14-7 Conodonts and the Dynamic Stratigraphy of the Pennsylvanian (Missourian) Dog Bend Limestone, Palo Pinto County, Texas.

Abstract:

The Dog Bend Limestone Member of the lower Salesville Formation demonstrates the dynamic stratigraphy along the margins of the Perrin Delta System on the Eastern Shelf of the Permian Basin. The Dog Bend, at its most well-known exposure (TX-4) consists of a lower and upper limestone bed separated by 2.5 meters of fossiliferous shale. The TX-4 locality is furthest from the influence of deltaic sedimentation with only a thin sand below, in the position of the Lake Pinto Sandstone (the prior major advance of the Perrin Delta to the west). At the Mineral Wells Fossil Park (MWFP) locality, the upper limestone of the Dog Bend caps over 5 meters of fossiliferous shale. The lower limestone is not exposed. MWFP deposition occurred in a restricted bay between two lobes of the Perrin Delta. At the newly discovered Highway 337 locality (337), the lower Dog Bend is a 10-centimeter vuggy sandy limestone overlain by a 12-centimeter micrite of the upper Dog Bend. The two are separated by approximately 20 centimeters of covered material. The 337 locality sits on top of the Lake Pinto deposits of the previous deltaic advance. Idiognathodus species have proven helpful in correlating these three distinct localities with I. turbatus, I. heckeli, and I. eccentricus confirming the correlation of the lower portion of the Salesville Formation with the Hertha Cyclothem of the Midcontinent Basin. The limestone facies is characterized by Idiognathodus specimens of reduced size, Idioprioniodus, and Adetognathus. Adetognathus dominates the fauna of the upper Dog Bend at 337. At TX-4, Adetognathus is less common while Idioprioniodus, and Idiognathodus more common.  At MWFP, conodonts are rare. The shale facies is characterized by a diverse Idiognathodus fauna with rare occurrences of the other genera. The shale facies fauna is much more uniform across the localities than is observed in the limestone facies. The conodont data has proven to be of great importance in correlating strata across these vastly different facies and provided evidence that, when incorporated with lithological and geophysical data, has provided great insight into the dynamic depositional system of the Perrin Delta.

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