount of marginal-lacustrine green mudstone and shallow-water limestone. These lithologic changes record a major, but gradual, expansion of Lake Uinta. 3. Three transgressive shallow-water limestones in the Sunnyside delta interval and transitional interval serve as local chronostratigraphic markers. These limestones, which were originally identified by Jacob {1969), are {from base to top): (1) the D marker, which occurs near the middle of the Sunnyside delta interval, (2) the C marker, which marks the top of the Sunnyside delta interval, and (3) the 8 marker, which occurs near the middle of the transitional interval. The boundary between the transitional interval and the overlying upper member of the Green River Formation is placed at the top of the 81 marker unit of Fouch and others (1976), a 4.5-11.5-m-thick trough crossbedded sandsheet. 4. The upper member overlies the transitional interval in the region of Nine Mile Canyon and consists of approximately 300 m of dark-colored mud­stone, dolostone, and kerogenous laminated dolostone (oil shales), and minor sandstone and siltstone that accumulated in a relatively low-energy open­lacustrine setting during a period when Lake Uinta was at its maximum size. The member contains several regional stratigraphic markers: (1) the Mahog­any oil-shale bed, a 1-2-m-thick kerogenous laminated dolostone (oil shale) that occurs 18-32 m above the base of the upper member, (2) the 82 marker unit (Fouch and others, 1976), a thin (1 m) but laterally-persistent, hummocky cross-stratified, very fine-grained sandstone, (3) the Horse Bench Sandstone 56 Bed, a 10-20 m thick interval of sandstone, siltstone, and greenish mudstone that occurs approximately 150 m above the base of the member, and (4) a 20- 35 cm thick unnamed tuff 80 m below the top of the upper member. {5) The upper Roan Cliffs near the Sunnyside tar sand quarry consists of several hundred meters of sandstone, red and green mudstone, and very minor limestone deposited in a lower delta plain to alluvial setting overlain, in places, by a 30-m-thick interval of limestone, green mudstone, dolostone, and minor sandstone deposited in shallow nearshore and open-lacustrine settings. The presence of the Mahogany oil-shale bed near the top of the Roan Cliffs demonstrates that the top 0-30 m of the cliff is stratigraphically equivalent to the lower part of the upper member of the Green River Formation in Nine Mile Canyon and the underlying rocks (including the tar sands), which represent a zone of interfingering between the marginal lacustrine and open­lacustrine Green River Formation and the alluvial Colton Formation, are strati­graphically equivalent to the lowermost upper member, the transitional inter­val, and the upper Sunnyside deltaic interval in the Nine Mile Canyon region. (6) Analyses of published paleontological data and 40Ar/39Ar, K/Ar, and zircon fission-track dates from tufts in the upper member suggest ages of approximately 54.0 Ma, 47.5 Ma, and 43 Ma for the base of the carbonate marker unit, the top of the transitional interval, and the top of the upper member, respectively, in the study area. ACKNOWLEDGEMENTS Acknowledgement is made to the Donors of The Petroleum Research Fund, administered by the American Chemical Society, for support of this 57 research. I would also like to thank Dag Nummedal, J. E. Hazel, C. L. McCabe, R. E. Ferrell, W. B. Cashion, T. 0. Fouch, and J. A. Campbell for their valuable comments and suggestions, J. H. Hutchison for identifying some turtle fragments for me, Xudong Ying, Sean Mclaughlin, and Richard Denne for aiding me in the field, and Xudong Ying for providing me with measured sections i 7, i 8, and 19 of this report. 58 CHAPTER Ill DEPOSITIONAL PROCESSES OF A FLUVIALLY-DOMINATED LACUSTRINE DELTA AND OF TRANSGRESSIVE DEPOSITS IN THE GREEN RIVER FORMATION, SOUTH-CENTRAL UINTA BASIN, UTAH 59 ABSTRACT Detailed lithofacies analysis of over 4,500 m of measured stratigraphic sections of the basal 1 ,000 m of the main body of the Green River Formation (Eocene) in the south-central Uinta Basin documents twelve lithofacies: Sa (nonsinuous trunk streams), Sb (meandering delta distributary channels), Sc (amalgamated delta mouth bars), Sd (regressive delta (front?