Characteristics and geological significance of carbon and oxygen isotopes of the Permian Lucaogou Formation dolomite in the southern Junggar Basin,northwestern China

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外文摘要：Anomalously positive δ13C values in ancient dolomites are very rare.Dark gray argillaceous rocks of the lacustrine sediments of the Permian Lucaogou Formation are important source rocks in the Junggar Basin,and dolomites of varying thicknesses from 10 cm to 150 cm are often interspersed in argillaceous rocks.Based on the study of petrographic sections,this paper systematically analyzes the carbon and oxygen isotopes of dolomite and discusses the causes of abnormally high carbon isotope values and their significance in reconstructing paleoenvironment and paleoclimate.The results show that carbon isotope values are abnor-mally high in the dolomite of Lucaogou Formation,and the δ13C value is between+3.2 ‰ PDB and+19.6‰ PDB,with an average of+9.7‰ PDB.The δ18O values range from-17.4‰ PDB to-1.7‰ PDB,with an average of-8.1‰PDB.From the lower part to the upper part of the Lucaogou Formation,the carbon isotope value gradually increases and becomes increasingly positive,and the carbon isotope of the dolomite deposited near the shore is more positive than that of the dolomite deposited far from the shore.The anomalously positive δ13C of the dolomite is mainly caused by microbial methanogenesis,with some contribution from evaporation.Microor-ganisms are mainly distributed at the redox interface.Evaporation controls the salinity and fluctuation of the redox interface in sedimentary water.The positive deviation difference in carbon isotopes between nearshore and offshore sedimentary dolomites may be related to the location of the redox interface during deposition.Together,the petrographic features and carbon and oxygen isotope signatures of the sections reflect the gradual evolution of the paleolake from a hydrologically open environment to a hydrologically closed one and the possible transition of the paleoclimate from a relatively warm to an arid condition,which is possibly a geochemical response to global climate change in the Permian period.

外文关键词：

Junggar BasinLucaogou FormationDolomitePositive carbon isotope anomalyPaleoenvironment

作者：

Gang Liu、Guo-Zhi Wang、Na Li、Hong-Ling He、Nan-Nan Lu、Qing Lei、Zi-Ang Wang

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作者单位：

College of Earth and Planetary Sciences,Chengdu University of Technology,Chengdu 610059,Sichuan Province,China

National Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Chengdu University of Technology,Chengdu 610059,Sichuan Province,China

Hebei Survey Institute of Coal Geology,Xingtai 054000,Hebei Province,China

Sichuan Earthquake Agency,Chengdu 610041,Sichuan Province,China

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出版年：

2024

DOI：

10.1016/j.jop.2024.08.008

古地理学报(英文版)

影响因子：0.186

ISSN：

年,卷(期)：2024.13(4)