10Be exposure age dating of moraine boulders and glacially polished bedrock surfaces in Karakoram and Ladakh ranges, NW Himalaya: implications in quaternary glaciation studies

Abstract

Terrestrial cosmogenic nuclide (TCN) dating has emerged as one of the most useful techniques in the last two decades for quantifying geomorphological processes and building the chronology of late Quaternary glacial advances/retreats. The chronology based on TCN and optically stimulated luminescence (OSL) dating of glacial landforms from the northwestern (NW) Himalaya suggests that glaciers responded to a complex interaction between temperature and moisture essentially derived from either of the climate systems, the Indian Summer Monsoon (ISM) and the Mid-latitude Westerlies (MLW). The discrepancies between the TCN ages obtained on moraine boulders/bedrock surfaces, and the OSL ages on the stratigraphically equivalent deposits, highlighted the need for a detailed investigation. The present study attempts to build the chronology of Quaternary glaciation events in the Karakoram and Ladakh Ranges using TCN dating of stratigraphically constrained moraine boulders and striated bedrock surfaces. The TCN ages from glacially eroded surfaces (GES) having prominent striations are narrowly clustered around the Marine Isotopic Stage-2 (MIS-2). Agreement between GES TCN ages and OSL ages on the stratigraphically equivalent moraines suggests negligible geological inheritance. The glacial advance during MIS-2 can be attributed to the combined effect of reduction in north hemispheric insolation and enhanced westerly precipitation. However, relict non-glacial surfaces and moraine boulders with minimal ice flow modifications yield wide age distributions, most likely suggesting denudational events (interglacials) and/or contribution from tributary valley flanks.