Seismites in Permian Barakar Formation, Raniganj Basin, India: implications on Lower Gondwana basin evolution

Fault-bound half-graben-type Raniganj Basin in eastern peninsular India hosts thick sedimentary succession of the coal-bearing Barakar Formation (Early Permian), which constitutes a part of the Lower Gondwana Supergroup. Sedimentological attributes of the upper Barakar succession are portrayed in two predominant facies associations, viz., (i) the lower part characterized by meandering fluvial facies association with distributary channel systems and (ii) the upper part represented by a transgressive, tide-wave-influenced, fluvio-estuarine facies association. Distinct beds with various soft-sediment deformation structures (SSDSs) manifesting paleoseismic events are reported as seismites from the upper Barakar succession. The SSDSs include convolute laminae, complex deformations with folded strata, syn-sedimentary growth faults, pseudonodules, loop bedding, and various water-escape structures including sand–silt flows/dikes. The seismites are restricted at two distinct stratigraphic horizons (S1 and S2) within the upper Barakar succession, separated by undeformed beds in between. The seismites record episodes of paleoearthquake events triggered by syn-sedimentary reactivation of basin marginal faults in the half-graben-type Raniganj Gondwana Basin. These demarcate phases of significant shift in the depositional conditions from fluvial-dominated to a transgressive tide-wave-influenced estuarine system, caused by post-glacial basinal adjustments in the peninsular Indian Gondwanaland.