A preliminary investigation into calcareous dinoflagellate cysts and problematic microfossils from an expanded Cretaceous/Paleogene boundary section at Kulstirenden, Stevns Klint, Denmark

Located to the north of the Stevns Klint Peninsula (Denmark), Kulstirenden shows the transition from Cretaceous chalks to Danian carbonates across the Cretaceous – Paleogene (K/Pg) boundary. The K/Pg boundary at Kulstirenden is represented by the Fiskeler Member (Fish Clay), a streaked marl interval with a smectite rich, red oxidised layer at its base marking the boundary. The Fiskeler Member is important as it includes the iridium concentration linked to the bolide impact which may have caused the end-Cretaceous mass extinction and is at its maximum thickness at Kulstirenden (c.45 cm). Calcareous dinoflagellate cysts (Calciodinelloideae) have been investigated from within the fine fraction (45–125 μm) at Kulstirenden in order to understand the ecological implications of these enigmatic microfossils. Several species were found within the Fiskeler Member, including Orthopithonella collaris Wendler et al. (2001, Rev. Palaeobot. Palynol. 115, 69–77). This species is of particular interest as it demonstrates reduced paratabulation and may indicate a transgressive period immediately after the K/Pg boundary event. O. collaris has been described as a morphotype formed under post-K/Pg environmental conditions and is, therefore, described as a “disaster” taxon that marks the K/Pg boundary at Stevns Klint. The distribution of this taxon is more extensive than previously documented, disappearing as carbonate sedimentation returned in the Cerithium Limestone Member of the Danian. Several calcareous microfossil specimens that were found cannot be associated with the dinoflagellates and display Bolboforma-like features. While the origins of Bolboforma are enigmatic, the current finding expands their stratigraphic range and suggests an appearance of this group of organisms found at Stevns Klint may give an insight into the inception of this group into the earliest Danian.

► Preliminary investigation of calcareous dinoflagellate cysts at Stevns Klint.
► Focus on Fiskeler Member which marks Cretaceous-Palaeogene boundary.
► Several species found within the Fiskeler Member, including Orthopithonella collaris.
► Several individuals display Bolboforma-like features.