Deccan Volcanism, Precession-Driven Climate Variability, and the Chicxulub Impact, Drivers of Ecosystem Stress and Mass Extinction at the K/Pg Boundary: Insights from the Eastern Tethys Region

The relationship between Large Igneous Provinces (LIPs) and major mass extinctions has long been recognized. The K/Pg boundary (KPB) extinction is particularly notable due to the near-simultaneous occurrence of two major catastrophic events: the Deccan volcanism and the Chicxulub impact. To gain a clearer understanding of how volcanic activity drives environmental stress, this study investigates the influence of the Deccan volcanism on ecosystems. Our approach includes detailed species counts alongside isotopic and geochemical analyses of two well-preserved sections from the Mudurnu-Göynük and Haymana basins in Central Anatolia (Turkey).

In the Haymana Basin, δ¹³C measurements from the late Maastrichtian display cyclical fluctuations, reflecting precession-driven climate changes. Each cycle ends with a rapid cooling event, indicated by a positive shift in δ¹⁸O values. Spectral analyses of high-resolution δ¹³C and δ¹⁸O isotopic records from planktonic and benthic foraminifera further confirm the influence of orbital forcing, particularly precession cycles, on Late Cretaceous climate variability. The precession-driven cycles reveal climate variations that influenced primary productivity and ocean stratification. During precessional highs, both planktonic and benthic δ¹³C values increase, accompanied by a decrease in Δ¹³Cplanktonic-benthic values and a shift towards more positive δ¹⁸O values, suggesting enhanced water column mixing. Notably, benthic δ¹³C values are consistently heavier than their planktonic counterparts, which may reflect local upwelling conditions. However, the decreasing trend in productivity marker trace elements such as nickel (Ni) and copper (Cu) raises questions about the persistence and extent of upwelling in the Haymana Basin during this period.

Concurrently, a quantitative analysis of planktic foraminifera reveals a progressive decline in species diversity throughout the late Maastrichtian, with an accelerated decline just before the K/Pg boundary. In the Göynük and Okçular sections, this decline in biodiversity coincides with intervals of low magnetic susceptibility, suggesting a possible link to ocean acidification during the late Maastrichtian. The K/Pg boundary is marked by a distinct reddish oxidized layer, 2-3 mm thick, which signals a sequence of critical events: the abrupt disappearance of large, specialized foraminiferal taxa (e.g., globotruncanids, racemiguembelinids, planoglobulinids), an increase in mercury (Hg) levels, and elevated concentrations of trace elements such as iridium (Ir), tellurium (Te), nickel (Ni), chromium (Cr), and cobalt (Co).

In terms of the faunal response, we observe peaks in Thoracosphaera and Guembelitria cretacea, indicating a collapsed ecosystem following the K/Pg boundary event. In conclusion, our comprehensive analysis of paleontological, isotopic, and geochemical data demonstrates that the detrimental effects of Deccan volcanism began prior to the Chicxulub impact, predisposing marine ecosystems to the K/Pg mass extinction event.