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The scavenging of dissolved trace metals such as chromium (Cr), molybdenum (Mo) and tungsten (W) and their authigenic enrichment in sedimentary archives mainly occur by particle shuttling that cause resolvable isotope fractionation. Because their scavenging is also dependent on the local marine redox potential and the overall marine chemical environment, the stable isotope composition of these elements in Archean sediments is widely used as paleoredox proxy. Tungsten, a new element in this tool box, is dissolved as the oxyanion tungstate (WO42-) at extremely low marine redox potentials and can thus help to reconstruct the earliest changes in the marine redox state. We tested the applicability of stable W isotopes as a new paleoredox proxy of the atmosphere-ocean system. We analyzed the delta W-186/184 of Precambrian igneous rocks to investigate the detrital background delta W-186/184 signature. This Precambrian igneous inventory (PII) shows delta W-186/184 values between -0.007 and +0.097%o, identical to the range of modern igneous crustal rocks, which indicates that the average Earth's crust delta W-186/184 remained constant over billions of years. Furthermore, we present delta W-186/184 values of euxinic sediments from the Black Sea as a modern sedimentary analog, which we then compare with delta W-186/184 data of Archean and Proterozoic black shales (3.47-2.3 Ga). Modern Black Sea sapropels reveal crustal-like delta W-186/184 values between +0.050 and +0.071%o suggesting limited authigenic enrichment of W in euxinic environments. Similarly, post-Great Oxidation Event shales (2.3 Ga) show crustal- or PII-like delta W-186/184 values indicating the deposition in euxinic or oxic environment. However, the Archean shale sample suites show elevated W concentrations and fractionated delta W-186/184 values up to +0.246%o, which we attribute to authigenic enrichment of heavy seawater W in a ferruginous setting. Thus, black shales delta W-186/184 values can help to distingu