川东地区寒武系洗象池群下段厚层白云岩特征及成因  

Characteristics and genesis of thick layer dolomites in the Lower Cambrian Xixiangchi Group,eastern Sichuan Basin

作　　者：杨明磊 刘晨虎 杨伟强 诸丹诚 喻雅敏 陈凡卓 邹华耀[1,2] YANG Minglei;LIU Chenhu;YANG Weiqiang;ZHU Dancheng;YU Yamin;CHEN Fanzhuo;ZOU Huayao(College of Geosciences,China University of Petroleum(Beijing),Beijing 102249,China;National Key Laboratory of Petroleum Resources and Engineering,China University of Petroleum(Beijing),Beijing 102249,China;Exploration and Development Research Institute,Zhongyuan Oilfield Company,SINOPEC,Puyang 457001,China;ZhenHua Oil Co.,Ltd.,Beijing 100031,China;Shenzhen Branch of CNOOC,Shenzhen 518054,China;CNOOC Deepwater Development Ltd.,Shenzhen 518054,China)

机构地区：[1]中国石油大学(北京)地球科学学院,北京102249 [2]中国石油大学(北京)油气资源与工程国家重点实验室,北京102249 [3]中国石化中原油田分公司勘探开发研究院,河南濮阳457001 [4]振华石油控股有限公司,北京100031 [5]中海石油(中国)有限公司深圳分公司,广东深圳518054 [6]中海石油深海开发有限公司,广东深圳518054

出　　处：《断块油气田》2024年第4期599-610,共12页Fault-Block Oil & Gas Field

基　　金：国家自然科学基金项目“四川盆地下寒武统龙王庙组深层不同相带颗粒岩压实-压溶-胶结作用定量模型”(42172152)。

摘　　要：四川盆地东部寒武系洗象池群厚层白云岩分布广泛,具有勘探潜力。文中以川东地区南川三泉洗象池群野外剖面为研究对象,基于其岩石学、沉积学、岩石地球化学和矿物学特征,分析其在沉积旋回中的变化,探讨白云岩化流体性质、来源与迁移路径。结果表明:洗象池群白云岩阴极发光弱,δ^(13)C,^(87)Sr/^(86)Sr值与洗象池群同期海水区间重叠,表明白云岩化流体来源于同期海水,白云岩化作用发生在准同生—浅埋藏时期;岩石地球化学和矿物学特征与沉积旋回具有相关性,在向上变浅的旋回中,白云石含量、化学计量数和δ^(18)O升高,有序度降低,表明随相对海平面下降,白云岩化流体的温度、盐度和Mg/Ca值升高,旋回顶部白云岩化程度高;相对海平面较高时,研究区西北侧潟湖中的咸化海水穿过刚形成不久的泥晶灰岩和先期形成的孔渗性好的颗粒灰/白云岩,发生以横向远源渗透回流为主的白云岩化作用;随着相对海平面逐渐下降,潟湖水体循环逐渐变差、盐度升高,潮间—潮下带古地貌高地处形成颗粒灰岩,发生暴露溶蚀;暴露区域经波浪和潮汐作用带来潟湖中的咸化海水,白云岩化流体向下流动,发生以垂向近源渗透回流为主的白云岩化作用;多期横向远源和垂向近源渗透回流白云岩化事件持续叠加,形成川东洗象池群下段潮间—潮下带厚层白云岩。The thick layer dolomites of the Cambrian Xixiangchi Group in eastern Sichuan Basin are widely distributed and have exploration potential.Taking the field profiles of Xixiangchi Group in Sanquan,Nanchuan,eastern Sichuan Basin as the research object,and based on the characteristics of petrology,sedimentology,petrogeochemistry and mineralogy,their changes in sedimentary cycles have been analyzed in order to discuss the properties,origin and migration path of the dolomitized fluid.The results show that dolomites of Xixiangchi Group have weak cathodoluminescence.Theδ^(13)C and ^(87)Sr/^(86)Sr values overlap with the synchronous seawater section of Xixiangchi Group,which indicates that dolomitized fluid originated from the synchronous seawater,and dolomitization occurred in the penecontemporaneous-shallow burial stage.Geochemical and mineralogical characteristics of the rocks are correlated with sedimentary cycles.Upward-shallowing cycles exhibit a pattern of increasing dolomite abundance,stoichiometry andδ^(18)O,and decreasing cation ordering,suggesting that with the decrease of relative sea level,the temperature,salinity and Mg/Ca of the dolomitized fluid increased,and the degree of dolomitization was high at the top of the cycle.When the relative sea level was relatively high,the saline seawater in the northwestern lagoon of the study area passed through the recently-formed micrite and the previously-formed granular limestone/dolomite with good porosity and permeability,resulting in dolomitization dominated by lateral far-from-source seepage-reflux.As relative sea level gradually fell,the circulation of the lagoon water body gradually deteriorated,and the salinity of the lagoon increased.Granular limestone was formed,exposed and erosed in the paleogeomorphic highs of the intertidal-subtidal zone.Saline seawater in the lagoon was brought to the exposed area by waves and tides,and dolomitization dominated by vertical near-source seepage-reflux occurred with the dolomitized fluid flowing downwards.Multi-stage latera

关 键 词：白云岩成因 沉积旋回 相对海平面变化 洗象池群 川东地区 

分 类 号：TE121[石油与天然气工程—油气勘探]