This paper presents the formal description of Impagidinium obscurum sp. nov. from the Thanetian strata of northwest Europe. The palaeogeographic distribution of this species covers a wide area, ranging from the North Sea to the Barents Sea. Palynologists working in the region have long referred to Impagidinium obscurum sp. nov. as Leptodinium? ‘obscurum’ and used it as an important intra-Paleocene marker species. The informal specific name was with reference to the incompletely defined tabulation of the cyst. However, although the tabulation is often obscured by the dense folding of the walls, the cyst tabulation formula has been partly deciphered in this work, based on the organisation of sutural crests in exceptionally well-preserved specimens, which allows confident attribution to the genus Impagidinium. This species is restricted to the ‘early’ Thanetian and is associated with diverse dinoflagellate cyst assemblages which include Alisocysta margarita and Areoligera gippingensis.