An integrated chemostratigraphic (δ13C-δ18O-87Sr/86Sr-δ15N) study of the Doushantuo Formation in western Hubei Province, South China

Abstract

High-resolution isotopic analyses were conducted on core samples from the Ediacaran Doushantuo Formation at the Wangjiapeng section, western Hubei Province in South China, whereby two laterally traceable, negative δ13Ccarb excursions (EN1 and EN3) were recognized. The magnitude and duration of these excursions permit intra-basinal and inter-basinal correlation, which indicates that they probably represent a global change in seawater composition. The occurrence of decoupled δ13Ccar-δ13Corg with almost invariable δ13Corg values at Wangjiapeng, Zhongling, Yangjiaping sections is consistent with remineralization of a dissolved organic carbon (DOC) pool by means of sulfate reduction, as recorded in EN3. The synchronous presence of EN3, a shift to higher 87Sr/86Sr and decrease of Mn and Fe contents and δ15N values together points to a glacial influence whereby oxygenation and remineralization of reduced carbon produced 13C-depleted DIC. Glaciations cause a drop in sea level, which itself leads to increased continental shelf area to be exposed to surface weathering, and ultimately to enhanced delivery of radiogenic 87Sr. The increase of 87Sr/86Sr ratios, sulfate and phosphate are consequences of surface runoff into oceanic environments and such perturbations induce biogeochemical changes.