Foraminiferal Effects of Regional Fire and Attendant Paleoenvironment During K/Pg Transition: Organo-Chemical Evidence from the Um Sohryngkew River Section, Meghalaya, India

Abstract

Palaeoenvironmental studies based on organic matter associated with the biostratigraphically continuous Cretaceous-Paleogene transition section of the Langpar Formation, Meghalaya promise to provide crucial evidence of foraminiferal effects close to K/Pg boundary. Present work primarily focuses on the upper Maastrichtian Pseudoguembelina hariaensis Zone (= Zone CF3) that records incidence of ‘regional fire’ to affect paleoenvironment, which facilitated planktonic foraminiferal disappearance. Incidence of coaly matter towards the upper part of the Racemiguembelina fructicosa Zone (= CF4 Zone) endorses that the incidence of ‘fire’ prevailed for a longer period, encompassing the upper Maastrichtian biozones CF4-CF3. The yellowish brown clay layer in biozone CF3 is marked with well established excursions in HMW PAH compounds which coincide with the Ce anomaly layer occurring below the PGE anomaly layer around the contact between Pseudoguembelina palpebra Zone (= CF2 Zone) and Plummerita hantkeninoides Zone (= CF1 Zone) and below the planktonic foraminiferal change at the K/Pg. Significantly, strong (~4 fold increase) peaks were noticed in biozone CF3 (sample JP12) as marked by sudden increase in the total PAHs—4, 5, 6 ring PAH compounds and few 3 (anthracene, fluorine) ring PAH compounds; biozone CF2 (sample JP-13) also shows excursions in 3 ring PAHs—phenanthrene, 3-methylphenanthrene, 2-methylphenanthrene, 9-methylphenanthrene, 1-methylphenanthrene, but the former shows n-alkane and fatty acid (including their CPI values) excursions. Besides, remarkably high amount of combustion marker PAHs [fluoranthene, (10.46 µg/gc), pyrene (7.20 µg/gc), chrysene (8.28 µg/gc), benzo(a)anthracene (9.92 µg/gc)] in the biozone CF3, similar to those of well studied K/Pg boundary sections of Stevns Klint (Denmark), Gubbio (Italy), Woodside Creek (New Zealand), and Arroyo el Mimbral, Tamaulipas, (Mexico) suggesting correspondence in the incidence of ‘fire’ in India where it was triggered presumably by the heat radiating from the epigenic plumes of Abor volcanic and Ninetyeast Ridge, and greenhouse effects of Deccan volcanism. The fire seemingly facilitated step-wise disappearances of planktonic foraminifera during biozones CF4-CF3 and instigated migration of some forms from the warm water environment. A very strong proton peak at δ1.51 ppm in yellowish brown clay layer (JP-12) indicating the presence of CH₂ group of alkane compound in the sample. FTIR spectra shows weak bands in the region of 2304–2370 cm⁻¹ and attributed to the presence of traces of CO₂ and CO, which are related to the combustion incidence. Such environment was possibly created in the interspaces of the sediments by burning of organic matter in the presence of oxygen whereby CO₂ formed and water released in the environment. High abundance of combustion derived PAH in the yellowish brown layer of biozone CF3 of the succession endorses this observation. The study considers ‘regional fire’ as one of the factors for step-wise disappearance of planktonic foraminifera prior to the advent of the K/Pg boundary in the shallow shelf of Meghalaya.