Sedimentary Processes on Earth and Mars: Canyon Erosion, Sand-Ripple Formation, and Mineral Composition Thesis by Mathieu G. A. Lapôtre In Partial Fulfillment of the Requirements for the degree of Doctor of Philosophy CALIFORNIA INSTITUTE OF TECHNOLOGY Pasadena, California 2017 (Defended May, 8th 2017) ii 2017 Mathieu G. A. Lapôtre ORCID: 0000-0001-9941-1552 iii There is life on Mars, and it is us — extensions of our eyes in all directions, extensions of our mind, extensions of our heart and soul have touched Mars today. —Ray Bradbury iv ACKNOWLEDGEMENTS This thesis is neither the end of my scholarly training nor the start of my scientific career, but it shall serve as proof that my advisors, mentors, colleagues, friends, and family have successfully fulfilled and surpassed their roles. To them, I am deeply indebted and grateful. I thank Prof. Michael Manga of UC Berkeley, who initiated me to the world of academic research in 2009, when as an undergraduate student who could barely speak English I asked him if I could take my first research steps in his lab. I thank Chris Huber and Profs. Taylor Perron of MIT and Andrew Woods of Cambridge University for helping me solidify my commitment to research and pave my way to graduate school. I am forever grateful to my Ph.D. advisors at Caltech – Profs. Bethany Ehlmann and Michael Lamb. I could not have hoped for better mentors. Both were generous with their ideas but let me pursue my own. They inspired me to work on big, multidisciplinary, and exciting problems. I am also thankful to other members of the Caltech faculty for their advice and/or mentorship during the past five years, and in particular to Profs. John Grotzinger, Woody Fischer, Joe Kirschvink, Dave Stevenson, Ken Farley, and Dr. Matt Golombek of JPL. My coauthors have been a boundless source of knowledge and ideas, and I thank them for all they taught me. In particular, I thank Profs. Ray Arvidson, Ryan Ewing, Nathan Bridges, and Drs. Dave Rubin, Sarah Minson, Rebecca Williams, and François Ayoub for countless email discussions. I also thank Dr. Ashwin Vasavada of JPL and the entire MSL team for allowing me to join them in this incredible adventure that is driving a rover on Mars. Numerous officemates over the years have made my graduate life joyful and fun. I thank the “pit” of 2012-2013 – Jennifer Buz, Brooke Dallas, Max Lloyd, Hayden Miller, Daven Quinn, Lewis Ward, and Junjie Yu, and all previous and subsequent officemates, including Austin Chadwick, Lauren Edgar, Ajay Limaye, Jeff Prancevic, Joel Scheingross, Katie Stack Morgan, and Jessica Watkins. Members of the Ehlmann and Lamb research groups have been a great source of support, inspiration, and fun. I give special thanks to Janice Grancich and Ulrika Terrones for their great support. While I cannot enumerate all v group members who have contributed to my time at Caltech, I would like to thank Fanny Brun, Roman DiBiase, Chris Edwards, Abby Fraeman, Vamsi Ganti, Hima Gudipati, Alistair Hayden, Isaac Larsen, Ben Mackey, Luca Malatesta, Odin Mark, Peter Martin, Lu Pan, Nathan Stein, and Cindy Tran for their individual help, from processing data to swaping MSL shifts, for stimulating conversations, and for their friendship. I simply cannot thank my friends enough for all they have contributed to my daily life at Caltech. In addition to those listed in previous paragraphs, I extend my gratitude to Kirsten Siebach for indulging my love of long walks on the beach, Nat Prunet, Murray Brightman, and Etienne Donckèle for our many runs and lunches, Perla Castillo, Quentin Maillet, and Paul-Hervé Tamokoué Kamga for our LA adventures, Christy Swann for letting me play in the NASA Ames wind tunnel with her, the French crew of my early Caltech days, Kristel Chanard, Rémi Lam, Baptiste Rousset, Quentin Bletery, and Marion Thomas, and those from back home who visited me and/or kept me entertained via Facebook – Sophie Bouscarat, Floriane Mottet, Alexandre Pachoud, Bruno Gavazzi, Michi Ruhnke, Marine Collignon, Marion Barbaray, and many others. I arrived in California in 2012 having one family, and found myself a few years later with three of them. First, my French family – mom, dad, and Sandrine – thank you for your unconditional love and infinite support. You mean the world to me. Second, my American family, the Coltons, who have welcomed me in their home throughout my time in Pasadena – Sue and Ed, Tony, George, Michael (a.k.a. Grand Bonhomme), and Bailey – thank you for your boundless generosity. Thank you Grand Bonhomme for being my friend, for all the “fun stuffs”, and thank you for introducing me to my playa family. Thank you awesomesaucers for being the best campmates in the world and all the fun and joy you bring into my life. Finally, I would like to thank Monique, my car, for staying alive over the years despite her old age. Living in Los Angeles sure would not have been the same if it