} sandsheet}, Se (overbank-shallow lacustrine sandsheets}, Sf (crevasse channels and splays), C (passively-filled abandoned channels}, Mg (subaqueous mudflats}, Mr (subaerial mudflats}, L (lake-margin carbonate flats}, and la and lb (open­lacustrine deposits). The carbonate marker unit, Sunnyside delta interval, and lower transitional interval accumulated within and adjacent to a large, fluvially­dominated lacustrine delta informally named the Sunnyside delta. Shallow water depths in the southern half of Lake Uinta attenuated lacustrine waves and currents and resulted in thin delta front deposits. The thin delta front deposits were cannibalized by meandering delta distributary channels in most of the study area. Most of the Sunnyside delta in the study area consisted of a broad, low-gradient, lower delta plain with meandering delta distributary channels, abundant overbank fines deposited in subaerial and subaqueous mudflats, crevasse splays and overbank sandsheets, and lake-margin carbonate flats. Lower delta plain deposits grade updip (southward) into upper delta plain deposits consisting of northeast-flowing nonsinuous trunk streams and associated sinuous fluvial channels, mudflats, and overbank and shallow-lacustrine sandsheets, and grade downdip into shallow nearshore­lacustrine deposits consisting predominantly of subaqueous mudflats, lake- 60 margin carbonate flats, and less common meandering delta distributary channels and overbank and shallow-lacustrine sandsheets. Nonsinuous trunk streams occurred in the updip portion of the study area where a relatively low rate of basin subsidence caused significant reworking of delta plain deposits by fluvial channels that swept across the floodplain more or less continuously, resulting in tabular, amalgamated sandbodies and a sandstone/mudstone ratio of 4:1. Downdip toward the lake the rate of subsidence increased, resulting in tabular to lenticular, generally nonamalga­mated meandering stream sandbodies and a sand- stone/mudstone ratio of 1 :4. As the sandstone/mudstone ratio decreased downdip, cohesive mud stabilized fluvial channel banks, resulting in the change in character of fluvial streams from nonsinuous to meandering. An arid to subarid climate prevented the growth of abundant vegetation on the delta plain and caused intense evaporation on subaerially-exposed mudflats, resulting in the production of saline and alkaline brines which altered detrital clay minerals to analcime and contributed to the salinity and alkalinity of Lake Uinta. Delta front deposits consisting of lenticular stacked and amalgamated delta mouth bars and associated meandering delta dis­tributary channels, overbank and shallow-lacustrine sandsheets, and mudflats occur in one region where presumably deeper water, perhaps resulting from a locally higher subsidence rate, resulted in delta mouth bars thick enough to avoid cannibalization by meandering delta distributary channels. The fact that non-amalgamated mouth bars that are less than 10-12 m thick commonly directly overlie red mudstone suggest that Lake Uinta experienced low amplitude (less than 12 m) fluctuations in relative lake level. These fluctuations in lake level, which were produced by a combination of a moderately high local subsidence and variations in lake volume, caused shifts 61 in shoreline position on the order of 40-50 km. During periods of rapid relative lake level rise the fluvial systems deposited most of their sediment upstream, resulting in the development of extensive, but thin, transgressive shallow­lacustrine carbonates in the central and northern part of the study area. Along the Roan Cliffs transgressions are probably recorded by a change from upper delta plain to lower delta plain sedimentation. Shallow water depths during transgressions attenuated waves and wave-generated currents, thereby preventing the development of shoreface ravinements, beaches, barriers, or extensive lacustrine siliciclastic bars. The regressive portion of each depositional cycle consists predominantly of aggradational upper and lower delta