AN ABSTRACT OF THE THESIS OF DONALD ALBERT HARTMAN for the MASTER OF SCIENCE (Name of student) (Degree) in GEOLOGY presented onMc (Major) (Date) Title: STRATIGRAPHY AND STRUCTURE OF THE SALT WELLS ANTICLINE AREA, SWEETWATER COUNTY, WYOMING Abstract approved: Redacted for Privacy Dr/Keith F.Ole s Approximately 4,210 feet of Late Cretaceous and 1,440 feet of Tertiary sedimentary rocks are exposed in the Salt Wells Anticliné area of southcentral Sweetwater County, Wyoming. Late Cretaceous units include the Blair, Rock Springs, Ericson, and Almond Forma- tions of the Mesaverde Group and the Lewis Shale; Tertiary units in- dude the Paleocene Fort Union and the Eocene Wasatch Formations, and the Oligocene or Miocene Bishop Conglomerate. Alluvium, ter- race gravels, and landslide debris are the most extensiveQuaternary deposits. The Late Cretaceous rocks of the Rock Springs Uplift exhibit intricate intertonguing of marine and nonmarine facies, and they re- cord the eastward regression of the Late Cretaceous sea.Inter- tonguing of environments in the region resulted from 1) deposition in a subsiding basin of detritus episodically shed from Laramide source areas to the west and northwest, and 2) periodic pulses of basin subsidence. Rocks of the Blair and Rock Springs Formations record marine depositional environments. Regressive littoral sandstones are found at the base and top of the Blair Formation and at the top of the Rock Springs Formation. Eastward encroachment of fluviatile deposits is marked by deposition of the Ericson and lower Almond Formations. Northerly coarsening of sandstones and southeasterly current direc- tions in the Ericson indicate that the Wind River Mountains area was one probable source area. A second, more westerly source area is indicated by conglomerate lenses and easterly current directions in the upper Ericson Formation and by the thick sequence of continental deposits in the lower Almond Formation. Return of marine condi- tions is recorded by the transgressive marine deposits of the upper Almond Formation and the offshore marine shales and mudstones of the Lewis Shale.The latest Cretaceous rocks exposed on the Uplift record the final regression of the Cretaceous sea.The Cretaceous period ended with uplift of the Rock Springs area. The continental deposits of the Paleocene Fort Union Forma- tion were deposited unconformably along the flanks of the Uplift; in turn, this formation is conformably overlain by the fluviatile red bed deposits of the Eocene Wasatch Formation. Contemporaneously with the deformation of the Uinta Mountains, the Salt Wells folds were superimposed on the southern part of the Uplift.During Oligocene or Miocene the Uplift was truncated by the Gilbert Peak pediment surface.Quaternary fluvial erosion has deeply dissected the Rock Springs Uplift. Stratigraphy and Structure of the Salt Wells Anticline Area, Sweetwater County, Wyoming by Donald Albert Hartman A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science June1968 APPROVED: Redacted for Privacy AssociatProfessor 6f Geology in charge of major Redacted for Privacy Chairman of the Department ofeology Redacted for Privacy Dean of Graduate School Date thesis is presentedM Typed by Donna Olson for Donald Albert Hartman ACKNOWLEDGMENTS The writer wishes to express his appreciation to Dr. K. F. Oles, his major professor, for suggesting the thesis problem and editing the manuscript.Drs. K. F. Oles and P. T. Robinson visited the area, and Drs. H. E. Enlows and L. D. KuIm critically read the manuscript; their helpful suggestions are very much appreciated.Sincere appreciation is extended to the Department of Geology at Oregon State University. The Union Oil Company of California provided financial assist- ance for work on the thesis problem. Specialthanks are due to Messrs. G. H. Feister, L. Brown, and J. P. Gillum of Union Oil Company who visited the thesis area and provided materials from their files.Union Pacific Railroad Company and Mountain Fuel Supply Company provided additional information of the region. The writer is particularly grateful to his wife, Ann, who assisted him in the field and in preparation of the manuscript. TABLE OF CONTENTS Page INTRODUCTION 1 Location and Accessibility 1 Previous Work 1 Purpose, Scope and Methods 3 Topography and Drainage 4 Climate and Vegetation 5 REGIONAL SETTING 8 STRATIGRAPHY 12 Subsurface Stratigraphy 12 Thesis Area Stratigraphy 14 Blair Formation 15 Distribution and Occurrence 17 Lithology and Thickness 18 Middle Shale Member 19 Chimney Rock Sandstone 20 Age and Correlation 22 Depositional Conditions 23 Rock Springs Formation 24 Distribution and Occurrence 25 Lithology and Thickness 26 Black Butte Tongue 28 Brooks Sandstone 30 Coulson Tongue 32 