Barnett Shale (Mississippian) Lithofacies, Fort Worth Basin, Texas
Philip J. Bunting1, John A. Breyer1
, and Daniel M. Jarvie2
1Department of Geology, Texas Christian University, Fort Worth, TX
2Humble Geochemical Services, Humble, Texas
Five facies are present in the Barnett Shale (Mississippian) in a core taken in the southern part of the Fort Worth basin. Facies A is a laminated, silty claystone to siltstone with glauconite grains and sand-sized shale rip-up clasts. It is found only at the top of the core and comprises just 7% of the cored interval. The facies is characterized by fine horizontal laminae undisrupted by bioturbation. Facies B consists of light-colored, limy layers that react vigorously with dilute HCl. The layers occur as thin interbeds in facies E throughout the core. Facies B comprises 4% of the cored interval. The contacts with the overlying and underlying dark, argillaceous claystones of facies E are flat and sharp. Calcite-rich concretions comprise facies C. Laminae in the surrounding claystones are bent around the concretions indicating that the concretions formed at an early stage of burial, before the claystones were completely compacted. Facies C comprises 2% of the core. Facies D is characterized by abundant, large, broken shell fragments. The layers containing the shells are interbedded with dark gray to black claystones of facies E. The shell layers make up only 1% of the cored interval. Facies E makes up the vast majority of the Barnett Shale—86% of the total core. It is a dark-colored, fine-grained rock. The color ranges from dark gray to black. The rock consists predominantly of clay-sized particles, but contains varying amounts silt-sized, and even sand-sized material. These coarser grains include calcareous and siliceous bioclasts, shale rip-up clasts, phosphatic material and quartz grains.
AAPG Search and Discover Article #90065©2007 AAPG Southwest Section Meeting, Wichita Falls, Texas