Characterization of primary and secondary magnetite in marine sediment by combining chemical and magnetic unmixing techniques

We present a novel technique for quantitative unmixing of primary and secondary ferrimagnetic minerals in sediments. Hysteresis and high-resolution first-order reversal curve (FORC) measurements are performed on sediment samples before and after digestion in a citrate-bicarbonate-dithionite (CBD) solution optimized for maximum selective extraction of secondary fine-grained iron oxides. The difference between magnetic measurements of untreated and CBD-treated sample materials is used to calculate the original magnetic signature of CBD-extractable minerals. Combination of selective chemical extraction and magnetic measurements suited for the detection of single-domain particles provides a cross-check between chemical and magnetic unmixing of primary and secondary iron-oxides and resolves the non-uniqueness of numerical unmixing methods. A fully quantitative magnetic characerization of secondary ferrimagnetic minerals in a magnetofossil-rich pelagic carbonate is presented for the first time. It can be used for calibartion of recently developed fast magentic unmixing techniques. CBD-based Fe extraction from sediments with minimal clascic and/or aeolian inputs, such as pelagic carbonates, is partcularly suited for the detection of cosmogenic ⁶⁰Fe signatures from supernova explosions, because ⁶⁰Fe dilution by dissolved primary Fe-bearing minerals is minimized.