陕西省紫阳县下寒武统黑色岩系有机地球化学特征  

Organic Geochemical Characteristics of Lower Cambrian Black Rock Series in Ziyang,Shaanxi Province

作　　者：赵慧博 冯彩霞[1] 刘燊[1] 刘芳晓[3] Zhao Huibo;Feng Caixia;Liu Shen;Liu Fangxiao(Department of Geology,Northwest University,Xi’an 710068,China;Xi’an Center of Geology Survey,China Geology Survey,Xi’an 710054,China;CCTEG Xi’an Research Institude(Group)Co.,Ltd.,Xi’an 710077,China)

机构地区：[1]西北大学地质学系,西安710068 [2]中国地质调查局西安地质调查中心,西安710054 [3]中煤科工西安研究院(集团)有限公司,西安710077

出　　处：《吉林大学学报（地球科学版）》2023年第4期1016-1032,共17页Journal of Jilin University：Earth Science Edition

基　　金：陕西省自然科学基金项目(2020JM-423,2017JM4031)。

摘　　要：陕西省紫阳县下寒武统黑色岩系富含大量有机质和丰富的金属元素(Ba、V、Cr、Ni、Mo、Au等),但对黑色岩系的有机地球化学特征仍缺乏应有的认识。本研究借助偏光电子显微镜、扫描电镜形貌观察,有机碳分析和饱和烃气相色谱-质谱分析等实验方法,针对研究区黑色岩系的有机质与无机质耦合关系、有机质来源、成熟度和沉积环境开展了系统探讨。研究结果表明:研究区有机质质量分数较高,有机质呈分散态和聚集态两种方式赋存,其中分散态的有机质与黏土矿物关系密切。总有机碳(TOC)质量分数均值为2.95%,岩性差异、黄铁矿含量及类型均会影响TOC质量分数的变化。黑色岩系样品富含正构烷烃、类异戊二烯烃、萜类化合物、甾类化合物等生物标志化合物,其中:正构烷烃碳数分布范围为C14—C34,呈明显的双峰式分布特征,且无明显奇偶优势;类异戊二烯烃指征显示具明显的植烷优势,具较低的Pr/nC17值(0.36)和Ph/nC18值(0.50);萜类化合物的丰度由高到底顺序为三环萜烷>五环三萜烷>四环萜烷,少量γ-蜡烷,三环萜烷C21-C23-C24呈不对称倒“V”字型分布,具较低的Tm/Ts值(1.03);甾类化合物中规则甾烷分布呈C29>C27>C28的不对称“V”字型分布,具较低的C27重排甾烷/C27规则甾烷值(0.18)和孕甾烷/C29-20R甾烷值(0.84)。综上所述,有机质母体主要为海相低等生物(如菌藻类、微生物)和浮游生物,部分岩石(如硅质岩)中有机质来源有少量陆源低等植物的参与;岩石整体有机质具有较高的成熟度,但未达到过成熟的阶段;黑色岩系来自半封闭—封闭缺氧还原的偏碱性海水环境,盐度较低。The Lower Cambrian black rock series in Ziyang,Shaanxi Province is rich in organic matter and metal elements(Ba,V,Cr,Ni,Mo,Au),while there is still a lack of understanding of its organic geochemical characteristics.Based on the experimental results of polarized electron microscope,morphology under scanning electron microscope,organic carbon(TOC)and saturated hydrocarbon gas chromatography-mass spectrometry(GC-MS),the coupling relationship of organic matter and inorganic matter,organic matter source and maturity,sedimentary environment were discussed.The results show that the content of organic matter is high in the study area,and there are two kinds of occurrence modes,dispersed organic matter and aggregated organic matter.The relationship between dispersed organic matter and clay minerals is close.The average total organic carbon(TOC)content was 2.95%,affected by lithologic differences,pyrite content and types.All the samples were rich in n-alkanes,isoprenoids,steroids and terpenes.The distribution range of carbon number was from C 14 to C 34,which showed obvious bimodal distribution characteristics and no obvious odd-even advantage.Isoprenoid alkenes indications showed obvious phytoalkane advantage,with low value of Pr/n C_(17)(0.36)and Ph/n C 18(0.50);The abundance of terpenoids was tricyclic terpane>pentacyclic terpane>tetracyclic terpane,a small amount of gamma wax,and the distribution of tricyclic terpane C_(21)-C_(23)-C_(24) is asymmetric inverted“V”with low average value of Tm/Ts ratio(1.03);The distribution of regular steranes in steroids showed an asymmetric“V”distribution of C_(29)>C_(27)>C_(28) with low average ratio of C 27 rearranged steranes/C 27 regular steranes(0.18)and pregnane/C_(29)-20r steranes(0.84).As indicated above,the origin of organic matter is mainly marine lower organisms(such as bacteria,algae,and microorganisms)and plankton,and a small amount of terrestrial lower plants are involved in the source of organic matter in some rocks(siliceous rocks);The organic matter of the whol

关 键 词：下寒武统 有机地球化学 生物标志化合物 黑色岩系 陕西紫阳 

分 类 号：TE12[石油与天然气工程—油气勘探]