Seismically Induced Soft‐Sediment Deformation Structures and Massflow Deposits in a Paleoproterozoic Shelf Setting (Chakrata Formation, Lesser Himalaya, India)

ABSTRACT A variety of soft‐sediment deformation structures (SSDs) and mass flows of varying rheology are present in the Paleoproterozoic argillaceous Chakrata Formation, Lesser Himalaya. SSD structures (intra‐ and inter‐bed) include contorted/convoluted beds, deformed laminations, load casts, and flame structures, pseudonodules, and sand dykes. Deposits of high‐ and low‐density turbidity currents and sandy debris flows represent mass flows that are included in the Chakrata shelf shale succession. The lateral continuity and recurrent incidence of SSD‐bearing disturbed layers through the Chakrata lithopackage indicate a seismogenic origin. The disturbed bed thickness and nature of SSD structures suggest the earthquake shock magnitudes (Mz) of 5 to in excess of 8. It is ascertained that besides generating SSDs, the seismic shocks, at times, caused extreme liquefaction and fluidisation that caused sediment failure and generation of gravity flows. Though from rock record establishment of synchronicity between SSD formation and mass flow generation always remains a challenge in the absence of historical data or adjoining fault systems, the physical association of SSDs and mass flows in the Chakrata Formation allows identification of their co‐genetic nature related to seismic activity.