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ABSTRACT: Three-Dimensional Geometries and Thicknesses of Reservoir Sand Bodies--Examples from Appalachian Plateau

J. C. Ferm

General anatomical characteristics of sandstone bodies in the Appalachian Carboniferous are reasonably well known and can be related to some primary depositional settings, distributary mouth bars, splay deposits, "mega-splays," and fluvial channels. Each of these deposits has characteristic external properties of size, shape, and contrast relationships with adjoining rocks as well as internal properties such as grain size trends and stratification that can be related to sedimentary bedforms. In addition, they have specific spatial relations to paleosoils and coal beds that provide a datum indicative of subaerial or subaqueous deposition.

While it is obvious that the spatial distributions of these different kinds of sand bodies are linked through controls of depositional setting, it is also true that the manner of sand deposition is also controlled by contemporaneous tectonism at the site of deposition. On a regional level of hundreds of miles, less rapidly subsiding areas are characterized by fluvial sandstones whereas areas of more rapid subsidence have a proportionally greater number of distributary mouth bar deposits. More surprising is the control exercised by small-scale (5-10 mi) growth faulting that can change the depositional setting of a single sand body within short distances. Such modifications could account for some of the rapid lateral variation in properties of reservoir rocks.

AAPG Search and Discovery Article #90999©1990 GCAGS and Gulf Coast Section SEPM Meeting, Lafayette, Louisiana, October 17-19, 1990