Abstract: Depositional Environments and Conodont Biostratigraphy of Wapanucka Formation (Pennsylvanian), Frontal Ouachita Mountains, Oklahoma

Robert C. Grayson, Jr.

The Wapanucka Formation crops out as a series of two to five subparallel, arcuate ridges along the northern margin of the Ouachita Mountains in southeastern Oklahoma. These thrust-fault exposures provide a unique opportunity for detailed three-dimensional stratigraphic analyses, for both basinward and lateral relations can be examined. Basinward the Wapanucka Formation thickens from approximately 400 to 700 ft (120 to 210 m); shale interbeds become volumetrically important; and shallow-water, marine carbonate rocks are replaced by deeper marine, flaser-bedded spiculites. Laterally, subtidal-lagoon, open-marine-carbonate, oolite-shoal, and skeletal-bar deposits interfinger and grade into a linear system of offshore bar sands and interbar muds. Presumably, the more basinwar flaser-bedded spiculites grade laterally and basinward into the shale facies of the Johns Valley Formation in the central Ouachitas.

Evaluation of the conodonts indicates that four faunal subdivisions can be recognized. In ascending order, the faunas are distinguished by the earliest local occurrence of: (1) Idiognathoides convexus; (2) Idiognathoides ouachitensis, and/ or Neognathodus kanumai, and Gondollela clarki; (3) Gnathodus orphanus; and (4) Streptognathodus sp. cf. S. elegantulus. Fauna 1 indicates a correlation of the lower Wapanucka Formation with the Dye Shale(?) and Kessler Limestone Members of the Bloyd Formation (type Morrowan) in northwestern Arkansas. The absence of faunas 2 and 3 in the Bloyd Formation suggests that an erosional gap is present at or near the base of the Trace Creek Shale Member of the Bloyd Formation in northwestern Arkansas. Fauna 4 occurs in the Trace Creek Shale and in the overl ing Atoka Formation in that area. The conodont evidence suggests that the Morrowan-Atokan chronostratigraphic boundary is contained within the Wapanucka Formation in the Ouachitas, where the preserved depositional sequence is more complete than that in the type Morrowan area in Arkansas.

AAPG Search and Discovery Article #90961©1978 AAPG Annual Convention and Exhibition, Oklahoma City, Oklahoma