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- Reconstruction of the Late and Mid-Pleistocene climate and landscape history in SE-Central Europe - A paleopedological and geochemical multi-proxy approach in loess-paleosol studies. (2011)
- Loess-paleosol sequences (LPSS) potentially are valuable archives for past environmental conditions. In SE-Central European lowlands thick loess plateaus can be found comprising several glacial-interglacial cycles. This work focuses on key sections in the middle and lower Danube Basin to i) investigate the origin of the loess and archive genesis, ii) to set up a reliable chronostratigraphy and iii) to contribute to the reconstruction of the Mid- and Late Pleistocene climate and landscape history of the region by a paleopedological – geochemical multi-proxy approach. Furthermore, methodological investigations aim to evaluate the validity of various paleoenvironmental proxies especially geochemically based weathering indices, as well as biomarker and stable isotope approaches in LPSS research. The results from geochemical analyses reveal that alluvial material of the Danube and its tributaries represent major sources for the loess in the middle and lower Danube Basin. From the geochemical point of view the studied loess can be regarded as a representative sample of the upper continental crust altered by at least one sedimentary cycle. The chronostratigraphy of the studied sections is based on the correlation of characteristic patterns of the magnetic susceptibility to the delta 18O record of benthic foraminifera from the Ocean Drilling Program site 677, a proxy record for the global ice volume. This is supplemented by correlating magnetic susceptibility fingerprints and pedostratigraphic marker horizons to previously established chronostratigraphies from profiles in the region as well as in China. The results show that the Batajnica/Stari Slankamen LPSS (Serbia) and Mircea Voda LPSS (Romania) comprise at least the last 700.000 years of climate history i.e. the last 17 marine isotope stages. The multi-proxy approach for paleoenvironmental reconstruction involves micromorphological parameters, silicate weathering intensity as given by element composition, grain size proxies for pedogenic clay formation and wind strength, as well as determination of sedimentation rates. As most suitable proxy for silicate weathering in calcareous sediments, the molar ratio Al2O3/(Na2O + Al2O3) × 100 is introduced as Chemical Proxy of Alteration (CPA) to loess paleosol research. Moreover, diffuse reflectance spectroscopy, soil color proxies and rock magnetic proxies are applied to gain paleoenvironmental information from the concentration and assemblage of iron minerals. Focusing on the warm periods, these proxies reveal a progressive decrease of interglacial weathering and soil formation intensity over the Mid - and Late Pleistocene. Also soil forming milieu was less oxidative as reflected by the iron mineralogical composition. These findings suggest cooling and a decline of rainfall linked to a change in seasonality from a Mediterranean type of climate to a more continental steppe climate. Results from n-alkane biomarkers support that summer dryness limiting the expansion of trees was a persistent feature of interglacial climate in SE-European lowlands. In the obtained proxy dataset, increase of wind strength, gradual cooling as well as decrease of rainfall since the early Mid-Pleistocene is also evident for glacial periods. After evaluation of potential triggers, this general climatic trend is proposed to be related to Pleistocene uplift of Eurasian mountain ranges. Changes in atmospheric circulation and rain shadow effects due to mountain uplift (Himalaya, Alps, Carpathians) would provide an explanation for the westward expansion of the Eurasian steppe belt into SE-Central Europe. Future studies on LPSS may also involve highly innovative proxies such as n-alkane biomarker and their D/H isotope signature. However, the methodological investigations on modern soil profiles and samples from litterbag experiments suggest that in a LPSS these proxies might be biased by microbial reworking. Procedures for correcting n-alkane ratios based on the odd over even predominance as reworking indicator have been developed. Hence, these studies highlight the limitations but also the persisting potential of innovative approaches from organic and isotope geochemistry in paleoenvironmental investigations of loess-paleosol sequences.