TURNOVER IN AGGLUTINATED FORAMINIFERA ACROSS THE CRETACEOUS/PALEOGENE BOUNDARY IN THE WESTERN TETHYS: AN INTEGRATED GEOCHEMICAL AND BIOSTRATIGRAPHIC APPROACH

Newly analyzed Paleocene samples from the Scaglia Rossa Formation of the Umbria Marche Basin, specifically the Contessa Highway and Bottaccione sections, were compared with our Upper Cretaceous record published previously (Kaminski et al. 2011). The comparison aimed to provide a broader understanding of the distribution and abundance of Deep-Water Agglutinated Foraminifera (DWAF) across the K/Pg boundary. The samples were collected bed-by-bed from the lowermost Paleocene. Our biostratigraphical analysis employed a robust methodology that allowed us to accurately determine the extinction rate of DWAF bioevents. This involved meticulous data gathering, consistent sample preparation, and thorough taxonomic investigation. We also conducted geochemical analyses, including mercury (Hg), on the Contessa Highway and Bottacione to assess the impact of large-scale volcanism on the marine environment and its impact on the DWAF communities.

Three groups of DWAF can be distinguished: survivor species (including Lazarus taxa), extinction species, and incoming species. The total foraminiferal record comprises 86 species, with the epifaunal morphogroup (Rhizammina, Caudammina, Ammodiscus, and Glomospira) dominating the assemblage. A notable decline in species richness is observed across the K/Pg boundary, particularly in the lowermost Paleocene, where approximately 38% of the species are lost, including Caudammina gigantea, C. ovuloides, Recurvoides retroseptus, and Gerochammina spp.. Blooms of opportunistic species are observed in the lowermost Paleocene, indicating a gradual reappearance of certain taxa that can be classified as Lazarus taxa. Our samples indicate the presence of approximately 9% incoming species, including some newly described species as well as Ammomarginulina aubertae and Spiroplectammina spectabilis.

No other study on benthic foraminifera has employed such an approach to quantify the extent of faunal turnover among the DWAF at the K/Pg boundary. By employing high-resolution sampling across the K/Pg boundary, a calculation of the extinction rate, detail recognition of foraminiferal assemblages, taxonomic studies, and paleoenvironmental analysis, we can now address the complex paleoecological problems associated with the K/Pg boundary in the western Tethys.