• ABHIK KUNDU

      Articles written in Journal of Earth System Science

    • Palaeoseismicity in relation to basin tectonics as revealed from soft-sediment deformation structures of the Lower Triassic Panchet formation, Raniganj basin (Damodar valley), eastern India

      Abhik Kundu Bapi Goswami Patrick G Eriksson Abhijit Chakraborty

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      The Raniganj basin in the Damodar valley of eastern India is located within the riftogenic Gondwana Master-Basin. The fluvio-lacustrine deposits of the Lower Triassic Panchet Formation of the Damodar valley in the study area preserve various soft-sediment deformation structures such as slump folds, convolute laminae, flame structures, dish-and-pillar structures, sandstone dykes, pseudonodules and syn-sedimentary faults. Although such soft-sediment deformation structures maybe formed by various processes, in the present area the association of these structures, their relation to the adjacent sedimentary rocks and the tectonic and depositional setting of the formation suggest that these structures are seismogenic. Movements along the basin margin and the intra-basinal faults and resultant seismicity with moderate magnitude (2–5 on Richter scale) are thought to have been responsible for the soft-sediment deformations.

    • Depositional environment and provenance of Middle Siwalik sediments in Tista valley, Darjiling District, Eastern Himalaya, India

      Abhik Kundu Abdul Matin Malay Mukul

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      The frontal part of the active, wedge-shaped Indo-Eurasian collision boundary is defined by the Himalayan fold-and-thrust belt whose foreland basin accumulated sediments that eventually became part of the thrust belt and is presently exposed as the sedimentary rocks of the Siwalik Group. The rocks of the Siwalik Group have been extensively studied in the western and Nepal Himalaya and have been divided into the Lower, Middle and Upper Subgroups. In the Darjiling–Sikkim Himalaya, the Upper Siwalik sequence is not exposed and the Middle Siwalik Subgroup exposed in the Tista river valley of Darjiling Himalaya preserves a ∼325 m thick sequence of sandstone, conglomerate and shale. The Middle Siwalik section has been repeated by a number of north dipping thrusts. The sedimentary facies and facies associations within the lithostratigraphic column of the Middle Siwalik rocks show temporal repetition of sedimentary facies associations suggesting oscillation between proximal-, mid- and distal fan setups within a palaeo-alluvial fan depositional environment similar to the depositional setup of the Siwalik sediments in other parts of the Himalaya. These oscillations are probably due to a combination of foreland-ward movement of Himalayan thrusts, climatic variations and mountain-ward shift of fanapex due to erosion. The Middle Siwalik sediments were derived from Higher- and Lesser Himalayan rocks. Mineral characteristics and modal analysis suggest that sedimentation occurred in humid climatic conditions similar to the moist humid climate of the present day Eastern Himalaya.

    • The role of pre-existing faults and fractures in shaping polygonal impact craters and its tectonic implications in the southern Margaritifer Terra region, Mars

      SUPRATIK BASU NILANJAN DASGUPTA ABHIK KUNDU SATADRU BHATTACHARYA DIPAYAN DASGUPTA

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      The presence of polygonal-shaped craters, i.e., craters with complete or incomplete polygonal rims along with circular or elliptical outlines, on the surface of celestial bodies has been known for nearly a century. However, many investigations on their distribution and formation have not been carried out, until recently. Scientists have proposed that the polygonal shapes of the crater rims owe their origin to the preexisting structurally weak planes like faults/fractures in the area adjacent to the impact. The present study area is the southern part of Margaritifer Terra, Mars; a mid-Noachian terrain, which has craters of different morphologies, including the polygonal impact craters (PICs). The study focuses on the reason for the development of PICs by identification and mapping of a population of 50 selected polygonal craters along with morphotectonic features namely grabens, wrinkle ridges, and lobate scarps. The analysis of orientations of the straight segments of polygonal crater rims shows marked resemblance with orientations of these morphotectonic features conforming to their control on the rim geometries.

      $\bf{Highlights}$

      ${\bullet}$ Structural mapping of the southern Margaritifer Terra region, Mars.

      ${\bullet}$ Generating rose diagrams and line graphs for the orientation of the straight edges of polygonal craters and the morphotectonic features within the southern Margaritifer Terra region.

      ${\bullet}$ Conducting statistical F-test to find out the bearing of weak planes on the formation of PICs.

      ${\bullet}$ Finding out the presence of buried weak planes by comparing the rose diagrams and spike graphs.

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