LITHOLOGIC EVIDENCE OF THE JURASSIC/CRETACEOUS BOUNDARY WITHIN THE NONMARINE CEDAR MOUNTAIN FORMATION, SAN RAFAEL SWELL, UTAH A thesis presented to the faculty of the College of Arts and Sciences of Ohio University In partial fulfillment of the requirements for the degree Master of Science James D. Ayers August 2004 LITHOLOGIC EVIDENCE OF THE JURASSIC/CRETACEOUS BOUNDARY WITHIN THE NONMARINE CEDAR MOUNTAIN FORMATION, SAN RAFAEL SWELL, UTAH BY JAMES D. AYERS has been approved for the Department of Geological Sciences and the College of Arts and Sciences of Ohio University by Gregory C. Nadon Assistant Professor Leslie A. Flemming Dean, College of Arts and Sciences of Ohio University AYERS, JAMES D. M.S. August 2004. Geological Sciences Lithologic Evidence of the Jurassic/Cretaceous Boundary Within the Nonmarine Cedar Mountain Formation, San Rafael Swell, Utah (189 pp.) Director of Thesis: Gregory C. Nadon The Jurassic/Cretaceous boundary in central Utah occurs at a major unconformity within a foreland basin. Paleontological data are absent and the boundary is typically placed at the lower contact of the Buckhorn Conglomerate Member of the Cedar Mountain Formation based on the assumption that this contact represents an erosional unconformity. Lithologic and petrographic evidence from this study indicate the presence of a Stage 6 calcrete and a groundwater silcrete, which both indicate long-term geomorphic stability. These data suggest that the Jurassic/Cretaceous boundary should be placed at the top of the calcrete within the basal Cedar Mountain Shale Member. The fluvial architecture of the strata below and above the boundary suggests that the lower Cedar Mountain Formation records the subtle transition from deposition within the proximal back-bulge depozone during the Late Jurassic to deposition within the distal foredeep depozone during the Early Cretaceous. Approved: Gregory C. Nadon Assistant Professor Acknowledgments I greatly appreciate the patients and support of my committee, family and friends throughout the research and writing of this thesis. To my wonderful girlfriend Kristin, thank you for all the love, understanding, and encouragement. Your faith in my ability to complete this project is greatly appreciated. To Gregory C. Nadon, thank you for your guidance, inspiration, and for providing me the opportunity to work on this exciting project. You have been a wonderful mentor and a great friend. To Xavier Roca, thank you for your assistance and extended discussions in the field. You were a great inspiration. To Elizabeth Gierlowski-Kordesch and David L. Kidder, thank you for your assistance. I benefited greatly from our conversations. 5 Table of Contents Page Abstract…………………………………………………………………………… 3 Acknowledgments…………………………………………………………….….. 4 List of Tables……………………………………………………………………... 7 List of Figures…………………………………………………………………….. 8 Chapter 1. Introduction…………………………………………………………… 11 1.1 Introduction…………………………………………………………… 11 1.2 Purpose....…………………………………………………………….. 17 1.3 Study Area……………………………………………………………. 17 Chapter 2. Previous Work………………………………………………………… 21 2.1 Introduction…………………………………………………………... 21 2.2 Stratigraphy…………………………………………………………… 21 2.2.1 Morrison Formation………………………………………… 21 2.2.2 Cedar Mountain Formation………………………………… 25 2.3 Late Jurassic-Early Cretaceous Foreland Basin Development………. 30 2.4 Nonmarine Sequence-Stratigraphy…………………………………… 33 Chapter 3. Methodology…………………………………………………………. 37 3.1 Fieldwork…………………………………………………………….. 37 3.2 Stratigraphic Data…………………………………………………….. 37 3.3 Sedimentologic Data………………………………………………….. 38 3.4 Petrographic Data……………………………………………………. 38 Chapter 4. Lithofacies Analysis………………………………………………….. 40 4.1 Introduction…………………………………………………………… 40 4.2 Facies A: Conglomerate Facies………………………………………. 40 4.2.1 Introduction………………………………………………… 40 4.2.2 Facies A1: Buckhorn………………………………………… 40 4.2.3 Facies A2: Buckhorn-equivalent……………………………. 51 4.2.3.1 Introduction………………………………………. 51 4.2.3.2 Indurated A2 Conglomerates……………………… 52 4.2.3.3 Poorly Indurated A2 Conglomerates……………… 54 4.2.4 Facies A3: Red Conglomerate………………………………. 57 4.3 Facies B: Sandstone Facies…………………………………………… 62 4.3.1 Introduction………………………………………………… 62 4.3.2 Facies B1: Buckhorn Sandstones…………………………… 62 4.3.3 Facies B2: Buckhorn-equivalent Sandstones……………….. 70 6 Page 4.3.4 Facies B3: White Sandstone………………………………… 71 4.3.5 Facies B4: Red Conglomerate Sandstones………………….. 78 4.3.6 Facies B5: Isolated Sandstone Bodies………………………. 79 4.4 Facies C: Siltstone Facies…………………………………………….. 80 4.5 Facies D: Mudstone Facies…………………………………………… 81 4.5.1 Facies D1: Mudstone……………………………………….. 81 4.5.2 Facies D2: Pebbly Mudstone……………………………….. 82 4.6 Facies E: Carbonate Facies…………………………………………… 85 4.6.1 Introduction………………………………………………… 85 4.6.2 Facies E1: Lacustrine Carbonate……………………………. 