Stratigraphy, Sedimentary Petrology, and Depositional Environments of Tillite in the Upper Precambrian Mount Rogers Formation, Virginia Richard L
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Louisiana State University LSU Digital Commons LSU Historical Dissertations and Theses Graduate School Spring 2-10-1978 Stratigraphy, Sedimentary Petrology, and Depositional Environments of Tillite in the Upper Precambrian Mount Rogers Formation, Virginia Richard L. Rexroad Louisiana State University and Agricultural and Mechanical College Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_disstheses Part of the Geology Commons, and the Sedimentology Commons Recommended Citation Rexroad, Richard L., "Stratigraphy, Sedimentary Petrology, and Depositional Environments of Tillite in the Upper Precambrian Mount Rogers Formation, Virginia" (1978). LSU Historical Dissertations and Theses. 8239. https://digitalcommons.lsu.edu/gradschool_disstheses/8239 This Thesis is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Historical Dissertations and Theses by an authorized administrator of LSU Digital Commons. For more information, please contact [email protected]. STRATIGRAPHY, SEDIMENTARY PETROLOGY, AND DEPOSITIONAL ENVIRONMENTS OF TILLITE IN THE UPPER PRECAMBRIAN MOUNT ROGERS FORMATION, VIRGINIA A Thesis 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 Master of Science in The Department of Geology by Richard L. Rexroad B.S., Michigan State University, 1974 May 1978 MANUSCRIPT THESES Unpublished theses submitted for the Master’s and Doctor's Degrees and deposited in the Louisiana State University Library are available for inspection. Use of any thesis is limited by the rights of the author. Bibliographical references may be noted, but passages may not be copied unless the author has given permission. Credit must be given in subsequent written or published work. A Library which borrows this thesis for use by its clientele is expected to make sure that the borrower is aware of the above restrictions. LOUISIANA STATE UNIVERSITY LIBRARY ACKNOWLEDGEMENTS This thesis was carried out under the direction of Dr. Donald R. Lowe. The author would like to express his sincere gratitude to Dr. Lowe for his advice, patience, and inspiration. Drs. Jeffrey S. Hanor and Donald H. Kupfer served as committee members, and provided numerous suggestions which improved the thesis. Additional support was provided by Drs. George F. Hart, Rex H. Pilger, and Prentiss E. Schilling. Many of the writer's fellow graduate students at Louisiana State University are thanked for their continued scientific and moral support, particularly Lynn M. Walter. Sally J. Bates helped type the manuscript. Financial assistance was provided by the Department of Geology, Louisiana State University, and by the Sun Oil Company. ii TABLE OF CONTENTS PAGE ACKNOWLEDGMENTS........................................... ii LIST OF TABLES.............................................. v LIST OF FIGURES........................................... vi ABSTRACT................................................. ix INTRODUCTION ................................................ 1 GEOLOGIC SETTING ........................................... 4 REGIONAL STRATIGRAPHY....................................... 13 STRATIGRAPHY OF THE UPPER MEMBER OF THE MOUNT ROGERS FORMATION............................................... 21 Lithology............................................... 21 Arkosic Sandstone................................... 21 Rhythmically Layered Argillite .................. 23 Greywacke........................................... 26 Polymict Conglomerate............................... 28 Conglomeratic Mudstone .......................... 29 Quartz Pebble Conglomerate ...................... 32 Metamorphism........................................... 34 EVIDENCE OF LATE PRECAMBRIAN GLACIATION.................. 41 PROCESSES OF TRANSPORT AND DEPOSITION IN GLACIAL ENVIRONMENTS........................................... 44 Non-stratified Glacial Deposits ...................... 46 Moraine Types..................................... 48 Stratified Glacial Deposits .......................... 53 Ice-contact Features ............................ 53 Proglacial Sedimentary Deposits.................. 58 Periglacial Deposits ............................. 62 iii PAGE METHODS AND TECHNIQUES..................................... 64 DETAILED CHARACTERISTICS OF THE TILLITIC INTERVAL OF THE UPPER MEMBER OF THE MOUNT ROGERS FORMATION .... 66 Stratigraphy ........................................... 66 Composition.............................................. 70 Texture.................................................. 85 Sedimentary Structures ................................. 