A mineral magnetic characterization of Plio-Pleistocene sediment material from the Heidelberg Basin (Germany)

The Heidelberg Basin (Germany) hosts a quasi-continuous sedimentary sequence of primarily fluvial sediments with pedogenetic overprints and lacustrine intercalations. This unconsolidated succession has been shown to record a consistent magnetic polarity stratigraphy of the Quaternary and the late Neogene. Previous work has reported that sulphides and high-coercive minerals are the carriers of the remanent magnetization. Here, we provide the results of an extended mineral magnetic study that aims to disentangle the complex magnetic mineralogy. In addition, we assess the reliability of these minerals as carriers of palaeomagnetic signals. A major obstacle to the analysis of the drill cores was the large number of samples that were taken from a total core length of 1150 m. Rapid measurements on bulk samples provided only limited information on the magnetic mineralogy. In contrast, time-intensive methods such as first-order reversal curves (FORCs) or coercivity analyses, for example, yielded valuable information. The combined results of all the analyses consider the heterogeneous compositions of the sediments and indicate a varying palaeoenvironmental history. The Pliocene Iffezheim Formation was formed under alternating reducing and oxidizing conditions. Magnetite, maghemite, haematite and goethite are the predominant magnetic minerals. Sulphides were only preserved under specific conditions. The Pleistocene sediments reflect predominantly reducing conditions during sedimentation and diagenesis. Greigite, pyrite and most likely pyrrhotite have been shown to occur. Taken together, our work provides a detailed environmental magnetic record of the Plio-Pleistocene and elucidates the capabilities and limitations of rock magnetic studies performed on fluvial dominated sedimentary successions.