85 4.6.2.1 Lower Carbonate………………………………….. 85 4.6.2.2 Middle Carbonate………………………………… 103 4.6.2.3 Upper Carbonate…………………………………. 104 4.6.3 Facies E2: Calcrete…………………………………………. 106 Chapter 5. Lithofacies Associations and Fluvial Architecture…………………… 119 5.1 Introduction…………………………………………………………… 119 5.2 Lithofacies Associations……………………………………………… 123 5.2.1 Unit 1: The Buckhorn Conglomerate………………………. 123 5.2.2 Unit 2: The Buckhorn-equivalent…………………………… 127 5.2.3 Unit 3: The Lower Carbonate………………………………. 129 5.2.4 Unit 4: The Pedogenic Calcrete Profile…………………….. 130 5.2.5 Unit 5: The White Sandstone………………………………. 136 5.2.6 Unit 6: The Middle Carbonate……………………………… 137 5.2.7 Unit 7: The Red Conglomerate…………………………….. 138 5.2.8 Unit 8: The Upper Carbonate………………………………. 142 5.3 Fluvial Architecture…………………………………………………… 143 Chapter 6. Conclusions…………………………………………………………… 150 References………………………………………………………………………… 152 Appendix A: Measured Sections and Cross-sections…………………………….. 160 Appendix B: Paleocurrent Measurements………………………………………... 180 Appendix C: Point Count and Pebble Count Data……………………………….. 188 7 List of Tables Table Page 5.1 Lithofacies assemblage, lithology, and depositional environment of units…… 120 8 List of Figures Figure Page 1.1 Generalized stratigraphic column…………………………………………….. 12 1.2 Diagrammatic cross-section of Late Jurassic-Late Cretaceous foreland basin.. 13 1.3 Generalized map of the Sevier orogenic belt and its foreland basin…………. 15 1.4 Chart of previous chronostratigraphic interpretations………………………... 16 1.5 Location map of the study area……………………………………………….. 18 1.6 Structural map of the Cedar Mountain region………………………………... 19 2.1 Generalized paleogeographic map of the Albian foreland basin system…….. 34 2.2 Nonmarine sequence-stratigraphic diagram………………………………….. 35 4.1 Diagrammatic cross-section of the facies within the study interval………….. 41 4.2 Map showing the location of measured sections……………………………... 43 4.3 a Outcrop photo of Facies A1 and B1…………………………………………. 44 b Close-up photo of Facies A1………………………………………………... 44 4.4 Paleocurrent map for Facies A1 and B1 as well as Facies A2 and B2………… 46 4.5 “Capping” megaquartz cement……………………………………………….. 48 4.6 Schematic section of a pedogenic silcrete……………………………………. 50 4.7 a Outcrop photo of the Indurated A2 Conglomerates and Facies B2…………. 53 b Close-up photo of the Indurated A2 Conglomerates………………………... 53 4.8 Outcrop photo of the Poorly Indurated A2 Conglomerates…………………... 55 4.9 a Outcrop photo of Facies A3………………………………………………… 58 b Outcrop photo of a well cemented portion of Facies A3…………………… 58 4.10 a Outcrop photo of oncoids within Facies A3……………………………….. 60 b Photo of a carbonate coated extraformational chert clast (oncoid)……….. 60 4.11 Paleocurrent map for Facies A3 and B4……………………………………... 61 4.12 a Ternary diagram of QmFL compositions…………………………………. 64 b Ternary diagram showing variations in lithic grain proportions………….. 64 4.13 a Outcrop photo of a highly indurated, silica-cemented area of Facies B1…. 66 b Slabbed sample from a highly indurated, silica-cemented area of Facies B1. 66 4.14 a Multiple generations of fracture-filling silica cements……………………. 67 b Multiple generations of fracture-filling silica cements……………………. 67 4.15 a GS-fabric silcrete………………………………………………………….. 69 b F-fabric silcrete……………………………………………………………. 69 4.16 a Outcrop photo of Facies B3……………………………………………….. 72 b Outcrop photo of Facies B3……………………………………………….. 72 4.17 a Outcrop photo of a conglomerate at the base of Facies B3………………... 74 b Outcrop photo of jasper within an intraformational carbonate clast……… 74 4.18 Paleocurrent map for Facies B3……………………………………………... 76 4.19 a Outcrop photo of Facies D2……………………………………………….. 83 b Outcrop photo of a centimeter-scale laminar calcic horizon……………… 83 9 Figure Page 4.20 Isopach map of the Lower Carbonate……………………………………….. 86 4.21 a Outcrop photo of the Lower Carbonate…………………………………… 87 b Outcrop photo of the Lower Carbonate…………………………………… 87 4.22 a Outcrop photo of desiccation breccia……………………………………… 90 b Outcrop photo of desiccation breccia……………………………………… 90 4.23 a Outcrop photo of fault breccia…………………………………………….. 91 b Photo of a slabbed sample of fault breccia………………………………… 91 4.24 a Outcrop photo of a jasper-filled vugs……………………………………… 93 b Close-up photo of a jasper-filled vugs…………………………………….. 93 4.25 a Outcrop photo of a chert-filled vug………………………………………... 94 b Outcrop photo of isopachous jasper cement………………………………. 94 4.26 Outcrop photo of a massive jasper accumulation…………………………… 95 4.27 Outcrop photo of a laminar jasper horizon………………………………….. 95 4.28 a Ostracodes within the Lower Carbonate…………………………………... 96 b Ostracodes within the Lower Carbonate…………………………………... 96 4.29 Map of pedogenic features within