Sedimentary characteristics of palaeolake deposits along the Indus River valley, Ladakh, Trans-Himalaya: Implications for the depositional environment

摘要

This study is an attempt to contribute to the data set of granulometric studies of sediments by measuring the sedimentary structure and texture, along with statistical parameters, of cold and arid lake systems. The palaeolake sequence along the River Indus on the western fringe of the Tibetan Plateau in Ladakh sector was selected in order to shed light on depositional environmental changes within the lake from post-last glacial maximum to 5ka. The River Indus was blocked by Lamayuru dam burst during the deglaciation, after the Last Glacial Maximum (LGM) and the subsequent increase in water level led to the formation of the Saspol-Khalsi palaeolake. This lake was ca 55km in length, extending from Nimo to Khalsi, had a surface area of 370km(2) and was in existence until 5ka. Two sections (Saspol and Khalsi) separated by an aerial distance of 35km show a similar trend in sediment character due to their deposition in the same lake system. Grain-size studies show a polymodal nature of sediments for both of the sections. However, sediments of the lower/downstream section (Khalsi) show a poorer degree of sorting, and coarser grain size and high energy depositional condition as compared with the sediments of Saspol section (positioned upstream) due to the location of the sections within the lake system. It was noted that, in high-altitude arid regions, the sedimentological characteristics of large-sized valley lakes may vary greatly, horizontally as well as vertically, owing to local stream input, inflow intensity from the catchment, outflow velocity of water channels, lithology and valley widths at the different sites.