Petrographic and micro-facies analyses of the Fort Terrett Formation of the Lower Cretaceous Edwards Group, In Kimble County, Texas

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Abstract

The Fort Terrett Formation was deposited on the western edge of the Comanche Shelf in central Texas. The predominate lithology of the Fort Terrett Formation is limestone which caps the hills that surrounding Junction, Texas. Deposition of the Fort Terrett Formation occurred within shallow, quiet waters during the Lower Cretaceous. Rose (1974) developed a general stratigraphic correlation and lithostratigraphic framework for the Cretaceous shelf and established a regional correlation. Four stratigraphic divisions have been recognized in the Fort Terrett Formation. These are: a basal nodular unit, a burrowed unit, a dolomitic unit, and the Kirschberg evaporites. In the Junction area, measured sections by Rose (1974) of the Fort Terrett Formation contain the lower two units which are the burrowed unit, distinguishable by bioturbation, and the dolomitic unit. This study has divided the Fort Terrett Formation into micro facies in the Junction area to determine smaller order sequences. Nine sections of the Fort Terrett Formation were measured along road cuts on I-10 near Junction, Texas and hand samples collected. This data was used to divide the Fort Terrett Formation into two lithostratigraphic units. The lower unit contains extensive chert nodules and fossils that indicate a shallow water shelf. The upper unit contained thick-bedded limestone representing an open carbonate shelf.

Author

• Richard Urwin, Stephen F. Austin State University