Patterns of Mixed Carbonate-Siliciclastic Sedimentation on an Inclined Shelf

Thomas E. Yancey

Deposition of carbonate and siliciclastic sediments on the Eastern shelf of the Pennsylvanian-Permian Midland basin consistently fits a pattern of nearshore siliciclastic sedimentation, inner shelf carbonate sedimentation, and outer shelf fine-grained siliciclastic sedimentation. This pattern was produced by the combination of carbonate sediment production in shallow waters of the inner shelf, superimposed on a trend of dispersal of fine-grained siliciclastics across the shelf from a shoreline source. Deep-water areas of the outer shelf lay outside the zone of carbonate sediment production and received little carbonate sediment, allowing fine-grained siliciclastics to accumulate. High-standing reefal masses on the outer shelf punctuate the pattern, but do not disrupt the rend. The shelf maintained an inclined slope surface, on which shoreline-parallel zones of contrasting sediments developed because of the restriction of carbonate sedimentation to depths where the photic zone intersected the shelf slope. Siliciclastic muds inhibited carbonate sedimentation near the shoreline, where large amounts of siliciclastics were deposited, and in the deeper waters of the outer shelf, where carbonate sediment production was low. Resedimentation of carbonate on the shelf was insignificant and the absence of planktic skeletal carbonate producers in the water column greatly limited carbonate deposition in deep-water areas. These patterns of sediment deposition are well-defined in Carboniferous and Permian cyclic deposits.

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