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.
The proglacial area of Bødalsbreen glacier in western Norway contains nine moraine ridges formed at the maximum of the `Little Ice Age' (~AD 1755) and during the subsequent glacier retreat (AD 1767—2000). The frontal moraines are composed of a sandy diamicton, whereas the lateral ones consist of only boulder-sized clasts without any matrix. These lateral moraines seemingly are composed of a very high proportion of mature clasts, a notion supported by detailed clast roundness and shape analyses. Furthermore, there is evidence for a decline in clast maturity between the outer (older) three and the inner (younger) three moraine ridges. This decline is interpreted as a change from recycled to freshly plucked clasts. Thus, the more mature clasts in the outer moraines are thought to consist of sediment that has been recycled in the glacial system, whereas the less mature clasts on the inner moraine ridges comprise younger glacially, freshly plucked material. The Holocene glacial history of the study area with a considerably fluctuating ice margin allowed much of the sediment in the catchment to undergo several cycles of erosion, transport and deposition. Moreover, an undulating subglacial topography with several major depressions may have acted as efficient sediment traps during deglaciation phases and as sediment sources during glacial advances. The concept of glacial sediment recycling may thus be applicable to many glaciers around the world, particularly those with a history of intensive glacier fluctuations.
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