Astronomical and terrestrial causes of physical, chemical and biological changes at geological boundaries
The boundary horizons of the Cretaceous-Tertiary (Um Sohryngkew River section, Meghalaya and Anjar section, Kutch), the Permo-Triassic (Guling, Lalung, Ganmachidam and Attargoo sections, Spiti valley) and the Eocene-Oligocene (Tapti River section, Gujarat) have been identified in the sedimentary records of the Indian subcontinent. These sections have been studied for geochemical anomalies. The results are discussed in the framework of extra-terrestrial and terrestrial causes proposed to explain the physical, chemical and mineralogical observations at these boundaries. A critical analysis suggests that although the astronomical causes, particularly the bolide impacts, can easily explain the geochemical and physical changes, the terrestrial causes (volcanism) may have played a significant role in creating the biological stress observed in fossil records (mass extinction) at or near some of these boundaries.