• AMRITA MUKHERJEE

      Articles written in Journal of Earth System Science

    • Soft-sediment deformation structures in a Permo-carboniferous glacio-marine setting, Talchir Formation, Dudhi Nala, India

      H N BHATTACHARYA AMRITA MUKHERJEE

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      The Permo-carboniferous glacio-marine Talchir Formation of Dudhi Nala, West Bokaro Coal Basin, India, hosts soft-sediment deformation structures that originated from liquefaction and concomitant fluidization of unconsolidated sediments at or close to the sediment–water interface. Since liquefaction of water saturated sediments may be initiated by different endogenic or exogenic triggering agents, identification of the trigger needs careful analysis of the deformation structure, as well as depositional mechanism and environment of deposition of the host sediments. In-depth analysis of the studied liquefaction- and fluidization-induced soft-sediment deformation structures and sedimentary attributes of the host sediments of the studied succession unequivocally stand against the role of strong wave and tidal action, rapid sediment loading, mass-flow and subaqueous slides related shear stress, and water or gas seepage as the triggering agent. However, development of the soft-sediment deformation structures, close to sediment–water interface, closeness to syn-sedimentary fault, flowage along the tilt towards the fault, confinement within undeformed beds, episodic character and close similarities with structures that are formed during recent earthquakes, are consistent with seismic triggering for liquefaction. The studied shallow marine sediments record a sequel of climatic amelioration, glacial retreat, shallow marine sedimentation, glacio-isostatic rebound and related syn-sedimentary faulting and development of soft-sediment deformation structures.

    • A reappraisal of the Jharol Formation in the context of stratigraphy of Aravalli Supergroup, Rajasthan, India

      BHATTACHARYA H N AMRITA MUKHERJEE

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      The enormously thick sedimentary succession exposed between Rishabhdev Lineament and rocks of the Delhi Supergroup constitutes Jharol Formation of the Aravalli Supergroup in Udaipur region of Rajasthan. The whole sedimentary succession is named Jharol Formation and designated as deep water turbidites. A detailed field examination indicates presence of two distinctly different litho successions juxtaposed across a crustal level fault along which brecciated ultramafics are tectonically emplaced. The sedimentary successions exposed immediate west of the Rishabhdev Lineament are deep water sediments with distinct facies types characterizing inner to outer lobe stacked turbidites. These turbidites are similar to the turbidites of the Udaipur Formation and Tidi Formation exposed east of the Rishabhdev Lineament. However, the sedimentary succession exposed west of these deep water sediments across the aforesaid fault contains facies types that represent continental to shallow marine deposits. This basin marginal sediments continue up to the contact with rocks of the Delhi Supergroup. Such litho-association suggests that a separate formation status of the sediments lying west of the Rishabhdev Lineament should be dropped and the turbidites of the Udaipur Formation should be considered as the youngest formation of the Aravalli Supergroup.

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