鄂尔多斯南缘奥陶系生物礁相碳酸盐岩碳氧同位素地球化学特征  

Characteristics of Carbon and Oxygen Isotopes Geochemistry of Organic Reef Facies Carbonates of Ordovician in Southern Margin of Ordos

作　　者：郝松立[1,2] 李文厚[1,2] 刘建平[3] 陈强[1,2] 李莹[1,2] 朱静[1,2,4] 谭晨曦[5] 张慧元[6] 

机构地区：[1]西北大学大陆动力学国家重点实验室,西安710069 [2]西北大学地质学系,西安710069 [3]中国石油长庆油田公司油田开发处,西安710021 [4]中国石油长庆油田公司勘探开发研究院,西安710021 [5]西安科技大学,西安710054 [6]中国地质调查局西安地质调查中心,西安710054

出　　处：《地质科技情报》2011年第2期52-56,共5页Geological Science and Technology Information

基　　金：国家科技重大专项子专题(2008ZX05005-004-HZ007)

摘　　要：为了研究生物礁相碳酸盐岩碳氧同位素地球化学特征,采用同位素比质谱仪对鄂尔多斯南缘奥陶系生物礁发育地区的碳酸盐岩样品进行了碳、氧同位素测定,并采用ICP-AES、ICP-MS进行了主、微量元素分析测试。结果显示,δ(13CPDB)值为-2.32‰~2.08‰,δ(18OPDB)值为-8.97‰^-4.15‰,w(Mn)/w(Sr)最大仅为0.32,远小于2~3的范围。研究表明,研究区碳酸盐岩样品基本保持了碳、氧同位素的原始组成;礁灰岩具有相对较低的δ(13CPDB)值,生物礁发育时海水的温度略低于、盐度略高于非礁相发育时海水的温度和盐度;并推测由平凉期至背锅山期,研究区相对水深增大,温度升高,盐度降低。同时指出,综合运用δ(13CPDB)和δ(18OPDB)值的经典盐度公式计算的Z值,对本区奥陶纪岩石的海相成因具有判别意义。但是,相关性分析表明Z值与δ(13CPDB)值密切正相关(相关系数0.95),与δ(18OPDB)值基本不具有相关性(相关系数仅-0.000 8),因而Z值不适合作为定量指标来解释研究区古盐度的相对变化。For studying the characteristics of carbon and oxygen isotope geochemistry,the carbonate samples collected from organic reef facies of Ordovician in southern margin of Ordos are studied with the methods of isotopes（C,O）,major element and trace element.The results demonstrate that the δ13C flunctuate from-2.32‰ to 2.08‰（PDB）,the δ18O flunctuate from-8.97‰ to-4.15‰（PDB）,the Mn/Sr have the extreme value 0.32 which is less than the interval of 2—3.It suggests that a basically complete preservation of primary ratios of C and O isotopes exist in this carbonate samples.δ13C of reef limestone is lower than δ13C of limestone.The temperature during the reef growing is lower than the regular temperature.However,the salinity is higher.The water in the study area becomes deeper from Pingling to Beiguoshan,where the sea water has a higher temperature and a lower salinity.At the same time,Z from the classics salinity formula plays its role in confirming the marine facies of Ordovician in the study area.While Z is positively correlated with δ13C,the related coefficient is 0.95,but there is no correlation between Z and δ18O,the with a related coefficient of-0.000 8.Hence,Z cannot be used as the quantitative index to explain the change of salinity in the study area.

关 键 词：碳氧同位素 碳酸盐岩 生物礁相 奥陶系 鄂尔多斯南缘 

分 类 号：P597[天文地球—地球化学]