MAASTRICHTIAN DINOFLAGELLATE ZONATION IN THE DAN FIELD, DANISH NORTH-SEA

Core samples from the Maastrichtian oil reservoir chalks in the Dan Fi eld (southern part of the Danish Central Trough) have yielded diverse dinoflagellate cyst assemblages which have been assessed in order to e stablish a high-resolution biostratigraphical framework. Eight success ive downhole events occur in a relatively consistent pattern and have been used to subdivide the Late Maastrichtian and the late Early Maast richtian in the Dan Field. The events are: (1) (Cretaceous/Tertiary bo undary) Last occurrence datum (LOD) of several taxa: Palynodinium gral lator, Spiniferites ramosus cavispinosus, ''Chytroeisphaeridia everric ula'' and ''Northidiniwn perforatum''. (2) First appearance datum (FAD ) of P. grallator. (3) FAD of Hystrichostrogylon borisii. (4) LOD of I sabelidinium cooksoniae. (5) The almost simultaneous FAD of Deflandrea galeata and LOD of Triblastula utinensis. (6) LOD of Alterbidinium ac utulum. (7) LOD of Eatonicysta hapala sp. nov. (8) FAD of T. utinensis . Four new zones and three new subzones are established below the Paly nodinium grallator Zone: Hystrichostrogylon borisii Zone; Palaeocystod inium denticulatum Zone; Isabelidinium cooksoniae Zone; Triblastula ut inensis Zone; Cannosphaeropsis utinensis Subzone; Alterbidinium acutul um Subzone; Eatonicysta hapala Subzone. A new stratigraphically import ant dinoflagellate species, Eatonicysta hapala sp. nov., is formally d escribed. The new subdivision of the oil reservoir chalks has added to the understanding of the extent of the thin high-porosity layers, whi ch are important for oil production from the field.