James W. Castle¹

(1) CU, Clemson, SC

ABSTRACT: Convergent-Margin Structural Control on Stratigraphy of the Appalachian Foreland Basin

Investigation of Paleozoic formations in the Appalachian foreland basin indicates that convergent-margin structural evolution controlled the distribution of facies tracts. Five major facies-tracts are recognized: interorogenic carbonate and shale; early collisional fine-grained siliciclastics of the deep, proximal foreland; syn-collisional aggradational sands of the proximal foreland; syn-collisional fine-grained siliciclastics of the shallow, distal foreland; and late orogenic progradational sands of the distal foreland. Two other facies tracts that occur are organic-rich fine-grained deposits, which accumulated in oxygen-deficient areas of low clastic-sediment influx, and incised valley-fill deposits, which formed in areas of low subsidence rate. The origin of each facies tract represents a specific combination of rate of sediment supply and rate of accommodation created by backward-rotational subsidence. Therefore, foreland-basin stratigraphic patterns are predictable from temporal and spatial patterns of subsidence and uplift associated with plate convergence.

In the Appalachian basin, the along-strike distribution of facies tracts was influenced by structural salients and recesses that evolved from collisional-margin reentrants and promontories. In salients, which are areas of relative subsidence, aggradational deposits grade distally to upward-coarsening progradational strata. In contrast, deep erosion, common unconformities, and incised-valley fills are present in areas corresponding to recesses, where the rate of eustatic fall exceeded the subsidence rate. Although stratigraphic variations caused by the interplay of tectonism with eustasy are present in foreland basins, this investigation demonstrates that the large-scale arrangement of facies tracts is tectonically controlled.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado