Siliceous microfossils from the warm Late Cretaceous and early Cenozoic Arctic Ocean

Abstract

More than 40 species of siliceous microfossils are present in both T-3 core Fl-437 (Cretaceous) and in core Fl-422 (Eocene) from the central Arctic Ocean. Previous identifications of the silicoflagellates were the basis of the ages for these cores, but diatoms of the two cores, previously unidentified, suggest that Fl-437 could be as old as Campanian rather than middle to late Maastrichtian and that Fl-422 may be early to middle Eocene rather than middle to late Eocene. Identification of archaeomonads and ebridians completes the cataloging of the known biosiliceous assemblages of the older Arctic Ocean.Strong seasonality for the Late Cretaceous and early Cenozoic Arctic Ocean is suggested from alternating layers of vegetative cells and resting spores in both cores. The abundance of fossils is interpreted as evidence for seasonal upwelling in a nutrient-rich and much warmer Arctic Ocean. No evidence of seasonal ice or of ice-rafting is present. The profound climate change from the warmer older Arctic Ocean to the ice-covered condition of the present occurred after deposition of the sediment of Fl-422.