wasn’t for our rides to the beach, the mountains, and the grocery store. vi ABSTRACT Over the past few decades, orbiters, landers, and rovers have significantly expanded our understanding of Mars’ hydrology and climate; however, significant knowledge gaps stand in the way of our quest for martian life. In particular, the global drying of the planet remains one of the grandest unsolved mysteries in planetary science. To help unravel this puzzle, we develop new quantitative theories for sedimentary processes with implications for both Earth and Mars. This thesis revolves around three main sedimentary processes – erosion (Chapters 2-4), deposition (Chapters 5-6), and sediment transport (Chapters 7-8). In Chapters 2-4, we focus on the erosion of bedrock canyons by water on Earth and Mars. After showing that groundwater seepage erosion is only efficient at carving canyons in restricted conditions (Chapter 2), we develop a new hydraulic theory for flow focusing upstream of horseshoe-shaped waterfalls (Chapter 3) and combine it with waterfall-erosion mechanics to constrain the discharge, duration, and volume of canyon-carving floods on Earth and Mars (Chapter 4). We show that martian Hesperian floods were large but short- lived. In Chapters 5-6, we investigate fluid and sediment controls on the equilibrium size of bedforms. We develop a comprehensive scaling relation to predict the size of ripples forming in various sedimentary environments, including martian brines and methane flows on Titan (Chapter 5), and show that the scaling relation predicts the size of large wind ripples forming under a thin martian atmosphere (Chapter 6). This new theory, combined with observations of large-ripple cross-strata in wind-blown sandstones of the Burns formation at Victoria crater, suggests that Mars had a thin atmosphere around the Noachian-Hesperian boundary. Finally, in Chapters 7-8, we use orbiter-based inferences of the mineralogy of sands of the Bagnold dunes of Gale crater to disentangle the magnitude of wind sorting and local sediment sources. We first develop a new probabilistic framework to invert for surface mineralogy (Chapter 7), groundtruth our predictions with compositional datasets provided by the Curiosity rover, and discuss the implications of our findings for mineral sorting by martian winds and paleoenvironmental interpretations of martian wind-blown sandstones (Chapter 8). Collectively, these results provide new mechanistic and quantitative constraints on the past hydrology and climate of Mars that are key to assess Mars’ astrobiological potential through space and time. vii PUBLISHED CONTENT AND CONTRIBUTIONS Chapter 2 is under consideration by Nature Geoscience as: Lapôtre, M. G. A., and M. P. Lamb, Substrate Controls on Valley Formation by Groundwater on Earth and Mars. M. Lapôtre and M. Lamb conceived the study. M. Lapôtre developed the model and performed the analysis. M. Lapôtre wrote the manuscript with help from M. Lamb. Chapter 3 is published as: Lapôtre, M. G. A., and M. P. Lamb (2015), Hydraulics of Floods Upstream of Horseshoe Canyons and Waterfalls, Journal of Geophysical Research: Earth Surface, 120(7), 1227-1250, DOI:10.1002/2014JF003412. M. Lapôtre and M. Lamb conceived the study. M. Lapôtre performed the numerical modeling and analysis. M. Lapôtre wrote the manuscript with help from M. Lamb. Chapter 4 is published as: Lapôtre, M. G. A., et al. (2016), Canyon Formation Constraints on the Discharge of Catastrophic Outburst Floods of Earth and Mars, Journal of Geophysical Research: Planets, 121(7), 1232-1263, DOI:10.1002/2016JE005061. M. Lapôtre and M. Lamb conceived the study. M. Lapôtre developed the theory and implemented the model. M. Lapôtre performed the data analysis with help from R. Williams. M. Lapôtre wrote the manuscript with help from all coauthors. Chapter 5 is published as: Lapôtre, M. G. A., et al. (2016), Large Wind Ripples on Mars: A Record of Atmospheric Evolution, Science, 353(6294), 55-58, DOI: 10.1126/science.aaf3206. M. Lapôtre, R. Ewing, and M. Lamb conceived the study. R. Ewing and M. Ballard performed the orbital measurements. M. Lapôtre performed the rover-based measurements, developed the theory, and implemented the model. M. Lapôtre performed the data analysis with help from R. Ewing, M Lamb, and W. Fischer. M. Lapôtre wrote the manuscript with help from all coauthors. Chapter 6 is published as: Lapôtre, M. G. A., et al. (2017), What Sets the Size of Current Ripples?, Geology, 45(3), 243-246, DOI: 10.1130/G38598.1. M. Lapôtre and M. Lamb conceived the study. M. Lapôtre performed the data compilation and scaling analysis. M. Lapôtre wrote the manuscript with help from all coauthors. Chapter 7 is published as: Lapôtre, M. G. A., et al. (2017), A Probabilistic Approach to Remote Compositional Analysis of Planetary Surfaces, Journal of Geophysical Research: Planets, in press, DOI: 10.1002/2016JE005248.