An effective method to distinguish between artificial and authigenic gypsum in marine sediments

Gypsum often occurs in marine sediments as an authigenic mineral, but it may also be produced artificially through oxidation of sulfide during sample storage and preparation. Therefore, the origin of the gypsum should be carefully checked, especially for those DSDP, ODP and IODP samples that have stored for a long time. It is nearly impossible to distinguish between gypsum formed by these two processes based on the mineral morphology or the sulfur and oxygen isotope methods currently used. In this study, we proposed a simple, quantitative scheme based on chemical extractions of iron and sulfur to distinguish whether the gypsum in marine sediment samples is an authigenic mineral or an artificial product formed after sample collection. The new method was tested on two suites of deep-water sediment cores sampled from Hydrate Ridge and Kaoping Slope, in which the origins of gypsum were known beforehand, and was successfully validated. Finally, the potential influence of artificial productions of elemental sulfur and jarosite on the application of this new method was evaluated and the corresponding solutions were given.