plain, shallow nearshore lacustrine, and delta front deposits. The 200-m-thick transitional interval records a major, but gradual expansion and deepening of Lake Uinta which drowned the Sunnyside delta in the study area. The overlying 300-m-thick upper member of the Green River Formation consists predominantly of mudstone and dolostone that accumulated in a generally quiet, but not necessarily very deep, distal (relative to sources of siliciclastic sediment) open-lacustrine setting. The presence of hummocky cross-stratified storm deposits, and nearshore lacustrine sandbodies indicate that sand and silt were intermittently trans­ported into the open-lacustrine environment, perhaps during regressions triggered by decreases in lake level. INTRODUCTION Basement deformation during the Laramide orogeny (Late Cretaceous­Eocene) broke the Late Cretaceous marine foreland basin into a number of 62 separate non-marine intermontane basins (Dickinson and others, 1988). Blockage of fluvial drainages within basins in the core of the Laramide province produced large fresh to saline lakes (ponded basins of Dickinson and others, 1988). The Green River Formation (Paleocene-Eocene) accumulated in two such large lakes: Lake Uinta in the Uinta and Piceance Basins of northeastern Utah and northwestern Colorado, respectively, and Lake Gosiute in southwestern Wyoming (Figs. 3-1, 3-2). Lake Uinta probably did not have a permanent outlet (Ryder and others, 1976; Johnson, 1985), although water may have flowed out of the lake during high stands in lake level (Dickinson and others, 1988). Following an initial fresh water stage, the salinity of Lake Uinta increased steady throughout most of its history, resulting in the early elimination of saline-sensitive molluscs and ultimately in the precipitation of nahcolite and halite (Johnson, 1985). According to the model proposed by Ryder and others (1976), the lower Green River Formation in the Uinta Basin can be divided into a central core of organic-rich open-lacustrine claystone and mud-supported carbonate surrounded by marginal-lacustrine facies consisting of claystone, sandstone, and carbonate deposited in the deltaic, interdeltaic, and lake-margin carbonate flat environments (Fig. 3-3). The formation is enveloped by alluvial claystone, conglomerate, and sandstone of the Paleocene and Eocene Colton and Wasatch Formations and the Eocene Uinta Formation that were deposited peripheral to the lake. Studies by a number of researchers (Cashion, 1967; Picard and High, 1970; Fouch, 1975; Ryder and others, 1976; Pitman and others, 1982, Dickinson and others, 1986) demonstrate that one of the largest of several fluvial/deltaic complexes in the basin accumulated along the southern shore of Lake Uinta (Fig. 3-1) and was centered around or east of the Green River 63 44° 40° 36° 112° 108° HIGH RELIEF LOW RELIEF ~ LAKES & RIVERS - DELTAS & ALLUVIAL FANS Figure 3-1. Paleogeography of the central Rocky Mountain region during the late early to middle Eocene showing the location of Lakes Gosiute and Uinta and the study area. Modified from McDonald ( 1972). 64 fm Oil/Gas field in Feldspathic ~ Sandstone of SunnysideDelta Position of Numbered • Measured Section Oil/Gas Field in Ouartzose Sand­stone Derived from Uinta Mountains A-A. Position of Cross-Section Figure 3-2. Map showing the location of the Green River Formation outcrop in the south-central Uinta Basin and the study area in Nine Mile Canyon and its tributaries and along the Roan Cliffs. Geologic base map from Hintze (1980). Positions of all oil and gas fields except Peters Point from Grugel and others (1983). Position of Peters Point field from Hendel (1957). 