engleski

Tephra hunt in loess-paleosol sequences – towards an interdisciplinary approach for tephra detection and characterization

Loess-paleosol sequences (LPSs) are valuable terrestrial archives of mineral dust and Quaternary environmental evolution. Their paleoclimatic significance depends on reliable age control, which is nowadays often provided by correlative methods such as matching LPS paleoenvironmental data to marine and ice core archives. Almost 40 years ago, Friedrich Heller and Tungsheng Liu succeeded with a seminal breakthrough in LPS chronology by applying a combined paleomagnetic and environmental magnetic approach employing temporal changes of the Earth’s magnetic paleo-field in combination with climatically controlled stratigraphical changes in magnetic susceptibility. The limitations of this approach lie mainly in the restricted temporal resolution on shorter timescales constraint by the few existing polarity changes during the Quaternary, and the long wavelengths of climatic changes reflected by environmental magnetic parameters. For shorter time scales, dating techniques like radiocarbon and luminescence dating applied to LPSs also present challenges. Here, we propose an interdisciplinary tephrostratigraphic approach relying on in-depth mineral magnetic methods for identifying tephra layers in LPS. Tephrochronology employs tephra deposits for linking and dating paleoenvironmental and other archives. As an age-equivalent dating method, tephrochronology represents a precise volcanic-event stratigraphy utilizing age transfers from an independently dated eruption center to tephra deposits. Our integrated approach relies on the specific magnetic properties of largely non-interacting soft magnetic particles preserved especially in volcanic glass and their characterization by FORC-analyses, IRM composition unmixing and low- temperature magnetic properties. Volcanic glass represents a sample of “frozen” magma and can be unambiguously identified by geochemical and magnetic methods, and linked to known volcanic eruptions.

tephra, FORC analysis, IRM composition unmixing

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