Magnetic properties of Iron-Phosphate mineral in Early Quaternary lacustrine deposits of Niederschönhagen, NW Germany — a paleoclimate implication

The Early Quaternary lacustrine deposits in the Niederschönhagen area (Detmold, NW Germany) represent an important archive for the paleoclimate record in continental northwestern Europe during the transition from the warm Pliocene to the cold Pleistocene. Niederschönhagen belongs to a subrosion series in the Weser Uplands in northwestern Germany. These subrosion structures were formed by the leaching of subsurface evaporitic rocks during the early Cenozoic. A large collapsed structure at Niederschönhagen resulted in the deposition of 170 m thick lacustrine deposits that span the latest Pliocene/earliest Pleistocene to present. Magnetostratigraphic analysis suggest a time span of ~2.7 – 1.9 Ma for the deposition of the lacustrine deposits at Niederschönhagen.

Our sedimentologic observation combined with X-ray diffraction (XRD) analyses indicate the presence of vivianite minerals in the context of greyish mudstone, which occurs between 140 m and 148 m. Vivianite is an authigenic ferrous iron phosphate mineral (Fe3(PO4)2·8H2O), associated with the development of redox conditions at the bottom of lakes. Dependence of magnetic susceptibility (MS) on the temperature of natural iron phosphate mineral are studied. The thermal MS curves for vivianite on heating curves shows an increase at 420 – 480 °C, and unstable magnetite (maghemite) is produced.

Our results suggest that northwestern Germany experienced a wet period during the latest Pliocene and earliest Pleistocene. This abstract is part of ongoing research, the main goal of which is to establish a rigid stratigraphic framework for the 170 m long lacustrine deposit of Niederschönhagen.