PETROGRAPHIC AND MICRO-FACIES ANALYSES OF THE FORT TERRETT FORMATION OF THE LOWER CRETACEOUS EDWARDS GROUP, IN KIMBLE COUNTY, TEXAS

During the lower Cretaceous, the Fort Terrett Formation was deposited on the western margin of the Comanche Shelf near central Texas. The Fort Terrett Formation is a massive limestone unit that makes up the dominate topography around the Junction area. Deposition of the Fort Terrett Formation occurred in quiet, calm waters along a shallow shelf during the Lower Cretaceous time. In 1974 Rose developed a universal stratigraphic correlation that became the primary lithostratigraphic framework of the Cretaceous shelf for much of west Texas. Four stratigraphic divisions have been observed and correlated in the Fort Terrett Formation. These are as follows: 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 two of the four units which are the burrowed unit, distinguishable by bioturbation, fossils, and a dark grey color, and the dolomitic unit. The dolomitic unit is distinct by the massive white limestone and lack of fossils, indicating a lower biodiversity. This study has divided the Fort Terrett Formation into micro facies around Junction 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 were 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.