Ancient acid rains in the Ediacaran period – An alternative story for sulfate sedimentation

Abstract

Vast deposits of anhydrite and magnesite are widely distributed in the Ediacaran strata of East Siberia near the Riphean unconformity. Anhydrite-rich rocks are likely not of evaporitic origin and mostly occur in the forms of nodules, the layers of chicken-wire structures otherwise disseminated as tiny sulfatic forms amongst the terrigenous rocks. Here, we propose an alternative point of view for anhydrite origin: the enrichment and increase of sulfur content in the Ediacaran atmosphere is due to high volcanic activity. It is suggested that the ancient Earth's atmosphere could have also been influenced by powerful sulfuric acid rains that eroded the Precambrian dolomites, causing their aggressive degradation. Chemical reactions with dolomite and sulfuric acid showed that an unstable phase of bassanite occurred in the early stages, which later stabilised as anhydrite after heating as an analogue of ageing. Aggressive acids have caused global dolomite karstification of the Siberian craton with the appearance of Ediacaran strata in addition to sulfate phases, including magnesite and sulfurous phases of pyrite and barite.