Records of the Ediacaran carbon cycle (635–541 million years ago) include the Shuram excursion (
The Ediacaran Doushantuo Formation in South China is a prime target for geobiological investigation because it offers opportunities to integrate chemostratigraphic and paleobiological data. Previous studies were mostly focused on successions in shallow‐water shelf facies, but data from deep‐water successions are needed to fully understand basinal redox structures. Here, we report δ13Ccarb, δ13Corg, δ34Spyr, δ34
- NSF-PAR ID:
- 10028544
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Geobiology
- Volume:
- 15
- Issue:
- 4
- ISSN:
- 1472-4677
- Page Range / eLocation ID:
- p. 552-571
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract 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 theSE . 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 theSE is a primary marine signature. Data compilations demonstrate that theSE was also accompanied globally by parallel negative shifts of δ34S of carbonate‐associated sulfate (CAS ) and increased87Sr/86Sr ratio and coastalCAS concentration, suggesting elevated continental weathering and coastal marine sulfate concentration during theSE . In light of these observations, we propose a heterogeneous oxidation model to explain the high spatial heterogeneity of theSE and coexisting δ13Corgrecords of the Doushantuo, with likely relevance to theSE in other regions. In this model, we infer continued marine redox stratification through theSE 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 theSE , future models must consider the evidence for spatial heterogeneity in δ13C presented in this study. -
Abstract The Ediacara biota features the rise of macroscopic complex life immediately before the Cambrian explosion. One of the most abundant and widely distributed elements of the Ediacara biota is the discoidal fossil
Aspidella , which is interpreted as a subsurface holdfast possibly anchoring a frondose epibenthic organism. It is a morphologically simple fossil preserved mainly in siliciclastic rocks, which are unsuitable for comprehensive stable isotope geochemical analyses to decipher its taphonomy and paleoecology. In this regard, three‐dimensionally preservedAspidella fossils from upper Ediacaran limestones of the Khatyspyt Formation in the Olenek Uplift of northern Siberia offer a rare opportunity to leverage geochemistry for insights into their taphonomy and paleoecology. To take advantage of this opportunity, we analyzed δ13Ccarb, δ18Ocarb, δ13Corg, δ34Spyr, and iron speciation of the KhatyspytAspidella fossils and surrounding sediment matrix in order to investigate whether they hosted microbial symbionts, how they were fossilized, and the redox conditions of their ecological environments.Aspidella holdfasts and surrounding sediment matrix show indistinguishable δ13Corgvalues, suggesting they did not host and derive significant amount of nutrients from microbial symbionts such as methanogens, methylotrophs, or sulfide‐oxidizing bacteria. δ13Ccarb, δ18Ocarb, and δ34Spyrdata, along with petrographic observations, suggest that microbial sulfate reduction facilitated the preservation ofAspidella by promoting early authigenic calcite cementation in the holdfasts before matrix cementation and sediment compaction. Iron speciation data are equivocal, largely because of the low total iron concentrations. However, consideration of published sulfur isotope and biomarker data suggests thatAspidella likely lived in non‐euxinic waters. It is possible thatAspidella was an opportunistic organism, colonizing the seafloor in large numbers when paleoenvironments were favorable. This study demonstrates that geochemical data of Ediacaran fossils preserved in limestones can offer important insights into the taphonomy and paleoecology of these enigmatic organisms living on the eve of the Cambrian explosion. -
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