ABSTRACT: Microfacies Analysis of the Wapanucka Formation (Morrowan), Frontal Ouachita Mountain, Oklahoma

CHOH, SUK-JOO, and BRIAN E. LOCK

The early Pennsylvanian Wapanucka Formation exposed in the northern part of the Ouachita Mountain thrust belt was deposited under open marine, outer ramp conditions gently sloping to the south. The formation gradationally overlies late Mississippian to middle Morrowan Springer Shale and is unconformably overlain by sub-Spiro Shale which is also known as the middle shale member of the Wapanucka Formation.

Two stratigraphic sections on the northemmost thrust sheet near the town of Hartshorne were investigated. More than 370 thin sections were petrographically studied from samples collected at an average vertical interval of 0.64 ft (0.2 m) for a total thickness of 240 ft (72 m).

Microfacies range from deep ramp deposits (facies 1 to 3), through shallow subtidal deposits (facies 4 to 7) to shallow ramp shoal deposits (facies 8 to 11). The description of each facies is as follows: (1) silty carbonate mudstones, (2) non- laminated siliceous sponge spicule wackestone/packstone, (3) non-laminated siliceous sponge spicule - benthonic foraminifera wackestone/packstone, (4) benthonic foraminifera wackestone, (5) siliceous sponge spicule - Donezella - pellet packstone, (6) Donezella packstone/boundstone, (7) benthonic foraminifera crinoid packstone, (8) coated grain - crinoid - Donezella packstone, (9) crinoid - coated grain packstone/ grainstone, (10) bioclastic grainstone and (11) ooid grainstone.

On the basis of vertical stacking patterns of microfacies, it is possible to identify repetitive meter-scale shallowing upward cycles separated by surfaces marked by sudden change to deeper water facies.

AAPG Search and Discovery Article #90947©1997 AAPG Southwest Section Meeting, San Angelo, Texas