A COMBINED BIO- AND TEPHROSTRATIGRAPHIC CORRELATION OF LATEGLACIAL PALYNOLOGICAL RECORDS IN THE NORTHWEST EUROPEAN LOWLAND REGION

Biostratigraphy and 14C dating have been the major tools for the correlation of numerous Lateglacial palynological records from the northwest European lowland. Detailed changes in spatial vegetation patterns over time can be constructed based on these correlations. The region is characterised by the occurrence of a predominantly sandy substratum, consisting of glacial, glacio-fluvial, fluvial, and aeolian sediments. This is the type region for the sub-division of the Lateglacial, where the classic Bølling and Allerød interstadials have been recognised since the late 1940s. The extensive dataset suggests that vegetation changes, at least in this region, occurred synchronously, but is this really the case?

Biostratigraphic correlations are, naturally, not the way to reveal a-synchronous shift in vegetation, and due to the limitations associated with radiocarbon dating such as 14C-plateaux the incomplete extension of the dendro-calibration curve and site-specific factors, this method is not the most reliable method to give accurate age estimates during this time-period. Therefore, other methods are required for time-stratigraphic correlation to evaluate synchroneity between palynological records. Unfortunately, laminated sequences are rare in this region, but the few sites that show annual resolution are investigated in great detail, and if vegetation changes appear to have occurred synchronously, biostratigraphy can be used for correlation between these sites.

The recent discovery of Lateglacial micro-tephra horizons in this region opens up a new potential for the precise correlation of sequences in widely separated localities, and accordingly for testing the synchroneity of vegetation changes. In this way, the value of biostratigraphy as a tool for time-stratigraphic correlation can be evaluated. Biostratigraphy can also be used to trace known micro-tephra horizons that have been previously undiscovered in this region. Thus, by interlinking terrestrial sites that have annual laminations, detailed biostratigraphy, 14C time-control, and isochronous marker horizons such as one or more known tephras, a comprehensive picture of vegetation changes can be compiled which can then be directly compared to other European palaeoclimatic records including marine and ice core sequences.