Origin of Inorganic Carbon Isotope Excursions in Ediacaran Doushantuo Cap Dolostone at Jiulongwan Section in East Yangtze Gorges
Cai Yingxiong
An Zhihui
Yang Wenwu
Wang Ningtao
Wang Baozhong
Mei Yuping
Ding Lixue
Yang Xiaoli
Song Song
Abstract：Extremely negative inorganic carbon isotope values(δ13CV-PDB<-40‰)from the Ediacaran Doushantuo cap dolostone in East Yangtze Gorges were taken as key evidence for a methane release event,but the origin of the cap dolostone remain contested.Here we investigated carbon,oxygen,sulfur,and strontium isotopes,and major and trace element compositions in both authigenic carbonates and dolostones from the Doushantuo cap dolostone at the Jiulongwan Section.Authigenic carbonates show extremely negative inorganic carbon isotope values,remarkably wide ranges of sulfur isotope values for sulfates and pyrites,a positive δ18O(CAS,Brt)-δ34S(CAS,Brt)correlation with a low slope,and a distinctly negative Δ33Spyrite-δ34Spyrite correlation,which indicates that the extremely 13C-depleted carbonates were deposited from seawater via anaerobic oxidation of methane coupled to microbial sulfate reduction(AOM-MSR)at paleo-marine cold seeps.Redox-sensitive elements reveal that the authigenic carbonates(JF1 and JF2)were deposited in an anoxic condition,while the whole cap dolostone was deposited in transitional conditions of suboxic-anoxic-suboxic-anoxic-suboxic.Paleodepth indicators imply that the sea level in the Jiulongwan area dropped during the JF1 and JF2 stages,respectively.Results of major and trace elements and strontium isotopes demonstrate that the input of terrigenous weathered materials increased during the JF1 and JF2 stages.In Early Ediacaran Epoch,two regressions in the Jiulongwan area resulted in an anoxic environment and altered hydrochemical conditions,which is an important origin for the extremely negative inorganic carbon isotopes observed in the cap dolostone in this area.
Keywords：EdiacaranDoushantuo Formationcap dolomiteauthigenic carbonatenegative carbon isotope excursiongeochemistry
Publication Date：2025-07-30
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：18( 2566-2583 )