豫西宜阳地区三叠纪早期孙家沟组上段湖相碳酸盐岩碳氧同位素和古环境分析  

Carbon and oxygen isotopic composition and palaeoenvironment analysis of lacustrine carbonate rocks in the upper member of Early Triassic Sunjiagou Formation,Yiyang area,western Henan Province

作　　者：曹高社[1,2] 余爽杰 孙凤余 方磅磅[1] 徐海亭 CAO Gaoshe;YU Shuangjie;SUN Fengyu;FANG Bangbang;XU Haiting(Institute of Resources&Environment,Henan Polytechnic University,Jiaozuo,Henan,454000,China;Collaborative Innovation Center of Coalbed Methane and Shale Gas for Central Plains Economic Region,Hetian Province,Jiaozuo Henan 454000,China)

机构地区：[1]河南理工大学资源环境学院,河南焦作454000 [2]中原经济区煤层(页岩)气河南省协同创新中心,河南焦作454000

出　　处：《地质学报》2019年第5期1137-1153,共17页Acta Geologica Sinica

基　　金：全国油气资源战略选区调查与评价项目(编号1211302108023-2);河南省两权价款项目(编号20111-36-8)资助成果

摘　　要：孙家沟组是华北板块二叠纪和三叠纪转折时期的沉积记录,选择记载气候变化的材料,揭示气候的连续性变化,对于分析华北板块在这一转折时期古环境的重大变革具有重要意义。本项研究选择地层出露良好的华北板块南部豫西宜阳地区,以孙家沟组上段呈韵律型发育的薄层碳酸盐岩为研究对象,分析这些碳酸盐岩层中碳酸盐矿物的碳氧同位素组成及其变化,结合宏观沉积环境的分析,揭示这些碳酸盐岩层的成因,以及它们所蕴含的古环境信息。研究表明,孙家沟组上段碳酸盐岩的碳酸盐矿物主要为自生碳酸盐,且没有发生显著的后期变化,碳氧同位素组成及其变化可以用于古环境的重建。根据孙家沟组上段碳酸盐岩碳氧同位素的组成和受控因素,结合宏观沉积环境分析,认为孙家沟组上段的盐酸盐岩形成于湖盆环境。δ^(18)O>-7.97‰时,δ^(13)C和δ^(18)O呈明显的正相关关系,湖泊处于封闭环境,碳酸盐矿物富含白云石,且结晶程度较差;δ^(18)O<-7.97‰时,δ^(13)C和δ^(18)O呈明显的负相关关系,湖泊处于开放环境,碳酸盐矿物富含镁方解石,且结晶程度较好。根据孙家沟组上段由下部到上部碳酸盐岩碳氧同位素的变化,揭示出当时的湖泊环境经历了由相对开放到相对封闭,再到相对开放的演化,并显示出温度变低,湿度变小,植被变差的演化趋势。孙家沟组上段湖泊环境的形成可能与南部北秦岭造山带的隆升有关,薄层碳酸盐岩层与上覆紫色泥岩层组成的韵律层主要与气候变化引起的降雨量有关。孙家沟组上段所记录的古环境及其变化与全球二叠纪末期生物大灭绝以后陆地环境的变化规律相吻合。The Sunjiagou Formation records the sedimentary history of the Permian and Triassic transition period in the North China Block.Therefore,its study is of great significance to understand the momentous paleoenvironment changes of North China Block during this transition period.C and O analysis was conducted for the rhythmic thin carbonate rocks in the upper member of Sunjiagou Formation,which crop out in the Yiyang area of western Henan Province in the south of North China Block,to reveal the cause of formation of these carbonate rocks beds and their implication for paleoenvironment.The results show that the carbonate minerals in the upper member of Sunjiagou Formation are mainly authigenic carbonates,and there are no significant changes after diagenesis.Therefore,C and O isotope compositions and their changes can be used to reconstruct the paleoenvironment.According to the composition and controlled factors of C and O isotopes in the upper member of Sunjiagou Formation,and combined with the analysis of macroscopic sedimentary environment,it is considered that the carbonate rocks in the upper member of Sunjiagou Formation was formed in the inland lacustrine basin environment.Whenδ18 O>-7.9‰,δ13C and δ18O are positively correlated,indicating that the lake was close and carbonate minerals consisted mainly of dolomite with poor crystallization;whenδ18 O<-7.97‰,δ13C and δ18O are negatively correlated,suggesting that the lake was open and carbonate minerals consisted mainly of magnesium calcite with good crystallization.The vertical variation of C-O isotopes of the carbonate rocks from lower to upper parts in the upper member of Sunjiagou Formation reveals that the lake environment underwent the evolution from relatively open to relatively close,then to relatively open,suggesting an evolution trend of lower temperature,lower humidity and worse vegetation.The formation of lacustrine environment in the upper member of Sunjiagou Formation may be related to the uplift of the North Qinling Orogenic Belt,and the rhy

关 键 词：孙家沟组 碳酸盐岩 碳氧同位素 古环境 豫西 

分 类 号：P597[天文地球—地球化学] P532[天文地球—地质学] P588.245