Stratified oceans and oxygenation of the late Precambrian environment: a post glacial geochemical record from the Neoproterozoic of W. Mongolia

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Abstract
The late Neoproterozoic (750–545 Ma) was a time of revolutionary environmental change, recurrent glaciation and tectonic upheaval, which culminated in the evolution of metazoans and animal biomineralization. Geochemical data are presented for a post glacial (∼ 700 Ma) limestone succession from W. Mongolia. 87Sr/86Sr is used to constrain the timing of early diagenetic exchange. Stratigraphic trends to high δ13C(carb)) and δ13C(org) mirror sea‐level fluctuations, which, we argue, is consistent with the hypothesis that late Precambrian ocean chemistry, was controlled by vertical stratification. Repeated establishment of stratification 700–545 Ma would have led to greater oxygen availability in the surface environment. A causal link between this oxygenation and the further evolution of animals is proposed.