西沙石岛礁相白云岩稀土元素地球化学特征及成岩环境分析

发布时间：2018-01-19 20:04

本文关键词： 西沙石岛岛礁西科井岩心白云岩层稀土元素成岩环境古气候变化　出处：《海洋通报》2017年02期 　论文类型：期刊论文

【摘要】：西沙群岛是南海生物礁体系发育的典型地区,也是我国生物礁油气资源勘探与开发的重点区域。对采自西沙石岛"西科1井"岩心7层共107个白云岩样品进行了稀土元素(REE)含量测试分析,旨在通过分析白云岩层的REE地球化学特征,探讨西沙岛礁白云岩的成岩环境及其与古气候事件的相互关系。研究结果表明:西沙石岛礁相碳酸盐岩中7层白云岩具有相似的REE地球化学特征(含量、配分模式和元素异常等),表明其形成于相近的成岩环境;埋藏压实及其所导致的成岩作用未造成白云岩层中REE主要特征的显著变化,白云岩的REE地球化学特征基本反映了白云岩化作用的成岩环境及成岩流体的性质;多种地球化学指标(REE、Sr含量和碳、氧同位素特征)表明,西沙岛礁白云岩主要形成于高盐海水作用条件下的低温偏氧化环境,o_湖环境下高盐卤水的渗透回流作用是导致白云岩层形成的主要形式;白云岩的形成在时间上与中新世以来的古气候变冷事件相对应,气候变化导致的海平面升降控制了岛礁白云岩层的分布;由于气候变冷在岛礁周围形成礁滩o_湖,相对封闭的o_湖和蒸发量大于降水量的气候环境形成高盐度卤水,这种比重较大的高盐卤水沿孔隙下渗,交代蚀变早先形成的方解石类碳酸盐,从而形成了西沙岛礁中的白云岩层。
[Abstract]:Xisha Islands is a typical area for the development of reef system in the South China Sea. It is also a key area for exploration and development of oil and gas resources on reefs in China. The REE content of 107 dolomite samples collected from core 7 layers of Xico 1 well in Xisha Island has been tested and analyzed. The purpose of this paper is to analyze the REE geochemical characteristics of dolomite. The diagenetic environment of Xisha reef dolomite and its relationship with paleoclimate events are discussed. The results show that 7 layers of dolomite in the reef carbonate rock of Xisha Island have similar REE geochemical characteristics (content). Distribution patterns and element anomalies indicate that they were formed in similar diagenetic environments. The buried compaction and its diagenesis did not result in significant changes in the main characteristics of REE in dolomite. The REE geochemical characteristics of dolomite basically reflect the diagenetic environment of dolomitization and the properties of diagenetic fluid. A variety of geochemical indicators, such as REE Sr content and carbon and oxygen isotopic characteristics, indicate that the dolomite on Xisha island reef is mainly formed in a low-temperature partial oxidation environment under the condition of high-salt seawater. The osmotic reflux of high-salt brine is the main form of dolomite formation in the environment of O _ lake. The formation of dolomite corresponds to the paleoclimate cooling event since Miocene. The sea level rise and fall caused by climate change control the distribution of reef dolomite. Due to the cooling of the climate, the reef beach och is formed around the islands and reefs, and the relatively closed och and the climate environment in which evaporation is larger than precipitation form high salinity brine. This kind of high salt brine, which has a large proportion, permeates along the pore. Calcite carbonate formed by metasomatic alteration formed dolomite in Xisha island reef.
【作者单位】：中国海洋大学海底科学与探测技术教育部重点实验室海洋地球科学学院;国家海洋局北海环境监测中心;中海石油(中国)有限公司湛江分公司;
【基金】：国家重大专项(2011ZX05025-002-03) 中国海洋石油总公司项目(CNOOC-2013-ZJ-01)
【分类号】：P618.13
【正文快照】： Lottermoser(1992)认为,从溶液中析出的矿物所具有的REE特征主要取决于流体中REE的地球化学特征,受矿物自身的晶体化学性质影响有限。对白云岩而言,其REE特征是成岩流体与原岩(灰岩)中REE重新分配、平衡的结果,记录了成岩流体和成岩环境的相关信息。近年来,不少salinity seawa

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