Duns: Intermontane Basins in the Himalayan Frontal Zone

Abstract

Duns are broad longitudinal intermontane depressions in the frontal parts of the Himalaya. Such basins are flanked by the outer Siwalik Hills in the south and the Lesser/Sub-Himalaya in the north. Duns consist of several landforms, prominent amongst which are relict surfaces, piedmonts, alluvial fans, floodplains, and river terraces. The geomorphic evolution of Duns is largely controlled by the combined influence of the basin margin structural regime as well as the tectonics of the structures that transect the Duns. Duns are formed in settings in which there is a forelandward migration of the Himalayan fold and thrust systems involving the progressive tectonic development of the Main Boundary Thrust (MBT) and the Main Frontal Thrust (MFT). Their evolution is connected primarily to the emergence of positive topography in the mid- to late Pleistocene associated with the hanging wall fold uplifts related to the MFT displacement, as well as the tectonic activity of the MBT on their northern flanks. Duns show variability within themselves and between them in length, area, slope and relief characters, because of the control exercised on these by the deeper structure of the Dun.