Basinwide High Resolution Surface/Subsurface Correlation of Late Mississippian Carbonate Sequences In The Appalachian Basin

AL-TAWIL, AUS, and J. FRED READ

Up to six Late Mississippian 4th order carbonate sequences in the Appalachian foreland basin have been mapped basinwide from the outcrop belts and into the subsurface on the basis of biostratigraphy, regional disconformities and shale markers. Along the basin margin, exposed parasequences in the lower 3 sequences consist of basal skeletal/ooid grainstone (reservoir facies), overlain by lime mudstone (locally dolomitized reservoirs), red-beds, eolianites and paleosols. Parasequences and sequences are disconformity-bounded updip but are relatively conformable downdip in the basin. The upper 3 sequences consist of thin near-shore shale and rare tidal sandstone, skeletal packstone, and ooid grainstone. Clay-draped paleosols, red-beds, and shale markers that bound sequences can be traced basinwide on wireline logs from adjacent to the outcrop belt into the subsurface to define regional 4th order sequences. Our detailed studies of the outcrop belts provide a detailed picture of the onlap/offlap relations of parasequences, and vertical and lateral distribution of potential reservoir facies and seals. When extended into the subsurface, this provides a 3-D picture of the sequences in the basin, a high resolution sequence stratigraphic framework for the basin, and allows a better understanding of the controls on the distribution of reservoirs and seals. Differential subsidence in the active foreland basin, moderate amplitude eustasy due to Gondwana glaciation, and location on a tidally-dominated ramp controlled the development of these depositional sequences and parasequences, and reservoir compartmentalization. 

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.