The quaternary glacial history of the Zanskar range, north-west Indian Himalaya

Abstract

Palaeoglacier margins from the Zanskar Range of the north-western Indian Himalaya are reconstructed through geomorphological mapping and sedimentology. These are dated ilsing Optically Stimulated Luminescence (OSL) techniques on quartz extracted from related fluvioglacial and lacustrine deposits. A glaciated palaeosurface with broad, gentle slopes >280m above river level and high grade metamorphic erratics represents the oldest and most extensive glaciation, the Chandra Stage. This formed an ice-cap with its ice-shed to the south over the High Himalaya. A change from broad glacial troughs to narrow V -shaped gorges along with large subdued moraine ridges and drift/erratic limits defines an extensive valley glaciation, the Batal Stage, with its maximum close to -78.0±12.3ka BP (Oxygen Isotope Stage (OIS) 4). Distinct sets of moraine ridges represent a less extensive glaciation, the Kulti Stage, which is dated to shortly after the global Last Glacial Maximum (OIS 2) and a minor advance, the Sonapani, is represented by sharp crested moraine ridges <2km from current ice bodies. The change in glacier extent and style from the Chandra Stage to the later glaciations may be related to uplift of more southerly ranges blocking monsoon precipitation and incision of the landscape such that ice reached lower altitudes over shorter horizontal distances. Batal and Kulti Stage Glacier Elevation Indexes (GEls) calculated for this and adjacent areas increase from south-west to the north-east, but decrease again towards the Indus valley, reflecting attenuation of the south-westerly monsoon and possible channelling of westerly depressions along the broad upper Indus valley. GEl values were depressed by ~500m during the Batal Stage and -300m during the Kulti Stage. Six new OSL age estimates from the Zanskar Range greatly improve the glacial chronology of the north-west Himalaya and reinforce the emerging asynchrony between this region and the Central and Eastern Himalaya, which experienced its maximum glaciation during OIS 2 rather than OIS 4. Improved glacier mass balance data, palaeoclimatic proxy data for the summer monsoon and particularly the winter westerlies, and numerical age estimates from Himalayan glaciers are required to explain this asynchronous maximum.