Numerous classifications and nomenclatures of the Wilcox section and various portions of that section in south Texas, determined on regional, subregional, and localized bases, lead to considerable confusion among geologists using different nomenclatures and the application of "upper," "middle," and "lower" designations to the section. An overall stratigraphic classification framework is proposed in which the various facies of the Wilcox and all other classifications and nomenclatures will fit, thereby standardizing recognition of the various facies and sections of the Wilcox throughout the south Texas area.

In the proposed informal classification, the Wilcox Group is subdivided in the updip subsurface, where the stratigraphy is primarily nonmarine, into the Indio Formation and the Carrizo Formation. The Carrizo Formation is further subdivided into the Wilcox-Carrizo Member, the Massive Carrizo Member, and the Carrizo-Bigford Member. In the downdip subsurface, where the stratigraphy is essentially marine, the Wilcox Group is subdivided into the lower, middle, and upper Wilcox Formations. The upper Wilcox Formation is divided into lower and upper members. The upper Member is further subdivided into the Massive, Mackhank, Luling, and Slick Sands in the areas where these sands are present.

Regional and area studies within the past 20 years, along with greater well control in sparsely or previously undrilled areas, have significantly increased our knowledge and understanding of Wilcox stratigraphy.

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