Киара Кёльтрингер: "Происхождение лессов долины нижнего течения р. Волга по результатам рентгенфлюоресцентного и петромагнитного анализов"

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Рады сообщить, что во вторник, 21 ноября, в 14-00 в 107 комнате ИФЗ РАН состоится палеомагнитный семинар, на котором выступит Киара Кёльтрингер (Швеция, университет г. Упсала) с докладом: "Происхождение лессов  долины нижнего течения р. Волга по результатам рентгенфлюоресцентного и  петромагнитного анализов".
"Provenance analysis of loess in the Lower Volga region of Russia using XRF and mineral magnetic analyses"
Introduction: In contrast to the well-studied loess areas of Europe and the very intensively investigated deposits in East Asia, notably the Chinese loess plateau, the Lower Volga loess has gained very little research attention. Its position near the middle of the vast Eurasian loess belt makes it somewhat of a missing link for developing full understanding of Eurasian climate, dust history and evolution. Furthermore, the Lower Volga region covers an area of alternating marine and continental influence with distinct deposits of both marine and continental environments. To understand how these environments evolved and which climate factors controlled this, it is important to determine the providence and formation of the sedimentary material. While the marine sediments can provide important information about sea level fluctuations of the Caspian Sea and its possible interaction with the Black Sea and Azov Sea, provenance analyses of terrestrial sediments can address dust dynamics and atmospheric conditions of the region during the Quaternary. In this work, loess from two Lower Volga sites, as well as interbedded sand, clay and soil material, is analysed by means of magnetic susceptibility and bulk geochemistry. The approach here is to test whether these methods, some of them not previously applied to loess deposits in this context, can be used as a tool for provenance analyses.
Methods and Materials: The study focuses on two sites along the Lower Volga River multi-channel system; Raigorod and Leninsk. Both sections show alternated stratification of marine and continental material, which are here investigated by applying magnetic susceptibility (MS) measurements as well as bulk X-ray fluorescence (XRF). Magnetic susceptibility was measured on a MFK1-FA Kappabridge instrument in two ways, by analysing frequency dependency and temperature dependency in samples. In this way, the susceptibility of sample material at three different magnetic field frequencies and along heating and cooling paths could be recorded in order to investigate the specific magnetic mineral composition of the samples. Geochemical analyses provided data on major, minor and trace elemental composition and was undertaken using a Brucker Tracer 5i portable XRF.
Results and Discussions: The frequency dependent MS data give a clear validation to the proposed lithology by representing typical MS properties of loess in contrast to soils or sand for example. Analysis of different magnetic field frequency responses allows estimation of which material actually is detrital (source related) and which represents “in situ” production, and by inference the intensity of weathering. We propose that some of the magnetic susceptibility features seen might be inherited from the source material and therefore may give a provenance sign. Initial temperature dependent magnetic susceptibility analyses seem to indicate that source inherited magnetic properties can be traced to the presence of specific detrital magnetic mineral phases. The bulk geochemistry results are analysed in terms of classical provenance weathering element ratios and indices in an attempt to test these initial results from the magnetic susceptibility data.