Diagenetic alteration of natural Fe-Ti oxides identified by energy dispersive spectroscopy and low-temperature magnetic remanence and hysteresis measurements

The EDS analyses confirm the LT magnetic results, Fe-rich magnetic phases dominate in the upper suboxic environment whereas Ti-rich magnetic phases comprise the majority of particles in the lower anoxic domain: The mineral assemblage of the upper suboxic environments is composed of magnetite (∼19%), titanomagnetite (∼62%), hemoilmenite (∼17%) and ∼2% other particles. In the lower anoxic sediments, reductive diagenetic alteration has resulted in more extensive depletion of the (titano-)magnetite phase, resulting in a relative enrichment of the hemoilmenite phase (∼66%). In these strongly anoxic sediments stoichiometric magnetite is barely preserved and only ∼5% titanomagnetite was detected. The remaining ∼28% comprises Ti-rich particles such as pseudobrookite or rutile.