PALEOHYDROLOGY OF REFLUX DOLOMITIZATION IN THE PERMIAN SAN ANDRES FM, GUADALUPE MOUNTAINS AND ALGERITA ESCARPMENT, TEXAS AND NEW MEXICO


Beatriz Garcia-Fresca

Jackson School of Geosciences - The University of Texas at Austin

Austin, Texas, USA

[email protected]

Dolomitization is a common phenomenon in carbonate rocks and although extensive petrographic and geochemical studies have been carried out to document its origin, the hydrologic mechanisms that control their formation are yet poorly understood. Dolomitization is a fabric altering process that affects the distribution of porosity and permeability in carbonates. Thus, increasing our understanding of the hydrogeology of dolomitization will improve predictions on the distribution of porosity and permeability in dolomitized aquifers and reservoirs.

The San Andres Formation is a succession of limestones, dolostones and evaporites deposited on a broad carbonate ramp in near-equatorial position during late Leonardian through mid-Guadalupian time. Seepage reflux is the dolomitization mechanism commonly invoked for the San Andres Formation. World-class platform-to-basin exposures in the Guadalupe Mountains and Algerita Escarpment (Texas and New Mexico) provide an ideal field laboratory for understanding seepage reflux dolomitization. I propose to integrate hydrologic, petrographic, and sequence stratigraphic analyses that will help us explore and constrain the hydraulic controls of this dolomitization mechanism. First, I will compile and expand preexisting descriptions of limestone/dolostone transitions and sequence stratigraphic context of the San Andres Fm. A second approach encompasses lab identification and description of fabrics, types and relative timing of dolomitization events. Petrographic analysis, cathodoluminescence microscopy, and geochemistry are approaches that will be applied. Finally, the stratigraphic and sedimentologic data will be used to construct and populate a numerical hydrologic model that will explore the suitability and controls of reflux seepage as the dolomitizing mechanism in the San Andres Formation.

AAPG Search and Discovery Article #90060©2006 AAPG Foundation Grants-in-Aid