94 Interbedded Units..................................... 100 CORRELATION OF TILLITE UNITS............................ 103 DISCUSSION................................................. 112 Processes and Environments of Deposition ............ 112 Directions of Ice Movement............................. 125 Type of Glacier....................................... 129 Physiography and Provenance............................. 132 SUMMARY................................................... 134 BIBLIOGRAPHY............................................... 136 APPENDIX 1............................................... 145 APPENDIX II............................................. 146 APPENDIX III............................................. 147 APPENDIX IV............................................. 148 APPENDIX V............................................... 150 VITA....................................................... 165 iv LIST OF TABLES TABLE PAGE I. Rock Fragment Composition within Mount Rogers Tillites......................................... 76 II. Composition of the Sand Fraction of Mount Rogers Tillites ................................. 82 III. Suggested Correlation of Mount Rogers Tillite Based on Textural Characteristics .... 108 v LIST OF FIGURES FIGURE PAGE 1. Geologic map and location of measured sections . 2 2. Geologic provinces of the Appalachian Mountains. 5 3. Upper Precambrian Sedimentary-Volcanic Assemblages of the Blue Ridge Province of the Southern Appalachian Mountains .................. 8 4. Outcrop area of the Mount Rogers Formation .... 9 5. Structural units and major thrust faults ........ 10 6. Generalized Structural Cross Section of study area............................................ 12 7. Representative section containing Mount Rogers tillite....................................... 22 8. Rhythmically Layered Argillite .................... 24 9. Outsized Clast............................... 27 10. Conglomeratic Mudstone ............................ 30 11. Sorting of Conglomeratic Mudstone............. 31 12. Spheroidal Weathering......................... 33 13. Matrix recrystallization in Mount Rogers tillite . 35 14. Cleavage in Mount Rogers tillites............. 37 15. Pebble orientation in Mount Rogers tillite. ... 39 16a. Generalized diagram showing features associated with piedmont glaciation ........................ 49 16b. Features associated with piedmont glaciation ... 51 17. Generalized cross section of a piedmont glacier deposit.......................................... 57 vi LIST OF FIGURES (CONTINUED) FIGURE PAGE 18. Thickness of the Mount Rogers tillitic interval......................................... 67 19. Total thickness of tillite in measured sections......................................... 68 20. Number of tillites within measured sections ... 71 21. Variation in pebble content of Mount Rogers tillites......................................... 72 22. Faceted (?)pebbles in Mount Rogers tillite .... 75 23. Rock fragments in Mount Rogers tillites.......... 77 24. Variation in sand content of tillites.......... 79 25. Sericitic alteration of feldspar in Mount Rogers tillite......................................... 83 26. Matrix of Mount Rogers tillite .................. 84 27. Ratio of quartz to feldspar in Mount Rogers tillite......................................... 86 28. Ratio of volcanic to granitic rock fragments in Mount Rogers tillite............................. 87 29. Percentage of matrix in Mount Rogers tillite ... 89 30. Rounding of sand grains in tillite for which (a+b)/2 lies between 0.125 and 1.0 mm in diameter. 90 31. Outcrop-averaged (a+b)/2 values for tillitic grains greater than 0.06 mm in diameter........ 91 32. Outcrop-averaged (a+b)/2 values for tillitic grains between 0.125 mm and 1.0 mm in diameter . 92 vii LIST OF FIGURES (CONTINUED) FIGURE PAGE 33. Ratio of the number of tillitic grains between 0.125 and 1.0 mm in diameter to the number of tillitic grains greater than 0.06 mm in diameter. 93 34. Diameter of the largest clast within the tillitic interval at each section.......................... 95 35. Deformed contact between Mount Rogers tillites. 96 36. Textural characteristics of tillite at Green Cove . 104 37. Textural characteristics of tillite at Discovery. 105 38. Textural characteristics of tillite at Creek Junction............................................. 106 39. Generalized model of a glacier protruding from land into water..................................... 116 viii ABSTRACT The upper member of the upper Precambrian Mount Rogers Formation of southwestern Virginia includes thick units of massive conglomeratic mudstone Interpreted as tillite (Rankin, 1970; Blondeau and Lowe, 1972; Blondeau, 1975; Schwab, 1976). The tillite is composed of unsorted angular