Regional deglaciation and postglacial lake development as reflected in a 74 m sedimentary record from Lake Vättern, southern Sweden

Abstract

M., 2015: Regional deglaciation and postglacial lake development as reflected in a 74 m sedimentary record from Lake Vättern, southern Sweden.Abstract: The withdrawal of the Late Weichselian ice sheet and rapid isostatic uplift in southern Scandinavia led to the entrainment of large volumes of melt water within the proglacial Baltic Ice Lake (BIL). The eventual western outpost of BIL, Lake Vättern, has been a focal point for studying the dynamic retreat history of the Late Weichselian ice sheet in south central Sweden. This part of the deglacial history is described from an abundance of terrestrial studies, but, to date, no complimentary long sediment cores from Lake Vättern have been available. Here, we present the results from a unique, 74 m borehole in southern Lake Vättern that recovered a Late Pleistocene to Holocene sedimentary sequence. Physical and chemical analyses of the sediment and pore water, together with geophysical mapping, reveal glacial as well as postglacial imprints implying an oscillating ice sheet margin, evidence for neotectonic activity and one or more marine incursions into the lake during deglaciation. We attribute the glaciotectonic deformation of the sediments at 54 m below the lake floor to an ice readvance that likely occurred at the same time or before the advance that formed the Levene moraine (,. After this event, potential readvances were likely restricted to a more northerly position in the basin. We identify the final drainage of the BIL, but find evidence for an earlier marine incursion into the Vättern basin (,13.0 cal. ka BP), indicating water exchange between the North Atlantic and the Baltic Ice Lake during the late Alleröd.

Multiple re‐advances of a Lake Vättern outlet glacier during Fennoscandian Ice Sheet retreat, south‐central Sweden

“…Detailed sedimentological and geotechnical analyses of this record are presented in Swärd et al . (in press) and O'Regan et al . (in press).…”

“…(Swärd et al . in press). Detailed sedimentological and geotechnical analyses of this record are presented in Swärd et al .…”

“…The composite drilled core lithostratigraphy, interpreted by Swärd et al . (in press) based on visual core description and a suite of physical and chemical property measurements (Fig. ), describes an upper, finely laminated gyttja clay (unit U1: 0–15 m b.l.f.…”

“…Swärd et al . (in press) interpreted U3 as a proglacial lake unit, U2 as postglacial lake clays deposited once significant glacial influence had been removed from the basin and U1 as Holocene‐to‐modern isolated lake sedimentation. A sharp colour and lithological change at the U3–2 transition marks the final drainage of the Baltic Ice Lake (Swärd et al .…”

“…A sharp colour and lithological change at the U3–2 transition marks the final drainage of the Baltic Ice Lake (Swärd et al . in press; cf. Björck & Digerfeldt ; Brunnberg ; Björck et al .…”