65 04- - MUD-SUPPORTED - GRAIN-SUPPORTED CARBONATE CARBONATE DSANDSTONE ALLUVIAL MARGINAL LACUSTRINE 1---i GREEN AND GRAY L__J MUDSTONE OPEN LACUSTRINE MARGINAL LACUSTRINE ALLUVIAL ~RED MUDSTONE ~ ~DARK GRAY AND ~BROWN MUDS TONE Figure 3-3. Model illustrating the distribution and interpreted depositional environments of open-lacustrine, marginal­lacustrine, and alluvial facies of western Lake Uinta. Width of Lake Uinta in the diagram is approximately 40 km. Vertical exaggeration is between 15 and 20. (From Ryder and others, 1976). (J) (J) (Fig. 3-2). This delta received feldspathic sand from basement rocks then exposed in the Laramide-age San Luis Uplift in southwestern Colorado (Dickinson and others, 1986). The presence of marginal-lacustrine feldspathic sandstone in Pariette Bench {Pitman and others, 1982), Duck Creek (Osmond, 1985), Pleasant Valley {Colburn and others, 1985), and Monument Butte and other oil and gas fields {Oleson, 1986) indicates that the delta extended into the center of the basin, where it interfingered with quartzose sediment derived from the Uinta Mountains to the north (Sanborn and Goodwin, 1965; Koesoemadinata, 1970; Castle, in press). The western edge of the delta occurred west of Willow Creek/Indian Canyon (Ryder and others, 1976, their Figs. 15 and 16) whereas the eastern edge of the delta is poorly constrained. The delta was, therefore, at least 100 km wide and prograded at least 40 km into Lake Uinta at times of maximum regression. In the Nine Mile Canyon region of the south-central Uinta Basin (Fig. 3-2), the western margin of the delta that was centered around the Green River is well-exposed. This portion of the delta was informally named the Sunnyside delta by Remy (1989a and Chapter 6) and consists of approximately 375 m of fluvial/deltaic sandstone and mudstone and carbonate {Chapter 2; Remy, 1989a and Chapter 6, 1989b; Fig. 3-4). Similar marginal-lacustrine rocks serve as the reservoirs for many of the oil and gas fields in the basin subsurface (Fouch, 1975; Franczyk and others, 1989), and their updip equivalents serve as the host for the Sunnyside tar sand deposit on the Roan Cliffs (see below). The fluvial/deltaic rocks are underlain by the carbonate marker unit (Fig. 3-4), a 130-m-thick carbonate-rich sequence which accumulated along the fluctuating southern shore of Lake Uinta before the major influx of sand represented by the Sunnyside delta. The fluvial/deltaic deposits are overlain by the transitional interval and upper member, which 67 meters SALINE FACIES 1000 Top of upper member 900 Tuff (unnamed) ::.<:::::..if- Horse Bench Sandstone Bed 800 Jt Wavy tuff S2 marker unit 700 Mahogany oil-shale bed . .. Curly tuft ..J S1 marker unit z <( Z..J 0 o< i= -> 600 < !:: ffi ~ Cl) I- B marker (base) a: ~~ u0.. I- 500 a: C marker (base) LU ....I (Middle Marker) >a: ~ a: z LU 400 LU I-LaU: ~ C) ~ ....I LU 300 Q D marker (base) LU Q en >- 200 z z :::> Jl'Color Change (/) 100 CARBONATE MARKER 0 UNIT TONGUE OF COL· TON FORMATION TONGUE OF GREEN RIVER FORMATION (LOWER BLACK SHALE FACIES OF ABBOTT (1957)) COLTON FOR· MATION (> 725 m) FLAGSTAFF MEMBER OF GREEN RIVER FORMATION NORTH HORN FORMATION Figure 3-4. Stratigraphy of the Green River Formation and underlying rocks in Nine Mile Canyon, south-central Uinta Basin, Utah. See Chapter 2 for a detailed description of the stratigraphy of the formation. 68 consist of about 500 m of generally fine-grained, carbonate-rich, marginal- to open-lacustrine rocks that accumulated during a major expansion of the lake. Preliminary analyses (Remy, 1989a and Chapter 6, 1989b) indicate that the Sunnyside delta was a large fluvially-dominated shallow water delta that accumulated in a region of low relief in a large, but shallow saline lake. The sedimentology and stratigraphy of this type of lacustrine delta is poorly documented in past investigations. Most previous studies on lacustrine deltas have focused on high-relief tectonic basins (Link and Osborn, 1978; Link, 1984; Hentz, 1985; Demico and Gierlowski Kordesch, 1986; Scholz and others, 1990), glacial lakes (Gustavson and others, 1975; Shaw, 1975), and on relatively small delta systems in small alluvial valley lakes (Tye and Coleman, 1989). Despite several studies of the Green River Formation in the vicinity of Nine Mile Canyon and the Roan Cliffs (Jacob, 1969; Fouch and others, 1976; Ryder and others, 1976; Banks, 1981 ), a detailed lithofacies analyses of the Sunny­side delta and overlying transgressive deposits has not been conducted. Therefore, the purpose of this study is to develop a lithofacies model for fluvial-deltaic and lacustrine sedimentation in