STRUCTURAL INFLUENCE ON STRATIGRAPHIC CONTINUITY WITHIN THE ATOKA FORMATION ACROSS THE WASHBURN ANTICLINE, CENTRAL ARKOMA BASIN, ARKANSAS

The Washburn anticline is a major, foreland uplift in the Arkoma basin of central Arkansas. A structural and stratigraphic interpretation based on well-log data was performed on the eastern end of the anticline. The study area is within T.7N, R.27W; T.6N, R.27W; T.7N, R.26W; and T.6N, R.26W, in the Booneville and Magazine quadrangles. Well logs from twenty-four wells were interpreted and correlated along four cross-sections trending from the north to the south side of the structure. Natural gas has been or is being produced from twenty of those wells.

Well-log correlation revealed a major thrust fault. The fault trends along the crest of the anticline, with an overall northeast strike. It dips to the south at a high angle. The coincidence of the anticline and the trace of the fault suggest that the Washburn anticline is a fault-propagation fold. The correlations also revealed a thickening of sandstone units on the south of the thrust trace and on the south side of the anticline compared to the north side. A lack of continuity of sandstone units from the north side of the anticline to the south side was also established indicating that the sandstone units to the south were deposited further off the shelf than the units to the north. Displacement along the hanging wall of the thrust moved them to their present position. Seismic data suggest that normal faults, which predate thrusting, are present beneath the axial region of the anticline and may have controlled the position of the anticline and of the thrust.