A Middle Weichselain ice‐free period in Western Norway: the Ålesund Interstadial

Abstract

Seven localities with fossil‐bearing tills were found in the Ålesund area. Fifteen radiocarbon dates of marine shells in the tills all gave ages between 28,000 and 38,000 years B.P. In spite of a general scepticism to shell dates giving high finite ages, these ages may be accepted mainly because of the quality of the shells, the geological situation in which they were found, and identical results for different fractions. The ice‐free period is named the Ålesund Interstadial. and its Middle Weichselian age is also suggested by amino acid D/L ratios in shells, compared with Late Weichselian and Eemian ratios. Shell and foraminifera faunas suggest arctic conditions with the Atlantic water present during the optimal period. The tills are non‐sorted, compacted and interpreted to be basal tills. Their age is bracketed between c. 28,000 and 12,800 years B.P.