Barnett Shale Geology and Petrology SCAL, Inc. SPECIAL CORE ANALYSIS LABORATORIES, INC.

Barnett Shale Paleogeography From: Mississippian Barnett Shale: Lithofacies and depositional setting of a deep-water shale-gas succession in the Fort Worth Basin, Texas, by Robert G. Loucks and Stephen C. Ruppel, AAPG Bulletin, v. 91, no. 4, p , April 2007

Barnett Shale Depositional Processes From: Mississippian Barnett Shale: Lithofacies and depositional setting of a deep-water shale-gas succession in the Fort Worth Basin, Texas, by Robert G. Loucks and Stephen C. Ruppel, AAPG Bulletin, v. 91, no. 4, p , April 2007

Barnett Shale Lithology LITHOLOGY The Barnett Shale is composed of a combination of marine clays, primarily illite and chlorite, detrital quartz silt, silicified and carbonate bioclasts and fossils, interstitial organic carbon, and phosphate. Most Barnett Shale samples are siliceous mudstones, not shales, such as the top photo. Many are so rich in quartz that they are really argillaceous siltstones, such as the lower photo. In both photos, quartz grains are white, but some elliptical grains are compressed silicified microfossils. SCAL, Inc. SPECIAL CORE ANALYSIS LABORATORIES, INC.

Barnett Shale Bedding DISTURBED BEDDING Barnett Shale sediments were often disturbed by bottom currents created by gravity, density, and turbidity flows. These flows would carry shelf and slope components, especially shallow-water fossils and bioclasts, down to the basin floor and deposit them in the carbon-rich muds. The density flows were strong currents that disturbed the bottom, creating ripple marks and disturbed, wavy bedding. SCAL, Inc. SPECIAL CORE ANALYSIS LABORATORIES, INC.

Barnett Shale Fossils FOSSILS Barnett Shale often contain macrofossils and bioclasts transported from the shelf to the basin by density and gravity currents. These fossils are composed of their original calcite, of recrystallized calcite or dolomite, or of quartz after undergoing silicification. The top photo shows bivalve mollusks (pelecypods) and skeletal fragments. The lower photo shows crinoid columnal bioclasts and flattened pelecypod shells. SCAL, Inc. SPECIAL CORE ANALYSIS LABORATORIES, INC.

Barnett Shale Microfossils MICROFOSSILS Barnett Shale samples often contain microfossils. These have two origins. The examples shown here are both shallow- water foraminifera that were swept into the basin environment by density and gravity currents. The top photo is an agglutinated foram whose walls were composed of calcite grains that have now been completely silicified and compressed. The lower photo is a uniserial foram that has been phosphatized. SCAL, Inc. SPECIAL CORE ANALYSIS LABORATORIES, INC.

Barnett Shale Phosphates MARINE PHOSPHATES The Barnett Shale often contains phosphates. Phosphates form at the edge of a basin just seaward of the slope. Here, upwelling creates an enormous phytoplankton productivity which causes the underlying sediments to become rich in organic components, including phosphorous. The phosphates accumulate in nodules or crusts, and phosphate can replace other minerals or precipitate in pore space. The orange-yellow mineral is phosphate. SCAL, Inc. SPECIAL CORE ANALYSIS LABORATORIES, INC.