Environmental changes since 13,000 cal. BP reflected in magnetic and sedimentological properties of sediments from Lake Holzmaar (Germany)

Abstract

Late- and Postglacial sediments from a German maar lake (Holzmaar) in the West Eifel Volcanic Field were investigated with rockmagnetic and sedimentological methods. The concentration of magnetic minerals is very variable and zones exist, where magnetic properties are dominated by paramagnetic minerals. Remanence carrying (ferromagnetic) minerals are dominated by a low coercivity fraction, identified by its Curie temperature and by scanning electron microscopy as titanomagnetite with a grain size range between a few microns and ≈25 μm. An additional high coercivity phase, probably hematite, is present throughout the entire record in low concentrations. Rockmagnetic results indicate the possible postdepositional dissolution of (titano-) magnetite and the authigenic growth of greigite in one confined section. A positive correlation between initial magnetic susceptibility ( κ) and sediment accumulation rate and between κ and the non-arboreal pollen percentage is observed while κ and organic carbon content show a negative correlation. These coeval variations are due to a nearly exclusively detrital sedimentary input. The variations show a broad dependence on climatic conditions for times prior to significant human activities in the region and the impact of the human settlement history afterwards. Early Holocene climatic variations, indicating two cooling events, agree with ice rafted debris events of the North Atlantic.