Isochronous provenance variability during the last glacial maximum revealed by heavy mineral analysis of loess deposits

Loess-Paleosol-Sequences (LPS) are important sedimentary archives that enable to infer climatological parameters during the Quaternary at high temporal resolution. Three isochronous, central European LPS sites (Nussloch, Münzenberg, Hecklingen) were accessed at high temporal resolution by means of heavy mineral, single-grain sedimentary provenance analysis (SPA) using a highly automated, correlative workflow guided by machine learning (Lünsdorf et al., 2023). The goals of this study are (1) to investigate if regional differences exists between the LPS in terms of heavy mineral composition (i.e. Alpine vs. Fennoscandinavian provenance) and (2) if short lived processes that affected the source-to-sink system can be detected.

The studied LPS compose a transect from SW to NE Germany and synchronicity of the archives was controlled by presence of the Eltville tephra (ET; ca. 23.2 – 25.6 ka, Zens et al. 2017) and/or precise OSL age modeling. Thus, the LPS recorded sedimentation during the last glacial maximum. From each LPS 1 m of sediment was continuously sampled in 5 cm intervals, whenever possible centered on the ET. 120 heavy mineral aliquots of the grain size fractions 10 – 30 µm and 30 – 62 µm were analyzed by optical microscopy, Raman spectroscopy and electron probe micro analysis (EPMA) at the single grain level. Resulting in a correlated dataset of optically derived grain parameters (size, shape, roundness, color, etc.), mineralogy and chemical composition for each individual grain analyzed.

First preliminary results suggest that the three LPS are readily differentiated based on heavy mineral composition, supporting a Southern, Alpine and Northern, Fennoscandinavian loess provenance. While heavy mineral ratios and garnet chemical composition reveal abrupt changes in the Southern (Nussloch) and Northern (Hecklingen) LPS. It is assumed that the abrupt changes at the Nussloch site are related to variation in storm intensity with periods of high storm activity reflecting a distal source and periods of low storm activity a more local source. A reasonable explanation for the abrupt change in provenance indicators at the Hecklingen site is the advancement of the Scandinavian Ice Sheet, potentially changing the fluvial drainage pattern and introducing more moraine material to the deflation area.