CALCAREOUS DINOFLAGELLATE CYSTS FROM THE EXPANDED K/PG 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 is said to include the fall-out from a bolide impact which caused the end-Cretaceous mass extinction and is at its maximum thickness at Kulstirenden (c.45cm). This is in comparison to the more extensively studied Højerup and Rødvig sections at the eastern and southern extremities of Stevns Klint respectively where it has a thickness of <15cm. Calcareous dinoflagellate cysts (Calciodinelloideae) were investigated within the fine fraction (45-125µm) at Kulstirenden in order to focus on the ecological interpretations of these enigmatic microfossils. Several species were found within the Fiskeler Member, including Orthopithonella collaris Wendler et al. 2001. This species is of particular interest as it demonstrates reduced paratabulation and may indicate a transgressive period immediately after the K/Pg boundary event. The benthic foraminiferal record also displays this increase in sea-level and probable transgressive period across the K/Pg boundary. 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 much more extensive than previously documented, disappearing as carbonate sedimentation returned in the Cerithium Limestone Member of the Danian. Several other species of calcareous dinoflagellate cysts are recorded, some of which are problematic as they display Bolboforma-like features, such as cyst size and ornamentation. The origins of Bolboforma are enigmatic and so these specimens found at Stevns Klint may give an insight into the origins of this group.