Pennsylvanian Sediments and Orogenies of Ardmore District, Oklahoma

Abstract During Pennsylvanian time, the Ardmore basin was the site of almost continuous deposition in long, narrow, and oftendeep basins lying in close proximity to structurally and topographically high islands. These islands and sea-mount archipelagoes formed and were rejuvenated during the several orogenic pulsations that mark the Pennsylvanian Period in southern Oklahoma as one of extreme unrest. As the islands were upfolded, they were truncated, and some of them buried—partly in their own detritus. The base of the Pennsylvanian is drawn at the base of the Rod Club sand. The underlying Goddard shale, which was formerly included in the Springeran Series, is now considered to be Chesterian in age. The Springeran Series as defined herein is apparently restricted to the Ardmore-Anadarko basin with only a very thin wedge, if any, within the western McAlester basin. It consists of shales with sandstone members, in many places oil bearing, which are “regionally persistent but locally very erratic” (phrase from Hubbard and Thompson, 1926, p. 457). The Morrowan Series began with a very widespread “transgression” of marine sands that covered the peneplained surface of most of Oklahoma north of the Wichita Mountains-Criner Hills axis, and extended northwest into southwestern Kansas and the Texas Panhandle. This was followed by marine shales and then limestones. Local uplifting (Wichita orogeny) began in the Criner Hills and elsewhere, possibly during late Springeran time, and increased in magnitude inthe Morrowan Epoch, producing coarse conglomerates east of the Criner Hills. It culminated in early Atokan time in intricate folding and faulting. These folds lie en echelon, with their axes about 10° from the major tectonic trend. Many of the upfolded insular structures that now contain vast amounts of oil were first formed duringthis period of unrest. Concomitant erosion of these islands stripped as much as 8,000-13,000 feet of sediments from many of them before their burial in late Desmoinesian time. The Atokan Series began with the deposition of thick conglomerates in the vicinity of the Criner Hills. Marine shales, sands, and some limestones make up the rest of the unit. Near the end of the epoch the Ouachita orogeny intensely compressed the Ouachita geosyncline to the east, raising the Ouachita Mountains into fairly high relief. The Desmoinesian rocks of the Ardmore basin tell the erosional story of that land mass. Great wedges of chert conglomerates, sands, and deltaic sediments extend northwestward into the Ardmore basin, where they intertongue with swamp and marine strata. The marine sands contain tremendous quantities of oil, in structurally high positions. Around the island uplifts a considerable accumulation of locally derived detritus was deposited. The presently exposed Arbuckle Mountains were strongly uplifted in late Desmoniesian time (first major phase of the Arbuckle orogeny), shedding detritus into adjacent submerged areas. An interval without severe tectonism resulted in slow subsidence of most of the region in Missourian time, with an influx of transgressive marine shales, sands, and limestones, interbedded with a few tongues of continental sediments.Bythe end of Missourian time most of the structural islands were completely buried. The end of this epoch was marked by the culmination of the Arbuckle orogeny, with great uplift in the Arbuckle Mountain area and intense compression ofthe Ardmore basin, continuing into Virgilian time. Close folding accompanied by major faulting occurred at this time. The Virgilian Series consists largely of terrestrial and shallow-water conglomerates and red shales that were deposited in the low areas surrounding the eroding mountain ranges that were formed during the Arbuckle orogeny. By the endofVirgilian time, both the erosional and the depositional surfaces were nearly flat.