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Gene Rankey
University of Kansas
Deposits and Dynamics of Carbonate Shorefaces around the Modern Yucatan Shelf, Mexico
Gene Rankey1, Rodrigo Garza-Perez, Michel Matysik, Tom Neal, Jennifer Lowery, Christian Appendini
1 Kansas Interdisciplinary Consortium on Earth, Energy, and Environment, University of Kansas
Carbonate ramps and associated shorefaces are ubiquitous in the stratigraphic record, including many important examples in the Permian Basin. Although numerous ancient examples have been characterized, there is a relative paucity of studies of modern ramp to provide analogs and insights into their dynamics. The purposes of this presentation are to describe the nature of variability in the nearshore parts of the Modern carbonate ramp around the Yucatan Peninsula, Mexico and to explore the physical, chemical, and biological controls on this variability; these results provide the basis for understanding controls on heterogeneous ancient ramp systems.
The Yucatan Peninsula and the flanking of the Yucatan Shelf extends northward, flanked to the east by the Caribbean Sea and to the north and west by the Gulf of Mexico. The eastern margin includes a narrow shelf, widest just north of Cancun. Here, the northward-flowing Yucatan Current impinges on the shelf and generates a strong, persistent current to the north. On the broader shelf between Cancun and Isla Mujeres, this current generates ubiquitous subaqueous bars and dunes that contain ooids. The oolitic shoreface includes evidence for longshore transport, but not marked progradation. In contrast, the north flank of the peninsula is shaped by the easterly trade winds and occasional Nortes, or cold fronts, which bring waves from the north. The easterly winds generate a weak west-flowing current that occasionally carries cool and nutrient-rich water along the shoreface, and favors a transitional heterozoan-photozoan association; ooids are absent. This northern shelf includes skeletal-rich sand with ubiquitous subaqueous dunes and evidence for prograding shorefaces with abundant longshore transport. The northwestern shoreface includes foreshore consisting largely of molluscan coquina, and upper shoreface deposits that include common subaqueous dunes to the northwest and abundant Halimeda meadows to the west of the peninsula. The western shoreface includes the most abundant biosilicious fraction, with diatoms sponge spicules, and radiolaria constituting up to 20% of the sediment, and a relative paucity of bedforms.
The results illustrate along-strike changes in energy level, sea-surface temperature, nutrient-rich upwelled waters, their impact on the geomorphology, biota, and sedimentology of the nearshore parts of this Holocene ramp system around the peninsula. They provide conceptual models for enhanced interpretation and understanding of ancient nearshore oolitic, skeletal-rich, or cherty analogs, including reservoirs and repositories.
Gene Rankey is a professor of Geology at the University of Kansas. His research program focuses on unravelling surface processes and quantifying the nature and controls on sedimentologic variability and geomorphic forms in modern tropical marine and nearshore sedimentary systems. Recent efforts have examined blue carbon and sediment dynamics of Pacific atolls and their islands in the face of climate shifts, and he was co-author of the book "A Global Atlas of Atolls" (2023) that describes all of the world's atolls. His research has direct application to understanding geologic analogs via development of quantitative and conceptual models for the nature and origin of facies and stratigraphic heterogeneity of ancient carbonate reef, shoal, ramp, and platform successions, and efforts have integrated seismic, log, petrophysical, and core data. Rankey serves as co-PI of the Kansas Interdisciplinary Consortium of Earth, Energy, and Environment (KICE3), an academic-industry consortium dedicated to research, training, and education for understanding pressing challenges of the energy transition, with a focus on carbonate systems.
