The biostratigraphy and palaeoecology of the dinoflagellate cyst Eatonicysta magna sp. nov. from the Middle Eocene (Lutetian) of the North Sea

This study formally describes a new chorate dinoflagellate cyst species, Eatonicysta magna sp. nov., from the Middle Eocene (Lutetian) succession of the Central North Sea Basin. The species is characterized by a large, subspherical central body and long, robust intratabular processes exhibiting an ectophragm with reduced ectophragmal network. It was identified from ditch-cutting samples taken from a well in Norwegian Quadrant 25, and additional occurrences have been recorded in wells from Quadrant 15. The strata containing this new species were deposited in a fully marine environment. Palynological assemblages from the Lutetian interval are diverse and dominated by dinoflagellate cysts, including species of Areosphaeridium, Cleistosphaeridium, Spiniferites, Deflandrea, Operculodinium, and Phthanoperidinium. The biostratigraphic framework used in this study follows the North Sea zonation of Bujak and Mudge, allowing the stratigraphic range of E. magna sp. nov. to be constrained between Subzone E6c and the top of Subzone E3d (ca. 48.1–43.5 Ma). Palaeoecological analysis of the assemblages suggests a dynamic depositional regime, with dinoflagellate cyst groups reflecting specific environmental conditions. This study underscores the continued potential for new taxonomic discoveries within underexplored Eocene intervals of the North Sea. Although rare, Eatonicysta magna sp. nov. may offer valuable biostratigraphic and palaeoenvironmental insights, particularly when high-resolution palynological techniques are applied to these complex marine successions.