Dinoflagellate biostratigraphy at the Campanian-Maastrichtian boundary in Zumaia, northern Spain

Dinoflagellate cyst assemblages from a well-exposed uppermost Cretaceous section at Zumaia (northern Spain) provide a basis for comparison with previous biostratigraphic and magnetostratigraphic studies on the problematic location of the Campanian-Maastrichtian boundary in the section. The position of the last occurrence of Corradinisphaeridium horridum and first common occurrence of Alterbidinium acutulum, correspond well with the bioevents defining the Campanian-Maastrichtian boundary in the Global boundary Stratotype Section and Point of Tercis les Bains (130 km to the North). Together with other age-diagnostic dinoflagellate cyst bioevents, we suggest that the boundary should be placed between 239.75 and 224.75 m below the Cretaceous-Palaeogene boundary, about 46 m lower than an interpretation based on the first occurrence of the planktonic foraminifer Pseudoguembelina palpebra and the last occurrence of the nannofossil Broinsonia parca subsp. constricta. A conspicuous acme of the dinoflagellate cyst Thalassiphora cf. delicata is encountered around the lower-upper Maastrichtian boundary (calibrated by foraminiferal, calcareous nannoplankton and magnetic polarity data), which may prove to be a useful correlatable event.