摘要
峡东地区埃迪卡拉纪陡山沱组盖帽白云岩中异常偏负的无机碳同位素(δ^(13)C_(V‒PDB)<‒40‰),是甲烷释放的关键地质证据,但其具体成因机制尚不明确.对九龙湾剖面陡山沱组盖帽白云岩中白云岩和自生碳酸盐岩的碳、氧、硫、锶同位素及元素地球化学进行对比研究.自生碳酸盐岩极低的无机碳同位素值,极大的硫酸盐和黄铁矿硫同位素变化范围,较低的δ^(18)O_((CAS,Brt))⁃δ^(34)S_((CAS,Brt))斜率,Δ^(33)S_(pyrite)⁃δ^(34)S_(pyrite)具有的负相关性,指示古海洋冷泉环境下AOM-MSR作用参与;氧化还原敏感元素显示自生碳酸盐岩(JF1和JF2)形成于缺氧环境,整个盖帽白云岩形成于氧化(/贫氧)‒缺氧‒氧化(/贫氧)‒缺氧‒氧化(/贫氧)环境转变;古水深指标指示在JF1和JF2阶段海平面分别下降;主、微量元素及锶同位素表明,JF1和JF2阶段陆源风化物质输入增加.九龙湾地区埃迪卡拉纪早期两次海退形成的海底缺氧环境和水化学条件改变,是形成极负无机碳同位素组成的重要原因.
Extremely negative inorganic carbon isotope values(δ^(13)C_(V‒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 positiveδ^(18)O_((CAS,Brt))⁃δ^(34)S_((CAS,Brt))correlation with a low slope,and a distinctly negativeΔ^(33)S_(pyrite)⁃δ^(34)S_(pyrite)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.
作者
蔡应雄
安志辉
杨文武
王宁涛
王保忠
梅玉萍
丁丽雪
杨小莉
宋松
Cai Yingxiong;An Zhihui;Yang Wenwu;Wang Ningtao;Wang Baozhong;Mei Yuping;Ding Lixue;Yang Xiaoli;Song Song(Hubei Key Laboratory of Paleontology and Geological Environment Evolution,Wuhan 430205,China;Wuhan Center,China Geological Survey(Geosciences Innovation Center of Central South China),Wuhan 430205,China)
出处
《地球科学》
北大核心
2025年第7期2566-2583,共18页
Earth Science
基金
古生物与地质环境演化湖北省重点实验室开放基金(No.PEL⁃202305)
中国地质调查局项目(Nos.DD20190315,DD20221777,DD20230218).
关键词
埃迪卡拉纪
陡山沱组
盖帽白云岩
自生碳酸盐岩
碳同位素负偏
地球化学
Ediacaran
Doushantuo Formation
cap dolomite
authigenic carbonate
negative carbon isotope excursion
geochemistry
作者简介
蔡应雄(1981-),男,正高级工程师,主要从事同位素地球化学研究.ORCID:0000⁃0001⁃9402⁃7199.E⁃mail:whcyx0226@126.com。
