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Stratigraphy and Depositional Environments of the Late Cretaceous

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Stratigraphy and Depositional Environments of the Late Cretaceous STRATIGRAPHY AND DEPOSITIONAL ENVIRONMENTS OF THE LATE CRETACEOUS (LATE TURONIAN) CODELL SANDSTONE AND JUANA LOPEZ MEMBERS OF THE CARLILE SHALE, SOUTHEAST COLORADO by Russell K. Lewis A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial fulfillment of the requirements for the degree of Master of Science (Geology). Golden, Colorado Date:____________________ Signed:____________________________ Russell K. Lewis Signed:____________________________ Dr. Stephen A. Sonnenberg Thesis Advisor Golden, Colorado Date:____________________ Signed:_________________________ Dr. Paul Santi Professor and Department Head Department of Geology and Geological Engineering ii ABSTRACT Late Cretaceous formations in the Rocky Mountains are of significant importance to petroleum exploration throughout the region. Recent exploration in the Codell Sandstone Member of Carlile Shale, Smoky Hill and Fort Hays Limestone members of the Niobrara and Greenhorn formations has rejuvenated interest in not only their petroleum potential, but also stratigraphy, petrography, biostratigraphy, geochemistry and other disciplines within the geosciences. Throughout most of northern, central and southeastern Colorado and eastern Kansas, the Codell Sandstone represents the final regressive deposit of the Greenhorn cyclothem and the Fort Hays Limestone represents the basal sequence of the Niobrara cyclothem. The intermediate, unconformity bound Juana Lopez Member of the Carlile Shale has been interpreted as a palimpsest deposit, and generally disregarded as a significant stratigraphic interval within the region. Southeast Colorado contains some of the world's best outcrops of Late Cretaceous strata and has been the focus of research for nearly a century. The purpose of this research was to better understand the impact and regional extent of the late Turonian unconformities on the Codell Sandstone and Juana Lopez members, and the implications on previous interpretations of the depositional environments and Late Cretaceous paleogeography. Analysis of outcrop, core, subsurface well logs and support from hand-held X-ray fluorescence geochemistry data indicates that significant faulting, topographic highs and subaqueous erosion removed the Codell Sandstone differentially throughout the region, creating a depositional remnant prior to and during deposition of the Juana Lopez and iii the basal Fort Hays Limestone. The Juana Lopez is a fossiliferous grainstone to calcareous sandstone, deposited in a sediment starved, high-energy, current winnowed, shallow marine shelf environment during the basal transgression of the Niobrara cyclothem. iv TABLE OF CONTENTS ABSTRACT ..................................................................................................................... iii LIST OF FIGURES ..........................................................................................................ix LIST OF TABLES .......................................................................................................... xiv ACKNOWLEDGEMENTS ..............................................................................................xv CHAPTER 1 .................................................................................................................... 1 INTRODUCTION ............................................................................................................. 1 1.1 Study Objectives .................................................................................................... 1 1.2 Area of Investigation .............................................................................................. 1 1.3 Dataset and Procedures ........................................................................................ 2 1.4 Previous Research ................................................................................................. 5 CHAPTER 2 .................................................................................................................. 10 BACKGROUND GEOLOGY .......................................................................................... 10 2.1 Geologic Overview ............................................................................................... 10 2.2 Stratigraphy .......................................................................................................... 13 2.3 Structural Framework ........................................................................................... 20 2.4 Regional Stratigraphic Unconformities ................................................................. 23 CHAPTER 3 .................................................................................................................. 27 SEDIMENTOLOGY ....................................................................................................... 27 3.1 Blue Hill Shale Facies .......................................................................................... 27 3.1.1 Facies BHS-1 – Lower Blue Hill Shale ........................................................... 28 3.1.2 Facies BHS-2 – Lower Blue Hill Shale ........................................................... 28 3.1.3 Facies BHS-3 – Upper Blue Hill Shale ........................................................... 28 v 3.2 Codell Sandstone Facies ..................................................................................... 29 3.2.1 Facies CDL-1 – Lower Codell Sandstone ...................................................... 30 3.2.2 Facies CDL-2 – Lower Codell Sandstone ...................................................... 30 3.2.3 Facies CDL-3 – Upper Codell Sandstone ...................................................... 31 3.2.4 Facies CDL-4 – Upper Codell Sandstone ...................................................... 32 3.3 Codell Sandstone Petrography ............................................................................ 34 3.4 Juana Lopez Facies ............................................................................................. 36 3.4.1 Facies JL-1 – Juana Lopez ............................................................................ 37 3.4.2 Facies JL-2 – Juana Lopez ............................................................................ 39 3.5 Juana Lopez Petrography .................................................................................... 40 3.6 Fort Hays Limestone Facies ................................................................................ 41 3.6.1 Facies FH-1 – Fort Hays Limestone .............................................................. 44 3.6.2 Facies FH-2 – Fort Hays Limestone .............................................................. 45 3.6.3 Facies FH-3 – Fort Hays Limestone .............................................................. 45 3.6.4 Facies FH-4 – Fort Hays Limestone .............................................................. 45 CHAPTER 4 .................................................................................................................. 49 CORE AND OUTCROP STRATIGRAPHY .................................................................... 49 4.1 Primary Outcrops and Core ................................................................................. 49 4.1.1 Portland 1 Core (PC) ..................................................................................... 49 4.1.2 Rebecca Bounds 1 Core (RBC) ..................................................................... 50 4.1.3 Deadman's Curve Outcrop (DCO) ................................................................. 50 4.1.4 Lake Pueblo State Park Outcrop (LPO) ......................................................... 52 4.1.5 Peck Creek Outcrop (PCO) ........................................................................... 53 vi 4.1.6 Pueblo Nature Center Outcrop (PNCO) ......................................................... 54 4.1.7 Verde Road Outcrop (VRO) ........................................................................... 55 4.1.8 Walsenburg Outcrop (WO) ............................................................................ 57 4.2. Secondary Outcrops ........................................................................................... 58 4.2.1 B.F. Rockafellow Ecology Park Outcrop (RFPO) ........................................... 58 4.2.2 Beaver Creek Anticline Outcrop (BCO) ......................................................... 59 4.2.3 Rock Hill North Outcrop (RHNO) ................................................................... 60 4.2.4 Sanders Arroyo (SAO) ................................................................................... 61 CHAPTER 5 .................................................................................................................. 63 SUBSURFACE STRATIGRAPHY ................................................................................. 63 5.1 Overview .............................................................................................................. 63 5.2 Blue Hill Shale Stratigraphic Distribution .............................................................. 63 5.3 Blue Hill Shale Regional Isopachs ....................................................................... 65 5.4 Codell Sandstone Stratigraphic Distribution ......................................................... 68 5.5 Codell Sandstone Regional Isopachs .................................................................. 71 5.6 Juana Lopez Stratigraphic Distribution ................................................................
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