Latest Albian-earliest Turonian deep-water agglutinated foraminifera in the Bottaccione section (Gubbio, Italy) - Biostratigraphic and palaeoecologic implications.

Resumen

Using semi-quantitative methods, the distribution of deep-water agglutinated foraminifera (DW AF) was analyzed within the Latest Albian-earliest Turonian pelagic limestones of the famous Bottaccione standard section. The characteristic bathyal communities include forms of purely agglutinated "flysch-lype" assemblages and elements which are typical of Upper Cretaceous abyssal environments of the North Atlantic. Well-established planktonic foraminiferal and calcareous nannofossil zonations allowed to directly gauge the stratigraphic ranges of DW AF, contributing to a better chronostratigraphic calibration of a deep-water agglutinated foraminiferal zonation. Differences in ranges of sorne biostratigraphic marker species were observed. The distribution of morphogroups enabled us to interpret levels of oxygenation and organic input. The effects of the Cenomanian-Turonian boundary event (here represented by the ichtyolithic-bituminous-radiolaritic Livello Bonarelli) on the DW AF were explored in detail. A major faunal change in agglutinated foraminiferal communities consisting of a marked decrease in faunal density and species richness was recognized in the middle of the Rotalipora cushmani Zone coinciding with a marked change in sedimentary regimes and related to extensive oxygen depletion on the sea bottom.