A modified dinoflagellate cyst biozonation for latest Palaeocene and earliest Eocene sediments from the central North Sea

Abstract

This paper considers the various published dinoflagellate cyst biozonation schemes for European late Palaeocene and earliest Eocene sediments. It assesses the alternative synonymous approaches and includes a modified biozonation scheme, tailored to industrial needs, consisting of four biozones. These are in down-hole order, the Deflandrea oebisfeldensis Acme Biozone, the Apectodinium augustum Interval Biozone, the Alisocysta margarita Interval Biozone and the Palaeoperidinium pyrophorum Interval Biozone. In particular, the paper examines the nature of the Palaeocene/Eocene boundary in the central North Sea. It concludes that the base of the Early Eocene Epoch coincides with the base of the calcareos nannoplankton NP 10 Biozone; that the standard northwest European dinoflagellate cyst Apectodinium hyperacanthum Biozone contains the base of NP 10; and that indirect correlation between the Goban Spur and northwest Europe indicates that the base of NP 10 lies at the base of the Sele Formation. Analysis of the dinoflagellate cyst assemblages in a reference section (BP well 21/10-2, Forties Field) demonstrates that the top of the Apectodinium augustum Interval Biozone lies close to the base of the Sele Formation. A change in microplankton biofacies, from the inner neritic Wetzeliella Association to the outer neritic “ Hystrichosphaera” Association, characterizes the basal Sele Formation succession. This “event” reflects a significant environmental change in the water mass. The paper makes the recommendation that stratigraphers should select the highest occurrence of Apectodinium augustum as the marker for the top of the Palaeocene succession in the central North Sea.