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Titel |
Flood-related variations in provenance of fine-grained palaeochannel sediments in the Rhine river basin |
VerfasserIn |
Marcel van der Perk, Willem H. J. Toonen, Jochem Ypma, Paul A. Brewer, Maarten A. Prins, Mark G. Macklin, Hans Middelkoop |
Konferenz |
EGU General Assembly 2014
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 16 (2014) |
Datensatznummer |
250095890
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Publikation (Nr.) |
EGU/EGU2014-11366.pdf |
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Zusammenfassung |
In this study, we examine flood-related variations in provenance of fine-grained
palaeochannel sediments from the Bienener Altrhein (Germany), an abandoned
river channel close to the apex of the Rhine river delta. Geochemical and grain size
analyses were conducted on channel-fill sediments from multiple core sections,
ranging from 1.15 m to 8.48 m depth, which represents pre-industrial sediment
deposited from approximately 1550 AD to 1850 AD. In addition, four sediment
cores of ~ 1 m length were retrieved from channel-fills or overbank deposits along
the Upper Rhine and the three main tributaries of the Rhine in Germany (Neckar
River, Main River and Moselle River). Sediment geochemistry was analysed using
an Itrax X-Ray Fluorescence (XRF) core scanner. Four elements (Ti, Co, Rb, W)
were selected for further analysis based on the following a priori criteria: (1) The
elements must be associated with minerals in the fine particle size fractions; 2)
they must not be susceptible to precipitation-dissolution reactions during early
diagenenis of the sediment; 3) the elements must be detected in the vast majority of the
measurements; 4) the difference between the minimum and maximum number of the XRF
counts for the upstream cores must be greater than 50% of the average number of
counts. The XRF counts for these elements were standardised to z-scores and were
subsequently corrected for the variation clay content (< 2 μm) within the core and
between the upstream cores by means of linear regression. The Mahalanobis distance
was adopted as a measure of dissimilarity between the Bienener Altrhein sediment
increments and the sediment from the upstream tributaries. The logtransformed
Mahalanobis distances to the mean sediment composition of the upstream sediments
were correlated to the medium to coarse sand particle size fraction (> 150 μm),
which was primarily deposited during historical flood events. The results show
the Mahalanobis distances are larger than 1 for most increments, which indicates
that the four sampled upstream sites do not entirely cover all sources of sediment
deposited in the Bienener Altrein channel. The logtransformed Mahalonibis distance
correlates significantly (α = 0.05) with the >150 μm particle size fraction for the
Upper Rhine River (negative) and the Moselle River (positive). This implies that the
proportion of fine sediment that originates from the upper parts of the river basin and,
hence, the sediment transport distance increases with flood magnitude. These results
provide an excellent starting point to reconstruct the origin of historic flood events as
documented in the sedimentary records of channel fills and dike breach ponds. |
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