Late Cenozoic uplift of the eastern United States revealed by fluvial sequences of the Susquehanna and Ohio systems: coupling between surface processes and lower-crustal flow

Fluvial and karstic data sets indicating Late Cenozoic surface uplift in the eastern United States are modelled for the first time using a technique, incorporating coupling between surface processes and flow in the lower continental crust, which has been extensively used for modelling similar data sets elsewhere in the world, notably in Europe. Distinct phases of lower-crustal flow forcing, starting in the early Middle Miocene, Late Pliocene, and late Early Pleistocene, are evident, as observed elsewhere, and relate to combinations of cyclic surface loading (by sea-level variations and ice loads) and to variations in regional erosion rates, as elsewhere. However, the detailed uplift histories inferred are rather different from those indicated in many other regions, notably Europe, primarily because of different properties of the crust. In particular, in the Late Proterozoic/Phanerozoic crust of the Appalachians, the mobile lower-crustal layer seems to be relatively thick, causing a prolonged uplift response for each phase of lower-crustal flow forcing, whereas in the Early Proterozoic crust of the Yavapai crustal province farther west, underlain by a thick basal mafic layer, this mobile layer is much thinner, leading to a very different response consisting of abrupt alternations of uplift and subsidence, as is also observed in other regions of Early Proterozoic crust. Another important difference relative to western and central Europe is the much smaller number of terraces in the eastern US rivers that have been studied. The general applicability of this type of physics-based modelling technique is thus confirmed.