CONSTRUCTING BALANCED STRUCTURAL CROSS-SECTIONS IN THE ARKOMA FORELAND BASIN, SOUTHEASTERN OKLAHOMA: DIFFICULTIES, ERRORS AND BENEFITS
The main difficulties and errors of balancing cross-sections in the Arkoma Basin are due to the lack of thick sandstone and limestone units. We attempted to construct cross-sections with using kink-band style of folding and the ramp-flat thrust model. However, we could not use the model because of the presence of competent sandstones scattered in over 20,000 feet thick incompetent shale units of the Atoka Formation in the basin. Consequently, we used concentric folding in our cross-sections and used the key-bed balancing method. The method created errors in shortening calculations because it relies on one wide-spread rock unit. However, we used kink-bend style of folding in the Potato Hills area of the Central Ouachitas where the Middle Ordovician to Mississippian brittle rock units is present on the hanging wall of the Winding Stairs fault. From the central Ouachitas to the leading edge of the frontal Ouachitas, strain portioning is accommodated by imbricate fan thrusts on the hanging wall of the Choctaw detachment. The strain partitioning is accommodated primarily by a triangle zone and a duplex structure in the frontal Ouachitas-Arkoma Basin transition zone where the Atokan Flycsh deposits are well exposed in both hanging wall and footwall of the Choctaw detachment. When restored to their original position prior to lower Atokan, the cross-sections indicate about 60% shortening from the Central Ouachitas to the Arkoma Basin. The shortening is, however, only about 20% in the Arkoma Basin in the footwall of the Choctaw Detachment.
Benefits of constructing balanced cross-sections in the Arkoma Basin include a) locating different facies of the gas-producing sandstones, such as Lower Atokan Spiro, Brazil, Cecil and Mid-Atokan Red Oak sandstones both on the deformed state and restored cross-sections; and b) determining likely areas for next gas plays in the Arkoma Basin.