On the use of Glacial Striae for Reconstruction of Paleo-Ice Sheet Flow Patterns

Abstract

The methods used to extract ice flow directions from striae data are discussed. Four types of change regarding the subglacial environment are recognized as important for the preservation of coherent striae patterns in formerly glaciated areas. These are: 1/ Deglaciation, 2/ Change to frozen-bed conditions 3/ Burial of bedrock surface beneath till, and 4/ Location near an ice divide. The general concept of a migrating “preservation borderline” is introduced in a discussion about the spatial striae patterns expected to be related to areal expansion of frozen-bed zones. The types of large-scale spatial patterns to be expected from the four described preservation scenarios are discussed, as well as the difficulties in obtaining flowline information from metachronous patterns. A stepwise procedure for deciphering of palimpsest-type striae patterns in core areas of the last ice sheets is outlined and applied on two areas placed centrally under the last Scandinavian ice sheet. From the southern study area it is concluded that there is no geological evidence for the ice flow from the east over central Sweden during the Late Weichselian maximum, modelled by Denton and Hughes (1981) and Boulton et al. (1985). If a Bothnian Gulf monodome configuration existed, it must have been cold-based under large central areas. A two-domed configuration provides a better fit to the geological evidence.