Abstract

Lower Pennsylvanian deposits in the Anadarko basin onlap eroded and truncated Mississippian age rocks. The basin is asymmetric with a mobile rim, basin deep, hinge zone, and stable shelf. Onlap is noticeable between the basin deep and the stable shelf. Successively younger time-rock units extend past older rocks and terminate against the post-Mississippian unconformity. In western Oklahoma, between the top of the Cherokee Formation (Desmoinesian) and the base of Morrowan rocks, there is 1,500 feet of stratigraphic onlap. This interval contains more than 12,380 cubic miles (135 × 11¹² tons) of sediment. Except for scattered, thin, silty, and agrillaceous limestone, all of this sediment consists of terrigeous elastics, transported into the basin by streams and deposited in relatively shallow marine water. Detailed study of core from the Cherokee and Morrow Formations indicates that most of the rock was deposited in a deltaic environment. Deltas prograded the shoreline and built lobes of regressive deposits which kept the subsiding basin nearly full. Lateral shifting of the major sites of deltaic sedimentation permitted deposition of thin impure limestone in interdeltaic areas. Continued and rapid subsidence of the basin established the pattern of onlapping stratigraphy. An understanding of the relationship between this onlap framework and the regressive deposits involved provides insight into the processes of basin filling.