地质学报2025，Vol.99Issue(6)：1918-1927,10.DOI:10.19762/j.cnki.dizhixuebao.2025046
扬子陆块埃迪卡拉纪早期海洋铁同位素组成演化及其地质意义
Iron isotope evolution of the early Ediacaran cap carbonate on the Yangtze block and its geological implications
摘要
Abstract
As a key element in biogeochemical cycles,iron provides critical insights into the evolution of marine environments.Its isotopic composition(δ56Fe)is particularly valuable for unraveling environmental conditions and controlling mechanisms during the early Ediacaran Period,offering essential tracers for marine environmental evolution and its impact on biological development.This study investigates the cap carbonate of the Ediacaran Doushantuo Formation from the Jiulongwan section in the eastern Three Gorges,Yangtze block.Using sequential dilute acetic acid leaching to extract carbonate-associated iron isotope signatures,we reconstructed a three-stage evolutionary pattern of seawater iron isotope composition(δ56Fe)during cap carbonate deposition:an initial slight negative excursion,a transient mid-stage positive shift,and a terminal extreme negative deviation.These isotopic shifts document fundamental transformations in marine redox conditions and iron cycling mechanisms.Our findings reveal distinct geological controls for each phase:the early negative excursion reflects iron oxide precipitation driven by glacial meltwater influx;the mid-stage positive fluctuation correlates with enhanced pyrite burial under anoxic conditions;and the late extreme negative deviation signals large-scale iron oxide deposition.Collectively,these processes indicate that early Ediacaran oceans transitioned through a"suboxic→reducing→ weakly oxidized"redox trajectory.During late cap carbonate deposition,intensified seawater oxygenation terminated transient reducing environments,suppressed sulfide(S2-)production,and significantly lowered dissolved ferrous iron(Fe2+)concentrations.This environmental shift created favorable conditions for the radiation of early eukaryotes and multicellular algae,offering novel isotopic geochemical constraints to elucidate the co-evolutionary mechanisms between the biosphere and Earth's surface systems during the Ediacaran Period.关键词
盖帽碳酸盐岩/铁同位素/九龙湾剖面/陡山沱组/扬子陆块Key words
cap carbonate/iron isotope/Jiulongwan section/Doushantuo Formaion/Yangtze block引用本文复制引用
闫斌,朱祥坤,李津,马健雄..扬子陆块埃迪卡拉纪早期海洋铁同位素组成演化及其地质意义[J].地质学报,2025,99(6):1918-1927,10.基金项目
本文为国家重点研发计划地球系统与全球变化重点专项项目(编号 2022YFF0800104)和中国地质调查局地质调查项目(编号 DD20221649)联合资助的成果. （编号 2022YFF0800104）
