Offshore Continuation of Narmada-Tapti Tectonic Zone along the Western Continental Shelf of India: Interpretation of High-Resolution Seismic Profile and Deep Bore Well Logs

ABSTRACT Geological interpretation of seismic profile and deep bore wells across the Narmada-Tapti Tectonic Zone is presented. This zone is represented by the Surat Depression, in offshore west coast of India. The study identifies closely spaced vertical faults, continuing up to approximately 10 km depth, formation of pullapart basin, subsidence with accompanying sedimentation; volcanism due to decompression melting and a long geological history. High resolution seismic profile acquired by long offset configuration and pre-stacking time and depth migration processing techniques have provided geological details of not only basalt stratigraphy but also sub-basalt Cretaceous and younger Tertiary succession. Logs of twenty drilled wells for hydrocarbon exploration and production are utilized to authenticate the seismic interpretation. This has led us to conclude that the extension of Narmada-Tapti tectonic Zone is also a half graben similar to other Gondwana grabens on peninsular India. The Cretaceous period is marked by formation of a unique volcano-sedimentary sequence where volcanic units are recognized by high seismic impedance as well as strong reflections. The sequence represents continued sedimentation and spasmodic volcanism in subsiding basin. This sequence is present all along the western off-shore of India and is utilized as significant marker horizon. Termination of volcanism and marked reduction of tectonics, characterizes the K-T Boundary. Folding is more pronounced with increasing depth. Maximum deformation is observed in the volcano-sedimentary sequence, followed by the Tertiary succession.