McCourt Sandstone 33 Age and Correlation 36 Depositional Conditions 37 Ericson Formation 38 Distribution and Occurrence 41 Lithology and Thickness 42 "Transition" Zone and "Rusty" Zone 44 Trail and Canyon Creek Members 45 Directional Characteristics of Ericson Cross-bedding 46 Petrography 51 Age and Correlation 57 Depositional Conditions 57 Almond Formation 61 Page Distribution andOccurrence 62 Lithology and Thickness 63 AlluvialMember 64 TransitionalMarine Member 65 Age and Correlation 68 DepositionalConditions 69 Lewis Shale 71 Distribution and Occurrence 72 Lithology andThickness 72 Age and Correlation 74 Depositional Conditions 75 Fort Union Formation 75 Distribution andOccurrence 76 Character and Thickness 77 Age and Correlation 79 DepositionalConditions 80 Wasatch Formation 81 Distribution and Occurrence 81 Character and Thickness 82 Age and Correlation 83 Depositional Conditions 83 Bishop Conglomerate 84 DistributionandOccurrence 84 Character andThickness 85 Age and Correlation 87 Depositional Conditions 88 Quaternary Deposits 89 Terrace Gravels 89 Landslide Debris 90 Alluvium 90 STRUCTURAL GEOLOGY 92 Folding 92 Faulting 93 Jointing 93 Deformational History 95 GEOLOGIC HISTORY 97 Page ECONOMIC GEOLOGY 104 Petroleum 104 Coal 106 Sand and Gravel 106 BIBLIOGRAPHY 109 LIST OF FIGURES Figure Page 1. Breached axial area of the Rock Springs Uplift. 6 2. West-facing cuesta along the east flank of the Rock Springs Uplift. 6 3. View south to Chimney Rock. 19 4. Strike valley of the Black Butte Tongue. 27 5. Brooks and McCourt Sandstones are the basal resistant units of the "White Wall". 27 6. The Brooks Sandstone. 34 7. The McCourt Sandstone. 34 8. View north to the type section of the Eric son Formation. 39 9. The "rusty" zone. 43 10. The dip slope of the Ericson Formation. 43 11. Current directions of the Trail Member. 48 12. Current directions of the Canyon Creek Member. 50 13. Classification of Ericson sandstones. 52 14. The contact between Ericson and Almond Formations. 62 15. Barrier island sandstone in the transitional marine member of the Almond Formation. 70 16. Regolith at the base of the Fort Union Formation. 73 17. The Gilbert Peak pediment surface. 86 18. The contact between Bishop Conglomerate and Ericson Formation. 86 Page 19. Thrust fault along the south flank of Salt Wells Anticline. 94 20. Jointing on the dip slope of the Chimney Rock Sandstone. 94 21. Diagrammatic section of the Late Cretaceous Mesaverde Group in the Salt Wells Anticline area. 98 LIST OF PLATES Plate Page 1. Map of Wyoming showing the location of the Salt Wells Anticline area. 2 2. Major structural features of southwestern Wyoming. 9 3. Geologic map of the Salt Wells Anticline area, Sweetwater County, Wyoming. 108 LIST OF TABLES Table 1. Subsurface section of the Salt Wells Anticline area. 13 2. Stratigraphic section of the Salt Wells Anticline area. 16 3. Modal analyses of a sandstone from the middle of the Chimney Rock Sandstone of the Blair Formation. 22 4. Modal analyses of sandstones of the upper Rock Springs Formation. 32 5. Modal analyses of sandstones of the Trail and Canyon Creek Members. 54 6. Modal analyses of sandstones of the "transition" and "rusty" zones. 56 STRATIGRAPHY AND STRUCTURE OF THE SALT WELLS ANTICLINE AREA, SWEETWATER COUNTY, WYOMING INTRODUCTION Location and Accessibility The Salt Wells Anticline area includes 112 square miles in parts of T. 14, 15 and 16 N. ,R. 102, 103, and 104 W. ,in south- central Sweetwater County, Wyoming (Plate 1).This area lies on the southeastern flank of the Rock Springs Uplift approximately25 miles southeast of Rock Springs, Wyoming. Wyoming State Highway 430 provides access to the area from Rock Springs.In addition there are five county roads in the area including the main road to Clay Basin. Numerous farm roads, jeep trails, seismic lines, and pipe lines are passable by jeep and contri- bute to the accessibility of the area. Previous Work Hayden (1872, 1873), Powell (1876) and King (1878) presented early descriptions of the Cretaceous and Tertiary sequences of the Rock Springs Uplift.Schultz (1907, 1908) in his evaluations of the coal resources of the region, described the structure of the Uplift and established the basic stratigraphic units.Schultz (1920) and Sears (1926) mapped the geology of the southern part of the Uplift and OUTH.KOTA IDAH( BRASKA Plate 1.Map of Wyoming showing location of the SaltWells Anticline area. 3 evaluated the petroleum possibilities and discoveries in and about South Baxter Basin. The first regional study of Cretaceous rocks of the Rock Springs Uplift was made by Hale (1950, 1955) who described the lithologies of the various formations and presented their facies rela- tions.Smith (1961, 1965)in more recent studies,