INTEGRATING FORELAND AND HINTERLAND DATA: TOWARD A GREATER SYNTHESIS OF APPALACHIAN TECTONICS AND OROGENESIS

Integrating data from the foreland basin and hinterland of an orogen has tremendous potential for tectonic reconstructions. The foreland basin contains a detailed, time-integrated record of sediment transfer from the hinterland, mediated by elevation differences, climate, and drainage patterns. The hinterland provides direct evidence for subduction, terrane accretion, crustal thickening, rifting, and tectonic exhumation. Advances in the precise U-Pb dating of zircon, and the recognition of widespread K-bentonites in the foreland, has made it possible to integrate more fully foreland and hinterland histories in the northern Appalachians, and to identify some specific tectonic events that were coeval with the formation of air-fall tephras in the foreland basin.

The foreland basin’s strengths lie in the patterns and trends of sedimentation, controlled at least in part by orogenesis. Key data include rock type/composition, stratal geometry, altered airfall volcanic tephras or byproducts thereof (e.g., terrestrial vertisols), and more. Changes in data over time often provide a detailed record of long- to short term changes in the orogenic belt often not available from the hinterland, especially from older deeply eroded orogens like the Appalachians.

Despite potential biases in the sedimentary record and possible non-orogenic factors, high quality data can provide insight into hinterland events. Over 100 altered airfall volcanic tephras are now reported from the Devonian Appalachian Basin, providing a coarse proxy of the timing of Acadian/Neoacadian paleovolcanism (terrestrial vertisols may provide a more detailed record). Vertical changes in sandstone and conglomerate grain composition reflect changes over time in rock type exposed in the orogen. Shifts in foreland basin geometry, seen as changes of foreland basin topography (e.g., foredeep, forebulge); sediment package geometries (e.g., tabular- to wedge-shaped); sediment condensation; and some unconformities may reflect changes in foreland basin kinematics, related to changes in the orogen (e.g., uplift and crustal loading, in-plane stresses, etc.).

Studies of the foreland basin and hinterland have complementary strengths and weaknesses. Integration of their unique insights can create a new, broader synthesis of Appalachian orogenesis.