• Falguni Bhattacharya

      Articles written in Journal of Earth System Science

    • Response of a dryland fluvial system to climate–tectonic perturbations during the Late Quaternary: Evidence from Rukmawati River basin, Kachchh, western India

      Archana Das Falguni Bhattacharya B K Rastogi Gaurav Chauhan Mamata Ngangom M G Thakkar

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      Dryland rivers, dominated by short-lived, localised and highly variable flow due to discrete precipitation events, have characteristic preservation potential, which serves as suitable archives towards understanding the climate–tectonic coupling. In the present study, we have investigated the fluvial records of a major, southerly-draining river – the Rukmawati River in the dryland terrain of southern Kachchh, in western India. The sediment records along the bedrock rivers of Kachchh register imprints of the Indian summer monsoon (ISM), which is the major source of moisture to the fluvial system in western India. The Rukmawati River originates from the Katrol Hill Range in the north and flows towards the south, into the Gulf of Kachchh. The field stratigraphy, sedimentology, along with the optical chronology suggeststhat a braided-meandering system existed during 37 ka period due to an overall strengthened monsoon. A gradual decline in the monsoon strength with fluctuation facilitated the development of a braided channel system between 20 and 15 ka. A renewed phase of strengthened monsoon with seasonality after around 15 ka which persisted until around 11 ka, is implicated in the development of floodplain sequences. Two zones of relatively high bedrock uplift are identified based on the geomorphometry and morphology of the fluvial landform. These zones are located in the vicinity of the North Katrol Hill Fault (NKHF) and South Katrol Hill Fault (SKHF). Geomorphic expression of high bedrock uplift is manifested by the development of beveled bedrock prior to or around 20 ka during weak monsoon. The study suggests that the terrain in the vicinity of NKHF and SKHF is uplifting at around 0.8 and >0.3 mm/a, respectively. Simultaneously, the incision in the Rukmawati River basin, post 11 ka, is ascribed to have occurred due to lowered sea level during the LGM and early Holocene period.

    • Pattern of dune accretion and its climatic implication in the southern Thar Desert margin, western India

      SHUBHRA SHARMA FALGUNI BHATTACHARYA GAURAV CHAUHAN

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      The present study summarizes the existing chronometric data of fossil dunes preserved in the southern Thar Desert margin (STM). The objective is to understand the episodes of dune accretion and causes of their spatial and temporal variability along the precipitation gradient. Based on the published ages, the study identifies three major phases of dune accretion. The oldest phase-I is dated between ${\sim}$ 25 and 17 ka (MIS-2); the second short-lived phase-II between ${\sim}$ 15 and 12 ka, whereas the phase-III occurred between 10 and 5 ka. The second phase terminates with the deposition of fluvially reworked aeolian sand which has the presence of microlithic artifacts and corresponds to the early Holocene strengthened Indian Summer Monsoon (ISM). The study suggests that during phase-I and II, the terrain witnessed a significant reduction in the ISM for which a more southerly position of the Inter-Tropical Convergence Zone (ITCZ) is implicated. During phase-III, an oscillating ISM with overall declining trend is attributed to mid-late Holocene minor fluctuations in the ITCZ (probably proximal to modern summer position). A conspicuous absence of dune building in the northern Thar Desert during the Last Glacial Maximum (LGM) is ascribed to the prevalence of hyper-arid conditions in comparison to the relatively moist conditions in the STM due to its proximity to the Arabian Sea. After ${\sim}$ 15 ka, both the STM and the Thar Desert show a broad synchroneity and that coincides with the gradual strengthening of the ISM.

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