The Last Interglacial-Glacial cycle in NE Fennoscandia: a nearly continuous record from Sokli (Finnish Lapland)

Abstract

Boreholes from the Sokli basin in Finnish Lapland have recovered a unique sequence of diamicts interlayered with fine-grained sediments that are rich in fossils. The diamicts are interpreted as till beds deposited by the Fennoscandian Ice-Sheet. The fine-grained intercalations seem to represent a series of warm stages that include one interglacial and three interstadials. The interglacial is characterized by a mixed taiga pollen assemblage and corresponds to a distinct diatom gyttja bed. The interstadials show progressively colder floras from open birch forest to arctic forest limit to shrub tundra. Their sediments comprise gyttja interlayered with wood and sand (interstadial 1); sands grading into sandy gyttja (interstadial 2); and sands overlain by laminated silt and clay (interstadial 3). The interstadial 2 and 3 deposits are underlain by diamict and are interpreted as deglaciation sequences. Silts with a tundra pollen assemblage separate the interglacial and interstadial 1 deposits. Luminescence dating evidence indicates that the interglacial bed most probably represents the NW European mainland Eemian Interglacial (marine isotope stage (MIS) 5e). The interstadial 1, 2 and 3 deposits are tentatively correlated with the Early Weichselian Brørup and Odderade Interstadials and an interstadial of Middle Weichselian age, respectively (MIS 5c, 5a and 3, respectively). The correlation implies that the easternmost part of the ice-divide zone of the Fennoscandian continental ice-sheet was deglaciated during part of MIS 3.