Evidence of biotic recovery through the Cretaceous/Palaeogene transition from the Mahadeo-Cherrapunji succession in the Meghalaya shelf, India

Earlier studies on the Mahadeo-Cherrapunji road (MCR) section have documented the Cretaceous-Palaeogene Boundary (KPB ca. ~ 66 Ma), but rare data exist on the Deccan volcanism induced KPB transition and related faunal crises. The environmental stress on biota has been postulated as the main cause of mass extinction. Thus, the study of organic matter (OM) entrapped in the Maastrichtian-Danian shelf sediments has attained importance, although the existing data is inadequate. In this situation, layer-wise n -alkanes and n -fatty acids analyses were carried out using GC-MS. Obtained data show sudden increase in the short chain n -alkane (SCA ~ 6-fold), n -fatty acid (FA) and hopane (> sterane) concentrations. This suggests enhanced continental runoff and soil bacteria biomass passage into the marine realm. Comparing the MCR to the published KPB bearing shallow-marine facies of the Um-Sohryngkew River (USR) section data, we document high SCA and FA contents together with the abundance of the even carbon numbered SCA ( n -C 16 and n -C 18 ). This suggests thermal degradation and partial combustion of non-woody biomass. The presence of C 17 n -alkane and hopane is indicative of their derivation from the algae, fungi and bacteria. A sudden SCA concentration increase coincides with the reported major foraminifers’ extinction between the CF1 and P0 biozones of the MCR section. Further, a similar anomaly exists in the lower part of the CF3 biozone of the USR section and precedes extinction of the main foraminifers’ assemblages. The excursions in SCA content along with hopane and FA are matching well with the major incidences of the Deccan volcanic episodes and convergence of the Indian-plate with the Eurasian plate occurred at 66 Ma (Beck et al. 1995 ) and with the Burmese-plate during Maastrichtian (Wakita and Metcalfe 2005 ). These events were responsible for the sea-water disturbances, eustatic and depositional changes, including the retreat of the Tethys. Thus, a combination of extra-basinal and tectono-thermal events together with the greenhouse effects led to unexpected temperature rise and recurrent local sea-level changes that may have resulted in stress and faunal crisis.