Palaeoenvironments in the North Sea Basin around the Paleocene-Eocene boundary: evidence from diatoms and other siliceous microfossils

Abstract

Abstract Assemblages of siliceous microfossils (diatoms, silicoflagellates, radiolaria, and ebridians) have been examined from calcareous concretions (cementstones) in the Fur Formation, an ash-bearing diatomite which crops out around the Limfjorden region of Jutland, northern Denmark. Although microfossil assemblages (particularly diatoms) change character through the deposit, only one major turnover occurs that is reflected by all of the microfossil groups examined. This biotic event indicates a marked increase in marine influence, and probably climatic warming. It appears to mark the beginning of the early Eocene transgressive phase that affected the whole of the North Sea Basin and eventually re-established this isolated basin’s links with the North Atlantic and Tethys. Other diatom assemblages examined from offshore samples towards the centre of the basin show strong similarities with those from the Fur Formation and confirm that the lower part of this deposit correlates to the Sele Formation, whilst the upper part correlates to the Balder Formation. The lowest occurrence of the widely occurring diatom Fenestrella antiqua is suggested as a practical marker for the base of the Eocene in both offshore and onshore sediments in the North Sea Basin. Restricted circulation processes involving seasonal, monsoon-driven upwelling leading to sporadic basin eutrophication and water-column stratification, are considered to account for the widespread proliferation of siliceous microfossils in the North Sea Basin during the late Paleocene to early Eocene.