New exposures of Baltic Ice Lake drainage sediments, Götene, Sweden

Abstract

New exposures created during the construction of highway E20 near Götene, Sweden, reveal poorly sorted gravelly sand overlain and underlain by varved clay. The stratigraphy at Pellagården consists of, from the bottom up, striated gneiss, till, varved marine clay, the gravelly sand unit, and varved marine clay. The varves represent deglacial marine sediment deposited in 40–50 m deep water. The gravelly sand unit contains graded bedding, indistinct horizontal bedding, mud clasts and interstitial mud. It is poorly sorted and poorly organised. The unit has a pebble fabric indicating flow to the northwest. These characteristics and the great water depth suggest that the gravelly sand was deposited from a hyperconcentrated traction current or from concentrated to hyperconcentrated density flows. We interpret the gravelly sand bed to be sediment deposited during the Baltic Ice Lake drainage at around 10,000 ¹⁴C years BP. The unit likely represents rapidly deposited sediment at the very start of the drainage and does not indicate the duration of the drainage event. The bed was deposited during a single drainage event rather than as a series of events over a few weeks or months. Based on the number of varves and regional ice retreat rates, the ice-margin was 0.2 to 5 km north of Götene at the time of the drainage. These sites represent the first reported occurrences of the drainage sediment in a stratigraphic sequence since the work of Simon Johansson (1926, 1937, and 1941).

Keywords:

• Baltic Ice Lake drainage
• Middle Swedish end-moraine zone
• glacial lake drainage
• varved clay

Acknowledgements

We wish to thank Skanska for allowing access to road cuts during excavations along E20. We also thank Mari Manderfeldt for field assistance and Thierry Mulder and Piret Plink-Björklund for conversations about sediment gravity flows. We have also had valuable discussions about this outcrop with Lena Adrielsson, Svante Björck, Jan Lundqvist, Tore Påsse, Rodney Stevens, Bo Strömberg, and Per Wedel and we wish to thank them. We thank Tore and Rodney for comments on an earlier draft of this paper and Bo and Helena Alexandersson for their helpful comments on our submitted manuscript.