108-1 The Cretaceous–Paleogene Extinction in Focus: Foraminiferal Dynamics, Morphogroups and Recovery Patterns in the Umbria-Marche Basin, Italy

Session: The Cretaceous-Paleogene (K-Pg) Boundary Interval: From Large-Scale Geological Events to Mass Extinction Mechanisms (Posters)

Presenting Author:

Authors:

Abstract:

A comprehensive analysis has been done using samples from the Upper Cretaceous and Lower Paleocene of the Scaglia Rossa Formation, Umbria-Marche Basin, Italy. The assemblage parameters include abundance, diversity, dominance and morphogroups of Deep–Water Agglutinated Foraminifera (DWAF) across the Cretaceous–Paleogene (K/Pg) boundary. With the addition of new data from the Maastrichtian and Danian intervals, our analysis yields a much more detailed and unbiased record. Our data set now consists of an equal number of samples collected at uniform spacing both above and below the boundary. Our data shows that the Maastrichtian samples reach a peak in terms of abundance, likely representing steady ecological conditions before the mass extinction event. A biological crash can be observed at the K/Pg boundary, with Danian samples showing fluctuations that indicate chaotic environmental changes and blooms of opportunistic taxa.

The Shannon H’ graph reflects species richness (the number of taxa) and evenness (how equally individuals are distributed across taxa). In the Maastrichtian, H’ values are moderate to high, representing diverse pre-extinction assemblages. In the middle part of our record, identified as the K/Pg boundary, values shows lower diversity, with reduced richness and evenness, indicating ecosystem collapse and/or an extinction event. In the upper part of our record H’ values increase again, owing to the return of Lazarus taxa during the recovery phase. This indicates a rebound in foraminiferal communities.

Dominance values are low the Maastrichtian, which reflects the high diversity of an assemblage in which many taxa contribute similarly. In the middle interval of the sampled interval, a sudden increase suggests ecological stress, representing the K/Pg boundary where species went extinct and opportunistic species bloomed temporarily. In the Danian samples, the decrease in dominance indicates a return to community recovery. Early Paleocene recolonization led to the re-establishment of normal assemblages. The dominance peak coincides with the drop in Shannon H’ diversity values, strengthening the case for an extinction layer.

By calculating benthic foraminiferal assemblage data across the K/Pg boundary in the Umbria-Marche Basin, this study sheds light on the ecological change that took place in the deep waters of the Tethys during the Cretaceous mass extinction.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-4771

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