shallow, saline southern Lake Uinta. The specific goals of the study are to: (1) describe lithofacies and lithofacies assemblages and interpret them in terms of processes operating in the basin (2) evaluate the effects of base-level fluctuations on sedimentation, and (3) describe the chronological development of south-central Lake Uinta. In addition to providing detailed information on the development of a hitherto poorly-documented type of lacustrine delta system, this study, by providing a detailed description of sandbody geometry and elastic sediment transport mechanisms in the southern Uinta Basin, may aid in the exploration and development of the petroleum resources in the basin. 69 STUDY AREA AND METHODS The study area in the south-central Uinta Basin is bounded on the north by Nine Mile Canyon and the lower 5 km of Gate Canyon, on the south by the Roan Cliffs near Sunnyside, Utah, on the west by the junction of Minnie Maude Creek and Nine Mile Creek, and on the east by the junction of Nine Mile Canyon and North Franks Canyon (Fig. 3-2). The study section in Nine Mile Canyon and its tributaries includes all but the basal 30 m of the carbonate marker unit of Ryder and others (1976, p. 497), the Sunnyside delta interval and transitional interval (as defined in Chapter 2), and the upper member as defined in Chapter 2 (Fig. 3-4). The study section along the Roan Cliffs includes the upper 500 m of the interfingering Green River and Colton Formations and the basal 30 m of the overlying upper member of the Green River Formation (Chapter 2; Chart 3). Seventeen stratigraphic sections (Fig. 2-1) totaling 4514.3 m were investigated in order to determine the lithology, color, bedding thickness, grain size, nature of bounding surfaces, sedimentary structures, geometry, and fossil content of the rocks and to determine the position of stratigraphic markers. The location of the measured sections are described in Appendix 1 and shown on topographic maps in Appendix 2. Symbols used in the sections are shown in Appendix 3, and fifteen of the seventeen sections which form the basis for the work are illustrated in Appendix 4. In order to facilitate description and interpretation, the rocks are divided into 12 lithofacies following the procedure described by Anderton (1985). The lithofacies are described and interpreted below, their primary lithologic and sedimentologic characteristics and interpreted depositional environments are summarized in Table 3-1, and their geographic and stratigraphic distribution 70 TABLE 3-1. Summary of major lilhologic and sedimentologic characteristics and intepretation ol litholacies Lllllofacies Definioon Code Lllllology and Grain Size Sedimentary Structures Geometry and Thickness Other Characterisncs Associated Utllofacies Interpretation Thick (>15 m). Sa Siitstone and sandstone Trough aossbeds, current Thinner sandbodies are Bases sharp and nat to Common: Mr. Mg, Se. Sf Non-sinuous streams scour-enclosed (62-280 μ,mean. 150 μ). and less common climbing lentleular to tabular. thicker scoured. basal IFC Less common: Sb, L. C on upper delta to sandsione some coarsen or fine rtpples. planar laminations, sandbodies are tabular, abundant. scours and IFC Rare: la alluvial plaln upward, most have much Is structureless. no 57"!. of sandbodies are within sandbodies Never: Sc, Sd, lb multiple vertical grain size consistent verlical amalgamated. 15-41 m abundant trends arrangement ol structures thick {mean • 23.2 m) 3-15-m-thick, Sb Siltstone and sandstone Trough aossbeds, current Lenticular to tabular geo- Bases sharp and ftat to Common: Mr, Mg, Se, Sf, L Meandering delta laterally-discontinuous (62-300 μ. mean • 125 μ), and wave ripples, planar metry. sloping channel scoured, lateral accrellon Less common: Sa, Sc, c. distrtbutary channels sandslone 30% nne upward, 7% lamlnallons, much Is edges common, about bedding and basal IFC are Ra1e: la, lb (?) on delta plain and coarsen upward, 43% structureless, many sand- 25% consist of stacked abundant. scours and IFC Never: Sd staeked aevasse have multiple trends, 20% bodies have upward de- sandbodies, mean within sandbodies are splays and overbank