Two exposures in Jylland, Denmark, encompassing beds of latest Oligocene to earliest Miocene age (latest Chattian-early Aquitanian) yielded well-preserved palynofloras. The assemblages indicate that Jylland was covered by extensive Taxodiaceae swamp forests in the mid-Cenozoic. Besides a Taxodiaceae-Cupressaceae association, which was overwhelmingly dominant, other common plants in this habitat were Alnus, Nyssa, Betula, Salix, Cyrilla and Myrica. Most of the trees and shrubs are well adapted to swamps and thrive under more or less flooded conditions in modern bald cypress swamps of the southeastern North America. Vegetation composition indicates that a warm-temperate climate prevailed in Denmark during the Oligocene-Miocene transition. According to calculations using the Coexistence Approach, the mean annual temperature during this time span ranged from 15.6 to 16.6 °C. An increase to 16.5-21.1 °C is inferred from the palynoflora in the upper part of the section. The earlier, cooler period possibly reflects global cooling associated with the Mi-1 glaciation event at the Oligocene-Miocene boundary. No data from the very coldest part of the Mi-1 event has been recorded, as this is represented by a gravel layer (representing a hiatus) in the lowermost part of the studied succession. The length of the missing time is not known precisely, but is probably in the order of some hundred thousand years. Correlation with the well-established chronostratigraphic and sequence stratigraphic framework for the studied succession reveals that the most distinctive change in palynoflora probably reflects a shift in depositional facies (due to an increase in sea level) rather than direct climatic change. The sea-level rise is herein interpreted to be eustatic and related to melting of Antarctic ice caps at the end of the Mi-1 glaciation event.
- Programområde 2: Vandressourcer