2009 (November): Litho-and chronostratigraphy of the Late Weichselian in Vendsyssel, northern Denmark, with special emphasis on tunnelvalley infill in relation to a receding ice margin.Lithostratigraphy and chronostratigraphy of samples from 18 deep boreholes in Vendsyssel have resulted in new insight into the Late Weichselian glaciation history of northern Denmark. Prior to the Late Weichselian Main advance c. 23-21 kyr BP, Vendsyssel was part of an ice-dammed lake where the Ribjerg Formation was deposited c. 27-23 kyr BP. The timing of the Late Weichselian deglaciation is well constrained by the Main advance and the Lateglacial marine inundation c. 18 kyr BP, and thus spans only a few millennia. Rapid deposition of more than 200 m of sediments took place mainly in a highly dynamic proglacial and ice-marginal environment during the overall ice recession. Mean retreat rates have been estimated as 45-50 m/yr in Vendsyssel with significantly higher retreat rates between periods of standstill and re-advance. The deglaciation commenced in Vendsyssel c. 20 kyr BP, and the Troldbjerg Formation was deposited c. 20-19 kyr BP in a large ice-dammed lake in front of the receding ice sheet, partly as glaciolacustrine sediments and partly as rapid and focused sedimentation in prominent ice-contact fans, which make up the Jyske Å s and Hammer Bakker moraines. In the northern part of central Vendsyssel, at least four generations of north-south orientated tunnel valleys are identified, each generation related to a recessional ice margin. This initial deglaciation was interrupted by a major re-advance from the east c. 19 kyr BP, which covered most of Vendsyssel. An ice-dammed lake formed in front of the ice sheet as it retreated towards the east; the Morild Formation was deposited here c. 19-18 kyr BP. Related to this stage of deglaciation, eight ice-marginal positions have been identified based on the distribution of large tunnel-valley systems and pronounced recessional moraines. The Morild Formation consists of glaciolacustrine sediments, including the sediment infill of more than 190 m deep tunnel valleys, as well as the sediments in recessional moraines, which were formed as ice-contact sedimentary ridges, possibly in combination with glaciotectonic deformation. The character of the tunnel-valley infill sediments was determined by proximity to the ice margin. During episodes of rapid retreat of the ice margin, tunnel valleys were quickly abandoned and filled with fine-grained sediments in a distal setting. During slow retreat of the ice margin, tunnel valleys were filled in an ice-proximal environment, and the infill consists of alternating layers of fine-to coarse-grained sediments. At c. 18 kyr BP, Vendsyssel was inundated by the sea, when the Norwegian Channel Ice Stream broke up, and a succession of marine sediments (Vendsyssel Formation) was deposited during a forced regression.

The Quaternary sedimentary succession in Vendsyssel, northern Denmark, contains a unique, high-resolution record of the last interglacial and glacial periods. There is still much debate, however, about the timing and ice extent in this southwestern part of the Scandinavian Ice Sheet, particularly during the Middle Weichselian. In this study, a detailed lithostratigraphical subdivision is established for the Late Saalian to Middle Weichselian Skaerumhede Group on the basis of numerous, up to 250 m deep, boreholes in Vendsyssel. The sediments mainly consist of marine clays, glaciolacustrine sediments and tills, and the total thickness of the Skaerumhede Group is up to 140 m. Marine intervals have been used as stratigraphical marker units to separate the formations indicative of ice-sheet activity in Vendsyssel, and the timing of the events has been constrained by a large number of optically stimulated luminescence (OSL) and radiocarbon ages. The Skaerumhede Group is subdivided into seven formations and two members, reflecting shifts between marine and terrestrial sedimentation caused by fluctuations of the Scandinavian Ice Sheet and changes in sea level. The lowermost Skaerumhede Till Formation was deposited directly on top of the bedrock during the Warthe advance c. 160-140 kyr BP. Above, there are fine-grained marine sediments, subdivided into the Lower, Middle and Upper Skaerumhede Clay Formations. The marine formations are separated by the Brønderslev Formation related to the Sundsøre ice advance from the north c. 65-60 kyr BP, and the Å sted Formation, deposited during the Ristinge advance from an east-southeastern direction c. 55-50 kyr BP. The uppermost formation in the group is the Lønstrup Klint Formation, which is an upwards-coarsening sequence of mainly glaciolacustrine sediments deposited prior to the Kattegat advance c. 30-29 kyr BP. The new evidence from Vendsyssel has shown that the Skaerumhede Group covers a large area, and that it can be used as a regional stratigraphical marker horizon. Furthermore, it contributes to a better understanding of the timing and extent of glacial events during the Late Saalian to Middle Weichselian in southwest Scandinavia.

Late Quaternary ice sheet, lake and sea history of southwest Scandinavia -a synthesis.