Sedimentary environment and geomorphic development of the uppermost Siwalik molasse in Kumaun Himalayan Foreland Basin, North India

Abstract

An area of about 250 sq. km. around Ramnagar and Garjiya within the Siwalik molasse in the Kumaun foothills was mapped for geomorphic evolution and sedimentation pattern. The area, bounded by Himalayan Frontal Thrust (HFT) in the south and Main Boundary Thrust (MBT) in the north, consists of the sediments of uppermost part of the Pinjor and overlying Boulder Conglomerate Formations. Sedimentologically, three facies associations (FAA-FAC) were recognized with their order of superposition as FAA → FAB, FAA → FAC, FAB → FAC and FAC → FAB with variability in depositional setting. Lithofacies FAA-FAC were seemingly deposited in sand-dominated fluvial channel belt, gravelly braided channel belt and cut-off channel settings, respectively. The sediment dispersal in the basin was influenced by active basinal tectonics that caused frequent avulsions during the Bounder Bed times. The compositions of the clasts of these lithofacies reveal a shift in the primary provenance from pre-Tertiary Himalayan hinterlands during the emplacement of FAA (of the Pinjor Formation) to evolving frontal Siwalik highlands during the emplacement of FAB and FAC (of the Bouldder Conglomerate Formation). This temporal shift in the provenance indicates exhumation of the older Siwalik sequences during the later phases of Himalayan orogeny. A number of subordinate faults, oblique to above mentioned intracrustal boundary thrusts and formed after the sedimentation was seized, were likely responsible for displacement between the sediments of different associations. The neotectonic rejuvenation is also reflected by the upliftment of two sister basins in opposite direction, rapid uplift in V-shaped valleys, fault escarpments, three levels of terrace development and displacement of rock types along the subordinate faults as well as deflection and entrenchment in the course of lower order streams.

Geomorphologic study of the valley floor in different tectonic segments along Kosi River valley between South Almora Thrust and Himalayan Frontal Thrust: Kumaun Himalaya, India

“…The Upper Siwalik Formation (5.26 to 0.5 Ma) is mainly made up of polymictic conglomerates, friable sandstones, and mixed sandstone/mudstone heterolithics. Kotlia, Goswami, Joshi, Singh, and Sharma (2017) suggested continuous westward shifting of the channel belts during the Boulder Conglomerate times, which indicates that the basin was up-tilting in the east that is attributed to activities of basement structures. The area is traversed by a major strike-slip fault known as the Garampani Fault (Luirei, Bhakuni, Kothyari, Tripathi, & Pant, 2016;Valdiya, 1988).…”

Quaternary landform study in Kosi and Dabka river valleys in Kumaun sub‐Himalaya: Implication of reactivation of thrusts

“…The Dun gravels in the intermontane basin are tilted by 5°–15°N and uplifted by 60–90 m above the plains due to the uplift along the HFT in the Kalagarh area of the mountain front. Kotlia, Goswami, Joshi, Singh, and Sharma () interpreted that the tilting of a 20‐m fluvial terrace in the area is as a result of an ongoing tectonic activity along the HFT. In the present study, a similar observation is made in the Himmatpur area, where the fluvial sediments are tilted by 7° towards N and uplifted by about 10 m (Figure d).…”

Data on morphotectonic indices of Dashtekhak district, Iran

“…V f and V are valuable morphometric indices to quantitatively differentiate the shape of a valley along its cross section. High values of these indices indicate U-shaped valleys that associated with low tectonic activity, while low values show deep V-shaped ones indicating active uplift [3] , [4] , [5] , [6] , [7] , [8] , [9] .…”