Postorogenic Development of the Appalachians

W. D. Thornbury has pointed out the need for a re-examination of the idea of a persistent Appalachia east of the Appalachian geosyncline during the Paleozoic and Mesozoic eras, as a means of resolving the problems that still obscure the postorogenic drainage history of the Appalachian Mountain system. Such an examination indicates that the late Paleozoic Appalachian orogeny raised the Piedmont–Blue Ridge–Valley and Ridge mountain elements differentially to heights that exceeded the elevation of any residual eastern oldland that may have survived Paleozoic denudation and Appalachian orogeny. Late Triassic faulting was a factor in determinining the boundary between the Blue Ridge and Piedmont, but it did not alter the general direction or pattern of the drainage. That pattern, set by Permian deformation, was one of west-flowing streams in the south and of southeast-flowing streams in the north. Superposition of drainage in the fold belt is not regional but local, with demonstrable relations to specific structural or lithologic features, or both. The fold belt served as provenance for part of the clastic sediment in all formations of the Newark Group and for a substantial fraction of the clastic content of Lower and Upper Cretaceous and early Tertiary deposits in the Atlantic Coastal Plain from New Jersey to Virginia. Late Tertiary (Miocene?) marine transgression of brief duration accounts for marginal stream diversion and stream superposition in southern New England and part of the Newark trough–Piedmont in New York and New Jersey.