Introducing an improved multi-proxy approach for paleoenvironmental reconstruction of loess–paleosol archives applied on the Late Pleistocene Nussloch sequence (SW Germany)

摘要

To study paleoenvironmental and paleoclimatic changes in loess–paleosol sequences (LPS),most proxies except for screening parameters have often been applied at low sampling density, typically 1–2 per stratigraphic unit. This might lead to results that overlook paleovegetation effects that were not only restricted to paleosols but also affected underlying loess material. Here, a new profile was investigated in the loess–paleosol sequence (LPS) at Nussloch, SW Germany using a high resolution multi-proxy approach to improve our understanding of the Late Pleistocene record which serves as a standard sequence in Central Europe. This approach included several geophysical and geochemical parameters, as well as frequencies of root-related features. Grain size distribution and OSL dating enabled correlation of the newsection with the nearby standard profile P4, revealing considerable variations of the thickness of stratigraphic units due to local small-scale variations in depositional conditions and paleogeomorphology of longitudinal greda structures. Magnetic susceptibility revealed weathering of the entire LPS under more humid conditions than those described for SE European and Chinese LPS. It further enabled a rough differentiation between an interval that was influenced by pedogenic processes (Lower Pleniglacial to lower part of the Upper Pleniglacial), and loess that was not markedly affected by soil formation. Colormeasurements confirmed these results and enabled the identification of several paleosols in the Upper Pleniglacial. For the uppermost part of the LPS, lowmagnetic susceptibility and inorganic geochemical parameters such as low Fe/Ti ratios indicated onlyweak or no pedogenic influence. In contrast, considerable variations e.g. in carbonatic carbon contents and organic carbonitrogen (C/N) ratiomight be related to the high frequency of calcified root remains (up to 200 rhizoliths m~(?2) and up to 12,500 microrhizoliths m~(?2)) in certain depth intervals of the LPS, entailing incorporation and degradation of organic matter. Frequencies of biopores, which are suggested to derive largely fromformer root growth and, to a lesser extent, frominsect and earthworm bioturbation, were related to paleosols, and thus confirmed the pedostratigraphy. An improved assessment of terrestrial sedimentary archives can be achieved by high-resolution multi-proxy analysis and three-dimensional investigation of terrestrial sediments that are prone to bioturbation.