El corte de Zumaya (España): registro de los foraminíferos bentónicos del Paleógeno inferior
The Zumaya section (Northern Spain, Basque-Cantabrian basin) has become a reference section for the study of Cretaceous and Paleogene marine sediments. In order to analyze the paleoenvironmental evolution across the lower Paleogene, we carried out a quantitative study of early Paleogene (Cretaceous/Paleogene boundary) to early Eocene benthic foraminiferal assemblages in the Zumaya section. The relative abundance of the most representative calcareous and agglutinated taxa, as well as the diversity and heterogeneity of the assemblages, were calculated in 72 samples.
Benthic foraminiferal assemblages indicate a depth of deposition of about 1000 m during the early Paleogene, and probably slightly shallower paleodepths during the late Danian. We suggest that, in addition to the paleodepth of deposition, other parameters (perturbation of the seafloor, turbidity currents, composition of the sediment) may have controlled the distribution and composition of the benthic assemblages. Hence, the abundance of Flysch-type agglutinated foraminifera (with organic cement) indicates a high flux of terrigenous, clastic material to the seafloor. This flux was particularly high during the Selandian and Thanetian.
This study allowed us to analyze in detail several global events, such as the Cretaceous/Paleogene boundary event, the Mid-Paleocene Biotic Event, or the Paleocene-Eocene Thermal Maximum, where the most significant benthic foraminiferal turnover has been recorded. Benthic foraminifera were affected by the Cretaceous/Paleogene impact event: the drop in diversity of the assemblages and in the percentage of the species reflects variations in the trophic conditions after the boundary. Trophic conditions recovered during the Danian. Agglutinated opportunistic species proliferate during the Danian/Selandian boundary, although the relation of these changes with a possible global hyperthermal event remains to be confirmed. A decrease in the heterogeneity of the assemblages and an increase in oligotrophic and opportunistic species are recorded during the Mid-Paleocene Biotic Event. These assemblage changes are similar to but of lesser magnitude than those recorded during the Paleocene-Eocene Thermal Maximum, when the largest mass extinction of benthic foraminifera (both agglutinated and calcareous) of the Cenozoic is recorded. After the extinction event, we show the recovery of the assemblages during the early Eocene.