Quaternary geology, tectonics and distribution of palaeo- and present fluvio/glacio lacustrine deposits in Ladakh, NW Indian Himalaya-a study based on field observations

We report the presence of three major lakes in the region in the late Quaternary. These formed due to the damming of the Indus river and its tributaries by debris avalanches initiated mainly by tectonic activity along the Indus Suture, Shyok suture and the Karakoram Fault. These are the Spituk-Leh palaeolake formed ∼>50,000 years BP; the Lamayuru palaeolake dated to 35,000 years BP in the Indus valley and the Khalsar palaeolake > 60 km in length in the Shyok valley. Vast exposures of the palaeolake deposits ranging from >25 to 150 m in thickness are reported-Spituk section (>25 m); Lamayuru section (>110 m) and Khalsar (>150 m) and Hundri (∼100 m) and which have a wide lateral extent. A glacial lake basin at Bhaktpur city, north of Baralacha La, is now completely filled, the TsoKar lake has been subdivided into smaller units now and the water level is lowering. Other lakes in the region (e.g., Pangong Tso, Tso Morari, the twin Kyun Tso lakes) are confined to the western side of the study area. Limited chemical weathering, rapid erosion and cold climatic conditions in late Quaternary times are suggested by the stable illite values in the Lamayuru section. Four levels of palaeoseismic structures (convolute structures, sand dykes, intraformational folds, micro faulting) are present in the Khalsar section and at three levels in the Tirit section (at Shyok, Nubra confluence). Palaeoseismic activity was also prevalent after 25,000 years BP as is evident from the three levels of palaeoseismic structures in the younger sediments.