The ratio of tellurium and selenium in geological material as a possible paleo-redox proxy

Only few data for both tellurium and selenium in different geological materials including international reference materials have been available so far. In this study, the Te/Se ratio has been investigated in more detail to provide a better understanding of the correlation of these two elements in the geological environment. Nine international reference materials (IRMs) and 79 different geological samples spanning a wide range of formation times and conditions from the Paleoproterozoic to present were analyzed with quadrupole dynamic reaction cell (DRC)-ICP-MS. These samples include basalts, shales, river and beach sediments, loess, dolomites, a recent cold water coral, Precambrian manganese- and iron-formations and Cenozoic marine ferromanganese nodules and crusts. A wide range of concentrations between 0.01 and 1.5 μg/g for Se and 0.01 and 90 μg/g for Te was measured, and the most interesting feature was found to be the Te/Se ratio in the different geological matrices. While most rock and sediment samples fall within the range of Te/Se ratios typical of the average Earthʹs crust, a significant enrichment of Te over Se is evident for modern marine Mn–Fe oxide precipitates, with the most pronounced Te enrichment found for hydrogenetic ferromanganese crusts, which form under fully oxidizing conditions. The apparent positive trend of the degree of Te/Se fractionation with the redox potential of the formation environment suggests that the Te/Se ratio may represent a potential (paleo)proxy for redox environments.