合川盐井溪嘉陵江组第二段盐溶角砾岩-次生灰岩的碳氧同位素组成  

Carbon and oxygen isotope composition of evaporite-solution breccia-secondary limestone of Member 2 of Triassic Jialingjiang Formation in Hechuan,eastern Sichuan Basin,China

作　　者：李小宁[1] 黄思静[1] 胡博[1] 黄可可[1] 黄树光[1] 陈永梅[1] 

机构地区：[1]油气藏地质及开发工程国家重点实验室成都理工大学,成都610059

出　　处：《成都理工大学学报（自然科学版）》2015年第6期734-745,共12页Journal of Chengdu University of Technology: Science & Technology Edition

基　　金：国家自然科学基金资助项目(41272130)

摘　　要：以四川盆地东部合川盐井溪剖面三叠系嘉陵江组第二段的盐溶角砾岩-次生灰岩为重点研究对象,在薄片观察、阴极发光和元素分析的基础上,探讨了盐溶角砾岩-次生灰岩和相邻地层中微晶灰岩、微晶白云岩的元素地球化学特征和碳、氧同位素组成。研究表明:盐溶角砾岩-次生灰岩锰、锶的质量分数和δ^(13) C、δ^(18) O平均值分别为268×10^(-6)、120×10^(-6)、-5.80‰和-8.97‰,微晶灰岩锰、锶的质量分数和δ^(13) C、δ^(18) O平均值分别为142×10^(-6)、767×10^(-6)、-1.60‰和^(-6).31‰。与相邻地层的微晶灰岩相比,盐溶角砾岩-次生灰岩具有较高的锰含量、较低的锶含量、较负的碳、氧同位素组成,显示盐溶角砾岩-次生灰岩的地球化学特征代表了表生成岩环境,其碳源主要与近地表大气水环境的CO_2有关,并可能掺和细菌硫酸盐还原作用产生的CO_2,氧除与近地表大气水有关外,并可能继承了硫酸盐中的氧;微晶灰岩则对海水地球化学信息具有更好的代表性。相邻地层微晶白云岩的锰、锶的质量分数和δ^(13) C、δ^(18) O平均值分别为291×10^(-6)、98×10^(-6)、-0.30‰和-4.23‰,具有和盐溶角砾岩-次生灰岩类似的锰、锶含量和较正的碳、氧同位素组成,碳同位素可能较好地代表了同期海水,氧同位素则代表了蒸发海水。On the basis of thin section observation, cathodoluminescence, elements and isotope analysis, this paper reports and discusses the elements and carbon and oxygen isotope composition δ3C、δ18O of the evaporite-solution breccia-secondary limestone of Member 2 of Triassic Jialingjiang Formation and the micrite and dolomicrite in the adjacent strata in Yanjingxi section located in Hehuan area of eastern Sichuan Basin. The average mass fraction of Mn and Sr, δ3Candδ18O 81sO are 268X 10-6 , 120 X 10-6 , --5.80%0 and --8.97%0 in the evaporite-solution breccia-secondary limestone, respectively and are 142 X 10 6, 767 X 10-6, -- 1.60‰ and -- 6.31‰ in the adjacent mierite, respectively. The evaporite-solution breccia-secondary limestone has the characteristics of higher Mn content, lower Sr content, more negative δ3Candδ18O compared with that in adjacent micrite strata. This indicates that geochemical information of the evaporite-solution breccia-secondary limestone represents an epidiagenetic environment. The carbon source of the evaporite-solution breccia-secondary limestone is mainly concerned with CO2 of the near-surface meteoric water environment, and maybe related to CO2 via bacterial sulfate reduction. In addition to the near-surface meteoric water, oxygen may inherit that in sulfate. The micrite better represents the primary seawater geochemical information. The mass fraction of Mn and Sr （291 X l0 6 and 98 X 10-6, respectively） of the dolomicrite in the adjacent strata are similar with that of the evaporite-solution breccia-secondary limestone, while 8~aC and 8180 （--0.30%0 and --4.23%o, respectively） are more positive compared with that of the evaporite-solution breccia-secondary limestone. The dolomicrite may preserve the 813C of coeval seawater and represent a signal of δ3Candδ18Oevaporate seawater.

关 键 词：合川盐井溪 嘉陵江组 碳 氧同位素 盐溶角砾岩一次生灰岩 

分 类 号：P588.245[天文地球—岩石学] P597.2[天文地球—地质学]