Calcareous microfossils and paleoenvironmental changes across the Cretaceous-Paleogene (K-Pg) boundary at the Cerro Azul Section, Neuquen Basin, Argentina

We investigate changes in calcareous nannofossil and ostracod communities, which reflect surface and bottom water conditions, respectively, across the Cretaceous-Paleogene transition (K-Pg) at the Cerro Azul Section, Jaguel Formation, Neuquen Basin, Argentina. The K-Pg transition at the Cerro Azul Section is characterized by calcareous nannofossil and ostracod turnovers, from assemblages dominated by Cretaceous forms to assemblages composed by incoming Danian taxa and several survivor species. These assemblage changes were associated with a collapse in carbonate production at the K-Pg boundary, probably related to a drop of surface water productivity, and a subsequent recovery in the early Danian, as suggested by carbonate content, log(Ba/Fe) and log(Ba/ Ti) trends. During the Late Maastrichtian, peak relative abundances of Eiffellithus spp., just before the K-Pg transition, were probably related to enhanced surface water productivity. High abundances of Cervisiella oper-culata suggest decreased surface productivity during the earliest Danian. This surface productivity collapse may have reduced food availability in the benthic habitat, which probably led to the stablishment of Citherudiae-dominated ostracod assemblages. Upward in the section, increased relative abundances of Braarudosphaera bigelowii, are probably related to overall intensified weathering conditions and, consequently, increased continental runoff and fresh water input.

Automated summary

The study investigates changes in calcareous nannofossil and ostracod communities in the Cerro Azul Section of the Neuquen Basin, Argentina, across the Cretaceous-Paleogene transition, reflecting surface and bottom water conditions. The transitions are characterized by turnovers in assemblages from Cretaceous forms to Danian taxa, associated with collapse and subsequent recovery of carbonate production, hinting at changes in surface water productivity. The relative abundance shifts in microfossils suggest fluctuations in surface water productivity and environmental conditions during the K-Pg transition.