Shiva impact event and its implications for Deccan Volcanism and Dinosaur Extinction

Abstract

We have identified a buried 500 km diameter Shiva structure on the western shelf of India as a possible impact crater that formed at the Cretaceous-Tertiary (KT) boundary time. The location of the Shiva crater was initially suggested between India-Seychelles block, when Seychelles was part of the Indian Plate at its western margin around 65 Ma. This work refines previous interpretations of the structure, morphology and the extent of the Shiva crater, which now appears to be located entirely on the Mumbai Offshore Basin encircling the Bombay High area. The Shiva crater is largely submerged on the passive western continental shelf and is buried by 7 km thick strata of post-impact Cenozoic sediments. It is the largest impact crater known on Earth, about 500 km diameter and is a rich source of oil and gas. It has the morphology of a complex peak ring structure with a multiring basin configuration, thus providing an ideal structural trap for petroleum entrapment. Four different ring structures have been identified, where the inner peak ring represents the central uplift of the Bombay High area with a core of Neoproterozoic granite basement. Inside the peak ring, a series of rugged mountainous peaks tower more than 7 km above the basin floor. We speculate that the Shiva bolide (~40 km diameter) crashed obliquely on the western continental shelf of India around 65 Ma, excavating the crater, shattering the lithosphere, initiated the rifting between India and the Seychelles and triggered the acceleration of the Indian Plate northward. The Cretaceous-Tertiary boundary sections of India have yielded several proximal ejecta components linked to the Shiva event such as shocked quartz, spherules and glass shards and iridium-rich alkaline melt rocks. Other cosmic signatures at the KT boundary of India from the vapourized meteorite include iridium anomaly, natural fullerenes, nickelrich spinels and magnetic nanoparticles. Although the Reunion hotspot responsible for Deccan eruption was close to the Shiva crater in time and space, impact did not trigger the hotspot because the first phase of the Deccan volcanism preceded the Shiva impact by 400,000 years or more. Two large impacts such as Shiva and Chicxulub in quick succession on the antipodal position, in concert with Deccan eruption, would have devastating effects globally leading to climatic and environmental calamity that wiped out the dinosaurs and many other organisms at the KT boundary.