An evaluation of the Late Weichselian Swedish varve chronology based on cross-correlation analysis

Abstract

The Swedish varve chronology is based on the correlation of overlapping varve-thickness diagrams. The traditional visual match between single diagrams has been based on, e.g., significant yearly thickness variations or specific marker varves, but attempts to verify these correlations by statistical methods are rare. To test if these visual correlations can be regarded as correct, i.e. statistically significant, we applied cross-correlation measures to overlapping varve diagrams from two local varve chronologies established in southeastern Sweden. Out of a total of 363 analysed connections, only 78 were found to fulfill the statistical requirements for a perfect match. In 96 cases the statistical measures suggested alternative placements to the published links. However, we found that for 179 correlations the published varve-diagram connections are statistically not valid and that in 11 cases the overlap between diagrams is too short to allow for valid cross-correlation analysis. This large number of uncertain varve-diagram correlations in both local chronologies shows that the detailed timing of the ice recession along the south Swedish east coast can only be reconstructed through complementary varve chronological investigations. Our investigations emphasize the need to corroborate visual varve-diagram correlations through statistical analyses, before the Swedish varve chronology can be regarded as a valid, high-precision time scale.