Non-traditional stable isotope signatures in geological matrices as a tool for interpreting environmental changes – a review

The development of new analytical techniques enabled the precise determination of the expanded set of stable isotopes and provided new insight into existing geological issues. This review outlines recent studies of non-traditional isotope signatures in geological matrices, summarizing in one place, new data for the stable isotopes of Ca, Mg, Sr, Li, Ni, Cr, and Cu and their application in the interpretation of environmental processes. Although some, such as δ44Ca and δ26Mg, have previously been used to track changes in seawater chemistry throughout geological history, recent studies report their application as geochemical proxies of post-depositional processes. Similarly, isotopic signatures of strontium, previously used in radioactive isotope chronology, and δ7Li, used in tracing plate subduction and crust/mantle material cycling, found a new application in studies of weathering patterns. The use of δ53Cr and δ 65Cu isotope signatures, on the other hand, reflects their fractionation under different redox conditions, whereas δ60Ni, due to its adsorption and co-precipitation with sulfide species and Fe-Mn phases, is used in interpreting the contributions of different material sources. And while the isotopic signatures of all these elements indicate certain environmental conditions and processes (e.g. post-depositional processes, redox conditions, organic matter input, the contribution of sources, etc.), by combining them a more comprehensive insight into the investigated environment can be achieved.