SPICE through the lens of cadmium-chromium; examining Late Cambrian oxygenation in the Lower Paleozoic Alum Shale, Sweden

The combination of cadmium (Cd) and chromium (Cr) isotopic signatures of marine sedimentary archives is an emerging tool in the reconstruction of bioproductivity and redox processes in paleo-oceanographic settings. Through understanding these processes with Cd-Cr, the aim is to make interpretations of global-scale processes, such as oxygenation of the oceans and atmosphere. This present study applies the combined Cd-Cr approach to the lower Paleozoic Alum Shale, in the form of analyses of 20 carbonate-poor, organic-rich shale samples selected from the Ottenby-2 core (southern Öland, Sweden). Previously published work on this core includes biostratigraphic, major and trace element, carbon isotope, and mercury isotope data [1]. This section is of specific interest for its occurrence along the Steptoean Positive Carbon Isotope Excursion (SPICE) and its enrichment in redox-sensitive trace elements. We report data from TIMS double spike Cd and Cr analyses in the form of δ114Cd and δ53Cr values and associated concentrations ([Cd], [Cr]). Initial values for δ53Crauth range from -0.65‰ to 0.1‰ and δ114Cd values range from -0.43‰ to 0.31‰. Associated concentrations measure between 4.25 mg/kg to 17.62 mg/kg for [Cr] and 0.11 mg/kg to 44.29 mg/kg for [Cd]. Preliminary results show a shift in δ114Cd values roughly corresponding with the SPICE event. These results are compared against previously published elemental and isotopic data to evaluate for potential additional controls on concentration and fractionation of Cd and Cr in the studied shales as well as to reconstruct surface Cd and Cr isotope signatures.