Mineral magnetic properties of Late Weichselian‐Holocene sediments from the northwestern Baltic Proper

Abstract

Mineral magnetic measurements were carried out on twelve sediment cores from the northwestern part of the Baltic Proper. The purpose was to use magnetic properties to correlate sediment sequences and to investigate changes in depositional conditions (e.g. rate of sedimentation and redox conditions). A general lithostratigraphy consisting of five units was established based mainly on mineral magnetic properties. Sediment has been deposited from the time of the Baltic Ice Lake (before 10 300 14C years BP) to the present, i.e. since the Late Weichselian deglaciation. Five of the cores were also investigated by means of biostratigraphical methods and three by 14C dates. Based on the general stratigraphy and hiatuses, variations in sedimentation rate were identified. The occurrence of authigenically formed ferrimagnetic greigite (Fe3S4), mainly in sediments deposited during the brackish Yoldia Sea and Litorina Sea stages, is implied. These sequences are characterized by low S‐ratios and high SIRM/z ratios. Glacial clay, deposited in freshwater during the Baltic Ice Lake stage and the early freshwater phase of the Yoldia Sea stage, seems to be unaffected by diagenetic processes. Gyttja clay, deposited in the Litorina Sea, has significantly lower susceptibility and SIRM than in the underlying clay. Dissolution of magnetic iron oxides (e.g. magnetite and hematite) in an anoxic environment was suggested as an explanation.