Testimonies from Tethys:  Faunal and environment shifts across the Cretaceous–Paleogene boundary (KPB)

The interplay between Large Igneous Provinces (LIPs) and significant mass extinctions has been widely acknowledged for a long time (e.g., Courtillot and Renne, 2003). What makes the K/Pg boundary (KPB) extinction significant is the simultaneous occurrence of two major catastrophic events – the Deccan volcanism and the Chicxulub impact – within a very brief timeframe (Schoene et al., 2019). To better understand the link between volcanic eruptions and the resulting environmental stress, it's crucial to delve into the impact of the Deccan volcanic activity on the ecosystem. To uncover this phenomenon, our focus lies in detailing this relationship using detailed counts of species along with isotope and geochemical analyses conducted on two complete sections within the Mudurnu-Göynük and Haymana basins in central Anatolia (Turkey). Over the late Maastrichtian period, our examination of δ13C measurements in the Haymana Basin exhibits cyclical patterns that underscore the influence of precession cycles on the δ13C record. Intriguingly, each cycle concludes with a sudden cooling event (a positive shift in δ18O values). A quantitative assessment of planktic foraminifera, on the other hand, shows a continual decline in species diversity throughout the late Maastrichtian (Karabeyoglu et al., 2019). This decline seems to accelerate just before reaching the K/Pg boundary. In the Göynük and Okçular sections, this decline aligns with distinct intervals of low magnetic susceptibility, hinting at a possible event of ocean acidification during the late Maastrichtian. The K/Pg boundary itself is identifiable by a reddish oxidized layer measuring 2-3 mm in thickness. This layer provides evidence of a sequence of events: the abrupt disappearance of large, specialized ecological specialists (such as globotruncanids, racemiguembelinids, planoglobulinids), a surge in mercury (Hg), and increased levels of trace elements (e.g., Iridium (Ir), Tellurium (Te), Nickel (Ni), Chromium (Cr), and Cobalt (Co)). Notably, the correlation between Hg/Te suggests that Te might serve as a proxy for volcanic activity. In terms of the faunal record, we observed peaks in Thoracosphaera and Guembelitria cretacea, signifying an ecosystem collapse following the KPB. In summary, our comprehensive examination of paleontological, isotopic, and geochemical data indicates that the detrimental impacts of Deccan volcanism had already begun prior to the Chicxulub impact. This predisposed the fauna to an eventual extinction event at the K/Pg boundary. References Courtillot, V.E., Renne, P.R. 2003. On the ages of flood basalt events. Comptes Rendus Geoscience, 335, 113–140. Schoene, B., Eddy, M.P., Samperton, K.M., Keller, C.B., Keller, G., Adatte, T., Khadri, S.F.R. 2019. U-Pb constraints on pulsed eruption of the Deccan Traps across the end-Cretaceous mass extinction. Science, 363, 862-866. Karabeyoglu, A.U., Özkan-Altıner, S., Altıner, D. 2019. Quantitative analysis of planktonic foraminifera across the Cretaceous-Paleogene transition and observations on the extinction horizon, Haymana Basin, Turkey. Cretaceous Research, 104, 104169.