Wesleyan University The Honors College Using Syndepositional Monoclines to Estimate Paleo-Elastic Properties of a Mixed Carbonate Siliciclastic Sequence, Guadalupe Mts, NM by Natchanan Doungkaew Class of 2014 A thesis (or essay) submitted to the faculty of Wesleyan University in partial fulfillment of the requirements for the Degree of Bachelor of Arts with Departmental Honors in Earth & Environmental Sciences Middletown, Connecticut April, 2014 Acknowledgments First of all, I would like to thank the Department of Earth and Environmental Sciences for giving me the opportunity to pursue my interests in earth science and write an honors thesis. I also would like to thank the department for the James T. Gutmann Field Studies Scholarship, which provided me with the opportunity to travel to New Mexico and Texas to conduct my field research at 1500 m above sea level. My utmost gratitude goes out to my advisor, Professor Phillip Resor, for his patience and generosity. Thank you so much for answering all of my questions and guiding me through this process. I wouldn’t be where I am today without you. I also would like to thank Professor Tim Ku and Professor Peter Patton for reading this thesis. Also, thank you to my field assistant, James Hall, for your help at the Guadalupe Mountain. We would not have been able to record more than 500 fracture orientations without your aid. Finally, I would like to thank all of my friends for their advice, companionship, and love. Last but not least, I would like to thank my family for their endless support and encouragement. Contents Abstract .................................................................................................................................... 1 Introduction ............................................................................................................................. 3 Geologic Background .......................................................................................................... 5 Methods .................................................................................................................................. 10 Part I: Field Study ............................................................................................................ 10 Part II: Petrographic Study ............................................................................................. 12 Part III: Construction of photorealistic models ............................................................. 13 Part IV: Creating models in COMSOL Multiphysics ................................................... 16 Model Definition............................................................................................................ 17 Creating Physics and Defining Global Parameters ................................................... 17 Creating geometry and defining boundaries, contacts, and continuity ................... 18 Setting Material Properties and Mesh ........................................................................ 21 Set up Solid Mechanics ................................................................................................. 23 Solving and Exporting Results ..................................................................................... 24 Results .................................................................................................................................... 26 Slaughter Canyon.............................................................................................................. 26 Field Study ..................................................................................................................... 26 Petrographic Analysis ................................................................................................... 27 3D Photorealistic Models .............................................................................................. 30 Stereonet ........................................................................................................................ 34 Indian Shelter .................................................................................................................... 38 Field Study ..................................................................................................................... 38 Petrographic Study ....................................................................................................... 39 3D Photorealistic Models .............................................................................................. 41 Stereonet ........................................................................................................................ 43 COMSOL Multiphysics Solid Mechanics Model ........................................................... 46 Discussion .............................................................................................................................. 58 Field Study, Petrographic Study and 3D Model ............................................................ 58 Slaughter Canyon.......................................................................................................... 59 Indian Shelter ................................................................................................................ 60 COMSOL Multiphysics Solid Mechanics Models .......................................................... 62 The Geometry of the Monoclines and COMSOL Models ......................................... 69 Conclusion ............................................................................................................................. 71 References .............................................................................................................................. 73 Appendices ............................................................................................................................. 76 Appendix I: Suggestions for Future work ...................................................................... 76 Appendix II: Methods of Constructing the Photorealistic Models ............................... 76 Appendix III: Petrographic Analysis .............................................................................. 83 Appendix IV: Coulomb Stress ......................................................................................... 96 1 Abstract The ability to predict the paleo-mechanical property of rocks is vital to the exploration and production of oil, gas, and geothermal energy and ground water resource analysis. The goal of this thesis is to demonstrate a possible new approach to determining the paleo-mechanical property of sedimentary rock. I combined traditional field study, petrographic study, and 3D photorealistic modelling with finite element modelling to determine the stiffness of sedimentary rocks during the time of faulting and folding. I conducted a field study at the fault E monocline at Slaughter Canyon, and the Indian Shelter monocline at Walnut Canyon, both of which are located within the Capitan platform in the Guadalupe Mountains, New Mexico. The field study suggests that the preexisting strata controlled the orientations of the fractures along the two monoclines. The absence of soft sediment deformation structures and the presence of fractures at both sites indicate that folding occurred through brittle deformation. Petrographic and field studies showed that the depositional environment of packstone folded in the fault E monocline was deposited in shallow waters of the Capitan back reef. They also showed that the depositional environment of the sandstone that made up the Indian Shelter monocline was a peritidal shelf-crest environment. I used the geometries of the outcrops from my photorealistic models of the two monoclines to build finite element models in COMSOL Multiphysics. The models show the effects of changing fault depth and Young’s modulus on the shape of monoclines and the magnitude of fault slip. The 2 fault throw increases as fault dip increases, but decreases as the Young’s modulus increases. The solid mechanics models of fault E monocline suggest that the Young’s modulus of the packstone was 25 GPa, while the Indian Shelter models suggest that the Young’s modulus of the sandstone was 10 GPa at the time of folding. These values are more than 60% lower than the present-day elastic stiffness. Both of the rocks might have become stiffer due to further cementation and compaction by deposition of the other high-frequency sequences above them. Overall, the combination of field study, petrographic study, photorealistic modelling, and finite element modelling has demonstrated the potential to infer paleo-stiffness of ancient sediments, but further modelling is needed to verify the method. 3 Introduction Sedimentary rocks deform in both fluid-like and elastic-plastic manners. The first case is usually referred to as soft sediment deformation, which is the rearrangement of unlithified sedimentary particles without internal deformation of the particles or any interstitial cement (Maltman, 1994; Waldron and Gagnon, 2011). The second type is usually referred to as brittle deformation. It tends to occur in consolidated or cemented rocks that experience stress greater than their yield strength and start to break. Below the yield strength, the rocks behave like elastic solids. However, above this limit, the rocks begin to behave plastically (David & Reynolds, 1942). The goal of this thesis is to demonstrate a new approach to determining