Loma Linda University TheScholarsRepository@LLU: Digital Archive of Research, Scholarship & Creative Works Loma Linda University Electronic Theses, Dissertations & Projects 12-2015 Soft-sediment Deformation and Dune Collapse in the Navajo Sandstone Colby Ford Follow this and additional works at: http://scholarsrepository.llu.edu/etd Part of the Geology Commons, Hydrology Commons, and the Sedimentology Commons Recommended Citation Ford, Colby, "Soft-sediment Deformation and Dune Collapse in the Navajo Sandstone" (2015). Loma Linda University Electronic Theses, Dissertations & Projects. 334. http://scholarsrepository.llu.edu/etd/334 This Thesis is brought to you for free and open access by TheScholarsRepository@LLU: Digital Archive of Research, Scholarship & Creative Works. It has been accepted for inclusion in Loma Linda University Electronic Theses, Dissertations & Projects by an authorized administrator of TheScholarsRepository@LLU: Digital Archive of Research, Scholarship & Creative Works. For more information, please contact [email protected]. LOMA LINDA UNIVERSITY School of Medicine in conjunction with the Faculty of Graduate Studies ____________________ Soft-sediment Deformation and Dune Collapse in the Navajo Sandstone by Colby Ford ____________________ A thesis submitted in partial satisfaction of the requirements for the degree Master of Science in Geology ____________________ December 2015 © 2015 Colby Ford All Rights Reserved Each person whose signature appears below certifies that this thesis in his/her opinion is adequate, in scope and quality, as a thesis for the degree Master of Science. , Chairperson Kevin E. Nick, Associate Professor of Geology Gerald Bryant, Director, Colorado Plateau Field Institute, Dixie State University H. Paul Buchheim, Professor of Geology iii ACKNOWLEDGEMENTS Funding and facilities for this project provided by the Department of Earth and Biological Sciences, Loma Linda University, and by a grant from the Geological Society of America. Special thanks to Paul Buchheim (Loma Linda University) for input during the development of this project, and to Rosmarie Bisquera for field assistance. iv CONTENT Approval Page .................................................................................................................... iii Acknowledgements ............................................................................................................ iv List of Figures ................................................................................................................... vii List of Tables ................................................................................................................... viii Abstract .............................................................................................................................. ix Chapter 1. Expanded Introduction and Background .................................................................1 Introduction ........................................................................................................1 Previous Research ........................................................................................4 History of eolian research ......................................................................4 History of SSD research.........................................................................6 References ..........................................................................................................9 2. Architectural Evidence of Dune Collapse in the Navajo Sandstone, Zion National Park, Utah .................................................................................15 Introduction ......................................................................................................21 Purpose of this report .................................................................................16 Methods............................................................................................................19 Results ..............................................................................................................22 Sedimentary and deformational structures.................................................30 Discussion ........................................................................................................37 Initial conditions in the dune field .............................................................38 Early liquefaction and incipient collapse ...................................................40 Dune Collapse ............................................................................................41 Production of uneven bounding surface ....................................................42 Re-establishment of normal dune migration ..............................................44 Implications for the Horowitz dune collapse model ..................................47 v Conclusions & future research .........................................................................48 References ........................................................................................................49 3. Expanded discussion ..............................................................................................52 Addressing Horowitz’ predictions ...................................................................52 Relationship to other projects underway..........................................................56 Conclusions ......................................................................................................56 References ........................................................................................................58 vi FIGURES Figures Page 1. Schematic of Horowitz dune collapse model...........................................................3 2. Schematic of Horowitz dune collapse model, based on outcrop ...........................17 3. Map showing study location ..................................................................................20 4. Overhead view of study location ...........................................................................22 5. Generalized stratigraphic column ..........................................................................23 6. Digital elevation maps of bounding surfaces .........................................................25 7. Cross-section of dune collapse complex ................................................................27 8. Photo of “Keystone” outcrop .................................................................................28 9. Photo showing contorted chert nodules .................................................................29 10. Thin section of the fractured end of a chert nodule ...............................................30 11. Photo showing evidence of vertical movement of fluidized material....................31 12. Photo of intense deformation in the North-central portion of the outcrop ............32 13. Photo of brecciated and displaced carbonate mudstone laminae ...........................33 14. Stereonet diagram of mapped faults ......................................................................35 15. Photo of a clastic injection pocket .........................................................................36 16. Photo of a small shear feature causing offset across the upper bounding surface ....................................................................................................................37 17. Conceptual dune collapse model part A ................................................................40 18. Conceptual dune collapse model part B.................................................................42 19. Conceptual dune collapse model part C.................................................................44 20. Conceptual dune collapse model part D ................................................................46 vii TABLES Tables Page 1. List and descriptions of named units in outcrop ....................................................24 viii ABSTRACT OF THE THESIS Soft-sediment Deformation and Dune Collapse in the Navajo Sandstone By Colby Ford Master of Science Graduate Program in Geology Loma Linda University, December 2015 Dr. Kevin E Nick, Chairperson The Canyon Overlook Trail of Zion National Park follows an outcrop of Navajo Sandstone, which displays a uniquely well-exposed assemblage of features associated with failure of the lee face of a large eolian dune, and run-out over an expanse of interdune sediments downwind of that bedform. Exposed features include dramatic folds in the interdune succession and a stacked series of thrust sheets incorporating both interdune and overlying dune deposits. Thrust surfaces display consistent strikes, parallel to those of undeformed foresets, and incorporate zones of brittle failure and fluid deformation, including folds overturned in the direction of foreset dip. These features correspond to predictions made by the Horowitz (1982) model of dune collapse, formulated from less fortuitously exposed architectures in the Navajo Sandstone. Unlike the Horowitz (1982) model, however, this site preserves distinct indications that the bulk of deformed material accumulated above the level of the contemporary interdune surface, in an aggradational succession. Paleotopographic reconstruction, based on preserved facies relationships at this site, indicates the presence of a large dune, partially encroaching upon a well-developed wet interdune succession, made up of two