• Joyeeta Bhattacharjee

      Articles written in Journal of Earth System Science

    • 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.

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


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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.


      $\bullet$ 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.

    • Geochemistry and petrogenesis of Neoarchaean Granitoids from the southwestern Bundelkhand Craton: Implications on Archaean geodynamic evolution


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      Bundelkhand Archaean–Proterozoic Granitoid Complex comprises of an amalgamation of older, deformed Palaeoarchaean Tonalite Trondjhemite Granodiorite (TTG) surrounded by the younger relatively undeformed Neoarchaean high-K calc-alkaline granites. These rocks commenced its evolution during the Palaeo-Archaean (3.3 Ga) and continued to Archaean–Proterozoic Transition (APT). Heterogeneity in granites from southwestern Bundelkhand Craton can be observed in their colour, textural feature and availability of mafic components, thereby dividing them into grey (mafic rich and intermediate variant) and pink granites, which further gets geochemically classified into Closepet-type granites (maBc-rich variant of grey granite: GG), Low Silica High Magnesium monzogranite (LSHM, an intermediate variant of grey granite: IG (for field classification purpose) and High Silica Low Magnesium monzogranite (HSLM, pink granite: PG) on the basis of their major elemental characteristics. The partial melting of the lithologically varied crust and the mantle/lithosphere took place approximately around the same time because of the incompatible element-enriched Cuids and melts. This caused the generation of granitoids from Bundelkhand to be varied in nature, resulting in the crustal evolution and stabilisation of the craton around ${\sim}$3.3 Ga followed by its steady reworking by ${\sim}$2.57–2.54 Ga. The Closepet type granite resulted from crust-mantle interaction and the monzogranites from crustal melting. Understanding the granitic emplacement within such a short time will help to further decipher the geodynamic changes and the crustal evolutionary processes that were operative during the APT in SW Bundelkhand craton.


      $\bullet$ The manuscript focuses on the geodynamic evolution of the varied granites from SW Bundelkhand Craton.

      $\bullet$ The granites are categorised into grey (mafic-rich grey and intermediate grey) and pink granite on the basis of field geology and petrology. Geochemically they are divided into Closepet type granites (mafic-rich variant of GG) and monzogranites (low silica high magnesium: LSHM, intermediate variant of GG and high silica low magnesium: HSLM, pink granite variant). Their field expressions and the corresponding geochemical signatures can be attributed to a combination of partial melting and fractional crystallisation.

      $\bullet$ The division of granites into a low-silica high-magnesium group indicates crust–mantle interactions (Closepet-granites), and a high-silica low-magnesium group points toward pure crustal melting (monzogranites).

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