Once again Oklahoma began to drift north, closer to the equator, taking a more low-latitude position than it had during the Siluro-Devonian. After a deep, anoxic water phase that leads to the deposition of black shales, the Lower Mississippian once again was a time of limestone formation. The deeper seas giving way to shallow marine shelf environments that extended across most of the northern half of the state.
By the Middle to Late Mississippian tectonic activity of the North American continent increased, indicated by formation of low-lands to the west of Oklahoma, and a deepening of the Anadarko and Ouachita basins in the south part of the state. Increased amounts of clastic material (sands, silts, and clays) were being deposited into these basins. As more clastic material was shed from ever expanding highlands to the west, the carbonate factory, which had been producing thick deposits of limestone and dolomite throughout lower half of the Paleozoic, was effectively stopped.
By the close of the Mississippian, Oklahoma, as well as all of North America, was entering a totally different deposition cycle. One typified by limited carbonate production, but pronounced clastic deposition. Clastics (i.e., sand, silt and clay) were being eroded from highlands building to the west and southeast. The close of the Mississippian also marks the start of the great coal swamps of the Pennsylvanian Era.
References:
Dott, R.H. and R.L. Batten. 1976. Evolution of the Earth. McGraw-Hill.
Johnson, K.S. 1996. Geology of Oklahoma, p. 1-9. In, K.S. Johnson
and N.H. Suneson
(eds.), Rockhounding and Earth-Science Activities in Oklahoma. Oklahoma
Geological Survey Special Publication, 96-5.