Journal de géologie et géophysique
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Lithofacies Superimposition in a Shallow Basin - Interplay of Tectonics and Sedimentation: Evidences from Kolhan Basin, Eastern India

Smruti Rekha Sahoo, Subhasish Das

The 2.2-2.1 Ga pear shaped Kolhan basin show the development of a time transgressive group in a half-graben setting developed during the fragmentation of the Rodinia supercontinent. The overall style of sedimentation reflect a switchover from low-sinuous avulsed channels developed within a braided-fluvial-ephemeral streams to a lacustrine fan-delta complex during the later part of the sedimentation history. The fan-delta facies indicate sediment dispersal by hyperconcentrated flows in the form of sheetfloods and channelized flows. These different-scale cycles are interpreted as the sedimentary response to pulses of deformation of the basin margin at variable frequencies, related to the contemporary thrusts (ca. 20 km away from the basin). The episodes of tectonism downwarped the basin margin sediments and made the basin shift periodically toward the margin, and created progressive lithological changes in the sedimentary succession. The immediate effects of a tectonic pulse included lake transgression and accentuation of the structural hinge of the basin margin, causing a decline of sediment supply from the source rock. As the basin margin was subsequently reduced by denudation, the fans prograded and fan deltas were formed in normal conditions of graben subsidence. The sediment geometries and the climate exerted a major control on the processes of sediment transfer. Our results show that the fluvio-lacustrine strata show on lap-pinch out relationship at the centre of the basin but only on lap relationship along the lateral edges. This transition can be best explained by the fault growth models.