The depositional redox conditions of Fe-speciation reference materials (BHW and WHIT) using redox-sensitive trace metal enrichment

Iron speciation has emerged as a robust proxy for discerning oceanic redox conditions; nonetheless, it is subject to certain limitations. Specifically, the applicability of the degree of pyritization is contingent upon the presence of unequivocal evidence of an anoxic water column and its discriminatory capacity is limited to distinguish between ferruginous (anoxic) and euxinic conditions. This study highlights that through the integration of redox-sensitive trace metal enrichment data with Fe-speciation data, the depositional redox conditions for marine sediments can be established with greater certainty. Recently, a set of dedicated geological reference materials (BHW and WHIT) have been developed for validating the Fe-speciation analytical results for redox reconstruction studies; however, to the best of our knowledge, these reference materials are not characterized for trace and rare earth elements (REEs). In this connection, the BHW (oxic) and WHIT (anoxic) reference materials are measured for major, trace and REEs. After careful statistical considerations for these reference standards, a complete set of trace and REEs is reported. Furthermore, considering BHW and WHIT as oxic and anoxic end-members, respectively, the utility of trace metal enrichment and Fe-speciation data in combination has been discussed. The trace and REE concentrations of BHW and WHIT reported in this study will enhance their applicability as a reference material to understand ocean chemistry and the oxidation state of the ancient oceans.