Cenozoic landscape evolution of the Middle Appalachian Mountains: How to get an erosional pulse from an ancient orogen
Date:
Authors: Victoria M. Fernandes, Alexander C. Whittaker, Gareth G. Roberts
The persistence of high topography in ancient orogens, such as the Appalachian Mountains, remains an outstanding question in geomorphology. It is often stated that the Appalachians have been a tectonically quiescent since the establishment of a passive margin in Late Jurassic times. However, thermochronology, the elevation of marine strata, and inverse modeling of river profiles suggest multiple episodes of surface uplift and erosion from the Cretaceous to present-day. Offshore, seismic and well data from the Baltimore Canyon Trough basin also suggest variable rates of tectonic subsidence sediment accumulation, with order-of-magnitude changes in the Middle Miocene, contradicting the notion of a stable passive continental margin and a decaying ancient mountain belt. Here, we explore whether landscape evolution modeling, integrated with independent uplift, erosion and stratigraphic datasets, can be used tobetter understand the history of denudation and sedimentary flux to the Middle Atlantic margin of North America. First, we generate a compilation of low-temperature thermochornology, catchment-averaged erosion rates, incision rates and uplift measurements. This data is used to examine evidence for proposed mechanisms for the geomorphic evolution of the Appalachian Mountains. Second, we revise existing records of sediment accumulation in offshore basins, notably the Baltimore Canyon Trough. We constrain the magnitude of the Neogene sediment pulse to the basin, and place errorbounds on the flux estimates. Third, we use a landscape evolution model to explore hypotheses proposed for theevolution of the Middle Appalachian Mountains including: a steadily eroding mountain belt from pre-existing high topography; erodibility contrasts due to variable bedrock lithology; flexural response to erosional unloading; andescarpment retreat. Our results have signifi cant implications for our understanding of Cenozoic evolution of Appalachian topography, as well as the fundamental controls on the decay and uplift of ancient mountain belts.