• Sanjoy Kumar Ghosh

      Articles written in Journal of Earth System Science

    • Pull-apart origin of the Satpura Gondwana basin, central India

      Chandan Chakraborty Sanjoy Kumar Ghosh

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      The Gondwana basins of peninsular India are traditionally considered as extensional-rift basins due to the overwhelming evidence of fault-controlled synsedimentary subsidence. These basins indeed originated under a bulk extensional tectonic regime, due to failure of the attenuated crust along pre-existing zones of weakness inherited from Precambrian structural fabrics. However, disposition of the basins and their structural architecture indicate that the kinematics of all the basins cannot be extensional. To maintain kinematic compatibility with other basins as well as the bulk lateral extension, some basins ought to be of strike-slip origin. The disposition, shape and structural architecture of the Satpura basin, central India suggest that the basin could be a pull-apart basin that developed above a releasing jog of a left-stepping strike-slip fault system defined by the Son-Narmada south fault and Tapti north fault in consequence to sinistral displacement along WSW-ENE. Development of a sedimentary basin under the above-mentioned kinematic condition was simulated in model experiments with sandpack. The shape, relative size, stratigraphic and structural architecture of the experimental basin tally with that of the Satpura basin. The experimental results also provide insights into the tectono-sedimentary evolution of the Satpura basin in particular and pull-apart basins in general.

    • Pattern of sedimentation during the Late Paleozoic, Gondwanaland glaciation: An example from the Talchir Formation, Satpura Gondwana basin, central India

      Chandan Chakraborty Sanjoy Kumar Ghosh

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      The Talchir Formation of Permian age is the lowermost lithostratigraphic unit of the Indian Gondwana successions preserving a record of the Late Paleozoic glaciation that affected the whole Gondwanaland.The formation unconformably overlies the Precambrian basement in all the Gondwana basins of India,and marks initiation of sedimentation after a long hiatus since the Pro- terozoic.The Talchir Formation of the Satpura Gondwana basin of central India shows features diagnostic of deposition under glacial regime such as the presence of diamictites,boulder pavements, bedding plane striation,faceted/striated gravels,bullet-shaped clasts,dropstone,cryoturbation, etc.The Talchir strata of the Satpura basin,in addition to tidal signatures,contain marine bivalve and trace fossils.A proglacial marine environment is thus inferred for their deposition.The dominant lithologies are conglomerate,pebbly sandstone,sandstone and shale with little limestone, which can be classified into the following major facies:

      matrix-supported conglomerate,

      clast-supported conglomerate,

      cross-strati fied,channel form pebbly sandstone,

      hummocky,swaley or low-angle cross-strati fied pebbly and non-pebbly sandstone,

      turbidite/tempestite sheet sandstone,

      massive to fissile,green to black claystone with carbonate layers and nodules.

      The conglomerates are interpreted as deposits of a spectrum of sub-aqueous sediment gravity lows including debris flow, hyperconcentrated/concentrated density flow and grain flow. The crossstratified pebbly sandstone bodies, on the other hand, represent braidplain delta deposits of glacial outwash origin. Hummocky, swaley, low-angle cross-stratified sediment bodies were deposited by storm-generated combined flows in a shoreface setting. In contrast, the sheet sandstone bodies are products of turbidity currents and storm-induced density currents in an inner shelf setting below fair weather wave base. The claystone facies is interpreted as a product of suspension fallout from hypopycnal sediment plumes in the outer shelf domain below storm wave base. All the lithofacies described above occur repetitively in the succession. Three facies-associations have been recognized in the Talchir Formation, representing ice-contact fandelta, outwash braidplain delta and a virtually ice-free, non-deltaic open marine realm. The different marine facies of the Talchir Formation define a number of shallowing-upward packages, which are arranged in the succession with a retrogradational trend to result in an overall fining- and deepening-upward succession. The overlying coal-bearing Barakar Formation has been interpreted to have formed in a tide-wave influenced deltaic setting with a marine, prodeltaic part. The strata that are transitional between Talchir and Barakar Formations show preservation of abundant plant materials suggesting gradual warming. The three facies-associations of the Talchir Formation also point towards progressive decrease in the intensity of glacial activity, inducing changes in the paleogeography from ice-contact depositional environment to an eventually relatively ice-free, open marine condition.

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