An integrated carbon, oxygen, and strontium isotopic studies of the Lantian Formation in South China with implications for the Shuram anomaly

A pronounced negative δ13Ccarb shift (EN3 or Shuram anomaly) has been reported from the middle Ediacaran in South China and elsewhere around the world. This carbon isotope event has been interpreted to result from the remineralization of dissolved organic carbon (DOC) from a deep ocean reservoir, riverine input of oxidized fossil organic matter, or the oxidation of methane. In the present study, a high resolution carbon (both inorganic and organic), oxygen, and strontium isotope study was carried out on the Ediacaran succession at the Shiyu section, South China, to further understand the causes for the negative carbon isotope shift. Isotopically light δ13Ccarb values down to − 19.2‰ (VPDB) are observed in the middle Ediacaran Lantian Formation before carbonate δ18O values decrease from − 10‰ to − 25‰ (VPDB). These negative shifts are accompanied by elevated 87Sr/86Sr ratios ranging from 0.708715 to 0.714690. The very negative δ18O values (− 20.2‰ to − 26.7‰, VPDB) are interpreted as reflecting deglacial meltwater input, which is consistent with the associated high initial 87Sr/86Sr ratios (0.711801 to 0.714690). The onset of the middle Ediacaran glaciation may result in more intense ocean ventilation, while deglaciation may deliver more oxidants into the ocean. Both may have triggered remineralization of a deep ocean DOC reservoir, and thus led to the pronounced negative δ13Ccarb shift in the middle Ediacaran.