During the Late Cambrian through Ordovician periods, a relatively shallow sea, termed an epicontinental, or epeiric, sea, inundated Oklahoma. This provided shallow, warm water, and abundant nutrients for marine (ocean) dwelling animals and plants. The animals at this time were all simple invertebrates (animals without backbones), and the most common of these were trilobites, brachiopods, bryozoans, and crinoids. Most sea plants consisted of algae. When these plants and animals died their skeletons would break apart, and form what geologists call carbonate sediment. When this sediment hardened limestone and dolomite are formed.
Much of the Cambrian and Ordovician rock is composed of limestone and dolomite, indicating that throughout much of this time Oklahoma remained a shallow sea. To the west, however, uplands, represented by the Transcontinental Arch, were the source of clastic sedimentation (sand, silt, and clay) that was deposited in the far western parts of the state. The Transcontinental Arch was a major positive feature that separated eastern and western North America into two distinct sedimentary regions during the early part of the Paleozoic. The arch may have affected the erosion, or non-deposition of Cambro-Ordovician sediments in the southwest part of Oklahoma. In the south and southeast part of Oklahoma, basins formed which acted like deep troughs from the collection of thick piles of sediment, much thicker than the shallow shelf areas. For example, shelf areas having limestone and dolomite have only have 1/5 the sedimentary thickness compared to these basins. These thick piles of sediment were deposited in what was called the Ouachita Basin, which will eventually be pushed upward by mountain-building forces, forming the present day Ouachita Mountains.
Paleomagnetic data supports the above interpretation that Oklahoma was situated closer to the equator during this time. Data also indicates indicate that Oklahoma was rotated about 90 degrees from its present orientation (Dott and Batten, 1976).
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.