title: Uncovering the spatial heterogeneity of Ediacaran carbon cycling.
abstract: Records of the Ediacaran carbon cycle (635-541 million years ago) include the Shuram excursion (SE), the largest negative carbonate carbon isotope excursion in Earth history (down to -12‰). The nature of this excursion remains enigmatic given the difficulties of interpreting a perceived extreme global decrease in the δ13C of seawater dissolved inorganic carbon. Here, we present carbonate and organic carbon isotope (δ13Ccarband δ13Corg) records from the Ediacaran Doushantuo Formation along a proximal-to-distal transect across the Yangtze Platform of South China as a test of the spatial variation of the SE. Contrary to expectations, our results show that the magnitude and morphology of this excursion and its relationship with coexisting δ13Corgare highly heterogeneous across the platform. Integrated geochemical, mineralogical, petrographic, and stratigraphic evidence indicates that the SE is a primary marine signature. Data compilations demonstrate that the SE was also accompanied globally by parallel negative shifts of δ34S of carbonate-associated sulfate (CAS) and increased87Sr/86Sr ratio and coastal CAS concentration, suggesting elevated continental weathering and coastal marine sulfate concentration during the SE. In light of these observations, we propose a heterogeneous oxidation model to explain the high spatial heterogeneity of the SE and coexisting δ13Corgrecords of the Doushantuo, with likely relevance to the SE in other regions. In this model, we infer continued marine redox stratification through the SE but with increased availability of oxidants (e.g., O2and sulfate) limited to marginal near-surface marine environments. Oxidation of limited spatiotemporal extent provides a mechanism to drive heterogeneous oxidation of subsurface reduced carbon mostly in shelf areas. Regardless of the mechanism driving the SE, future models must consider the evidence for spatial heterogeneity in δ13C presented in this study.
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan, China.
authors.forename: C
authors.initials: C
authors.lastname: Li
authors.affiliation: Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA, USA.|Department of Earth Sciences, University of California, Riverside, CA, USA.
authors.forename: D S
authors.initials: DS
authors.lastname: Hardisty
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan, China.
authors.forename: G
authors.initials: G
authors.lastname: Luo
authors.affiliation: State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, China.
authors.forename: J
authors.initials: J
authors.lastname: Huang
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan, China.|State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, China.|Department of Geology, University of Cincinnati, Cincinnati, OH, USA.
authors.forename: T J
authors.initials: TJ
authors.lastname: Algeo
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan, China.
authors.forename: M
authors.initials: M
authors.lastname: Cheng
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan, China.
authors.forename: W
authors.initials: W
authors.lastname: Shi
authors.affiliation: Faculty of Earth Sciences, China University of Geosciences, Wuhan, China.
authors.forename: Z
authors.initials: Z
authors.lastname: An
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan, China.
authors.forename: J
authors.initials: J
authors.lastname: Tong
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan, China.
authors.forename: S
authors.initials: S
authors.lastname: Xie
authors.affiliation: State Key Laboratory of Marine Environmental Sciences, Xiamen University, Xiamen, China.
authors.forename: N
authors.initials: N
authors.lastname: Jiao
authors.affiliation: Department of Earth Sciences, University of California, Riverside, CA, USA.
authors.forename: T W
authors.initials: TW
authors.lastname: Lyons
mesh_terms: D057486:Carbon Cycle; D002247:Carbon Isotopes / Q000032:analysis*; D002681:China; D005580:Fossils; D019015:Geologic Sediments / Q000737:chemistry*
chemical_list: D002247:Carbon Isotopes
keywords: Doushantuo Formation; Ediacaran carbon cycle; Shuram excursion; spatial heterogeneity; surface-ocean oxygenation