Sediment provenance

The mid-late Holocene deposits in Moskusoksefjord and Nordfjord are interpreted to be dominated by glacimarine sediments mainly deposited through suspension fall-out, mass-wasting and ice rafting. Therefore, the sediments are thought to derive from the surrounding land areas including the catchment areas of the glaciers.

Of all the analyses performed on the sediment cores, the XRF core scanning and the measured magnetic susceptibility of the sediments appear to be the most useful when interpreting the provenance of the sediments. Both methods provide high-resolution records of the sediments, giving information about the geochemical elements as well as materials ability to be magnetized. Below, the magnetic susceptibility will be discussed first, followed by the XRF.

The magnetic susceptibility of the sediments in core HH13-008-GC-TUNU and HH13-009-GC-TUNU located in the inner and middle basins of Moskusoksefjord range between 11-33 (*10^-8 SI(m³/kg)) (Table 6-1). These values are relatively low compared with the other studied sediment cores of this study. Two additional cores that show similar values in terms of the measured magnetic susceptibility are cores HH13-010-GC-TUNU and HH13-012-GC-TUNU located in the outer basin of Moskusoksefjord and in sub-basin 1 in Nordfjord. Their values range from 33-69 (*10^-8 SI(m³/kg)) and have means of 45 and 44 (*10^-8 SI(m³/kg)), respectively. Core HH13-011-GC-TUNU, however, stands out with comparatively high values ranging from 70-96 (*10^-8 SI(m³/kg)). As the magnetic susceptibility generally decreases with distance from Waltershausen Gletscher, it is suggested that sediments with higher magnetic susceptibility are derived from the catchment area of Waltershausen

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Gletscher. The bedrock located below the glacier is made up of Neoproterozoic to Ordovician Caledonian fold belts comprising pale sandstones and darker mudstones with local granite formation. The area surrounding Moskusoksefjord consists of Devonian continental siliciclastic sediments mainly comprising red sandstones (Henriksen et al., 2000; Henriksen, 2008).

The application of XRF scanning of fjord sediments is a generally new research area and little is known about the interpretation within these environments. Authors performing studies in other settings have attempted to correlate their results with sediment provenance, composition and nature and the degree of terrestrial sediment discharge (Croudace et al., 2006; Rothwell et al., 2006; Calvert & Pedersen, 2007; Bertrand et al., 2012). In this study the XRF data has been used to i) correlate the cores and ii) relate the sediments with the surrounding bedrock.

The Ca/Fe ratio is thought to be an indicator of biogenic carbonate:detrial clay indicator (Rothwell et al., 2006). The amount of Ca decreases with distance from Waltershausen Gletscher and in the in-fjord direction of Moskusoksefjord, meaning that the abundance of carbonate material is highest proximal to the glacier front. However, study of the five sediment cores reveals that there is very little carbonate microfossils available in the cores closest to the glacier front. Thus, the brownish/reddish sediments derived from the surrounding land areas of Moskusoksefjord have a lower amount of Ca than the grayish sediments coming from Waltershausen Gletscher. However, the coarse dark reddish brown sediments from the two inner cores of Moskusoksefjord have a higher amount of Ca compared to the finer sediments within the cores, indicating that the brownish sediments in core HH13-008-GC-TUNU and HH13-009-GC-TUNU were derived from at least two separate sediment input sources. The concentration of Fe within the sediments decreases slightly with distance to the glacier front, making the bedrock located beneath the glacier slightly deficient in Fe. Unlike the other measured elements, Zr occurs exclusively in the two innermost cores, with the ratio Zr/Rb providing marked increases in the base of turbidites.

Both cores contain weak red intervals of mud with small decreases in Al compared to the surrounding brown mud.

The three cores located in the outer basin of Moskusoksefjord and in Nordfjord contain mostly fine gray sediments with layers or lenses of coarser dark grayish brown sediments. K

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is thought to be associated with clay minerals, which can be seen in all three cores. Thus, the layers containing coarse dark grayish brown sediments are characterized by decreases in K, Ti and Fe and subsequent increases in both Ca and Si.

In summary, the coarser dark reddish brown sediments observed in the inner- and middle basins of Moskusoksefjord are inferred to have come from the fjord side walls whereas the finer brown mud is suggested to have mainly come from the river entering the fjord head. The weak red/grayish sediments in the inner-and middle basins of Moskusoksefjord are interpreted to have derived from Waltershausen Gletscher. The three outer cores in the study area, located in the outer basin of Moskusoksefjord and in sub-basin 1 and 2 of Nordfjord, are assumed to contain sediments mainly originating from Waltershausen Gletscher.

Finally, the previously suggested application of the different geochemical elements for sediment provenance has proven to be partly incorrect for the study area of this thesis.

Whereas the concentration of Ti is thought to show an increase in the base of turbidites, it has proven to be the opposite for the turbidites present in all five cores. Also, the element ratio Ca/Fe has in this study shown to be applicable for indicating sediments derived from the glacier rather than for variations in biogenic carbonate:detrial clay. A possible interpretation is that the carbon derived from the bedrock beneath Waltershausen Gletscher overprints the carbonate production in the area.

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