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

Abstract

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 ~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.

Fire activity across Cretaceous/Paleogene transition: Evidence from pyrogenic biomarkers preserved in the Mahadeo‐Cherrapunji section, Meghalaya, India

“…Universally prevalent wildfire incidences [evidenced by enormous fusinite (Tschudy et al, 1984) and soot layers (Wolbach et al, 1985(Wolbach et al, , 1988] as well as abundant PAHs (Arinobu et al, 1999;Venkatesan & Dahl, 1989), including within the Chicxulub impact structure (Gulick et al, 2019;Lyons et al, 2020), are linked to the Chicxulub impact (e.g., Belcher et al, 2005;Lyons et al, 2020) and present in the KPB layers, coinciding with the Ir spikes. Elevated PAH concentrations within centimeters of the KPB layer are also found in Denmark, Italy, New Zealand (Venkatesan & Dahl, 1989), México (Kruge et al, 1994), Spain (Arinobu et al, 1999), Canada, United States (Belcher et al, 2009), India (Pal et al, 2015a),…”

“…Owing to spatial proximity (800-1000 km; Gertsch et al, 2011) to the Deccan Volcanic Province, the Meghalaya area was amenable to receiving atmospherically transported volcanic materials. Pal et al (2015aPal et al ( , 2015b provided evidences of wildfire in the region on the basis of n-alkanes (C 14-22 ), n-fatty acids (C 14-18 ), and highmolecular PAH excursions. These excursions preceded the biostraigraphic KPB layer of Mukhopadhyay (2008), which occurred in the late Maastrichtian period.…”

“…Derivation of these biomarkers is possible from combustion resulting from paleo-forest fire incidences (Jiang et al, 1998;Killops & Massoud, 1992). Secondary and Um-Sohryngkew river section (Pal et al, 2015a(Pal et al, , 2015b. It has been found that almost all the PAHs are present in the MCR section, but at relatively much higher level.…”

“…Overall, integration of shelf and shallow-marine biomarker data (Figure 8) was used as an additional limit on the paleoenvironmental changes that occurred across the KPB. (1994), Mukhopadhyay (2008Mukhopadhyay ( , 2009Mukhopadhyay ( , 2010Mukhopadhyay ( , 2012aMukhopadhyay ( , 2012bMukhopadhyay ( , 2016, Shrivastava et al (2013), Pal et al (2015aPal et al ( , 2015bPal et al ( , 2015c. Therriaghat blocks (Mukhopadhyay, 2016).…”

“…Mukhopadhyay (2008) on the basis of the planktonic foraminiferal biostratigraphy identified continuous KPB successions in the Langpar Formation of the Therriaghat and Mahadeo sections. In the Therriaghat section ( Cited Figure 2; Shrivastava et al, 2013), Pandey (1981, 1990) recognized an unconformity at the KPB and Bhandari et al (1994) identified a 1.5‐cm‐thick limonitic layer enriched with Ir, Co, Ne, Os, Fe, Zn, Sb (by a factor of 4 to ~1200), and REEs (by a factor of 1.7 to w5). Subsequent biostratigraphic studies of Mukhopadhyay (2008) indicated that this clay layer ( Cited Figure 2; Shrivastava et al, 2013) actually occurs in biozone CF4 occurring below the actual boundary (Mukhopadhyay, 2008).…”