Vegetation and its Environment in Denmark in the Early Weichselian Glacial (Last Glacial)

Abstract

The present work deals with the layers found above certain Eemian Interglacial fresh-water deposits in Denmark. Earlier investigations at these sites had indicated a "Lower Temperate Stage" and an "Upper Temperate Stage" separated by clay layers ("Middle Bed"). The existence of an upper temperate stage has been doubled by some authors. The "Lower Temperate Stage" is now usually considered the Eemian Interglacial, and the post-Eemian layers have been referred to the Last Glacial of Northern Europe, or the Weichselian Glacial, which may be defined as the time interval, which separated the Eemian Interglacial from the Postglacial. Methods of investigation are described in the chapters II-III. The basis for establishing the pollen diagrams is discussed, and it is maintained that the pollen zones should be considered bio-stratigraphic units. Problems in the identification of pollen grains and spores are discussed, and selected identifications are mentioned briefly. Statistical observations are mentioned in a special part. Chapter IV deals with the individual sites investigated, and their sediments and pollen diagrams. It can be shown that certain layers earlier referred to the "Upper Temperate Stage" contain abundant plant fossils rebedded from the Eemian Interglacial layers, but layers of interstadial character also occur. The segregation of the secondary (rebedded) elements in the fossil floras, and zonation of the pollen diagrams are discussed. The chapter on the earlier vegetation and its environment includes a discussion of various problems in palaeoenvironmental analysis. The vegetation and indications of temperature, precipitation and soil conditions in the various pollen zones are discussed. A list of remains of higher plants referred to the pollen zones is presented with indications of their probable primary or secondary status. The primary flora is compared with the Danish Late-Glacial flora. The chapter on climatic development and chronology deals first with principles of Pleistocene chrono-stratigraphy. The author supports the opinion that climatic changes may serve as chronological limits. Glacials and interglacials constitute main stages, and stadials and interstadials are considered substages within the glacials. Vegetational succession and climatic changes within the sequence studied are summarized in table 24 (p. 115). The limit between the Eemian Interglacial and the Weichselian Glacial is distinguished as a large decrease of temperature. The Rodebæk and the Brørup Interstadials, two interstadials within the early Weichselian Glacial, are delimited by temperature changes. Some of the layers earlier referred to the "Upper Temperate Stage" mentioned above belong to the Brørup Interstadial. The probable composition of the vegetation in Northern Europe in the early Weichselian Glacial is mentioned. A development similar to the Danish sequence occurred in the Netherlands, and various plant-bearing deposits from Germany, Poland and England can be correlated with these sequences. Finally, radiocarbon dates are mentioned. The Amersfoort (Rodebæk) Interstadial is dated at 64 000 years before present, and the Brørup Interstadial at 59 000 years before now. Other "old" dates from Germany, England and Italy are mentioned. The results corroborate Emiliani's palaeotemperature curve.