Crossing redox boundaries-Aquifer redox history and effects on iron mineralogy and arsenic availability

► Geochemical and mineralogical proxies of terrestrial paleo oxidation in sediments. ► Reduced Fe phases via redox-transitional co-existence to Fe hydroxides. ► Changing As control from sulphidic to oxidic, high reactivity in transition zone. ► Varying depths of oxidation front: effect on As mobilization potential to groundwater. ► As uptake in glauconite: sorption and pyrite inclusion rather than substitution.