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VOLCANIC INFLUENCE OVER FLUVIAL SEDIMENTATION in the CRETACEOUS Mcdermott MEMBER, ANIMAS FORMATION, SOUTHWESTERN COLORADO

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VOLCANIC INFLUENCE OVER FLUVIAL SEDIMENTATION in the CRETACEOUS Mcdermott MEMBER, ANIMAS FORMATION, SOUTHWESTERN COLORADO VOLCANIC INFLUENCE OVER FLUVIAL SEDIMENTATION IN THE CRETACEOUS McDERMOTT MEMBER, ANIMAS FORMATION, SOUTHWESTERN COLORADO Colleen O’Shea 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: 2009 Committee: James Evans, advisor Kurt Panter, co-advisor John Farver ii Abstract James Evans, advisor Volcanic processes during and after an eruption can impact adjacent fluvial systems by high influx rates of volcaniclastic sediment, drainage disruption, formation and failure of natural dams, changes in channel geometry and changes in channel pattern. Depending on the magnitude and frequency of disruptive events, the fluvial system might “recover” over a period of years or might change to some other morphology. The goal of this study is to evaluate the preservation potential of volcanic features in the fluvial environment and assess fluvial system recovery in a probable ancient analog of a fluvial-volcanic system. The McDermott Member is the lower member of the Late Cretaceous - Tertiary Animas Formation in SW Colorado. Field studies were based on a southwest-northeast transect of six measured sections near Durango, Colorado. In the field, 13 lithofacies have been identified including various types of sandstones, conglomerates, and mudrocks interbedded with lahars, mildly reworked tuff, and primary pyroclastic units. Subsequent microfacies analysis suggests the lahar lithofacies can be subdivided into three types based on clast composition and matrix color, this might indicate different volcanic sources or sequential changes in the volcanic center. In addition, microfacies analysis of the primary pyroclastic units suggests both surge and block-and-ash types are present. Several trends can be noted: (1) there is an overall fining-upward trend seen throughout the McDermott Member in a transition from lahars and fluvial conglomerates at the base to isolated sandstone-rich channels and extensive mudrock deposits near the top of the unit, (2) there is a lateral trend change in the grain size and thickness of lahars, and the thickness of well-developed fluvial deposits, and (3) there is evidence of drainage disruption following the deposition of lahar deposits by the iii deposition of fine-grained silt/mudstones and sandstones which may indicate the creation of natural dams. Stratigraphic relationships and paleoflow directions suggest lahars and other volcanic sediments were transported SSE from the La Plata Mountains through one or more paleovalleys. In comparing modern and ancient volcanically-influenced environments, it is evident the thin sheets of volcanic ash which dominate modern environments have low preservation potential. Rather, the volcanic signature in the geologic record consists of: (1) lahars interbedded with fluvial deposits, (2) volcaniclastic sediment such as reworked tuff or tuffaceous sandstone, and (3) paleocurrent and provenance data. iv Acknowledgements I’d like to thank Phil Wheeler, the Terry Palmer Ranch, and Steve Whiteman from the Southern Ute Indian Tribe for allowing me access to the McDermott Member from their properties and/or gates. Thank you to both Dr. Jim Evans and Megan Castles who aided me in field work in Durango. This research could not have been done without financial support from the Bowling Green State University Geology Department and from the Katzner and University Bookstore Funds for Graduate Research and Professional Development Fund. I’d also like to thank my committee, Dr. Jim Evans, Dr. Kurt Panter, and Dr. John Farver for all their input and time. v TABLE OF CONTENTS Page INTRODUCTION ................................................................................................................. 1 CHAPTER I. GEOLOGICAL BACKGROUND................................................................. 11 CHAPTER II. METHODS ................................................................................................... 19 CHAPTER III. RESULTS.................................................................................................... 21 Facies Analysis.......................................................................................................... 21 Petrographical Observations...................................................................................... 30 Paleogeography ......................................................................................................... 32 CHAPTER IV. DISCUSSION.............................................................................................. 37 Depositional Environments........................................................................................ 37 Volcanic Inputs on Fluvial Environment................................................................... 39 Signature of Volcanic Events in the Geologic Record .............................................. 44 CHAPTER V. SUMMARY & CONCLUSIONS................................................................. 49 Summary ............................................................................................................ 49 Conclusions ............................................................................................................ 50 REFERENCES ...................................................................................................................... 78 APPENDIX A. SAMPLE LOCATION DESCRIPTIONS .................................................. 84 APPENDIX B. PETROGRAPHY DATA............................................................................ 87 APPENDIX C. PALEOCURRENT DATA ......................................................................... 89 vi LIST OF FIGURES Figure Page 1 Proximal and Distal Volcaniclastic Environments .................................................... 52 2 Study Area Map of Durango, CO .............................................................................. 53 3 Cretaceous and Tertiary Rocks of Durango, CO ....................................................... 54 4 Biostratigraphy of Late Cretaceous Rocks in Study Area ......................................... 55 5 Previous Paleocurrent Data of Animas Formation .................................................... 56 6 Geologic Map of Bedrock Units in Durango, CO ..................................................... 57 7 Clast Count Histograms ............................................................................................. 58 8 Stratigraphic Column of Section 1............................................................................. 59 9 Stratigraphic Column of Section 2............................................................................. 60 10 Stratigraphic Column of Section 3............................................................................. 61 11 Stratigraphic Column of Section 4............................................................................. 62 12 Stratigraphic Column of Section 5............................................................................. 63 13 Stratigraphic Column of Section 6............................................................................. 64 14 Photos of McDermott Member Lithofacies ............................................................... 65 15 Photos of McDermott Member Lithofacies 2 ............................................................ 66 16 Photos of McDermott Member Thin Sections........................................................... 67 17 Petrography of McDermott Member ......................................................................... 68 18 Paleocurrent Rose Diagram of McDermott Member................................................. 69 19 Vertical Stratigraphic Columns of Sections 2 and 4.................................................. 70 20 Photomosaic of Outcrop at Section 6......................................................................... 71 21 Representation of Fluvial Recovery within the McDermott Member ....................... 72 vii 22 3-D Representation of Lahar Deposition near Volcanic Center ................................ 73 viii LIST OF TABLES Table Page 1 Palynomorph Taxons Used for Dating in CO ........................................................... 74 2 Fossils Used for Dating in McDermott Member ....................................................... 75 3 Radiometric Ages of Volcanic and Plutonic Rocks................................................... 76 4 Lithofacies of McDermott Member........................................................................... 76 5 Statistical Analysis Data of Petrographic Data.......................................................... 77 1 INTRODUCTION Volcanic Processes It is widely acknowledged that volcanic processes can effect adjacent depositional environments. For example, volcaniclastic deposits up to 3 km thick found within the Cascade Range in California suggest large sediment loads imposed on fluvial systems by volcanic processes (Smith, 1987). As another instance, the remobilization of pyroclastic materials by fluvial processes following the 1800 Taupo eruption in New Zealand caused shallow reworking of fluvial channels and deep incision of hillslope rills and gullies (Manville et al., 2004). A further example, the Pliocence Mushono tephra beds in Japan, suggests that overloading of fluvial systems by pyroclastic debris led to the development of low-sinuosity channel systems (Kataoka, 2005). Volcanic environments can be divided into proximal
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