OSL and TL dating of buried podsols and overlying sands in Ostrobothnia, western Finland

Abstract

In Ostrobothnia, western Finland, buried fossil soils have been recognised in a number of places in the sandy sediments that occur between glaciofluvial deposits and overlying till. Samples from the soil horizons as well as below and above them were taken for optically stimulated luminescence (OSL) dating. The same sites were also sampled for thermoluminescence (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 order 135‐155 ka. A comparison between the results obtained from the two dating methods shows that OSL dates are generally younger than the TL dates for the same sample. The discrepancy may arise partly from problems 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 soils were formed during the last interglacial, that the soil‐forming processes possibly also continued during the first Early Weichselian stadial and interstadial (Brørup 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.