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Ozona sandstone, Val Verde Basin, Texas: Synorogenic stratigraphy and depositional history in a Permian foredeep basin

¹ Bureau of Economic Geology, John A. and Katherine G. Jackson School of Geosciences, University of Texas at Austin, Austin, Texas 78713-8924;scott.hamlin{at}beg.utexas.edu

H. Scott Hamlin is a research scientist associate at the Bureau of Economic Geology. He received his B.A. and M.A. degrees and his Ph.D. from the University of Texas at Austin. His research interests include depositional systems, stratigraphy, reservoir characterization, and hydrogeology. His current research focuses on Wolfcampian and Leonardian slope and basin reservoirs in the Midland Basin of west Texas.

ABSTRACT

The Ozona sandstone is a record of Permian synorogenic sedimentation in a foreland basin. The Ozona comprises terrigenous clastic slope and basin systems overlain by mixed clastic-carbonate shelf-ramp systems. Ozona sandstones form low-permeability gas reservoirs in Crockett County, Texas. I used wire-line logs and cores to map Ozona genetic stratigraphy and to reconstruct the depositional and tectonic history during the final phase of the Ouachita orogeny. Ozona depositional systems are composed of sandy turbidite channel and lobe genetic facies enclosed in laterally extensive muddy turbidite sheets and hemipelagic drapes. Channel and lobe complexes and turbidite sheets together form basin-floor apron systems. Coeval slope systems are mud-dominated products of mass transport processes. Sediment dispersal systems evolved from point sourced to line sourced.

Ozona sequence development was primarily controlled by tectonic uplift and subsidence. Stratal geometries, facies associations, sediment input patterns, and depocenter locations are stable within sequences, but they change across sequence boundaries in response to tectonically driven changes in basin geomorphology. Onlapping stratal geometries in the lower sequence record excess accommodation space in the study area as plate convergence progressed from south to north. Offlapping strata in the middle and upper sequences formed in response to reduced accommodation space and intraforeland uplift in the north. At the base of each sequence, sandstone depocenters step toward the thrust belt in response to thrust-sheet loading and foredeep subsidence, but within each sequence, depocenters migrate away from the thrust belt. Foredeep migration through time provides a predictive tool for locating Ozona reservoir analogs farther south in Val Verde Basin.