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 135-1 55 ka. A comparison between the results obtained from the two dating methods Journal of Quaternary Science 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 stadia1 and interstadial (Brplrup 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.

The SE sector of the Middle Weichselian Eurasian Ice Sheet was much smaller than assumed

“…Our analysis shows further that the OSL dates for the sections are mostly unreliably young (Fig. 9), pointing to severe methodological problems (Hutt et al, 1993;Alexanderson, 2008a), whereas the TL ages give a somewhat closer match with our interpretation.…”

Lithostratigraphy and Optically Stimulated Luminescence age determinations of pre‐Late Weichselian deposits in the Suupohja area, western Finland

“…2) (Gibbard et al 1989;Bouchard et al 1990). Tynni 1979;Donner 1988;Gibbard et al 1989;Kujansuu et al 1991;Niemelä & Jungner 1991;Kujansuu 1992;Hütt et al 1993;Nenonen 1995;Auri & Räsänen 2006;Auri et al 2008;Pitkäranta 2009a, b). These units have been interpreted as being of Eemian to Middle Weichselian (c. MIS 5e-3) age (Niemelä & Tynni 1979;Gibbard et al 1989;Bouchard et al 1990;Niemelä & Jungner 1991;Hütt et al 1993;Nenonen 1995;Pitkäranta 2009b).…”

TL dating of feldspars using their far-red emission to deal with anomalous fading

“…With volcanic feldspars it results in the loss of most, if not all, their natural TL. With other feldspars which displayed some natural TL and were eventually well dated (Hütt et al, 1993;Preusser, 2003, etc. ) it cast an a priori suspicion of partial fading which had to be withdrawn.…”

“…We made similar comparative B ir tests between prompt and natural TL for other sedimentary K-feldspars dated by Preusser (2003) (e.g. SHB1, also from Switzerland; ESE, from Siberia, SL2, from Oman) or by Hütt (1993) (Norinkylä from Finland). They are not shown for lack of space.…”