Petrographic and stratigraphic analysis along the Lower Cretaceous strata, in Kimble county Texas

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Abstract

In the Kimble County area, the upper Trinity Group is predominantly a carbonate system with minor clastic couplets that were deposited during the Middle Cretaceous in the south Llano Uplift region. Stratigraphic units of the upper Trinity Group are the Hensel Formation, determined to be supratidal claystones, the Glen Rose Formation, which are mudstones that were deposited in a carbonate lagoon, and the Walnut and Fort Terrett formations, which are wackestones to packstones interpreted to have been deposited on a shallow carbonate shelf. Nine stratigraphic sections were measured along Interstate 10 and U.S Highway 377 in Kimble County, Texas to analyze the lithostratigraphy, sequence stratigraphy, petrography, and paleotologic deposition. The upper Hensel Formation contact with the Lower Glen Rose Formation is based on the uppermost red bed of the Hensel Formation, forming the first sequence. Sequence 2 begins at the mudstones atop of the Hensel Formation and end at the burrowed mudstone unit. This forms the Glen Rose Formation. Sequence 3 extends from claystones atop of the burrowed unit of the Glen Rose Formation and terminates at the disconformable contact with the Fort Terrett Formation. It represents the Walnut Formation. Petrographic study of the Hensel, Glen Rose and Walnut formations indicate that marine diagenesis has altered all units present. Common bivalves in the above the Glen Rose Formation were Ceratostreon texana, which are index fossils for the Walnut Formation and provided evidence for the placement of the Walnut Formation above the Glen Rose Formation in Kimble County, Texas.

Author

• Austin C Wilkerson, Stephen F. Austin State University