摘要
灯影组白云岩是四川盆地超深层油气勘探的重点领域,但目前人们对该套白云岩成因争议仍较大,且缺乏系统研究.通过对四川盆地灯影组白云岩C-O-Sr同位素和稀土元素数据的系统分析来研究白云石化流体的化学性质和成因,进而约束白云岩的差异性成因机制.研究表明:(1)灯影组白云岩碳同位素值较均一,δ^(13)C值基本分布在0‰~+5.0‰之间,而氧同位素值变化较大.近地表环境基质白云岩和早期白云石胶结物δ^(18)O均大于-8.0‰,埋藏环境白云石胶结物δ^(18)O均小于-8.0‰,而热液白云石化胶结物δ^(18)O均小于-10.0‰.(2)基质白云岩和早期白云石胶结物具有与同期海水相似的^(87)Sr/^(86)Sr值(0.708~0.709),指示其继承于海水流体;而埋藏环境白云石胶结物^(87)Sr/^(86)Sr比值明显大于同期海水,指示其为地层流体和深部热液流体来源.(3)灯影组白云岩稀土元素均亏损轻稀土元素、富集重稀土元素.基质白云岩和早期白云石胶结物可见Ce负异常、未见Eu明显异常,说明白云石化流体来源于海水;埋藏环境白云石胶结物可见明显Eu正异常.不同沉积环境下白云石化流体化学性质和来源的不同,是四川盆地灯影组白云岩成因的控制因素.近地表环境下海水来源的白云石化流体,主要受新元古代震旦系灯影组“文石‒白云石海”环境下高频海平面波动的控制;而在埋藏环境中地层流体和深部热液来源的白云石化流体,则主要受后期构造作用控制.本研究可为认识白云岩成因、晚埃迪卡拉系海水化学条件及超深层油气勘探开发提供了有益参考.
The dolomite in the Sinian Dengying Formation is a new and significant field for ultra-deep oil and gas exploration in the Sichuan basin.However,the forming model remains controversial without systematic research.In this study,detailed C-O-Sr and the rare earth element(REE)analyses were carried out on the Dengying Formation dolomites to investigate the geochemical characteristics and the source of dolomitization fluids,and further to constrain the differences of their origins.(1)The carbon isotopic values of the dolomites in the Dengying Formation are relatively homogeneous(0‰to+5.0‰),while their oxygen isotopic values range widely.The dolomitic matrix and early dolomite cement in the near-surface realm show higherδ^(18)O values than-8.0‰,δ^(18)O values of the dolomite cement in the burial condition are more negative than-8.0‰,and those of the hydrothermal dolomite are more negative than-10.0‰.(2)The strontium isotopic ratios of the dolomitic matrix and early dolomite cement vary in a narrow range of 0.708-0.709,which is close to the Ediacaran marine carbonate,indicating the source of seawater.While those of dolomite cement in burial realm are more positive than the coeval seawater,indicating the source of formation fluids.(3)The dolomites in the Dengying Formation show depletion of light rare earth elements(LREEs)and enrichment of heavy rare earth elements(HREEs).The matrix and early dolomite cement have negative Ce anomalies with the absence of Eu anomalies,indicating a marine source.The dolomitic cements in the burial condition have negative Ce anomalies and significant positive Eu anomalies.The geochemical features and the origin of dolomitization fluids in different sedimentary environments are the essential factors controlling the formation of the Dengying Formation dolomite in the Sichuan basin.Dolomitization fluid in the near-surface environment is mainly derived from seawater,which is controlled by high-frequency sea-level fluctuations in an‘aragonite-dolomite sea’environment during the S
作者
李文奇
刘汇川
李平平
倪智勇
王艺壬
Li Wenqi;Liu Huichuan;Li Pingping;Ni Zhiyong;Wang Yiren(National Key Laboratory of Petroleum Resources and Engineering,China University of Petroleum(Beijing),Beijing 102249,China;College of Geosciences,China University of Petroleum(Beijing),Beijing 102249,China)
出处
《地球科学》
EI
CAS
CSCD
北大核心
2023年第9期3360-3377,共18页
Earth Science
基金
国家自然科学基金项目(Nos.2462018YJRC030,2462020YXZZ020).
关键词
四川盆地
灯影组
白云岩
差异性成因
高频海平面波动
石油地质
地球化学
Sichuan basin
Dengying Formation
dolomite
genesis difference
high⁃frequency sea⁃level fluctuation
petroleum geology
geochemistry
