Quantitative and Qualitative Insights into Bedrock Landform Erosion on the South Indian Craton Using Cosmogenic Nuclides and Apatite Fission Tracks
Résumé
Due to the scarcity of datable chronostrati-graphic markers and the related difficulties of quantifying depths of erosion in cratonic landscapes, conceptual models of tropical pediplain and etchplain evolution commonly lack time and vertical elevation scales. Here, we present the first quantitative study of relief development in South India based on in situ–produced 10Be dating aided by previously acquired apatite fission-track data. Erosion rates measured on the summits of inselbergs concur with the perception of inselbergs as islands of low erosion, but they also reveal a critical contrast between slowly evolving (≤2 m/m.y.) higher-relief landforms and more rapidly eroding (8–12 m/m.y.) lower-relief landforms. This relationship is independent of lithology and climate but suggests that erosion rates on the surrounding plain, which are controlled by fluvial incision rates into the plateau surface, feed back on inselberg dynamism. A discussion on the most suitable sites for dating bedrock land-forms highlights the problems of sampling design, the difficulties of linking measured erosion rates to the minutiae of process, and the limitations of both single- and multiple-chronometer denudation chronologies in low-energy cratonic environments.