Figure 1 Econ Geol 94
Figure 1. Combination pH-pE (Eh) diagram showing redox donation of black shales based on mineral dissolution (from Quinby-Hunt and Wilde, 1994). Boundaries are based on dissolution of minerals from concentrations observed oxic seawater. Reduction of NO3 to N2(indicatedby the line of short dashes) is usually considered the boundary between oxic and anoxic conditions. Reduction of SO42-- to H2S
and HS- (long dashes) roughly marks the boundary between oxic and sulfidic species. Note that the correspondence is not exact --pyrite can appear within the sulfate stability zone.