Himalayan glacial sedimentary environments: a framework for reconstructing and dating the former extent of glaciers in high mountains

Abstract

Reconstructing paleoenvironmental change from glacial geologic evidence in the Himalayas has been difficult because of the lack of organic material for radiocarbon dating and the problems of correctly identifying the origin of highly dissected landforms. Studies of the contemporary glacial depositional environments, and ancient landforms and sediments in the Hunza valley (Karakoram Mountains), the Lahul and Garhwal Himalaya, and the Khumbu Himalaya illustrate the variability in processes, landforms and sediment types. These studies can be used to interpret ancient landforms and sediments for paleoenvironmental reconstructions, and aid in forming strategies for sampling sediments and rocks for the developing techniques of cosmogenic radionuclide (CRN) surface exposure and optically stimulated luminescence (OSL) dating. Many Himalayan glaciers have thick covers of supraglacial debris derived from valley sides, and such debris-mantled glaciers exhibit important differences from ‘clean’ glaciers, both in terms of debris transport processes, and the depositional landforms that they produce. Analysis of sediment-landform associations can be used to reconstruct processes of sediment transport and deposition, and the relationship between moraines and other landforms and climatic forcing cycles. Such analysis is of fundamental importance in guiding sampling and interpretation in CRN and OSL dating work.