Hydrogeologic and Speleogenetic Constraints of a Coastal Karst Aquifer: Sistema Jaguar, Quintana Roo, Mexico

Jenson, Aubri A
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Karst aquifers are self-organizing, scale-dependent systems with highly heterogeneous hydrogeologic properties. Coastal karst systems are especially complex because sea level changes affect porosity development through geologically rapid processes that result in dissolution or deposition. Regional-scale coastal aquifer models often fail to describe heterogeneity at smaller scales because detailed data is unavailable for parameterization. This research evaluated hydrogeologic heterogeneity in the context of formative processes related to sea level history in a coastal karst aquifer sub-basin in Quintana Roo, Mexico. I used new data and approaches to test models and assumptions of speleogenesis and tectonic stability on the Yucatan Peninsula. First, I measured and analyzed data describing morphology, distribution, and orientation of sinkholes and cave passages, and investigated their utility as indicators of structural and hydrogeologic controls on karstification. Results suggest that karst feature are primarily controlled by hydrogeologic properties and secondarily by structural features. Second, I quantified and constrained aquifer properties of diffusivity, transmissivity, hydraulic conductivity, and hydraulic gradient using long-term, high-resolution water level data collected in cave passages that intersect the water table. The hydraulic gradient steepens near the coastline, which differs from previous measurements near coastal springs and has implications for water budgets. Finally, I constrained the timing of speleogenesis by comparing sea level records with U-Th dates of speleothems, and calcite overgrowths that form at the water table. Together, these data revealed that conduits are much older than previously assumed, formed at much lower elevations than their current positions, and that significant amounts of both regional uplift and landscape denudation must have occurred. These findings contradict long-held but untested assumptions of recent conduit formation, and tectonic stability in the Yucatan Peninsula throughout the Quaternary. The modern hydrogeologic function and position of conduits is the combined result of dynamic uplift, speleogenesis, and changing sea levels that occurred over the past >650,000 years, rather than tectonic stability and in-situ speleogenesis occurring during relatively brief sea level high stands.
Yucatan Peninsula, Karst controls, Coastal aquifers, Tectonic uplift
Jenson, A. A. (2019). <i>Hydrogeologic and speleogenetic constraints of a coastal karst aquifer: Sistema Jaguar, Quintana Roo, Mexico</i> (Unpublished dissertation). Texas State University, San Marcos, Texas.