Influence of Sample Preparation on Portable XRF-analyses of Aeolian Sediments: a Case Study

Detta är en Master-uppsats från Uppsala universitet/Institutionen för geovetenskaper

Författare: Markus L. Fiola; [2017]

Nyckelord: portable XRF; loess; sediment; bärbar XRF; lössjord; sediment;

Sammanfattning: The geochemical composition of aeolian sediments like windblown dust particles is of major importance for the exploration of dust origin and weathering conditions. This allows for the reconstruction of dust transport pathways and thus wind directions and palaeoclimate conditions. The loess deposits of the Carpathian Basin are the most complete terrestrial sediment climate archive in Europe, yet their development is still not fully understood. With the advancement of accurate field portable X-ray fluorescence (XRF) spectrometers, field applications have become possible, allowing in-situ geochemical analysis and potential advances in understanding the source of Carpathian Basin loess. However, previous work has failed to address the question of sample preparation and device interchangeability in the context of loess analyses. This study uses both Bruker Tracer 5i and Titan S1, as well as secondary data obtained with an Ametek SpectroXepos, to investigate sample preparation influences on aeolian sediment samples from Irig (Serbia) and Madaras (Hungary). Results showed that although absolute values deviate substantially between devices using different calibrations, some elemental ratios like Ca/Ti or Rb/Sr can still be compared when only relative changes are interpreted. Absolute concentrations of light elements, such as magnesium and calcium, were strongly influenced by milling or acid treatment. Absolute concentrations of light elements were also strongly influenced by changes in sample moisture, whereas the effect on the absolute concentrations of heavier elements was comparably small. Results also show that the influence of sample moisture needs to be considered when computing paleoclimatic indicator ratios involving aluminium or strontium, as sample moisture has a strong effect on the absolute concentration of these elements. Most deviations in measured absolute concentrations between untreated and prepared samples were attributed to the special nature of compositional data and could be removed through the application of additive or centred log-ratio transformations. This highlights the importance of considering the closure effect, using proper and robust statistical analyses in sediment provenance research.The geochemical data provided in this study shed light on dust provenance and the paleoclimatic development of the southeast European loess and highlight the effects of analysis technique on interpretation of this geochemical data.

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