Deposition or diagenesis? Probing the Ediacaran Shuram excursion in South China by SIMS

http://manuscript.elsevier.com/S0301926822001206/pdf/S0301926822001206.pdf

An authigenic response to Ediacaran surface oxidation: Remarkable micron-scale isotopic heterogeneity revealed by SIMS

Ediacaran carbon cycling and Shuram excursion recorded in the Tarim Block, northwestern China

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

The late Ediacaran Shuram Excursion (SE) records the most prominent negative δ13C excursions (δ13C = −12‰) during Earth’s history. It has been hypothesized to have resulted from oxidation of dissolved organic matter, diagenetic or authigenic precipitates. However, the origin of the SE remains enigmatic; current models face challenges regarding the significant amount of atmospheric oxygen needed to balance such extensive oxidation and sustained inputs of light carbon with extremely negative C isotope compositions. Here, we show that the Doushantuo Formation at the Jiulongwan section in South China, a key stratum recording the SE event, contains mineralogical and geochemical signatures related to igneous processes. Both the occurrence of ankerite, feldspar, moissanite and euhedral quartz in the SE samples and the relatively consistent Ce anomalies of carbonate and O isotopes of quartz indicate a contribution from an igneous source. In particular, the SE samples have trace element and C isotope compositions similar to those of recycled carbonatites formed by decarbonation and melting of sedimentary carbonate rocks. These observations suggest that the deep cycle of ancient carbonate rocks, which were subjected to decarbonation during subduction, melting and eruption related to the breakup of the Rodinia supercontinent, contributed to the SE. This igneous model for the SE may provide a connection between the deep and shallow carbon cycles of the Earth.

Junhua Li

Papers

The largest negative carbon isotope excursions in Neoproterozoic carbonates caused by recycled carbonatite volcanic ash