Due to the complexity of events that were occurring in Oklahoma during the Pennsylvanian, this period has been divided to three separate stages. The first stage, the Early Pennsylvanian Period, represents the time when the Wichita Orogeny occurred. An orogeny is a fancy name for a mountain building event, and in this case one that started the formation of the Wichita Mountains. The orogeny compressed, folded, and faulted older rocks up into mountain chains along the Oklahoma-Texas border. It has been estimated that some 10,000 to 15,000 feet of uplift occurred in the area from the Wichitas to the Criner Hills south of Ardmore (Johnson, 1996).
A broad highland was also forming in north-central Oklahoma that almost split the state into half, called the Nemaha uplift, which was really a low-lying, fault-block mountain range. This area represented a land area during this time, and which separated the Arkoma basin in the east from the Anadarko Basin in the western part of the state. Far to the west, the Ancestral Rocky Mountains continued to form in Colorado and New Mexico. All of these mountainous regions and highlands became sites of extensive erosion of older rocks that were exposed at the Earth’s surface due to this extensive mountain building. Consequently, there was a tremendous amount of sediment shed from these highlands into the Anadarko, Ardmore, and Arkoma basins to the north and south.
Much of the area surrounding these newly formed highlands was
still covered by tropical oceans. So shallow marine deposition of mostly gravel
and sand was going on, except in the deep basins (the Arkoma Basin just south
of present day McAlester, and the Anadarko Basin, just north of present day
Lawton), which were the sites of thick accumulations of fine-grained silt
and clay.