The Barnett Shale (Mississippian) in the central Midland Basin (Andrews, Ector, Martin, and Midland Counties)

Abstract

Fine-grained units underlying the Atoka Lime Formation in the Midland Basin have historically been interpreted as Pennsylvanian (Atokan) or Mississippian (Chesterian) strata. Recent palynology data suggest that the shale was deposited during the late Mississippian (Osagean-Chesterian), making it equivalent to the Barnett Shale. The trend of the Barnett was studied in a 25-mi2 (~65 Km2) area in the Central Midland Basin. In the study area, siliceous-calcareous units comprising the Barnett shale can be divided into an upper and lower unit. The upper unit can be further subdivided into six subunits by log curve markers, interpreted as gravity-flow deposits consisting of silty bioclastic debris. Isopach maps of the flow deposits suggest a source to the north. Preliminary TOC analyses suggest that the upper Barnett section is relatively TOC lean, whereas the lower Barnett has higher values. Exploration focus can be enhanced by detailed mapping of flows for the upper Barnett.