Abstract
A historical review of the extinction, survival, and evolutionary models of planktic foraminifera proposed for the Cretaceous/Paleogene boundary (KPB) mass extinction event sometimes leaves the impression that there is still no conclusive evidence to support any single one of them. Two main models have been put forward: i) catastrophic mass extinction, almost total for some authors, compatible with the geologically instantaneous paleoenvironmental effects of a large meteorite impact (Chicxulub impact, Mexico); and ii) gradual mass extinction, compatible with the paleoenvironmental effects of massive, long-lasting volcanism (Deccan Traps, India). Over the years, a lot of evidence has been proposed supporting one hypothesis or the other, highlighting isotopic (δ18O, δ13C, 87Sr/86Sr) as well as taphonomic, biostratigraphic, quantitative (relative and/or absolute abundance), phylogenetic, and even teratological. We review previous planktic foraminiferal and stable isotope studies, and provide new quantitative and statistical tests from two pelagic sections: the El Kef section (Tunisia), recognized as the most continuous and expanded lowermost Danian section worldwide, and the Sidi Ziane section (Algeria), affected by relevant hiatus in the lower Danian. The results indicate that all the latest Maastrichtian planktic foraminiferal species except those of Guembelitria went extinct exactly at the KPB, supporting the hypothesis of an almost total extinction. In the light of this new evidence, we maintain that the Maastrichtian planktic foraminiferal specimens found worldwide in lower Danian samples could be the result of similar reworking and vertical mixing processes to those at El Kef and Sidi Ziane.
Highlights
The accuracy of planktic foraminiferal extinction models across the Cretaceous/Paleogene boundary (KPB) has been a matter of controversy since the 1980s
To delve further into this topic, we propose two types of tests to verify or refute whether the Maastrichtian species found in the lower Danian of El Kef and Sidi Ziane are in situ or ex situ: a statistical test based on nonlinear regression analyses to find equations that fit the downward curves of relative abundance in Maastrichtian specimens, and a quantitative test to calculate the average relative abundance distribution (RAD) of Maastrichtian species in both upper Maastrichtian and lower Danian samples
This dispute is grounded in the controversy over the relative importance of “reworked specimens vs. survivor taxa”, i.e. the question how many Maastrichtian species identified in the lower Danian of pefr.pensoft.net lagic sections were survivors and how many were the result of reworking processes
Summary
The accuracy of planktic foraminiferal extinction models across the Cretaceous/Paleogene boundary (KPB) has been a matter of controversy since the 1980s. Because the dispute among KPB specialists focused on the controversy over the causes of the extinction, the debate on the presence of “reworked specimens vs survivor taxa” in lowermost Danian samples waned in the 2000s, and virtually nothing else was published in the 2010s, with only a few exceptions (e.g., Gallala et al 2009; Gallala 2013, 2014; Punekar et al 2014; Molina 2015) This is a relevant issue both for the verification or refutation of the two main hypotheses about the causes of the KPB extinction (asteroid impact vs massive volcanism) and for the reconstruction of the phylogenetic relationships among early Danian planktic foraminifera (e.g., Koutsoukos 2014). We have quantitatively and statistically analyzed the planktic foraminiferal survival patterns after the KPB extinction in two western Tethyan localities: El Kef (Tunisia) and Sidi Ziane (Algeria)
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