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The AAPG/Datapages Combined Publications Database

South Texas Geological Society Special Publications


Contributions to the Geology of South Texas, 1986
Pages 135-159

Proposed Stratigraphic Classification of the Wilcox of South Texas

Richard N. Hargis


Numerous systems of stratigraphic nomenclature of the Wilcox Group and various portions of that group exist in South Texas on regional, subregional, and localized bases, leading to considerable confusion among geologists using different nomenclatures. A broad, regional, stratigraphic classification is proposed in which other classifications and nomenclatures will fit, thereby standardizing recognition of the various stratigraphic intervals comprising the Wilcox throughout the South Texas area.

Many of the Wilcox depositional systems have been identified and defined in previous studies. The proposed classification is based on the natural subdivisions of the Wilcox progradational sequence and the lithology and depositional systems contained therein.

This classification follows the North American Stratigraphic Code. The Wilcox Group is subdivided into lithostratigraphic units as follows: the Upper Wilcox Subgroup, the Middle Wilcox Subgroup, the Lower Wilcox Subgroup, the Carrizo Formation, the Indio Formation, and an unnamed downdip shale unit. The Carrizo Formation is further subdivided into the “Carrizo-Bigford” Member, the “Massive Carrizo” Member, and the “Wilcox-Carrizo” Member. The Upper Wilcox Subgroup is divided into an Upper Member and Lower Member, and the Upper Member is subdivided into the Slick, Luling, Mackhank, and Massive sandstone units in the areas where these sands are present. Chronostratigraphic and diachronic units are also proposed, and each of the lithostratigraphic units is briefly defined and described as to stratigraphic position, vertical and lateral boundaries, time span, depositional systems, and other pertinent information.

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