DO FORELAND BASIN SEDIMENTS ACCURATELY RECORD THE TECTONIC HISTORY OF THE OROGENIC HINTERLAND?

Subsidence of foreland basins is linked mechanically to thrust emplacement of an associated tectonic load, which can be envisioned as an orogenic hinterland. Erosion of the orogenic hinterland provides potential sediment fill to the foreland basin, linking the supply of foreland sediment to erosion of the orogenic belt. The composition of sedimentary detritus eroded from an orogenic belt has been used frequently in interpretations of the tectonic framework of the orogen, for example trying to discriminate between different types of orogenic terranes based on sandstone composition. The rationale for this approach is that erosion of a approaching orogenic load should supply detritus to a dispersal system which can easily reach the foreland basin, and that the sediment composition reflects specific, identifiable, tectonic elements of the orogen. In effect, the sedimentary system has often been viewed as the “mirror image” or “inverted record” of the orogen being denuded.

This rationale has recently been challenged, at least for sedimentary rocks within the Appalachian orogen, suggesting that the foreland basin record may be closer to “one orogeny behind”. This concept will be examined for the Taconic foreland basin based on the results of U-Pb analyses of detrital zircons from synorogenic sandstones, neodymium isotopic ratios of clastic sedimentary rocks, and chemical and isotopic compositions of altered ash beds that occur throughout the basin. These results will also be compared with those obtained from syn-orogenic Mississippian-Permian sedimentary rocks from the Alleghanian orogen to more broadly exam the question of the utility of foreland basins as recorders of orogenic activity.