摘要
西湖凹陷平湖斜坡北段平湖组受河流与潮汐作用共同影响,水动力条件复杂,分支流水道砂体与潮汐水道砂体的成因存在争议。通过煤层与泥岩的微观岩石学特征分析,探讨其岩石结构与矿物组成、泥岩中碎屑颗粒排列方式、水动力条件与水介质环境,进而划分岩性相类型,展开砂-泥岩一体化的微相划分与水动力分析。其中,薄煤层可分为封闭洼地含草莓状黄铁矿煤层、分支流间湾沼泽纯煤层与天然堤粉砂质纹层煤层;泥岩可分为封闭洼地水平纹层状菱铁矿、分支流间湾含结核状菱铁矿,以及砂岩中交错纹层状菱铁矿。泥岩中广泛发育的菱铁矿指示平湖组沉积时期,发育富铁的局限潟湖环境;泥岩中黏土矿物以高岭石与伊利石混合的黏土为主,指示淡水-海水混层的沉积水介质环境。泥岩中微古生物与煤的显微组分指示其互层的箱形、钟形砂体为三角洲背景下的水道沉积,砂体为多期水道叠置的复合体。薄煤层与碳质泥岩及相关砂岩的微观岩石学分析表明,平湖斜坡北部平湖组具有典型的缓坡局限浅水沉积背景,陆源有机质供给丰富,泥岩中普遍富含碳质,砂体以单向水流沉积作用为主。薄煤层与泥岩岩相分析为薄煤层与砂岩成因分析提供了新的沉积学信息,为砂体预测评价提供了新的依据。
The Pinghu Formation in the northern part of the Pinghu Slope is rive-tidal deposits.The hydrodynamic conditions were complex,and there is a controversy on the origin of sandbodies for distributary channels and tidal channels.Through the analysis of micro-petrological characteristics of coal seams and mudstones,the rock structure and mineral composition,the arrangement of clastic particles in mudstones,hydrodynamic conditions,and water medium environment were discussed,and the types of lithologic facies were divided,after which the sandstone microfacies were divided based on sandstone-mudstone integration,and hydrodynamics was analyzed.In particular,the thin coal seam can be categorized into the strawberry-shaped pyrite coal seam indicative of a closed-basin environment,the pure coal seam reflecting an interdistributary bay,and the silty laminated coal seam formed in natural levee.Mudstone can be categorized into horizontal lamellar siderite formed in a closed sag,siderite concretion formed in an interdistributary bay,and crisscrossed lamellar siderite in sandstone.The widely developed siderite in mudstone indicates that an iron-rich and restricted lagoon was developed during the deposition of Pinghu Formation in the north of Pinghu Slope.Minerals in mudstone are mainly clays mixed with kaolinite and illite,indicating a fresh-marine mixed water medium environment.The micropaleontological assemblage in mudstone and macerals of coal indicate that the interbedded box-shaped and bell-shaped sandbodies are channel deposits under delta background,and the sandbodies are the complex of multi-phase channel superposition.The microscopic petrological analysis of thin coal seams,mudstones,and related sandstones shows that the Pinghu Formation was formed in a typical gentle-slope water-restricted shallow background,in which terrigenous organic matter was rich,mudstones were carbon-abundant,and sandbodies were dominated by one-way flow sedimentation.This study provided new data and a reference for reconstructing the sedimentar
作者
何贤科
李文俊
段冬平
荣乘锐
夏振通
HE Xianke;LI Wenjun;DUAN Dongping;RONG Chengrui;XIA Zhentong(Shanghai Branch of CNOOC Ltd.,Shanghai 200335,China)
出处
《海洋地质与第四纪地质》
CAS
CSCD
北大核心
2024年第2期210-222,共13页
Marine Geology & Quaternary Geology
基金
中海石油(中国)有限公司重大科技专项“西湖凹陷在生产油气田中后期综合调整关键技术研究与实践”(CNOOCKJ135ZDXM39SH03)
中海石油(中国)有限公司上海分公司科技项目(KJZL-2023-SH01)。
