Varvighed i danske og skaanske senglaciale Aflejringer

Richardt, N. 2003 (March): Ice-flow patterns and dispersal of erratics at the southwestern margin of the last Scandinavian Ice Sheet: signature of palaeo-ice streams. Boreas, Vol. 32, An extensive set of proxy-data was acquired from eastern and central Denmark in order to study the dynamic behaviour of the southwestern margin of the last Scandinavian Ice Sheet. We examine the last three glacier advances of the Late Weichselian: the Main advance from central Sweden, representing the maximum ice extent at this time (c. 21-20 ka BP), and the two succeeding Baltic advances (c. 18-15 ka BP). Directional properties from tills and glaciotectonic overprints are used to reveal large-scale flowline patterns. Together with the geomorphological outline of ice margins, flowlines were successively more fan-shaped, indicating that the dependence of the subglacial topography increases as ice advances become younger. It is suggested that while the ice thickness decreases, more lobate configurations of ice margins are created as a result. Clast-compositional data derived from the fine-gravel fraction in tills are used to reconstruct dispersal patterns of erratic material. The dispersal patterns during the three advances show a gradually diminishing influence of local Pre-Quaternary bedrocks and older glacial deposits, and progressively longer transport distances of far-travelled erratics. We speculate that the principal factor governing this development is a successively decreasing interaction between the ice and its bed, which influences the concentration of erratics, debris comminution processes and the basal ice velocity. We envisage the Main advance from central Sweden as a slow-flowing inter-stream ice body with high bed interaction compared to the succeeding Baltic advances, which we regard to have been rapid flowing ice streams with limited bed interaction.

Section: Main (Ne) Advancementioning

confidence: 99%

Ice‐flow patterns and dispersal of erratics at the southwestern margin of the last Scandinavian Ice Sheet: signature of palaeo‐ice streams

Kjær¹,

Houmark‐Nielsen²,

Richardt³

2003

“…The Lund Till is an alternating or interfingering layer together with a clay facies, the Lomma Clay, which is also within the b;karp Member. The only positive marine indicator in the Lomma Clay, as well as in all late-glacial clays of SkHne, is an old record of Gadus polaris Sabine (Torell 1887;Hansen 1940). The diamicton facies of the Lund Till is composed partly of clayey till floats which have flowed into a sediment basin characterized by clay deposition, and partly of sedimentary clay in which plenty of till material has dropped during the sedimentation.…”

Section: Definition Of Till-stratigraphical Unitsmentioning

confidence: 99%

Eemian and Weichselian stratigraphy in South Sweden

Berglund¹,

Lagerlund

1981

The stratigraphy of Pleistocene sequences within three main areas of the province of Skane, South Sweden, is discussed. The traditional stratigraphy is revised. New lithostratigraphic units are deficned and named according to international stratigraphic terminology. Lithostratigraphical correaltions are based on sedimentological development and palaeoenvironmental changes. Organic beds are correlated with the Eemain interglacial and some of the Early and Middle Weichselian interstadials. The chronostratigraphic key site, Stenberget, is described in greater detail. Stratrigraphy and palaeoenvironment are summarized in a scheme indicating that South Sweden was glaciated only during the period 21,000–13,000 B.P.

“…This was refuted by Fredericia (1988), who argued that these fine‐grained sediments were deposited in a glaciolacustrine environment after the Main advance and prior to the Lateglacial marine inundation. The ‘unfossiliferous Yoldia clay’ is located 5–7 m above the highest elevation of the Lateglacial marine clay (Mertz 1924; Hansen 1940; Fredericia 1988), which further suggests that it pre‐dates the Lateglacial marine inundation. Accordingly, both the depositional environment and relative age correspond to the glaciolacustrine deposition of the Morild Formation (see below).…”

mentioning

confidence: 98%

Litho‐ and chronostratigraphy of the Late Weichselian in Vendsyssel, northern Denmark, with special emphasis on tunnel‐valley infill in relation to a receding ice margin

Krohn¹,

Larsen²,

Kronborg³

et al. 2009

111

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.