COVER: Cathodolumiscence photomicrograph of fibrous dolomite marine cements filling a sheet cavity from the Cryogenian Balcanoona reef, South Australia. These cements show finely preserved cathodoluminescent growth zones and optical characteristics that indicate they originally precipitated as dolomite. Uranium isotope values of well-preserved marine cements such as these suggest anoxia and iron-rich marine conditions at ca. 650 Ma. In contrast, depositional components (red-mottled micrite at edges) and late-stage diagenetic dolomites (center, bright orange) may show uranium isotope compositions spanning almost the entire range of the Earth system. See “Integrated geochemical-petrographic insights from component-selective δ238U of Cryogenian marine carbonates” by Hood et al., p. 935–938.