Himalayan Foredeep Neotectonics and Deformed Riverscape Landforms: An Integrated Discussion, West Bengal, India

Abstract

AbstractThis book chapter provides immense documentation of Himalayan foredeep neotectonics and evolutionary processes that focus on landform deformation and channel succession in terms of morphotectonic discussion at a glance. The Himalayan foredeep foothill is composed of successive sediment deposition of 16.0–0.5 Ma BP i.e. Middle Miocene-Middle Pleistocene and late Quaternary Siwalik, which is overlain by young thick sandy to loamy sediments of Holocene near surface (Jain AK, Banerjee DM, Kale SV (2020) Tectonics of Indian subcontinent, society of earth scientists series, ISSN 2194-9204 ISSN 2194-9212 (electronic), ISBN 978-3-030-42844-0 ISBN 978-3-030-42845-7 478 (eBook), 111–433. 10.1007/978-3-030-42845-7). This elongated section is formed by series of alluvial fans, which are deformed and restructured by the neotectonic activities evident by earthquake magnitude in the last 120 years with the presence of Matiali scarp (MBT) 34 ka, Chalsa scarp (MFT) 11–6 ka (Kar et al. Geomorphology 227:137–152, 2014). The MIS-3(marine isotope stage 3) of 34 ka (Mukul M, Singh V (2016) Active tectonics and geomorphological studies in India during 2012–2016. In: Proceedings of the Indian national science academy, p 82 10.16943/ptinsa/2016/48480) initiated the alluvial fan formation (Matiali fan) which had been interrupted by repeated tectonic activities and accompanied by hydrological flow alteration due to climate change as the emergence of LGM (Last Glacial Maximum) and MIS-2 in Holocene (Martinson et al. Quatern Res 27:1–29, 1987). Upliftment and erosion sequences assemblaged by slope differentiation and flow/velocity alteration prompted the reframed alluvial fans and two tire river terraces. The alluvial fan in a fan formation extended towards the south with distinctly identified three geomorphic units as apex, mid fan, and lobes. These fans are cast around as mega fans and meso to micro-scale dimensions. The outcome of the study is recapitulated in one pictorial image to make a clear understanding of its morphological units. In the field, artificially initiated water flow in varying discharge (Q) has been experimented to set an idea of expanded coverage area in both monsoon and flood seasons. The morphotectonic indices on River Kaljani specify the active tectonics over the area where fans have developed in an elongated shape with changed SL and concavity along the channel. It is a comprehensive study of foreland active tectonics of North Bengal foothill. It clarifies the mechanism of deformed landforms and modification of channel succession in response to the active tectonics.KeywordsNeotectonicsDeformed alluvial fansChannel geometry