REDOX STABILIZATION IN THE TERMINAL EDIACARAN: THE RECORD OF THE NAMA GROUP, NAMIBIA
Here we describe the first evidence for progressive oxygenation at a basin-scale derived from iron speciation analyses of multiple interbedded carbonate and shale sections. Data from Lower Nama Group (~550-547 Ma) outer-ramp sections indicate persistent ferruginous anoxia, whilst time-equivalent inner-ramp sections show intermittently oxic conditions, even though mid-ramp sections record persistent oxic conditions. Disruption of oxic conditions within inner-ramp settings occurs during periods of high stand and is inferred to be a consequence of incursion by deeper anoxic waters within a redox stratified water column. By contrast, upper Nama Group (~547-541 Ma) sections document a protracted basin-wide redox stabilisation, with more stable oxia found in both inner and particularly mid-ramp settings. The latter environments are characterised by larger and more ecologically complex calcifying metazoan communities. The trend towards sustained oxygenation of outer-ramp settings approaching the end of the Ediacaran indicates a deepening of the chemocline consistent with fewer incursions of anoxia into shallow waters.