NORTHWESTERN UNIVERSITY Advancements in our Understanding of the Yucatán Platform: Sedimentary Geology and Geochemistry, Speleogenesis, Chicxulub Ring of Cenotes, and Tectonic Stability A DISSERTATION SUBMITTED TO THE GRADUATE SCHOOL IN PARTIAL FULFILLMENT OF THE REQUIREMENTS for the degree DOCTOR OF PHILOSOPHY Field of Earth and Planetary Sciences By Emiliano Monroy-Ríos EVANSTON, ILLINOIS December 2020 1 2 © Copyright by Emiliano Monroy Ríos 2020 All Rights Reserved 2 3 Abstract Carbonates constitute Earth's largest carbon (C) reservoir, with most shallow marine deposition occurring on the low-latitude carbonate platforms covering ~800,000 km2. The Yucatán Platform situated between the Western Caribbean and Gulf of Mexico basins, is one of the largest present-day carbonate platforms. As with post-Paleozoic carbonates generally, it is readily weathered and karstified, as these retain primary porosity and remain close to the surface, with dissolution leading to order of magnitude permeability increases. This addresses questions of the Yucatan geological history using a combination of literature research, geophysical and geodetic data, and geochemical analyses, along with field observations. The genesis and hydrogeological function of the surface expressed Ring of Cenotes remains an active question in the Yucatán geological understanding. A genetic model for the formation of the Chicxulub Ring of Cenotes (ROC) is presented based on the published geology and stratigraphy, geophysical surveys, and general carbonate platform hydrogeology and hydrogeochemistry. Hydrogeothermal circulation of marine water through the platform pre-dates the impact, with density-driven fluxes exiting the sub-marine platform top, and dolomitization and anhydritization along the platform flow paths from the platform sides. Platform scale circulation continued post-impact, but enhanced vertical fluxes constrained around the perimeter of the hot and low-permeability melt plug. The numerous impact ring fault sets provide likely flow paths, but it is the fracture set circumscribing the perimeter of the impact melt plug that is significantly karstified by bottom-up hypogene processes to produce the observed Ring of Cenotes. Epigene karstification was only in the Late Miocene (<10 Ma) with exposure of the Yucatán Peninsula to meteoric inputs. 4 The Yucatán Block (YB) has been considered to be tectonically stable. Geodetic data from UNAVCO (DAI v2) stations with 5+ year records show the present-day motion to include NW direction and counterclockwise rotation, along with N and NE coastal subsidence of ~1 m / 1000 year. Major fault systems are now considered here as a continuous bank-marginal fracture system subjected to rotation. Coastal ecology, geomorphology, and archeological observations are consistent with the observed vertical motions and cast to at least the Late Holocene. The YB is tectonically rigid in the strict sense, without apparent deformation, yet block tilting and rotation is of broad significance in interpretation of the karst hydrogeology, paleoenvironmental records, and coastal adaptation to sea level rise. This work delivers a significant 30 element geochemical atlas of the Pleistocene and Holocene of the NE Yucatán Peninsula. Comparison of the bulk rock geochemistry to ocean chemistry helps constrain diagenetic post-depositional processes such as leaching, dolomitization and pedogenic pathways, including the origin of terra rossa formed on karst. The knowledge provided by this thesis provides the foundation for (re) assessing and the significance of vertical motion in the interpretations of sea level records and coastal adjustments including under already rising sea levels, depth stratification of epigene speleogenesis, and the hydrogeological function of bank marginal fracture sets, and the Chicxulub ring faults and the Ring of Cenotes. 5 Acknowledgements Monroy-Ríos gratefully acknowledges graduate research fellowship support from the Mexican National Science and Technology Council (CONACyT). This research was possible through funding to Beddows from the Institute for Sustainability and Energy at Northwestern (ISEN), and the National Science Foundation (NSF-1530345). 6 Dedicated to Michelle and Martina, for all the love. To my parents, Henriette D and Mario B. To my beloved families in México and Puerto Rico. To all the people who taught me the underwater and underground worlds. To Trish & Ed. 7 Table of Contents List of Figures ....................................................................................................... 11 List of Tables ......................................................................................................... 21 I General Introduction ............................................................................ 24 I-1 PREFACE .......................................................................................................................... 24 I-2 CONTEXT AND MOTIVATION .................................................................................... 25 I-3 OUTLINED ORGANIZATION ........................................................................................ 32 II Hypogene Hydrogeothermal Convective Circulation Model for the Formation of the Chicxulub Ring of Cenotes in the Yucatán Peninsula, Mexico .................................................................. 36 ABSTRACT .................................................................................................................................. 36 II-1 INTRODUCTION ............................................................................................................. 37 II-2 KARSTIFICATION .......................................................................................................... 39 II-2.1 CENOTES - MORPHOLOGY AND GENESIS .......................................................... 40 II-2.2 THE YUCATÁN PLATFORM OVERVIEW ............................................................. 43 II-2.2.1 Paleozoic Granodiorite Basement ................................................................... 43 II-2.2.2 Mesozoic Pre-Impact – Upper Jurassic, Lower Cretaceous, and Upper Cretaceous ....................................................................................................... 46 II-2.2.3 k-Pg Chicxulub Impact, Breccia Blanket, and Melt Plug ............................... 48 II-2.2.4 Cenozoic Post-Impact – Paleogene, Neogene, Quaternary ............................. 50 II-2.3 THERMAL ANOMALY & HYDROTHERMAL FLUX IN IMPACT STRUCTURES ........ 51 II-2.4 MULTIPLE SETS OF RING FAULTS ..................................................................... 52 II-2.5 SEA LEVEL HISTORY ........................................................................................ 52 8 II-3 GEOTHERMAL CONVECTIVE CIRCULATION ......................................................... 53 II-3.1 DIAGENESIS: EARLY BURIAL DOLOMITIZATION AND COUPLED ANHYDRITIZATION ........................................................................................... 56 II-3.1.1 Burial anhydrite: Refutation of Evaporite Origin ............................................ 58 II-3.2 HYPOGENE kARSTIFICATION DURING SUBMARINE STAGE ............................... 58 II-3.3 EPIGENE kARSTIFICATION DURING SUBAERIAL REGIME .................................. 61 II-4 HYPOGENE HYDROGEOTHERMAL MODEL FOR GENESIS OF THE RING OF CENOTES ................................................................................................................... 63 II-5 DISCUSSION .................................................................................................................... 65 II-6 CONCLUSIONS ............................................................................................................... 70 III On the Tectonic Stability of the Yucatán Block: Tilt and Rotation .................................................................................................. 72 ABSTRACT .................................................................................................................................. 72 III-1 INTRODUCTION ............................................................................................................. 73 III-1.1 TECTONIC SETTING AND FEATURES OF THE YUCATAN PLATFORM AND PENINSULA ....................................................................................................... 73 III-1.2 WESTERN CARIBBEAN SEA LEVEL RISE (SLR) ................................................ 82 III-1.3 UPPER PLEISTOCENE RIDGES ............................................................................ 83 III-2 DATA AND METHODS .................................................................................................. 83 III-3 RESULTS .......................................................................................................................... 84 III-3.1 GPS/GNNS STATIONS ..................................................................................... 84 III-3.2 MAYA COASTAL SITES ..................................................................................... 86 III-3.2.1 Additional Sites - North & Gulf Coast Maya Sites ......................................... 88 III-3.3 COASTAL MANGROVE ...................................................................................... 88 III-4 INTERPRETATION & DISCUSSION ............................................................................. 90 III-4.1 GEODETIC DATA – TILT ...................................................................................