have uniform grain size crease In size ol structures thickness: 5.8 m common sand sheets Thick (>15 m). Sc Siitstone and sandstone Current and wave rtpples, Lenticular geometry with Bases generally sharp and Common: Mr, Mg, Se, Sf, Slacked and amal-laterally- lnterfingering (62-275 μ, most less lllan planar and wavy planar irregular edges that Inter- Hat, basal IFC rare, L, Sb gamated lenticular sandslone 150 μ).uniform grain size laminadons, HCS (?). rare finger laterally with other Internal scours and IFC Rare: c delta mouth bars or muldple fining- and trough aossbeds and rocks, thick sand bodies common. rare downstream Never: Sa, Sd, la. lb coarsening-upward cydes convolute bedding, consist of amalgamated accretion bedding wave-generated structures lenticular sandbod les. more common In lower amalgamated sandbodies halves of sandbodies are 15-40+ m thick 3-15-m-lllidl, Sd Sandstone (62-350 μ). Trough aossbeds and Tabular geometry (can be Base always sharp, basal Common: Se. Mg, la. lb Della (front?) deposits laterally-continuous most sandbodies have planar laminations com- traced for over 20 km). scour with IFC common. Never: all other tithofacies that accumulated in sandsrone multiple fining- and mon, ripples. oonvolute consists of slacked Lake Uinla during a coarsening-up cydes, bedding and structureless sandbodies, 4.5-11.5 m regional regression some line upwa1d, some zones occur locally. no thick sandbodles conlain green cons is tent vertical and gray mudstone arrangement of structures Thin (<3 m) Se Siltstone and fine-grained Current ripples, planar Tabular geometry (lateral Individual beds commonly Common: Sa. Sb, Sc, Sd, Fluvial overbank and sandstone w1th0ut sandstone (generally laminations. small-scale continuity commonly > few have sharp and flat bases Sf, Mg, Mr. L. la. C deltaic sandsheets that basal or internal under 125 μ),most trough aossbeds, and 100 m), lithofades Is and tops, lithofades Rare: lb accumulated 1n nuvial. scour. coarsernng sandbodies have uniform mudcracks common, 0.5-3.0 m thick, individual generally encased In lower delta plain. and upward grain size. or grain size, few tine locally abundant wave beds are a few cm to 3.0 m muds tone Shallow lacustrine accretion bedding upward rtpples and wavy planar thick (but most are less settings laminations than 1.5 m thick) Thln(<3m) Sf Siltstone and fine-grained Same as lithofacies Se Tabular to lenticular Basal scour and amal· Common: Sa, Sb, Sc, Sa, Crevasse splays, sandstone with basal sandstone (generally less except trough crossbeds geometry. lithofacies Is gamauon of sandstone Se, Mg, Mr, L, la. C crevasse splay or internal scour. than 175 μ), most have more common 0.5-3.0 m thick, individual beds are common, Rare: lb channels. and small, coarsening upward uniform grain size, some beds are as much as 3.0 m doWnstream accretion della dlstrlbutaty grain size. or fine or coarsen upward thick locally abundant, channels that accum· accretion bedding lithofacies generally ulated in ftuvial, lower encased In mudstones delta plain, and stial· low lacustrine semngs -..,j TABLE 3-1. Summary of major lithologic and sedimentologic characteristics and intepretation ol lithofac1es, continued lilhotacies Definition Code Lithology and Graln Size Sedimentary Structures Geometry and Thickness Other Characteristics Assooated llthofacies lnterpretatiOn Sand- and/or c Red and green muds tone. Mudsronelsgenerally Mudstone-. sandstone-, Scours generally cut Common·. Mg, Mr, Se, Sf, Passively-filled mud-tilled channel siltstone, and fine-gralned structureless, sandstone and siltstone-filled chan- intertledded sandstone l, Sa. Sb, Sc(?) abandoned Channels sandstone (generally less and siltstone have ripples nets, size of channels and mudstone. basal IFC Never: la, lb, Sd (most appear to be than 150 μ) and planar laminations, varies from few meters common crevasse channels) and are commonly wide to about 100 m wide structureless by 10 mdeep Green mudstone Mg Green, greenish gray, and Most mudStone Is Tabular geometry. Base and top of individual Common. all litholacies Shallow water sut>- gray mudstone. structureless, rare planar llthofacies Is