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Tephra Detection; ITRAX; Lake Suigetsu; Lake sediment; μXRF core scanning
Abstract:
Here, we evaluate the ability of micro X-ray fluorescence (µXRF) core scanning to identify non-visible volcanic ash (cryptotephra) layers in sedimentary records. Its suitability is assessed using the annually resolved lacustrine sediments of Lake Suigetsu (Japan) for which there is high-resolution ITRAX µXRF core scanning data, and a detailed crypto-tephrostratigraphy (formerly established via density separation techniques). The studied core sections contain 10 visible and 30 cryptotephra markers that span a range of glass concentrations (from 1000 to >20 000 shards per gram of dried sediment) and compositions (basalts, trachy-andesites, phonolites, trachytes and rhyolites), thus providing an ideal case study. The ITRAX core scanner produced recognisable µXRF elemental responses for the visible ash layers, including those just 1 mm thick. However, just 10% of the cryptotephra layers could be unequivocally identified. Although this study demonstrates that µXRF core scanning should not be used as an independent method within a similar geological setting, we show it can provide a powerful tool alongside traditional techniques. Where detected, µXRF profiles can verify and refine cryptotephra positions (here to a sub-millimetre resolution), and help establish reworking signatures. These insights create possibilities for ultra-precise synchronisation of records, improved chronological modelling and help generate more complete eruption histories.
