DEVELOPMENT OF THE SILURIAN-DEVONIAN CARBONATE PLATFORM RESULTED FROM ISOLATION OF THE HINTERLAND BY SILURIAN EXTENSION

The relatively abrupt change in the northern Appalachian basin from the clastics of the Taconic-Salinic foreland basin to a stable carbonate platform could only have occurred by the removal or isolation of the mountains that served as the source for the clastics. Recent advances in our understanding of the structural development of the Champlain Valley indicates that the Champlain-Hudson corridor experienced a series of extensional events between the Salinic and Acadian orogenies. It is proposed that these extensional events isolated the basin from the source higlands, enabling the establishment of the carbonate platform.

Based on evidence from Champlain Valley, the extensional events occurred in three stages, 1) a N-S extension with relatively narrow (measured at the top of basement) grabens, 2) a NW-SE extension with much wider grabens (this is the dominant set in the subsurface of southeastern Quebec); and 3) an E-W extension that produced a >40km wide graben that includes the entire Champlain-Hudson corridor. The first of these is proposed as the cause of the rapid reduction in clastic delivery in Early Silurian time. The second may well be related to the development of the Salina salt basins. The third resulted in a 6+ km drop of a wide graben system in western New England and eastern New York that would have effectively severed any connection between the remnant hinterland topography to the east and the foreland basin to the west. The resulting isolation of the basin from clastic input allowed the development of the carbonate platform.