Evidence for a Middle Pleistocene glaciation of MIS 8 age in the southern North Sea

摘要

In the cores of borehole 89/2, situated at 54° 00 01′N and 5° 00 04′E about 70 km north of the Frisian Islands in the southern North Sea, two diamictons levels are found at ± 70 and 100 m below sea floor (i.e. ± 110 and 140 below present sea level), respectively. Both diamictons appear to be older than Saalian ( = MIS 6), in contrast to earlier interpretations. The upper diamicton is overlain by about 20 m of shallow marine sands followed by a chaotic alternation of fine-grained clay-rich Eemian (MIS 5e) sediments and sands deposited in a glacially excavated basin. It was originally assumed that this diamicton was Saalian (MIS 6) in age and lined the base of the basin. Seismic lines crossing the borehole location, however, show that the upper diamicton is truncated by the basin, and, consequently must be older than Saalian. This is corroborated by new investigations on the Saalian-Eemian transition in the Netherlands and new data on the age of the molluscs and foraminifera in the sands directly overlying the upper diamicton. The age data, based on measurements of the isoleucine epimerisation of mollusc shells and foraminiferal tests favour an MIS 8 age.