As in modern oceans, there is ample evidence that sands bypassed shelf-edges of ancient interior basins and accumulated in deeper parts of the basins. Although water depths in these basins were never in the abyssal zone, these deposits are today recognizable as “deep-water” sands.
Based on a seismic, subsurface, and sedimentologic study of the Tonkawa Sandstone (Missourian), we have developed a seismic-stratigraphic model for Pennsylvanian sands in the Anadarko basin. Typically, the Tonkawa and other sands are regressive and cyclic and are bounded at the base and top by transgressive limestones. The sands consist of three facies: (1) an upper shallow-water shelf facies, (2) a middle submarine slope-channel facies, and (3) a lower submarine fan-lobe facies. Each sandstone unit exhibits characteristic electric log and seismic signatures and distinctive sedimentary structures and textures. For each depositional cycle, the shelf edge may be formed by a contemporaneous reef, and the break in bathymetric gradient at the base-of-slope may be marked by an older reef. Besides the Tonkawa Sandstone, this model is applicable to the following formations: (1) Springer/Morrow (Springeran/Morrowan); (2) Red Fork (Desmoinesian); and (3) Cleveland and Cottage Grove (both Missourian).
The model predicts that both individual slope sands and submarine fan lobes are potential stratigraphic traps. Associated carbonate banks may also form traps. We suggest that many deep-water traps remain to be found in the Anadarko basin.
