Seismites in the Lokapur Subgroup of the Proterozoic Kaladgi Basin, South India: A testimony to syn-sedimentary tectonism

Abstract

Syn-sedimentary deformation structures (SSDs) can indicate disturbance caused by autogenic or allogenic processes affecting the depositional system. Such structures are prolific in the Proterozoic shallow marine sediments of Kaladgi Basin, especially in the basal part of the succession (Lokapur Subgroup), in both clastics and carbonates. Widespread distribution, lateral traceability of the deformed horizons across several hundreds of meters, their occurrence between undeformed beds and proximity to NW–SE to E–W trending faults and shears are used to attribute a seismic origin to some of these SSDs . Release of accumulated stresses in the basin floor undergoing extension caused the episodic seismic activity producing the seismites. These “seismites” record the syn-sedimentary tectonism that controlled facies distribution patterns in the Mesoproterozoic Bagalkot Group in conjunction with sea-level fluctuations. On one hand, this is a contribution towards recognition of seismic events during the Mesoproterozoic, a period from which few seismites have been recorded. On the other hand, recognizing that the crustal processes that operated in brittle regimes during the creation of this extensional supracrustal basin around 1800 Ma were comparable to those operating in present day extensional systems opens a window of understanding how the Proterozoic platform basins hosting thick shallow marine sequences evolved.