Recurrent interaction between the Norwegian Channel Ice Stream and terrestrial‐based ice across southwest Norway

Abstract

The occurrence of till beds alternating with glaciomarine sediment spanning oxygen isotope stages 6 to 2, combined with morphological evidence, shows that the southwestern fringe of Norway was inundated by an ice stream flowing through the Norwegian Channel on at least four occasions, the last time being during the Late Weichselian maximum. All marine units are deglacial successions composed of muds with dropstones and diamictic intrabeds and a foraminiferal fauna characteristic of extreme glaciomarine environments. Land‐based ice, flowing at right angles to the flow direction of the ice stream, fed into the ice stream along an escarpment formed by erosion of the ice stream. Each time the ice stream wasted back, land‐based ice advanced into the area formerly occupied by the ice stream. During the last deglaciation of the ice stream (c. 15 ka BP), the advance of the land‐based ice occurred immediately upon ice stream retreat. As a result, the sea was prevented from inundating the upland areas, allowing most of the glacioisostatic readjustment to occur before the land‐based ice melted back at about 13 ka BP. This explains the low Late Weichselian sea levels in the area (10–20 m) compared with those of the Middle Weichselian and older sea‐level high stands (∼200 m). Regional tectonic movements cannot explain the location of the observed marine successions. The highest sea level recorded (>200 m) is represented by glaciomarine sediments from the Sandnes interstadial (30–34 ka BP). Older interstadial marine sediments are found at somewhat lower levels, possibly as a result of subsequent glacial erosion in these deposits. Ice streams developed in the Norwegian Channel during three Weichselian time intervals. This seems to correspond to glacial episodes both to the south in Denmark and to the north on the coast of Norway, although correlations are somewhat hampered by insufficient dating control.

Weichselian sediments at Foss‐Eikeland, Jæren (southwest Norway): sea‐level changes and glaciation history

“…However, this would make the correlation with other sites on Jaeren difficult, as an interstadial with similar glaciomarine sediments has been confined to ca. 30-39 ka Larsen et al, 2000;Sejrup et al, 2000). Another possibility is that the Kalberg clay represents a hitherto unknown interstadial, but as discussed above we find this possibility unlikely.…”

“…Feyling-Hanssen (1964) and Fugelli and Riis (1992) suggested they were tectonically uplifted glaciomarine sediments, whereas Andersen et al (1987Andersen et al ( , 1991 thought they were glaciomarine sediments deposited in periods of large glacio-isostatic depression owing to an ice sheet centred over central Norway. Sejrup et al (1998) suggested that glacio-isostatic loading by an ice stream in the Norwegian Channel could explain the high relative sea-levels during deposition of the marine clays on Jaeren, and this interpretation was later supported by Stalsberg et al (1999), Jonsdottir et al (1999) and Larsen et al (2000). Sejrup et al (1998) also suggest that the boundary between Høgjaeren and Lågjaeren is the easternmost boundary of the Norwegian Channel Ice Stream (NCIS).…”

“…14). This is in the upper range of Sandnes interstadial ratios from western Norway (between 0.04 and 0.06) Larsen et al, 2000). Thus, the amino acid analyses indicate a Middle Weichselian age for the deposition of the Kalberg clay.…”

“…Several Weichselian interstadials have been reported from the Jaeren and Karmøy areas Larsen et al, 2000;Sejrup et al, 2000). All of the interstadials are towards the upper limit of the 14 C method or older, and the chronology is still uncertain.…”

“…The oldest of these is dated to ca. 300 ka, whereas the youngest, the Sandnes interstadial, is dated to around 32 ka (Sejrup et al, 1998;Larsen et al, 2000).…”