THE CRETACEOUS-PALEOGENE CRISIS AND ITS AFTERMATH: TECTONIC, MAGMATIC, BIOTIC, CLIMATIC, AND EVOLUTIONARY UPHEAVALS OF INDIAN PLATE

Impact cratering has played a crucial role in the geological and biological evolution on Earth. Evidence for twin impacts at the Cretaceous-Paleogene (K-Pg) boundary extinctions has come from opposite sides of the globe—the Chicxulub crater in Mexico and the Shiva crater in India. India was ground for two catastrophic events at the K-Pg boundary, the Shiva impact and Deccan volcanism. The buried and multiringed Shiva crater (~500 km diameter) on the western shelf of India is the largest hydrocarbon reserve in India. The Shiva bolide (~40 km) generated lethal amount of kinetic energy to trigger major tectonic, plate tectonic, thermal, magmatic, and environmental episodes. It created radial rift basins in central India and extruded iridium-contaminated alkaline fluid ejecta along these basins. It sheared, fragmented, and deformed lithosphere mantle, where the crust-mantle boundary has been uplifted more than 50 km. The ejecta/fallout components have been identified at various K-Pg boundary sections of India. The close proximity of the Shiva crater and Reunion plume head suggests that the impact might have enhanced the most voluminous eruptions of the Deccan volcanism within ~50,000 years of impact by seismic shaking of magma chamber at the K-Pg transition. During the Early Paleocene, as India began to accelerate northward, the Seychelles Island separated from India with the spreading of the Carlsberg Ridge, perhaps induced by the impact. The sudden acceleration of the Indian plate (~20 cm/year) probably caused by the push force of the Reunion plume head and the subduction of the Neotethyan Kshiroda plate. As India collided with Asia during the Paleocene-Eocene Thermal Maximum (~55 Ma), the plate motion slowed down dramatically to ~5m/year. The K-Pg extinction was a game changer in the evolution of vertebrates. There was an explosive radiation of tetrapods, especially placental mammals in India during its initial collision with Asia because of the unprecedented ecological opportunity provided by the vacant niches of dinosaurs. An extraordinarily warm climate opened up when India became a new member of the Holarctic faunal province. The faunal interchange between India and Eurasia was a landmark paleobiogeographic event that led to the origin of the modern orders of mammals, supporting the “out-of India” hypothesis.