Rapid Warming at the PETM and Its Influence on Vegetation in Denmark

Lowermost Eocene expanded marine sedimentary successions in Denmark are of global chronostratigraphic significance, due to the excellently preserved terrestrial and marine fossil assemblages, combined with a number of radiometrically dated ash layers. A detailed study of vegetation changes across the Palaeocene-Eocene Thermal Maximum (PETM) interval have not yet been carried out, nor has the microflora (e.g., spores and pollen) been related to existing macrofloral remains (e.g., seeds and leaves) stored in Danish Museums. This palynological research project on vegetation changes across the PETM interval is significant because there are extremely few PETM vegetation records where a complete, highresolution plant response to this transient event can be examined. Herein, we present preliminary microflora results from an expanded marine PETM record obtained from the Osterrenden drill core (DGI 83101), located in Store Baelt, Denmark. This preliminary study reveals that a distinct microflora change correlates with the Carbon Isotope Excursion (CIE) in the Osterrenden drill core, including a change from low to high diversity across the Palaeocene-Eocene boundary. The Palaeocene assemblages comprise a high relative abundance of Inaperturopollenites spp. (taxodiaceae), but above the stratigraphic level corresponding to the onset of the CIE event this Palaeocene assemblage type is replaced by species such as Caryapollenites circulus, Platycaryapollenites platycaryoides, and Tricolpopollenites librarensis. These typical early Eocene pollen species originated from ancestors of Juglandaceae (walnut) and Fagus (beech) families. Palaeotropical floral elements such as palm pollen (Arecipites spp.) and angiosperm pollen from Anacolosa spp. (Olacaceae) also occur for the first time in the basal Eocene part of the Osterrenden drill core. An increased abundance of pollen typical of wet lowland areas, such as Sparganiaceaepollenites spp. (Typhaceae), is also observed, indicating a change in the hydrological regime towards increased seasonality during the earliest Eocene.