REINTERPRETATION OF THE IGNACIO AND ELBERT FORMATIONS AS AN INCISED VALLEY FILL USING FACIES ANALYSIS AND SEQUENCE STRATIGRAPHY; SAN JUAN BASIN, SOUTHWEST COLORADO Joshua T. Maurer A Thesis Submitted to the Graduate College of Bowling Green State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE August 2012 Committee: James E. Evans, Advisor Margaret Yacobucci Charles Onasch ii ABSTRACT James E. Evans, Advisor The Ignacio Formation and the Devonian Elbert Formation of southwest Colorado represent the lowest succession Paleozoic strata in the San Juan Basin of Colorado and New Mexico. This study reinterprets the Ignacio Formation-Ouray Limestone as Devonian (Famennian) in age and finds that the succession represented a laterally continuous depositional system of fluvial and estuarine environments (Ignacio Formation), prograding shoreline environments (McCracken Sandstone Member, Elbert Formation), tidal flats and shallow marine shales (Upper Member, Elbert Formation), and marine limestone and shales (Ouray Limestone). The present study is based on lithofacies analysis, 137-m of measured stratigraphic sections at 11 outcrops, provenance analysis from 24 representative thin sections, 72 paleocurrent measurements, and photomosaics. Lithofacies analysis identified 14 lithofacies that are organized into fluvial channel, tidal channel, tempestite, and tidal flat sequences. This study suggests that the Ignacio and Elbert formations may be reinterpreted an incised valley sequence. Evidence for this conclusion include variations in thickness, facies distribution, the conformable contact between the Ignacio Formation and the McCracken Sandstone Member, lithofacies associations and ichnology, which confirm the shift from fluvial to estuarine to marine environments, and the onlap of these Paleozoic sedimentary rocks onto Precambrian basement paleohighs. It is suggested that initial accommodation space was provided by paleotopography on the Precambrian basement surface. Later accommodation space was provided by relative sea-level rise, and the paleovalleys were backfilled by fluvial – estuarine sediments and later overtopped by marine sediment. iii Ignacio Formation type section at Electra Lake iv This thesis is dedicated to Jerry Calendine. v ACKNOWLEDGMENTS The ideas presented here have resulted from the research of Joshua T. Maurer and Dr. James E. Evans in ancient incised-valley and estuarine systems in Southwest Colorado. This work was supported by the Colorado Scientific Society and the Ogden Tweto Memorial Fund in conjunction with funding from Bowling Green State University as well as the Geological Society of America for travel grants to present our research at the Northeastern region GSA meeting. I, Joshua T. Maurer, thank the valuable input and support from the following people: Colleagues within Bowling Green State University (Richard R. Hoare Research Scholarship) as well as several friends and family. Thanks to Dr. James E. Evans who served as my advisor and constant source of guidance and knowledge. Without Jim, this research would not have been possible. Thank you to my committee members Charles Onasch and Peg Yacobucci for being open to my numerous questions and providing amazing input and assistance. Specifically, thank you Charlie for your help in sample preparation and thin section making, and Peg for your help with the paleontological work and identification. Thanks to my field assistant Bharat Banjade for continual motivation in the field and a positive attitude when conditions looked bleak while scurrying around the San Juan National Forest. Thank you to my longtime friend Robert Tolley for logistical aid including the procuring our rental car. Thanks to Benjamin Nelson for your constant support and motivating me to accomplishing my goals throughout our time at BGSU. Thank you Udita Datta for being a continuous source of inspiration and competition while completing this project. Finally, thank you to my entire family for the support. vi TABLE OF CONTENTS Page INTRODUCTION ………………………………………………………………………… 1 Sequence Stratigraphy ……………………………………………………….…… 1 Incised Valley Sequences ………………………………………………...………. 6 Facies Analysis ……………….………………………………………………….. 16 Purpose and Objective ……………………………………………………………. 18 BACKGROUND……………………………………………………….………………… . 20 Regional Tectonic Setting……………………………………………………….... 20 Precambrian Basement …………………………………………………………… . 20 Hiatus and Early Paleozoic Sedimentation.……………………………………… .. 21 Ancestral Rocky Mountain Uplift and Paradox Basin …………………………..... 22 Sevier and Laramide Orogenies …………………………………………………... 23 Regional Stratigraphy…………………………………………………………….... 26 Precambrian Basement ……………………………………………………………. 26 Ignacio Formation …………………………………………………………………. 