Arbuckle Source for Atoka Formation Flysch, Ouachita Mountains Frontal Belt, Oklahoma: New Evidence from Paleocurrents

Charles A. Ferguson, Neil H. Suneson

The 10-mi wide Ouachita Mountains frontal belt consists of Morrowan-Atokan flysch exposed in steeply south-dipping imbricate thrust slices. Two spatially distinct groups of paleocurrents were recognized during detailed mapping of 120 mi² in the frontal belt (between 95°15^primeW and 95°30 ^primeW). The east-west-trending Morrowan shallow-water shelf margin (now allochthonous) marks the boundary between these two domains. Westerly azimuths (259°n = 213), typical of almost the entire Ouachita flysch sequence, are from the Atoka Formation south of the shelf margin. Easterly azimuths (66°n = 75), previously unrecognized in the Ouachitas, are from the Atoka Formation where it overlies Wapanucka Limestone north of the margin. A third group of pale currents (193°n = 21) are from the Johns Valley Shale (an olistostrome that is the basinward equivalent of the Wapanucka Limestone).

Easterly paleocurrent azimuths indicate a western source for the Atoka Formation north of the Morrowan shelf margin. Sediment from the Arbuckle uplift was apparently channeled northeastward down a trough that was isolated from the Oucahita basin to the south where sediment had an Appalachian provenance. We suggest that a trough was formed by listric fault blocks (tilted toward the continent) of the foundered Morrowan shelf margin. The bounding faults would be the southernmost of a series of northward-facing south-side-down growth faults that have been recognized in the subsurface of the Arkoma basin to the north.

There are two important implications of our work in the Ouachitas. High-angle thrust faults in the frontal belt may be reactivated listric normal faults. Proximal-fan facies equivalents of turbidites along the north edge of the frontal belt are to the southwest, and not to the north and east as has been previously suggested.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.