The Carboniferous period lasts from approximately 362 to 295 million years ago. This era has been divided into two different era's in the United States as the Missisipian (Early Carboniferous) and Pensylvanian (Upper Carboniferous). During the Early Carboniferous, Oklahoma still remained under a shallow sea, however in the Upper Carboniferous we begin to see the formation of mountains in the state and eventually parts of Oklahoma will finally be above water.
Early Carboniferous (Mississippian) Earth
From the PaleoMap Project
During the Early Carbiniferous, Oklahoma was positioned just south of the Equator on the Euramerica Continent. Major Early Carboniferous (Mississippian) limestones are prevelant in eastern rock outcrops in Oklahoma today and these shales are a primary source of oil in Oklahoma today. Early Carboniferous is sometimes called the "Age of the Crinoids" due to the abundance of these marine filter feeding life forms.
Upper Carboniferous (Pennsylvanian) Earth
From the PaleoMap Project
The greatest period of mountain building in Oklahoma was in Pennsylvanian time. Flat-lying sedimentary rock layers in the southern half of the State were sharply folded, tilted, and faulted; earlier-formed igneous-rock masses were pushed upward; and the three mountain chains (Ouachita, Arbuckle, and Wichita Mountains) were thrust high above surrounding seas. Gravel and boulders eroded from the rising mountains were deposited to form conglomerates at the foot of the mountains and in the nearby seas. Thus, by the end of the Pennsylvanian Period, the mountain systems of Oklahoma were substantially as we know them today, although subsequent gentle uplift and accompanying erosion have cut more deeply into the cores of these mountains.
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