Quaternary geology in Zanskar, NW Indian Himalaya: evidence for restrictedglaciation and preglacial topography

Research into the Quaternary geology of the NW Himalaya has concentrated on the elucidation of the glacial sequence. However, whilst the main ranges o f the Himalaya have been subjected to numerous glaciations and are now an o bvious alpine glaciated terrain, much of the landscape in Zanskar and Ladak h is more equivocal and does not appear to have been glaciated during this rime. These landscape facets may therefore have a much older origin and rel ate to preglacial events. In Zanskar, the main ice source in all glaciations was the strongly glaciat ed and still glacierized north slope of the main Himalaya. This ice then fl owed generally northwards in the valleys of the Zanskar river and its tribu taries leaving between them a landscape supporting only a few and scattered minor local glaciers. Evidence of early glaciation has been found on isola ted valley-side remnants > 200 m above the present rivers. Reconstruction o f these preglacial valley cross profiles show them to be generally broad an d shallow, with gentle slopes. This is in distinct contrast to the present major valley systems which can usually be divided into two parts-a lower un glaciated fluvially eroded section, such as the Lungnak (Tsarap Lingti Chu) Gorge and an upper broad glacial section, such as the Stod (Doda) valley. Down-valley extent of glaciation is defined by the upper ends of unglaciate d fluvial gorges. Laterally, the glaciers were confined progressively to th eir valleys. Inevitably there is only evidence of successively smaller subs equent glaciations, but the tectonic uplift of the southern ranges may have been a factor in this forming an increasing barrier to the snow-bearing mo nsoon winds. (C) 1999 Elsevier Science Ltd. All rights reserved.