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Evaluation and comparison of multi-proxy data in sedimentological and geochemical studies – examples of a loess/palaeosol-sequence from the Lower Rhine Embayment

Florian Steininger1, Peter Fischer1, Jens Protze2, Frank Lehmkuhl2, Renate Gerlach3
1 Geographisches Institut, Universität zu Köln
2 Geographisches Institut, RWTH Aachen
3 LVR-Amt für Bodendenkmalpflege im Rheinland

P 2.12 in Löss und terrestrische Archive

 

Loess research in the Rhineland is looking back at a long tradition, but recently only few investigations using the modern spectra of analytical methods in high resolution are available.

For the first time extensive systematically laboratory analyses were carried out on loess sequences from the Lower Rhine embayment. In this contribution the influence of different sedimentological and geochemical analyses on the palaeoenvironmental interpretation of a drill core from Düsseldorf-Grafenberg will be presented. The location of the sequence in the transition from the Rhine valley to the Rhenish Slate Mountains favours the accumulation of thick loess sediments but also supports intensive reworking processes during phases of surface instability. Therefore, the sequence under investigation reflects different morphodynamic phases due to climate changes especially during the last glacial cycle.

Grain size ratios (e.g. U-ratio and Grain Size Index) reflect the geomorphic response to climate cyclictiy; it highlights the variability within loess (re-)deposition and accentuates stratigraphical unconformities. Grain size analyses were performed using a laser diffraction particle size analyser (Beckman Coulter LS 13320) on 359 samples. Two concentrations (0.3g and 0.4g) of the samples were measured with at least two repetitions. Within the laser diffraction analyses two different optical models, the Fraunhofer and the Mie theory have been applied. The latter is appropriate for the measurement of submicron particles but requires the knowledge of the absorption coefficients (AC) and refractive indices (RI) of the particles and the medium (Antoine et al. 2009, Machalett et al. 2008, Özer et al. 2010). The results of laser diffractometry were exemplary compared with sedigraph (Micromeritics 5100) results and tested for their palaeoenvironmental significance.

Calcium carbonates are primary components of loess sediments and cannot be separated from secondary carbonate precipitation. To check whether calcium carbonates influence results of grain size analyses or not, selected samples were treated with 10 % HCl and measured again. Comparisons of variations in the grain sizes (Figure) before and after decalcification show very close results. Hence, calcium carbonates cover the whole range of grain sizes and have no significant influence on laser diffraction measurements of loess samples.

Geochemical element ratios have enabled identification and characterisation of sediments, soils and reworked soil sediments. High resolution X-ray fluorescence analyses to determine element contents on 659 samples were conducted using a portable EDXRF Niton Xlt 700 device. To test accuracy and reproducibility of the measurements, selected samples were prepared in different modes for a stationary EDPXRF device (Spectro Xepos).

However, it will be demonstrated that the applications of various analytical techniques and sample preparation have considerable effects on measurement results and the deduced palaeoenvironmental evidence. 

 

References

Antoine, P., Russeau, D.-D., Moine, O., Kunesch, S., Hatté, C., Lang, A., Tissoux, H., Zöller, L. (2009): Rapid and cyclic aeolian deposition during the Last Glacial in European loess: a high-resolution record from Nussloch, Germany. – Quaternary Science Reviews 28: 2955-2973. DOI: 10.1016/j.quascirev.2009.08.001

Machalett, B., Oches, E. A., Frechen, M., Zöller, L., Hambach, U., Mavlyanova, N. G., Marković, S. B., Endlicher, W. (2008): Aeolian dust dynamics in central Asia during the Pleistocene: Driven by the long-term migration, seasonality, and permanency of the Asiatic polar front. – Geochemistry Geophysics Geosystems 9 (8): 1-22. DOI: 10.1029/2007GC001938

Özer, M., Orhan, M., Işik, N. (2010): Effect of particle optical properties on size distribution of soils obtained by laser diffraction. – Environmental & Engineering Geoscience 16 (2): 163-173.

Comparison between the variation of the Grain Size Index of the main stratigraphical units before and after decalcification (after Antoine et al. 2009, modified: RI=1.333 (medium), RI=1.55, AC=0.1 (particles), e-factor=0.6)
Comparison between the variation of the Grain Size Index of the main stratigraphical units before and after decalcification (after Antoine et al. 2009, modified: RI=1.333 (medium), RI=1.55, AC=0.1 (particles), e-factor=0.6)

Letzte Änderung 26.07.2012