• Biplab Bhattacharya

      Articles written in Journal of Earth System Science

    • Significance of transition between Talchir Formation and Karharbari Formation in Lower Gondwana basin evolution — A study in West Bokaro Coal basin, Jharkhand, India

      H N Bhattacharya Abhijit Chakraborty Biplab Bhattacharya

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      Basal part of the Gondwana Supergroup represented by Talchir and Karharbari Formations (Permo-Carboniferous) records an abrupt change-over from glacio-marine to terrestrial fluviolacustrine depositional environment. The contact between the two is an unconformity. Facies analysis of the glacio-marine Talchir Formation reveals that basal glaciogenic and reworked glaciogenic sediments are buried under storm influenced inner and outer shelf sediments. Facies associations of the Karharbari Formation suggest deposition as fluvio-lacustrine deposits in fault-controlled troughs. An attempt has been made in this paper to explain the sedimentation pattern in Talchir and Karharbari basins, and the abrupt change-over from glacio-marine to terrestrial fluviolacustrine depositional environment in terms of glacio-isostacy.

    • Early Permian transgressive–regressive cycles: Sequence stratigraphic reappraisal of the coal-bearing Barakar Formation, Raniganj Basin, India

      Biplab Bhattacharya Joyeeta Bhattacharjee Sandip Bandyopadhyay Sudipto Banerjee Kalyan Adhikari

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      The present research is an attempt to assess the Barakar Formation of the Raniganj Gondwana Basin, India, in the frame of fluvio-marine (estuarine) depositional systems using sequence stratigraphic elements. Analysis of predominant facies associations signify deposition in three sub-environments: (i) ariver-dominated bay-head delta zone in the inner estuary, with transition from braided fluvial channels (FA-B1) to tide-affected meandering fluvial channels and flood plains (FA-B2) in the basal part of the succession; (ii) a mixed energy central basin zone, which consists of transitional fluvio-tidal channels (FA-B2), tidal flats, associated with tidal channels and bars (FA-B3) in the middle-upper part ofthe succession; and (iii) a wave-dominated outer estuary (coastal) zone (FA-B4 with FA-B3) in the upper part of the succession. Stacked progradational (P1, P2)–retrogradational (R1, R2) successions attest to one major base level fluctuation, leading to distinct transgressive–regressive (T–R) cycles with development of initial falling stage systems tract (FSST), followed by lowstand systems tract (LST)and successive transgressive systems tracts (TST-1 and TST-2). Shift in the depositional regime from regressive to transgressive estuarine system in the early Permian Barakar Formation is attributed to change in accommodation space caused by mutual interactions of (i) base level fluctuations in responseto climatic amelioration and (ii) basinal tectonisms (exhumation/sagging) related to post-glacial isostatic adjustments in the riftogenic Gondwana basins.

    • Characterization of middle Eocene tide-influenced delta: A study from core samples of Hazad Member, Ankleshwar Formation, South Cambay Basin, India

      Sapana Jaiswal Biplab Bhattacharya

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      The Hazad Member (Middle Eocene) of the Ankleswar Formation in Cambay Basin, India, is traditionally reported as deltaic system. Present work documents three major facies associations, namely, (i) sandstone-rich upper delta plain (FA-1) deposits, (ii) sandstone-mudstone heterolithic lower delta plain–delta front (FA-2) deposits, and (iii) shale-dominated prodelta (FA-3) deposits, in an overallcoarsening-up to fining-up succession. Tidalites are well preserved in FA-2 and are represented by laterally accreted tidal bundles, tidal beddings and vertically accreted tidal rhythmites, described from drill core samples in this communication. Laterally accreted tidal bundles with reactivation surfaces in sanddominatedheterolithic units indicate time-velocity asymmetry in subtidal condition. Tidal beddings and tidal rhythmites in mud-dominated heterolithic units, associated with asymmetric/symmetric ripple forms and desiccation cracks, indicate periodic subaerial emergence in intertidal flat depositional setting. Systematic analysis of the architecture of the tidalites in different parts of the basin signifies rapid shiftin sedimentation from subtidal to intertidal flat within the lower delta plain. Transitions from prodeltaic to tidally (subtidal-intertidal) affected delta front to lower delta plain and fluvial-dominated upper delta plain depositional systems attest to high frequency transgressive-regressive cycles in response to changingaccommodation, as a result of sea level fluctuations and basinal tectonisms in the Cambay Basin.

    • Palaeogeographic implications of ichnotaxa assemblages from early Permian fluvio-marine Barakar Formation, Raniganj Basin, India

      BIPLAB BHATTACHARYA JOYEETA BHATTACHARJEE SUDIPTO BANERJEE TAMANYA ROY SANDIP BANDYOPADHYAY

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      The sandstone-shale-coal succession of the Barakar Formation (early Permian) of the Raniganj Basin, India hosts low-diversity ichnoassemblages, containing ichnogenera Arenicolites, Chondrites, Diplocraterion, Monocraterion, Ophiomorpha, Palaeophycus, Planolites, Skolithos, Taenidium, and Thalassinoides, produced by shallow marine infaunal invertebrates. Sedimentary facies architecture depicts a transgressive, fluvio-tidal (with a minor wave) interactive estuarine depositional setting. The fluvial deposits, lying beyond the zone of tidal encroachments, record absence of trace fossils, which is attributed to a low colonization window caused by high fluvial discharge and frequent channel migrations. Tidal interactions with high fluvial discharge led to bay-head deltas in the inner-middle estuary with the dominance of suspension-feeding and deposit-feeding ichnotaxa in coarser- and finer-dominated sediments, respectively, suggesting a mixed Skolithos–Cruziana ichnofacies. Increasing tidal influence with very less fluvial input allowed opportunistic colonizers and deposit feeders of the Cruziana ichnofacies to flourish in the central estuarine setting. Intermittent low-oxygenated restricted conditions marked by the chemosymbiotic ichnoassemblages of the Zoophycos ichnofacies indicate very low energy conditions. The outer estuary with increasing wave dominance is inhabited by suspension-feeding, domicile ichnotaxa of Skolithos ichnofacies, frequently mixed with the ichnotaxa of the Cruziana ichnofacies. The recurrent juxtaposition and lateral distribution of the Seilacherian marginal marine ichnofacies is attributed to complex sediment–organism interaction patterns in response to prevalent energy conditions, sediment discharge and substrate conditions in different zones of the fluvio-tidal estuarine setting. The integrated sedimentological-ichnological model signifies marine transgressions that affected the palaeogeography of the Permian continental Gondwanaland.

      $\bf{Highlights}$

      $\bullet$ Sedimentological–ichnological analysis signifies marine encroachment in Barakar Formation in peninsular India.

      $\bullet$ Ichnoassemblages point to complex pattern of sediment–organism interactions with gross energy distribution.

      $\bullet$ Sustained marine transgression event within the continental Gondwanaland during early Permian is visualized.

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