COMPARATIVE INVESTIGATIONS INTO THE UPPER EOCENE AND QUATERNARY PALAEOENVIRONMENT AND PALAEOCLIMATE BY GEOCHEMICAL STUDIES OF FLUVIAL SEDIMENTS AND INCORPORATED FOSSIL TREE TRUNKS (CENTRAL GERMANY)

Fluvial deposits from the Eocene and the Quaternary in central Germany exhibit significant differences in terms of both their geochemical-mineralogical indicators (minerals, trace and main elements) and the geochemical parameters of the fossil wood they contain, such as the content of stable isotopes in wood cellulose. During the Eocene the climate was subtropical to humid; during the Quaternary it was humid to cold and arid. Whereas the substances contained and the geochemical 'maturity' of the sediment reflect the prevailing type and degree of weathering processes, the isotope-geochemical parameters of the fossil wood are indirect indicators of the temperature and the level of CO2 in the atmosphere. The weathering processes predominating in the humid, subtropical tertiary climate led to more intensive leaching processes and the extensive removal of chemically mobile elements. This resulted in sediments with high geochemical maturity containing enriched levels of SiO2, Corg, S and largely immobile trace elements (e.g. Zr, Y, Sn) mainly bound to the heavy mineral fraction. By contrast, the Quaternary sediments - which were mainly exposed to physically controlled weathering processes, contained feldspar and had a lower geochemical maturity - were characterized by higher levels of alkalis and alkaline earths. In the Upper Eocene river sediments in Germany, the wood cellulose of the numerous coniferous trees contains carbon with an isotope pattern (given as delta values in ‰ versus PDB) differing sharply from the isotope values of tree trunks from the Quaternary (Upper Eocene, central Germany: C-13 ca. -20‰; Late Glacial, southern Germany: ca. -24‰; Early Holocene, southern Germany: ca. -23‰; Early Holocene, central Germany: ca. -24‰; middle Holocene, northwest Europe: ca. -25‰; medieval time, northwest Europe: ca. -24‰) and Recent (central Germany: ca. -25‰; northwest Europe: ca. -26‰) periods. Compared to the Quaternary and Recent findings, the isotope data for the Upper Eocene document higher temperatures accompanied by the natural higher availability of atmospheric CO2 for photosynthesis in trees. In addition to the geochemical findings in the fluvial sediments and the isotope data obtained from wood cellulose, the article also highlights additional conclusions on the palaeoflow directions derived from orientation on trunks deposited in the sediments.