Barite in the Ediacaran Doushantuo Formation and its implications for marine carbon cycling during the largest negative carbon isotope excursion in Earth’s history

•Doushantuo excess Ba shows a rapid increase with a lateral gradient over the Shuram Excursion.•Barites at Jiulongwan and Siduping were respectively formed in the SMTZ and upwelling water column.•Higher δ34S in barite than in CAS indicate limited influence of methane oxidation on Shuram at JLW.•Reverse spatial pattern of Ce/Ce* versus Baex indicates productivity control on local oceanic oxygenation during the Shuram.•Oxidation of DOC upwelled to the ocean-surface layer contributes to the Shuram Excursion.