CHEMOSTRATIGRAPHY AND GEOCHEMICAL ANALYSIS OF TWO DRILL CORES FROM THE BARNETT SHALE, HAMILTON COUNTY, TEXAS

Correlation of geochemical data from different drill cores can be helpful in refining the stratigraphy of a spatially extensive unit or series of units, as well as understanding the paleoceanography of a region during deposition. The Mississippian-age Barnett Shale of the Fort Worth Basin, Texas, is of particular interest due to its economically beneficial natural gas production. The Lake Davis #1 and the Mesquite #1 drill cores from Hamilton County, Texas, show stratigraphically unconformable boundaries between the underlying unit, a carbonate-rich unit that could be the Chappel Limestone, the Viola Limestone, or the Ellenberger Limestone. However, the Barnett Shale is gradationally conformable with the overlying Marble Falls Limestone. These units can be defined based on %Ca content and/or variability. The lower carbonate-rich unit is characterized by high %Ca concentrations (>40% Ca). The Barnett Shale is characterized by significantly lower %Ca concentrations (~4% to 10% Ca), with relatively low variability, but calcite nodules are observed throughout the core. The top of the shale unit shows a thick, oscillatory, gradational change into the Marble Falls Limestone. TOC values for the Mesquite #1 core range from 0.1% to 9.6% C.