沉积学报2025，Vol.43Issue(6)：1952-1967,16.DOI:10.14027/j.issn.1000-0550.2023.112
鄂尔多斯盆地T-OAE时期湖泊硫循环及其地质意义
Sulfur Cycle Change and Its Geological Significance During the Toarcian Oceanic Anoxic Event(T-OAE)in the Ordos Basin
摘要
Abstract
[Objective]At present,research on the Early Jurassic Toarcian Oceanic Anoxic Event(T-OAE;～183 Ma)in the Ordos Basin primarily emphasizes paleoclimate conditions,the evolution of the sedimentary environment,and biodiversity changes.However,the mechanisms governing sulfur cycling in lakes during the T-OAE remain un-clear.Consequently,further examination of the sulfur cycling mechanism is essential.[Methods]Twenty-eight sam-ples were selected from the Anya section.Mineralogy and isotope geochemistry analyses were performed on mudstone and black shale samples from the Anya section.The mechanisms of sulfur isotope fractionation during the T-OAE were investigated using major and trace elements,as well as pyrite sulfur isotopes(δ34Spy).To avoid interference from marcasite and siderite,mineral morphology and energy spectra were examined using a scanning electron microscope(SEM).[Results]The pyrite in the samples from the Anya section predominantly were tetrahedral and octahedral crystals,forming framboidal pyrite.The mineral surface exhibits a smooth texture without the presence of platy marca-site.The coexistence of radial siderite with pyrite is also observable.The δ34Spy values of these samples consistently display positive values,ranging from 2.7‰ to 14.1‰,with an average of 8.3‰.By analyzing the fluctuations in δ34Spy and total organic carbon(TOC),along with the use of geochemical indicators such as δ13C,total sulfur(TS),Corg/P,and(La/Yb)N,we delineated the evolution of the lacustrine sedimentary environment during the T-OAE into four dis-tinct stages,comprising periods characterized by high(Stages Ⅰ and Ⅱ)and low organic matter(Stages Ⅰ and Ⅱ).[Conclusions]The δ34Spy values during the T-OAE in the Anya section of the Ordos Basin align with those of atmo-spheric precipitation and surface runoff,suggesting that sulfate in the water mass serves as the primary source of sul-fur in the lake.Atmospheric precipitation and surface runoff mainly consist of dissolved sulfate ions exhibiting lacus-trine sulfate isotope compositions between 0 and 10%.However,the samples from the Anya section include black shale,mudstone,sandstone,and other low sulfur source rocks,likely resulting in smaller sulfur isotope composi-tions within the lakes.It is improbable that the sulfur isotope composition of pyrite is inherited from lacustrine sulfate.The sulfur isotopes in the pyrite of the samples are primarily influenced by the redox conditions of the lake bottom water and the organic matter content/type within the sediment.When the lake bottom water is oxygen-rich and the or-ganic matter content is low,dissolved oxygen infiltrates into sediments,activating anaerobic oxidants such as NO-2 and Mn2+,while promoting H2S reoxidation.This process leads to a positive δ34Spy shift,as described by the Rayleigh fractionation model.In contrast,when the lake bottom water is oxygen-deficient and the organic matter content high,sulfate-reducing bacteria become more active,promoting the microbial sulfate reduction(MSR)reaction,which preferentially incorporates 32S,which results in a negative δ34Spy shift.During the T-OAE,the lake redox conditions and climate underwent significant changes,exerting a substantial influence on the form,content,and fractionation of sulfur within lake.The sulfur cycle during the T-OAE in the Anya section is predominantly dictated by local and regional sedimentary environments,although it is also affected by global warming and intensified hydrological circula-tion during the T-OAE.关键词
硫同位素/黄铁矿/鄂尔多斯盆地/大洋缺氧事件Key words
sulfur isotopes/pyrite/Ordos Basin/oceanic anoxic event分类
天文与地球科学引用本文复制引用
CHEN Yang,JIN Xin,LANG XianGuo,LI BinBing..鄂尔多斯盆地T-OAE时期湖泊硫循环及其地质意义[J].沉积学报,2025,43(6):1952-1967,16.基金项目
成都理工大学沉积地质研究院创新人才培养基金项目[Innovative Talent Development Fund of Institute of Sedimentary Geology,Chengdu University of Technology] （）
