Polycyclic aromatic hydrocarbon compound excursions and K/Pg transition in the late Cretaceous-early Palaeogene succession of the Um Sohryngkew river section, Meghalaya

摘要

A combustion-derived polycyclic aromatic hydrocarbon (PAH) compounds based high-resolution stratigraphic records across the Cretaceous/Palaeogene boundary section of the Um Sohryngkew river section is presented in this paper. The yellowish brown, organic-rich, 1 to 2 mm thick, clay layer in biozone CF3 is marked by sudden increase in the high molecular weight fluoranthene, pyrene, chrysene, benzo(a) anthracene PAH compounds. These componds are similar to those associated with the well-known K/Pg boundary sections across the world. Besides these, high abundance of low molecular weight 3 ring anthracene and fluorine, and 4 ring PAH compounds is also noticed in this layer. Subordinate amount of low molecular weight 3-ring phenanthrene, 3-methylphenanthrene, 2-methylphenanthrene, 9-methylphenanthrene and 1-methylphenanthrene PAH compounds have also been found in the successive layer of biozone CF2. Occurrence of high molecular weight PAH compounds in the biozone CF3 (66.83-65.45 Ma age) imply global fire, induced by the heat supplied by Abor/Deccan volcanic activity, possibly linked with the K/Pg boundary transition events as later initiated prior to the K/Pg boundary, however, the main episode of Deccan volcanic activity occurred similar to 300 ky earlier or at the K/Pg boundary itself. PAH compound anomalies in the biozone CF3 is well coinciding with the well documented Ce anomaly layer, but, preceded by planktonic foraminiferal break and PGE anomaly bearing layer in the biozone P0. It is inferred that the K/Pg boundary related global fire played significant role in the collapse of the ecosystem, causing sudden demise of organisms.