Browsing by Author "Satyabrata Das"

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Chronology and sediment provenance of extreme floods of Siang River (Tsangpo-Brahmaputra River valley), northeast Himalaya
(John Wiley and Sons Ltd, 2020) Sandeep Panda; Anil Kumar; Satyabrata Das; Rahul Devrani; Santosh Rai; Kuldeep Prakash; Pradeep Srivastava
This study explores paleoflood deposits of the Siang River, known as the Tsangpo in Tibet. The river that often experiences large floods brings down huge amount of sediment and water that adversely affect the downstream regions with large human populations in the states of northeast Himalaya and its foreland. Along it's ~300 km mountainous stretch we collected samples for sedimentological, petrographic and Sr–Nd isotopic study to explore sediment provenance and dated the paleofloods (via optically stimulated luminescence, OSL). Geomorphic indices including precipitation and a geomorphic swath profile across the Brahmaputra catchment were studied to understand the interplay of mountain relief and rainfall that determine potential zones of high erosion and sediment supply. The OSL technique indicated the Siang River experienced at least eight large floods between 7 and 1 ka, possibly under the influence of warm and wet climatic conditions. The petrographic and isotopic data suggests that the eastern Himalayan syntaxis, which has the highest uplift and exhumation rate in the area, is not always the highest sediment producing zone. In some instances, the Tibetan plateau produces higher fluxes of sediments via glacial and landslide lake outburst floods (GLOFs and LLOFs). © 2020 John Wiley & Sons, Ltd. © 2020 John Wiley & Sons, Ltd.
Deciphering the role of late Quaternary sea level fluctuations in controlling the sedimentation in the Brahmaputra Plains
(Elsevier B.V., 2022) Sandeep Panda; Anil Kumar; Pradeep Srivastava; Satyabrata Das; R. Jayangondaperumal; Kuldeep Prakash
Continent-continent collision between Eurasian and the Indian plate during the Cenozoic period lead to the formation of the Himalayan Mountain chain and the development of the Indus-Ganga-Brahmaputra foreland basin to the south. Complex climate-tectonic interactions in this orogenic belt are responsible for the rapid erosion and filling of the Indus-Ganga-Brahmaputra foreland basin with the eroded materials. This study based on geomorphic mapping, lithofacies analysis, and geochemical (Strontium-Neodymium i.e., Sr–Nd analysis) provenance characterization, as well as optically stimulated luminescence (OSL) ages, provides a dated sedimentation framework for the western Assam lowland areas. The dated relict fan surface lies ~40 m above mean sea level (msl), is incised and forms a regional valley terrace T1 composed of meandering channel deposits. Modern braided rivers flow on the T0 surface. The findings suggest that the alluvial fan is composed of three distinct lithofacies associations and aggraded during 27 to 3 ka. The bottom-most gravelly-sandy facies indicates progradation of the fan during the last glacial maximum (LGM), owing to the increased gradient of the Himalaya bound rivers. The middle facies is a sheet flood deposit which formed during the Latest Pleostocene-early Holocene period with rising sea level and increasing precipitation. During the Mid-Late Holocene, the uppermost facies is deposited as rivers lost their gradient in response to high sea level stand, resulting in inland sedimentation within muddy meandering channels. Our analysis found that falling sea level during the late Holocene was associated with greater precipitation and allowed the river to incise, to form gullies over the fan surface and form the valley terrace T1. The Sr–Nd isotope fingerprints have been used to identify varying fan sediment sources in the Himalaya's southern front (i.e., Lesser and Higher Himalaya) as a function of changing monsoon conditions. © 2022 Elsevier B.V.