Tectonic implication in the evolution of lake and Quaternary landforms in the Lohawati river basin, Kumaun outer Lesser Himalaya

The evolution of the Quaternary landforms in the Champawat area of the outer Kumaun Lesser Himalaya is reconstructed from the paleolake sections and the geometry of the landscape. Conjugate sets of normal faults are observed in both the bedrocks and Quaternary deposits at Banlek. The most prominent normal faults are those striking NE-SW and NW-SE and most of them are steeply dipping faults while some are vertical faults. Sediments akin to the lacustrine deposits are observed at four sites; while the contact between the bedrock and the lake sediments is observed at only one site in the peripheral side. The exposed sediments thicknesses vary from 8.30 m to 4.8 m and consist of an alternation of black carbonaceous mud and sandy horizons indicating different depositional regimes. The total thickness of the lake sediments appears to be more than 75 m as deduced from elevational differences between the exposed sites. From Site 1, two OSL samples collected from 2.5 m and 8 m from the present ground surface, were analyzed which give OSL ages of 16 ka and 17 ka, respectively; while one sample collected from Site 4 gives an OSL age of 13 ka. A total of 3653 lineaments were mapped encompassing 2,277.8 sq km from the eastern Kumaun Himalaya. Maximum of the lineaments trend ENE-WSW or almost E-W (∼46.5%); the major principal stress is deduced to be in NE-SW direction. Lake, mature topography and gentle stream gradient in the Champawat area are the result of highly weathered bedrocks and development of the normal faults.