西沙群岛石岛根管石特征、成因及地质意义  

Characteristics,origin and geological significance of rhizolith in Shidao of Xisha Islands

作　　者：魏喜[1,2,3] 贾承造[4,5] 孟卫工[6] 祝永军[6] 

机构地区：[1]中国石油杭州地质研究院,杭州310023 [2]中国石油 勘探开发研究院博士后流动站,北京100083 [3]中国石油 辽河油田公司,盘锦124010 [4]中国石油勘探开发研究院博士后流动站,北京100083 [5]中国石油天然气股份有限公司,北京100011 [6]中国石油辽河油田公司,盘锦124010

出　　处：《岩石学报》2008年第10期2415-2422,共8页Acta Petrologica Sinica

基　　金：中国石油辽河油田公司西沙海域油气勘探重大项目的资助

摘　　要：西沙群岛石岛由第四纪地层构成,包括4个风成生物砂屑灰岩层和3个化石土壤层,生物砂屑灰岩层和化石土壤层相间分布,在化石土壤层中发育根管石。研究表明,根管石在结构构造、成分和沉积成岩变化方面具有三层分带性。其中,内带由泥晶碳酸盐组成,具有泥晶结构,环形纹层或纤维状构造,是原始植物根系交代和石化的结果;中带和外带均为细粒砂屑结构,块状或层理构造,砂屑颗粒由珊瑚、珊瑚藻、有孔虫、软体动物、棘皮类等古生物化石和砂屑组成,中带钙质胶结较强,中带、外带及寄主岩石多为过渡关系。根管石的中带和外带是植物根系附近微化学成岩环境和后期差异风化作用的产物。西沙群岛石岛存在3个根管石发育层,标志着三期成土作用和植被化作用的存在,反映了气候条件的重大变化。西沙群岛石岛风成生物砂屑灰岩层和化石土壤层的相间分布特征,及CaO/MgO比值、锶元素和有机质含量变化,记录了4个气候演变和风成沉积演化旋回。The strata in Shidao of Xisha Islands is Quaternary, including four layers of eolian biocalcarenite and three layers of fossil soil, which alternate with each other. Rhizolith exist in fossil soil. Studies indicate that rhizolith has three zones in texture, structure, component and the aspects of sedimentation and diagenesis. The intrazone, composing of micrite carbonate, with micritic texture and ringlike lamina or filiform structure, is the result of replacement and petrifaction of plant root. Mesozone and exozone, composing of fragments of coralline algae, coral, mollusca, echinoderm and foraminifera and arene, with fine grain psammitic texture and blocklike or bedding structure, is the product of chemical diagenesis in special micro-milieu around plant root and difference weathering after diagenesis. Three layers of rhizolith in Shidao of Xisha Islands mark three stages of pedogenesis and vegetation growing, reflecting magnitude alteration of climatic condition. Alternating beds between eolian biocalearenite layer and fossil soil layer, variation of CaO/ MgO ratio, strontium and organic content record four cycles of climate and eolian deposition evolution.

关 键 词：根管石 风成生物砂屑灰岩 化石土壤层 西沙群岛石岛 第四纪 

分 类 号：P588.245[天文地球—岩石学]