Abstract
Wilcox Group sediments are classified into three main formations: a lower Hooper Formation, a middle Simsboro Formation, and an upper Calvert Bluff Formation. The Calvert Bluff and Simsboro formations have been interpreted as fluvial-delatic sediments. However, with the application of regional and detailed analyses, a new model has been developed. Lignite zones within the Calvert Bluff and Simsboro formations are of particular interest. These zones represent depositional environments that are distinctly different from the surrounding sediments. Sediments within the zones include ripplelaniinated sands and shales, interbedded with laterally extensive lignites. Regional and localized correlations of the lignite zones show development of incised valleys that were subsequently filled with braided stream sandstones, followed by tidally-influenced sands and shales interbedded with lignites. Incorporating well log analysis, seismic interpretations, and outcrop descriptions together, a sequence stratigraphic model is proposed. The model depicts highstand, transgressive, and lowstand deposition. This type of modelling is a necessary tool for future coal and hydrocarbon exploration. Primary petroleum production in east central Texas is from the Austin Chalk Formation. However, as seen in development of the Martins Prairie field in Grimes County, production is from braided stream deposits within incised valley fills of the Simsboro Formation in the Wilcox Group.
May, Audrey Gail (1994). Stratigraphy of the Calvert Bluff Formation of the Wilcox Group, Brazos County, Texas. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1994 -THESIS -M466.