Himalayan Geology (Journal), Dehradun...........

Abstract: Abstract: Lake Ziro is ~11 km long and ~5 km wide, N-S trending, situated within the ranges of Lesser Himalaya at the height of ~1600 m amsl. The lake valley is drained by a low gradient, ~2 m wide channel known as Kale River a tributary to Subansiri River. The lakebed profile suggests N-S asymmetry in the basin geometry and indicates that the southern part of the lake is geomorphologically rejuvenated. The initial ~6 km from its northern extremity the lakebed gradient is ~4.5 m/km where the relict sedimentary deposits are preserved as <10 m high mounds within the lake basin. Whereas in the remaining southern part the gradient rises to ~10 m/km and the ~20-25 m thick sequences located ~20 m above the lakebed are exposed. The Kale River presently carries silty fine sand to clayey silt. The sedimentological analysis indicates the presence of a paleochannel in the area that carried coarse sand (mean size = 0.67 ö) as bed load. This therefore indicates towards hydrological transformations in the Kale River catchments during the past. The southern end of the lake is traversed by a transverse fault that shows development of fault gouge in granite gneisses. Palaeoseismicity in and around Lake Ziro is also evidenced from the soft sediment deformation structures of different kind preserved in the basal part of the relict deposits and also in the dug pits of the modern lakebed. The Luminescence chronology indicates the fluvial aggradation in the modern lake valley occurred between 22-10 ka and the last major reactivation along the fault occurred at ~21 ka. This suggested that the valley filling at Ziro took place during the phase that spanned the Last Glaciation and subsequent monsoon strengthening. The geomorphic profile of the modern lake Ziro formed in response to the neotectonically active transverse normal faults implying that the extensional tectonics in the Himalaya may create the transient sedimentary storages that archive the past climate records