Abstract: Basinward Facies Changes in Wapanucka Limestone (Lower Pennsylvanian), Indian Nations Turnpike, Ouachita Mountains, Oklahoma
Patrick K. Sutherland, Robert C. Grayson, Jr.
Important new exposures of the Wapanucka Limestone in the frontal belt of the Ouachita Mountains are on the new Indian Nations Turnpike, about 16 mi (26 km) south of McAlester, Oklahoma. The Wapanucka Formation in this area is repeated four times by faulting within a north-south distance of less than 2 mi (3 km). These exposures demonstrate a basinward change in facies southward, showing increases in thickness and in shales and an increase in spiculites as compared to crinoidal and oolitic grainstones. These exposures apparently represent the first documented case of basinward facies change southward from the main Wapanucka Limestone ridge.
The northernmost Wapanucka roadcut represents typical Wapanucka Limestone, as seen at many points along the frontal Ouachita belt. This exposure, 364 ft (111 m) thick, consists predominantly of interbedded spiculiferous, crinoidal, and oolitic limestones. Exposures south of this ridge are much more subdued topographically, because of increasing percentages of shale. The third faulted "Wapanucka" exposure is 1.0 mi (1.6 km) south of the main ridge. Here the section measures 714 ft (218 m) from the lowest to the highest limestone, and is predominantly shale, with a few thin spiculiferous limestones. This sequence is considered to represent a basinward and deeper water facies of the Wapanucka, as present in the north, and was deposited approximately contemporaneously.
Conodonts from the lowest exposures in both sections suggest a correlation with a horizon probably no lower than the Dye Member of the Bloyd Shale of the type Morrowan in northwestern Arkansas. Goniatites from the middle part of the section have been placed by Mackenzie Gordon in the Diaboloceras neumeiri Zone, which is in the Trace Creek Member of the Bloyd Formation in northwestern Arkansas. Conodonts from this interval support the correlation. Conodonts from the highest beds indicate either a latest Morrowan or early Atokan age.
AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA