MODELING SPELEOGENESIS AND AQUIFER DEVELOPMENT IN A COASTAL CARBONATE PLATFORM: QUINTANA ROO, MEXICO

Mixing-zone speleogenesis is traditionally assumed to dominate conduit development in carbonate platforms; however, both mixing zone and vadose CO₂ reactions contribute to cavernous porosity, and mixing-zone dissolution alone does not adequately explain patterns of cavern development that are observed in many systems. Horizontal and vertical bedrock heterogeneity, and a mixing zone that moves with sea level, complicate efforts to understand linkages between geologic, hydrologic, and geochemical controls on aquifer development. Ultimately, models of carbonate platform speleogenesis must include interactions between all of these parameters over time and space. The objective of this project is to create a model that simulates patterns of cave development observed along a 100km stretch of the eastern coastline of the Yucatan peninsula in Quintana Roo, Mexico.

In the last 2 million years, sea-level has fluctuated between -120m and +6m relative to modern sea level. If cave development is primarily controlled by the position of the freshwater-saline water mixing zone, then conduit horizons should be coincident with past locations of the mixing zone, the depth of which increases with distance inland. Over 150km of passage have been mapped above current sea level within 10km of the modern coastline, and mapping continues. Many of these conduits are 9-12m above modern sea-level, which suggests that alternative modes of speleogensis such as soil-derived CO₂should be considered to explain observed karstification. While the majority of underwater conduits are found between -10 and -30m, no extensive conduit network is known that corresponds with cumulative stillstands at depths near -50m; suggesting that speleogenesis in the past is poorly understood.

We will test the current conceptual model by simulating conduit development in a hypothetical cross-section using mixing zone depths and water table elevations reconstructed from sea level curves and recharge rates from paleoclimate records. Speleothem dates from other studies will help constrain the timing of conduit development. Drill core data will provide initial conditions for permeability and porosity. Model predictions will be tested using cave survey and remote sensing data, as well as field observations.