The Ordovician (from 510-439 million years ago) in Oklahoma started much as the Cambrian ended, with shallow epieric seas covering most of the state. Deposition of the Arbuckle Group limestones continues throughout the Lower Ordovician, while shale and sandstone deposition occurs in the area of the Ouachita Basin in the southeast. The Ardmore, Anadarko, and Ouachita basins were all active at this time. These basins represent deep troughs (much like the Atlantic Ocean or Gulf of Mexico are today), and are sites of thick sediment accumulation. Most of the sediment shed into the Ouachita Basin are sands, silts and clays (which eventually harden into sandstones, siltstones, and shales, respectively), along with some limestone and chert (these sediments will later become part of the Ouachita Mountain Uplift); whereas the Ardmore-Anadarko basins were sites of thick accumulations of limestone and dolomite (Arbuckle Group and Viola Limestone) and only minor shale (Sylvan Shale). Within these basins, sediments attain a thickness of 10,000 feet or more, whereas in the shallower northern shelf areas of Oklahoma these same sedimentary units only reach a thickness of 2,000 feet (Johnson, 1996).
To glimpse what Oklahoma might have looked like during this time, go to Paleogeography of Late Cambrian-Ordovician.
Reference: 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.