Iodine content of the carbonates from the Doushantuo Formation and shallow ocean redox change on the Ediacaran Yangtze Platform, South China

•The I/(Ca + Mg) data of the Doushantuo Fm. were reported in three sections.•The I/(Ca + Mg) data suggest a dynamic redox evolution of shallow waters.•A prominent I/(Ca + Mg) rise corresponds to the Shuram δ13Ccarb excursion.•Integrated I/(Ca + Mg) indicate redox heterogeneity during Shuram excursion.•The Shuram excursion partially recorded primary seawater signal.