Projects

The vanishing of the Last Glacial ice sheet and the subsequent eustatic sea level rise resulted in a flooding of the North Sea region and in a reorganization of the regional drainage system.

During the Weichselian the «Elbe-Urstromtal» (Elbe Palaeovalley) was parallel to the margin of the Scandinavian ice sheet and drained toward the modern central North Sea area. The Elbe River was only a tributary during this period. The existence of a bridge between the British and the Scandinavian ice sheets may have prevented a further drainage towards the northern North Sea area and the Norwegian trench. Plausible is the development of a huge proglacial lake. Recent studies on sediments from the Bay of Biscaye show that the North Sea Basin was connected to the English Channel river system allowing the transport of reworked glacial material into the Atlantic during Marine Isotopic Stage 2 (with a rapid sea level rise from about 130 m to 90 m below present level).

The opening of the northern North Sea at the end of the Last Glacial Maximum allowed the drainage towards the north. In the Early Holocene the Elbe Palaeovalley was developed as a major receiving stream; maybe using relicts of a former proglacial lake. Two diverse tributary systems feeding the Elbe Palaeovalley were seismically mapped in the course of the SD2 Project.

The northern section is located within the hypothetical 9000 B.P. coastline (sea level about 50 m below the present level) and seems to drain in a northwest to southeast direction, from the Dogger Bank towards the Elbe Palaeovalley. The area is dominated by a complex meandering river system, which is associated with tributary or distributary channels and wetlands or lakes.

The southern section is located within the hypothetical 8700 B.P. coastline (sea level about 36 m below present level) and shows a single meandering river valley with oxbow structures and potential estuarine settings. The drainage direction is from south to north and the southern part of the river can be linked to modern rivers on land (e.g. Ems River).

Radiocarbon dating of basal peat samples from the infill of the southern river valley gives an total averaged age of about 10,500 cal. yrs. B.P.; with an averaged age of about 11,300 cal. yrs. B.P. at the base of the peat deposits and about 9800 cal. yrs. B.P. at the top of the peat (marine transgression?). The youngest peat ages suggest that the Elbe Palaeovalley was an open receiving river system after 9800 B.P. and the river valley was already directly connected to the hypothetical coast line, located about 250 km northwards.

A combination of a dense reflection seismic grid and up to 50-m-long records from sediment cores and cone penetration tests was used to study the geometry and infill lithology of an E–W-trending buried tunnel valley in the south-eastern North Sea. In relation to previously known primarily N–S-trending tunnel valleys in this area, the geometry and infill of this 38-km-long and up to 3-km-wide valley is comparable, but its E–W orientation is exceptional. The vertical cross-section geometry may result from subglacial sediment erosion of advancing ice streams and secondary incision by large episodic meltwater discharges with high flow rates. The infill is composed of meltwater sands and reworked till remnants on the valley flanks that are overlain by late Elsterian rhythmic, laminated, lacustrine fine-grained sediments towards the centre of the valley. A depression in the valley centre is filled with sediments most likely from the Holsteinian transgression and a subsequent post-Holsteinian lacustrine quiet-water setting. The exceptional axis orientation of this tunnel valley points to a regional N–S-oriented ice front during the late Elsterian.

Project in the context of the DFG-Schwerpunktprogramm IODP/ODP

Expedition 317 was aimed to understand the relative importance of global sea level changes versus local tectonic and sedimentary processes in controlling continental margin sedimentary cycles. Nineteen regional sequence-bounding unconformities, know from high-frequency sequence stratigraphy, were investigated on four drill sites of a late Miocene to recent continental shelf-slope transect.

First onboard results show that the interpretation of the unconformities is problematical because the thicknesses of the missing intervals, caused by hiatuses and/or the drilling process, are unknown. For further investigations, e.g. age-depth estimation, lithological sequence correlation, two dimensional backstripping, it is crucial to get these information.

An auspicious approach is the reconstruct of the “missing strata” on the basis of the determination of compaction and dewatering properties via geotechnical measurements (oedometer and sediment strength tests) on 56 whole-round samples from areas above and below the unconformities. A second goal is to respond to the question if the sediment compaction history can be traced horizontally across a shelf-slope transect and vertically down to a sediment depth of more than 980 m. The results and additional analyses of physical property, down-hole logging and sedimentological shipboard data will support the quantitative analysis of subsidence and sea level change in Canterbury Basin.