o.5 to 25 m beds are sharp to except lb aqueous mudhats in •r sandstone, faminadons, rlppleS, small thick, individual beds are a gradallonal, ostracodes Rare: lb interdistributary bays, in siltstone, limestone, and burrrows, rootlets (?), 1-cm to 5 m thick common in mudstone shallow nearshore red and purple mudstone mudcracks, and syneresis portions ol lhe lake. and aackS perhaps in delta plain ponds and lakes Red mudstone Mr Red and purple Same as lltholades Mg Same as lltholacies Mg Base and top of Individual Common: all lilholades lntermlnently mudstone, minor beds Sharp to gradational, except l, la, lb subaer1aJly-exposed sandstone, siltstone, ostracodes rare Rare:l mudttats limestone, and green, Never: la, lb greenish gray, and tight gray mudstone Limestone l Ostracode,oold, lntraclast, Ripples, small-scale Tabular geometry for both Bases or beds generally Common: all lllholades and pellet gralnstone, trough aossbeds, planar litholades and individual nat and unscoured, except Mr. la, lb limes tones deposited in mlc:tlte, and stromatolite, and wavy planar beds, lllholacies Is 0.5-25 complex interbeddlng and Rare: Mr, lb, lb shallow, quiet to minor thin beds of faminadons, and HCS (?) m thick, Individual beds are lnter1arninations of wave-agitated water In sandstone. slllstone, occur In gralnstones, some a few an to a lew m thick different limestone types lnterdlstrlbutary bays, in green mudstone, and mlcrite has planar common nearshore regions or the dolostone (Including oil faminallons but most Is lake, and perhaps in shale) strucl!Jreless, stromalllllte delta plain ponds and has algal lamlnallons lakes Brown and gray la Gray IO brown mudstone t.lJci1 dolostone and BOlh lltholades and beds Some coarsening and Common: lb, Mg, Se, Sd, Proximal opan-lacus-mudstone, dolostone and dolostone (including mudstone Is struerureless, are tabular In geometry. fining upward trends, Sf tr1ne environment: cat· (<30%), and minor oll shale). minor green some has planar litholades Is 0.5 to over lndlllidual beds commonly Less common: Sb, L bonate and sillciclastic sandstone and muds tone, limestone, laminations In places, 100 m thick, Individual have Sharp nat bases and Rare: Sa, c. Sc mud deposited in low slllstone sandstone, and siltstone sandstones have a variety beds are as much as 10 m tops and are laterally Never: Mr energy nearshore to off-structures Including thick continuous,ostracodes shore regions of lake, ripples, planar and wavy abundant in places occasional storm trans-planar laminations, HCS, port of sand into lake and trough crossbeds Distal open-lacustnne Brown and gray lb Similar to lilholacles la Same as llthOfades la Same as litholacies la Same as lllholades la Common: la, Sd environment; same as JRJdstone, dolostone except more dolostone less common: Mg, Se, Sf. lithofades la except (>30%), and minor and less gray to brown l generally deeper water sandstone and mudstone, siltstone, Rare: Sa. Sb, Sc. (?) and lower energy siltstone sandstone, and green Never: Mr, C mud stone -.J N are shown in Table 3-2. The lithofacies are grouped into five depositional assemblages (Fig. 3-5; Charts 2, 3) which are described and interpreted below. Photomosaics of the walls of Nine Mile Canyon and its tributaries and the Roan Cliffs were used to analyze the geometry of the rocks and to trace stratigraphic markers. Limestones, tuffs, distinctive sandstone units, and other types of lithologic markers were used to correlate the sections (Chapter 2, Appendix 1 ). The stratigraphic position of the markers employed in this study are listed in Appendix 1 and shown in Figure 3-4 and correlations of the measured sections are shown in Charts 2 and 3. X-ray diffraction analyses were conducted to determine the mineralogy of 76 samples of mudstone, carbonate, siltstone, and sandstone (Remy and Ferrell, 1989, and Chapter 5). Thin section analyses were conducted to determine the mineralogy, texture, and grain size of the rocks. DESCRIPTION AND INTERPRETATION OF LITHOFACIES Introduction The rocks of the Green River and Colton Formations in the study area are divided into 12 lithofacies (Table 3-1) following the procedure