Equatorial, tropical conditions continued throughout Oklahoma during the Silurian and Devonian Periods as it was during the previous Ordovician Period. By the Late Silurian, however, Oklahoma had drifted further south of the equator than its’ location during the Ordovician (Dodd and Batten, 1976). Due to near equatorial position, limestone deposition continued across the shelf area throughout the Silurian and into the Early Devonian. The Ouachita Basin in the southeast was still the sight of thickening deposits of sand, silt and clay, although during most of the Devonian these clastic sediments were supplanted by the Arkansas Novaculite (a very distinct deposit of chert).
A major regression of the seas occurred across most of the state (except in the Ouachita Basin) sometime during the Middle and Late Devonian. Severe erosion of Early Devonian, and older rocks, occurred primarily in the southwest and northeast parts of the state. The seas returned by the Late Devonian, which deposited black, marine shales across most of the state.
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.