OSL AND TL DATING OF BURIED PODSOLS AND OVERLYING SANDS IN OSTROBOTHNIA, WESTERN FINLAND

In Ostrobothnia, western Finland, buried fossil soils have been recogn ised in a number of places in the sandy sediments that occur between g laciofluvial deposits and overlying till. Samples from the soil horizo ns as well as below and above them were taken for optically stimulated luminescence (OSL) dating. The same sites were also sampled for therm oluminescence (TL) dating. Altogether five TL dates and seventeen OSL dates were obtained. The OSL dates can be grouped into two age classes , (i) 120-163 ka and (ii) 76-106 ka, whereas all TL dates are of the o rder 135-155 ka. A comparison between the results obtained from the tw o dating methods shows that OSL dates are generally younger than the T L dates for the same sample. The discrepancy may arise partly from pro blems of setting a correct residual level in TL dating. If this is the case then the TL dates may indicate an upper limit for the true age. The results support the geological interpretation that the fossil soil s were formed during the last interglacial, that the soil-forming proc esses possibly also continued during the first Early Weichselian stadi al and interstadial (Brorup sensu lato), and that in general the till- covered glaciofluvial sequences, interpreted as eskers in Ostrobothnia , were deposited during the Saalian or Early Weichselian deglaciation.