described by Anderton (1985). The first-order division of the rocks is based on lithology and geometry: sandstone (lithofacies S). sand- and/or mud-filled channel (lithofacies C), mudstone (lithofacies M), limestone (lithofacies L), and interbedded brown and gray mudstone, dolostone, and minor sandstone and siltstone (lithofacies I). The S lithofacies is further divided on the basis of 73 TABLE 3-2. Stratigraphic and geographic distribution of lithofacies Nine Mile Canyon and tributaries 1 ~IC carbonate Sunnyside transitional interva13 I marker unit delta interval lower upper Sa - - - - Sb 12.5% 23.6% 9.5% 10.7% Sc 4.0% - - Sd - - 7.8% Se 9.9% 12.8% 12.4% 9.4% Sf 5.7% 2.8% 2.3% 1.8% c - - - - Mr - 7.8% 0.4% - Mg 14.2% 19.0% 33.2% 19.8% L 16.3% 6.2% 13.7% 4.7% la 25.3% 0.5% 0.6% 6.7% lb 5.4% - - 7.5% Covered interval 10.7% 23.3% 27.9% 31.6% 11ncludes measured sections 4, 6, 7, 8, 9, 10, 11, 13, 14, 15, 16, and 17. 2 1ncludes measured sections 1 and 2. upper member - 4.4% - - 0.5% - - - 0.1% 53.5% 8.6% 32.9% 3 soundary between upper and lower parts of transitional interval placed at the B marker. Roan Clitts2 lnterfingering Green upper member of River and Colton Fms. Green River Fm. 37.7% - 14.8% - - - - - 8.8% 4.4% 0.4% - - - 9.7% - 9.7% 24.3% 2.9% 15.7% 0.6% 7.8% - 47.8% 15.4% - -...J ~ Lower delta plain assemblage Upper delta plain assemblage Lower delta plain assemblage REGRESSION TRANSGRESSION ------------ .. -=~-=-=-=~~~"';,. : -------------------- ~~ti}~~~~~~ -_':. :_;::_;:;_:;_::_-::. _ -- ...... ------- .. :.· ------------- -------------------­- Eili Red mudstone Im Green mudstone - (lithofacies Mr) - (lithofacies Mg) ~ Limestone ~ Gray to brown mud- (lithofacies L) stone and dolostone (lithofacies la, lb) • Shallow near shore lacustrine assemblage Delta front assemblage Open lacustrine assemblage Shallow near shore lacustrine assemblage Sandstone (lithofacies Sa, Sb, Sc, Se, Sf) Figure 3-5. Model illustrating the distribution of lithofacies assemblages along the south-central shore of Lake Uinta during late early Eocene to early Middle Eocene time. See text for description. Width of diagram is approximately 40 km. 75 sandbody thickness: under 3 m thick, 3-15 m thick, and greater than 15 m thick. Sandbodies less than 3 m thick are classified as lithofacies Sf if they exhibit basal or internal scour, accretion bedding, and/or an upward­coarsening grain size trend, and are classified as lithofacies Se if they do not exhibit any of these characteristics. Sandbodies that are 3 to 15 m thick are classified as lithofacies Sd if they exhibit lateral continuity that exceeds 1 O km and as lithofacies Sb if they can not be traced for at least 1 O km. Sandbodies that are at least 15 m thick are subdivided on the basis of the relationship of the sandbody to surrounding rocks: lithofacies Sa occupies scours cut into surrounding mudstone, limestone, and sandstone, whereas lithofacies Sc interfingers laterally with surrounding mudstone and sandstone. The geometry of the six sandstone lithofacies are schematically illustrated in Figure 3-6. Lithofacies M (mudstone) is subdivided on the basis of color: lithofacies Mr consists of red and purple mudstone whereas lithofacies Mg consists of greenish gray, grayish green, and light gray mudstone. Lithofacies I is sub­divided on the basis of the proportion of dolostone: lithofacies la contains less than 30% dolostone whereas lithofacies lb contains at least 30% dolostone. In the following discussion, the lithofacies are described and interpreted in terms of depositional processes and environments. The definition and principal characteristics of the lithofacies are compared in Table 3-1 and their stratigraphic and geographic distribution are quantified in Table 3-2. Thick (> 15 m), Scour-Encased Sandstone {Sa) Description. By definition, lithofacies Sa consists of sandbodies that are at least 15 m thick that occupy scours cut into underlying and laterally adjacent 76 Sa Sd Lateral continuity exceeds 1 0 km Sc -<r§ffi'.§Ep Se and Sf 1-:-:. ·'.>:·:·:-:-:-:-: :·:-: :-:::·-:·:·: ....... ,.:-:-:·:n -:-.. :-::-:-: ..... ·.,., ..... :---:-:-:-:- ..............................