Raster log images were analyzed to study the subsurface stratigraphy of the Middle Atoka in the Arkoma Basin of the western portion (Sebastian County) of Arkansas. The most significant sandstone units of the Middle Atoka in this area were determined to be two generally coarsening-upward sequences in the lower portion of the formation. Based on lithologic correlations, these two units were determined to be the informally named Casey and Freiburg members of the Middle Atoka. Thickness information based on picked tops was used to create isopach maps of the units of interest. The log signatures and geometry of the sand bodies indicate that they were deposited in a deltaic system that prograded across this portion of this basin. Distributary-mouth bar deposits dominate the Casey member, and are occasionally overlain by localized channel deposits. Avulsion of the delta lobe possibly occurred, and a new lobe then began to prograde, depositing the sediments that formed the Freiburg. This unit is also dominated by distributary-mouth bar deposits.
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