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Abstract
Eight sites with a dark, clayey basal till in central Sweden have been studied by means of microfossils in order to clarify the stratigraphic position of the till. The composition of the identified reworked pollen and diatom floras shows interstadial or interglacial “signatures”. Pollen spectra dominated by herbs, shrubs and Betula are supposed to be of interstadial origin. The interglacial composition is mostly characterised by 80-90% tree pollen including thermophilous trees and brackish water diatoms (Spånga). However, to distinguish reworked pollen spectra of interstadial origin from spectra in sediments deposited during the initial or final phase of an interglacial is hazardous. The vegetation zonation in central Sweden especially during the Early Weichselian interstadials is incompletely known. An outline is given of different age alternatives for the studied till. According to our present knowledge it is most likely that it was accumulated by advancing ice, in most cases in the third Weichselian stadial (MIS 4), i.e. after the Odderade Interstadial, in some cases possibly in MIS 5b after the Br⊘rup Interstadial. The results show that the composition of redeposited microfossil spectra can give additional information to lithostratigraphical data on the age and origin of a till unit.
