Diatom succession of a dislocated Eemian sediment sequence at Mommark, South Denmark

The Mommark sequence represents a nearly complete record of sedimentation in the Eemian (MIS 5e), and the diatom succession covers almost the entire interglacial. A floating chronology of the deposits is based on correlation of the local pollen stratigraphy with annually laminated sequences in northern Germany. The diatom succession starts with a short freshwater stage followed by a similarly episodic transitional brackish phase, which began c. 300 years after the beginning of the Eemian interglacial. A few hundred years later, simultaneously with the start of deposition of the shallow marine sediment, Cyprina Clay, the flora turns almost fully marine, suggesting salinities clearly higher than at present. The culmination of the marine transgression occurs close to the climatic optimum of the Eemian interglacial, c. 3000 years after the beginning of the interglacial. In the several metres thick Cyprina Clay, only marginal changes in the composition of diatom taxa are noticed. According to the diatom stratigraphy and chronostratigraphy based on regional pollen zones, the total duration of the Eemian Sea phase with brackish/marine conditions was c. 10 500 years. As the sedimentation of the Cyprina Clay ends, the proportions of diatom species thriving in freshwater increase, but the marine taxa remain common. The mixture of species with non-compatible ecological requirements suggests allochthonous input from freshwater and/or tidal estuary environment. The results of this study are consistent with studies of other aquatic fossil assemblage data from this site.