Biostratigraphy of Carboniferous Rocks, San Saba County, Central Texas: ABSTRACT

Abstract

Increased understanding of complex carbonate facies patterns in Carboniferous rocks of central Texas permits systematic investigations of macropaleontology and biostratigraphy. Fossils studied were collected from exposures of Chappel, Barnett, Marble Falls, and Smithwick formations in the north-central part of the Llano uplift. The first purpose of this investigation was to identify and describe the macrofauna as completely as possible. Brachiopods, particularly productids and chonetids, dominate the fossil assemblages. However, colonial and solitary corals, bryozoans, gastropods, pelecypods, goniatites, nautiloids, crinoids, and a few trilobites are also present. A second purpose of the investigation was to assess relations among faunas and the several different carbonate and shale facies. For example, the fauna preserved in Chappel beach sediment is completely different from the fauna preserved in conformably overlying Barnett Shale. Most of the taxa from the Barnett range upward into the Marble Falls Limestone, where initiation of carbonate sedimentation resulted in greatly increased fossil abundance and species diversity. This population explosion was halted by the rapid influx of prodeltaic Smithwick mud. An examination of the faunas across the Mississippian-Pennsylvanian and Morrowan-Atokan boundaries determined that changes within specific groups were adaptations to different ecologic conditions. End_of_Article - Last_Page 849------------