Seismic-aseismic impact on marine depositional dynamics and sedimentary architecture: Study on multilayer-multiscale SSDS in Proterozoic Rohtas Limestone, India

The present study explores a diverse suite of soft-sediment deformation structures (SSDSs) preserved at multiple levels within the Mesoproterozoic carbonate succession of Rohtas Limestone in the Vindhyan Supergroup of India. The carbonate succession shows lithological heterogeneity, characterized by a sharp change of facies association and depositional environment. Three layers of SSDS, traced over 57 km, demarcate the lower lagoonal from upper open shelf deposits. Contorted laminae, load casts and flame structures, convolute laminae, ball and pillow structures, accordion folds and pillar structures within the limestone beds infer liquefaction-fluidization and plastic deformation. The lateral continuity, vertical repetition and confinement of SSDS beds at the interface of lagoon and open shelf deposits indicate the role of seismicity on facies succession. The SSDS beds show lateral variation in thickness and structures, depending on the distance from epicenter. The seismic trigger was accompanied by sudden deepening of the depositional environment and related marine transgression. The coarsening up packages within the lagoonal succession comprise load cast and flame structures, syn-sedimentary faults and intraclastic conglomerates. The open shelf succession shows several fining up cycles, with multiple load and flame structures with intraclastic conglomerate at the top. Origin of SSDS in association of the coarsening up sequence, and fining up cycle infers that intrabasinal tectonics and storms were the triggering agents for lagoon and open shelf successions respectively. The seismite in the studied succession not only reveals the seismicity during the Proterozoic, but also changed the sedimentary facies association, which may use as a diagnostic criterion for the identification of seismite. This study also highlights that seismic and aseismic impacts on sedimentary architecture and paleoceanography evolution.