Escarpment retreat rates derived from detrital cosmogenic nuclide concentrations

Abstract

High-relief great escarpments at passive margins present a paradoxical combination of high-relief topography but low erosion rates suggesting low rates of landscape change. However, vertical erosion rates do not offer a straightforward metric of horizontal escarpment retreat rates, so we attempt to address this problem in this paper. We show that detrital cosmogenic nuclide concentrations can be interpreted as a directionally dependent mass flux to characterize patterns of non-vertical landscape evolution, e.g., an escarpment characterized by horizontal retreat. We present two methods for converting cosmogenic nuclide concentrations into escarpment retreat rates and calculate the retreat rates of escarpments with published cosmogenic Be-10 concentrations from the Western Ghats of India. Escarpment retreat rates of the Western Ghats inferred from this study vary within a range of hundreds to thousands of meters per Myr. We show that the current position and morphology of the Western Ghats are consistent with an escarpment retreating at a near-constant rate from the coastline since rifting.