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.

Keywords:

• Lake Vättern
• Deglaciation
• Ice sheet
• Overconsolidation

Acknowledgements

The authors want to thank Asera Mining AB and Ove Göting for providing the opportunity to use their drilling equipment. They thank the Asera Mining drilling crew and supervisor Steen Sörensen for their excellent support. The County Administrative Board Jönköping is thanked for supporting the project. M. O'Regan is supported by a Swedish Research Council (VR) Junior Research Grant and S. Greenwood by the Geological Survey of Sweden. Stockholm University scientists are affiliated with the Bert Bolin Centre for Climate Research, supported through a grant from FORMAS. This project also forms part of the Stockholm University Research School focusing on Natural Hazards and financed by VR.

Disclosure statement

No potential conflict of interest was reported by the author(s).