Cave stratigraphy in western Norway; multiple Weichselian glaciations and interstadial vertebrate fauna

Skjonghclleren is a marine-cut cave with 15–20. m thick pre-Holocene sediments. Corings and excavations reveal three beds of extremely fine-grained, laminated sediments alternating with blocky sediments. The laminated beds are interpreted as glaciolacustrine sediments deposited subglacially at times when ice sheets covered the area, suggesting at least three glaciations after the cave was formed. The blocky/diamictic sediments were formed by frost-shattered blocks from the roof of the cave during ice-free periods, and mixing with the fines through slow mass movements along the floor of the cave. In the diamictic sediment beneath the uppermost laminated bed, almost 7,000 bone and teeth fragments of birds, mammals and fish were found. Birds dominated, with little auk and brunnich's guillemot as the most frequently occurring species. Arctic fox was the dominating mammal. During climatic optimum of the interstadial, conditions seem to have been similar to present-day coastal Finnmark, with North Atlantic warm water entering the Norwegian Sea. Two radiocarbon dates on bones and three Uranium series dates on speleothems from this bed all cluster around 30,000 B.P., i.e., the end of the Ålesund interstadial. Above the uppermost laminated bed, bone fragments of birds, fish and mammals, deposited between c . 12,000 and c . 10,000 B.P., were found. Little auk dominate. The occurrence of squirrel is worth noting since it is limited mainly to areas with coniferous forest today. The beds below the 30,000B.P. bed are poorly dated or undated, but it is tentatively concluded that the entire sediment sequence was deposited during the Weichselian stage. It seems that the cave was formed at a high relative sea-level stand sometime during the Early Weichsclian. Two recorded palaeomagnetic excursions seem to correlate with the Laschamp/Olby and the Lake Mungo events, respectively.     

Stratigraphic architecture and infill history of a deglaciated bedrock valley based on georadar, seismic profiling and drilling

The sediment fill of a silled bedrock valley in Western Norway has been investigated with respect to stratigraphy and infill history using a combination of mapping, georadar, seismic profiling and drilling. A small outlet glacier occupies the head of the valley that displays a stepwise down-valley profile and terminates in a lake at 29 m above sea-level. The valley is surrounded by high, steep bedrock slopes and is characterized by a series of filled basins each limited by sills of bedrock or moraine accumulations. Till, glacial outwash and/or rockslide deposits fill in the lower half of the two larger basins. (Fan) delta deposits fringed by the deposits of alluvial fans and colluvial cones dominate the upper fill of most basins. (Fan) delta deposits interfinger downstream with lake sediments in the larger basins and fluvial deposits comprise the top fill. The overall infill pattern was controlled by deglaciation as well as basin size and shape. An overall decreasing sediment supply following deglaciation is shown in the fill of a larger basin down-valley, whereas a recently increasing sediment supply during glacier growth is reflected primarily in an upstream basin. Only the lowermost basin was exposed to a sea-level drop from 75 m above sea-level to the present lake level associated with incision and river migration. This observation is in contrast to the basins above marine influence where incision has been limited due to fixed downstream sills resulting in insignificant erosion except for some fan-head entrenchment. It follows that the fills of these small valley basins display progradational and aggradational trends of deposition and paraglacial reworking has been limited. Additionally, the study demonstrates that georadar profiling, combined with other methods, is very useful for comprehensive investigation of valley basins.