Geotechnical and sedimentary evidence for thick-grounded ice in southern Lake Vättern during deglaciation

Abstract

A 74-meter Late Pleistocene to Holocene sedimentary sequence was recovered from southern Lake Vättern in the autumn of 2012. At ,54 m below the lake floor, shear strength and high-resolution bulk density measurements suggest the presence of an unconformity in the varved proglacial clays. Incremental load consolidation tests reveal highly overconsolidated sediments below this level. Preconsolidation pressures for the underlying sediments are between 1250 and 2100 kPa, up to ,1700 kPa more than the current in-situ effective stress. The highly overconsolidated sediments indicate either substantial erosion (the removal of 215-360 m of sediment), or consolidation under a large grounded ice mass sitting up to 230 m above paleo-lake level. Glaciotectonic deformation in underlying sediments supports the interpretation of a grounded ice mass. It is likely that this horizon is either contemporaneous with or older than the Levene moraine, formed between 13.4 and 13.8 ka. In the ,30 m of overlying proglacial clays, there is no further evidence for grounded ice, indicating that any ice advance to southern Lake Vättern during the Younger Dryas would have been limited to an extremely thin ice tongue.

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

“…O'Regan et al . (in press) found that this subunit is over‐consolidated, with pre‐consolidation pressures an order of magnitude greater (1250–2100 kPa) than the overlying normally consolidated sediments (<135 kPa), indicating either substantial erosion of up to 350 m of material, or consolidation under an ice load with an elevation of up to 230 m above the palaeo‐lake level. O'Regan et al .…”

“…(in press) and O'Regan et al . (in press). In this paper, we use their key findings to guide and support interpretations of newly acquired geophysical data, which in turn extend the results from the drill site both regionally and temporally.…”

“…O'Regan et al . (in press) interpreted an ice‐grounding episode as having occurred after the initial deposition of proglacial lake clays in the last deglaciation.…”

The early Quaternary North Sea Basin

“…The effects of changes to groundwater drainage under a significant ice load can result in strongly differential compaction. Over-consolidation of sediment is common in glacially loaded regions, as the weight of the ice forces dewatering and effective stress increases dramatically (Boulton & Dobbie 1993;Saettem et al 1996;Piotrowski & Kraus 1997;O'Regan et al 2010O'Regan et al , 2016. However, restricted meltwater discharge has been known to cause excess pore pressures and thus underconsolidation of sediment, particularly in fast-moving ice (Boulton & Dobbie 1993;Saettem et al 1996;Piotrowski & Kraus 1997;O'Regan et al 2010O'Regan et al , 2016.…”

“…Ice sheets are known to have an impact on isostasy both through the loading of the ice sheet itself (James & Bent 1994;Klemann & Wolf 1998;Davis et al 1999;James et al 2000;Stewart et al 2000) and the changes to groundwater conditions affecting compaction of sediment (Boulton & Dobbie 1993;Saettem et al 1996;Piotrowski & Kraus 1997;O'Regan et al 2010O'Regan et al , 2016. The effects of changes to groundwater drainage under a significant ice load can result in strongly differential compaction.…”