Porosity Development within Lobes to Downslope Ramp Deposits on a Prograding Carbonate Shelf of the Kinderhookian to Osagean Series in Northwest Arkansas

Elizabeth Marchese

Carbonate bodies with lobate geometries form a substantial part of the Osagean (early Mississippian) section in northwest Arkansas. The purpose of this study is to isolate and describe a single lobe from three-dimensional exposures in quarry walls and to compare the descriptive data with core data from north- central Oklahoma to provide criteria by which lobe and lobe porosity can be recognized in the subsurface. Carbonate sediment generated on the Mississippian Burlington shelf moved southward by gravity flows from the shelf margin to positions on a prograding ramp in Arkansas where overlapping deposits with lobate geometries accumulated. These deposits are recognized in outcrops of the Boone Formation. Stratigraphic units within the Boone are identified in north central Oklahoma within the "Mississippian lime" and are targets for hydrocarbon exploration. A quarry near Avoca Arkansas has four exposed walls each in excess of 1000 feet in length and wall heights near 40 feet. The walls were photographed with the purpose of creating panoramic views of each of the walls. Stratigraphic boundaries within each wall were positioned on the mosaic to define lobe dimensions and internal facies. Selected intervals were then sampled and thin sections were prepared for petrographic study. The chert content in each section was also recorded. Two cores from wells that penetrate reservoir facies in north-central Oklahoma have been identified and examined at the Oklahoma Geological Survey repository for comparison with outcrop data. Productive intervals within the Mississippian carbonates of north-central Oklahoma have not been positioned with respect to depositional or diagenetic facies. Criteria derived from outcrop studies should provide criteria by which lobe boundaries can be recognized in the subsurface. Petrographic data should also indicate where within the lobe porous and permeable units exist. 

AAPG Search and Discovery Article #90176©AAPG Mid-Continent Meeting, Wichita, Kansas, October 12-15, 2013