Evaporite deposition in the mid-Neoproterozoic as a driver for changes in seawater chemistry and the biogeochemical cycle of sulfur

We utilized a novel approach to modeling the oceanic sulfur cycle by combining delta 34S and Delta 33S curves from sulfate evaporite minerals in order to investigate redox conditions during the mid-Neoproterozoic. This technique allowed us to estimate the oxidized and reduced proportions of the total oceanic sulfur sink. Isotopic data from the mid-Neoproterozoic Minto Inlet Formation (Victoria Island, Northwest Territories, Canada; ca. 850 Ma) show a limited range (16.8 ppm + or -1.4 ppm) in delta 34S of seawater sulfate and a sulfur cycle that is strongly shifted toward the sulfate sink (pyrite burial fraction, (f)p, =0.2), suggesting oxidizing conditions in the ocean and atmosphere at the time of deposition. These evaporites and others, which were deposited contemporaneously within a huge intracontinental basin, acted as a chemical pump, removing sulfate from the oceans and oxygen from the atmosphere to be buried as sulfate evaporites.