28 Elbert Formation ………………………………………………………………… ... 33 vii Ouray Limestone ………………………………………………………………… ... 36 Stratigraphy and Age ……………………………………………………………… 36 METHODS……………………………………………………………………………… ... 38 Stratigraphic Sections ……………………………………………………………... 38 Paleocurrent Analysis ………………………………………………………… ...... 41 Petrographic Analysis ……………………………………………………………. 43 Contact Relationships ……………………………………………………………. 46 RESULTS ………………………………………………………………………………… 47 Lithology…… ............................................................................................................ 47 Lithofacies Analysis .................................................................................................. 58 Ichnofacies Analysis …………….. ........................................................................... 91 Paleocurrent Analysis ............................................................................................... 99 Provenance Analysis……………………………………………………………… .. 100 Contact Relationships ………………………………..………………………….. ... 101 DISCUSSION …………………………………………………………………………….. 114 Valley Incision …………………………………………………………………...... 114 Valley Fill …………………………………………………………………………… 123 viii Depositional Model ………………………………………………………………… 130 SUMMARY AND CONCLUSIONS……. ........................................................................... 130 REFERENCES……………………………………………………………………………… 133 APPENDIX A. PALEOCURRENT DATA…………………………………………………. 148 APPENDIX B. COLUMNAR SECTIONS .......................................................................... 153 APPENDIX C. POINT COUNT DATA...……………………………………...………….. 168 ix LIST OF FIGURES Figure Page 1 Depositional Sequence Model………………………………………………….…… 5 2 Type-1 Incised Valley Sequence Model……………………………………….…… 10 3 Type-2 Incised Valley Sequence Model…………………………………………… 12 4 Incised Valley Sequence Longitudinal Facies Distribution…….…………………. 15 5 Shoreline Facies Model……………………………………………………………. 17 6 Ancestral Rocky Mountain Paleogeography………………………………………. 24 7 Coal Bank Pass and Snowdon Fault Block Cross-Section………………………… 25 8 Regional Stratigraphy……………………………………………………………… 27 9 Study Area Map……………………………………………………………………. 40 10 Paleocurrent Tilt Correction……………………………………………………….. 42 11 Dickinson Petrofacies Ternary Diagrams……………………………………... ....... 45 12 Ignacio Formation Outcrop Photographs………………………………………… ... 48 13 Ignacio Formation Photomicrographs……………………………………………… 49 14 McCracken Sandstone Member Outcrop Photographs…………………………….. 52 15 McCracken Sandstone Member Photomicrographs………………………………… 56 x 16 Lithofacies Sm …………………………………………………………………….. 62 17 Lithofacies Se …………………………………………………………………….... 64 18 Lithofacies Sp …………………………………………………………………….. 66 19 Lithofacies St …………………………………………………………………….. .. 68 20 Lithofacies Sx …………………………………………………………………….. 70 21 Lithofacies Sr …………………………………………………………………….. .. 71 22 Lithofacies Sh …………………………………………………………………….. 73 23 Lithofacies Sl …………………………………………………………………….. .. 75 24 Lithofacies Sw …………………………………………………………………….. 77 25 Lithofacies Gm & Gt ………………………………………………………….. ...... 80 26 Lithofacies Gl …………………………………………………………………….... 83 27 Lithofacies SSm ………………………………………………………………….. .. 86 28 Lithofacies SSl …………………………………………………………………….. 87 29 Lithofacies MSf ……………………………………………………………….. ...... 89 30 Lithofacies MSb ……………….…………………………………………………... 90 31 Sultan Creek Ichnofacies ………………………………………………………….. 96 32 Mile Marker 54 of US 550 Ichnofacies ………………………………………….. .. 97 xi 33 Bioturbation Photomicrograph …………………………………………………….. 98 34 Regional Paleocurrent Data ………………………………………………….. ........ 102 35 Petrofacies Data ………………………………………………………….. .............. 103 36 Ignacio Fm. – Unnamed Conglomerate Contact …………………………………... 105 37 McCracken SS Mbr. – Baker’s Bridge Granite Contact ……………………….. ..... 106 38 McCracken SS Mbr. – Unnamed Conglomerate Contact …………………….. ....... 107 39 McCracken SS Mbr. – Ignacio Fm. Outcrop Contact …………………….. ............. 109 40 McCracken SS Mbr. – Ignacio Fm. Contact Detail …………….. ............................ 110 41 Longitudinal Hanging Stratigraphic Sections …………………….. ......................... 119 42 Cross-Sectional Hanging Stratigraphic Sections ………………………………… .. 121 43 IVS Depositional Model ………………………………….. ..................................... 128 xii LIST OF TABLES Table Page 1 Outcrop Geographic Coordinates …………………………………………….…… 39 2 Summary of Point Count Data ……………………………………………….…… 53 3 Fluvial Lithofacies ………………………………..………………………….…… 59 4 Marine and Estuarine Lithofacies …….…………………………………………… 61 5 Summary of Ichnofacies ………………………………………………………….. 93 6 Summary of Lithostratigraphic Contacts ………………………………………….. 113 1 INTRODUCTION Sequence Stratigraphy The method of sequence stratigraphy was developed and refined by Exxon in the 1970’s and continues to be an important