Dinoflagellate cysts and acritarchs from the Oligocene–Lower Miocene interval of the Alma-1X well, Danish North Sea

Abstract. This palynological study of cuttings samples from the Lark Formation in the Danish North Sea well Alma-1X documents for the first time in the public domain the succession of last occurrences of dinoflagellate cysts and acritarchs in the Oligocene–Lower Miocene interval of the Central North Sea. The distribution of dinoflagellates and acritarchs in the well demonstrates the potential for the development of a detailed subdivision of the Oligocene–Lower Miocene in the Central North Sea, based on the first downhole occurrences of key taxa. Five regional intra-Lark Formation seismic and petrophysical log markers can be dated with precision using dinoflagellate biostratigraphy. Four new species and one new subspecies of dinoflagellates are described from the study interval: Amphorosphaeridium? almae sp. nov., Filisphaera pachyderma sp. nov., Pentadinium corium sp. nov., Spiniferites pseudofurcatus verrucosus ssp. nov. and Thalassiphora rota sp. nov. Pseudospiniferites manumii Lund, 2002 is emended and transferred to the genus Spiniferites.