No abstract

The ridge-shaped Penttilänkangas accumulation in western Finland is glaciofluvial in origin: probably an ice-marginal subaquatic fan, reworked and covered with younger deep water, littoral, eolian and glacial sediments. Two cycles of glacial melting and land emergence to littoral and subaerial conditions can be distinguished at Penttilänkangas, separated by one glacial advance. Special attention is paid to a fairly well preserved buried podzol soil profile and to permafrost features. The podzol soil is interpreted as having developed in littoral sand and subsequently covered with eolian sand and till. The permafrost features are observable in all the sediments below the covering till, indicating prolonged periglacial ice-free conditions after the soil formation and before the latest glacial advance. The physical properties (content of <0.0625 mm fraction, magnetic susceptibility, colour, dry bulk density and LOI) of the buried podzol soil profile are compared to the Holocene podzol soil with similar parent material in the same area. These properties, as well as the identified microfossils and cell tissue, imply that the paleosol probably developed over a longer period and/or in similar or warmer and moister conditions than the Holocene soil. The podzolisation possibly initiated in the Eemian Stage (MIS 5e), and according to the OSL datings, it ceased in the beginning of the Middle Weichselian Substage (MIS 4). After that, ice-free permafrost conditions prevailed for several thousand years before the Weichselian ice-sheet advanced to western Finland around 65 ka at the earliest.

The lithostratigraphy of pre‐Late Weichselian sediments and OSL‐dating results from four localities in the Suupohja area of western Finland, adjacent to the centre of the former Scandinavian glaciations, are presented. The studied sections expose glacifluvial, quiet‐water, littoral and aeolian deposits overlain by Middle and/or Late Weichselian tills. Litho‐ and biostratigraphical results together with seven OSL age determinations on buried glacifluvial sediment at Rävåsen (94±15 ka) and on till‐covered littoral and aeolian sediments at Risåsen, Rävåsen, Jätinmäki and Kiviharju (79±10 to 54±8 ka), accompanied by previous datings and interpretations, suggest that the glacifluvial sediments at Risåsen were deposited at the end of the Saalian Stage (MIS 6) and those at Risåsen were deposited possibly in the Early Weichselian Substage (MIS 5d?). Palaeosol horizons and ice‐wedge casts together with the dated littoral and aeolian sediments between the Harrinkangas Formation (Saalian) and the overlying till(s) indicate that western Finland was ice‐free during most of the Weichselian time. Littoral deposits, dated to the Middle Weichselian (MIS 4–3), occur at altitudes of 50–90 m a.s.l., which indicates significant glacio‐isostatic depression. The depression resulted from expansion of the ice sheet in the west of Finland at that time.