海南岛西北部晚更新世海滩岩地球化学特征及其古环境意义  

Geochemical Characteristics of Late Pleistocene Beach Rocks in Northwest Hainan Island and Their Paleoenvironment Implications

作　　者：林义华 梁定勇[1,3] 魏昌欣 吕昭英 吴迪[1,2] 黄武轩 许国强[1,3] 杜鹃 LIN Yi-hua;LIANG Ding-yong;WEI Chang-xin;L Zhao-ying;WU Di;HUANG Wu-xuan;XU Guo-qiang;DU Juan(The Key Laboratory of Marine Geological Resources and Environment of Hainan Province,Haikou 570206,China;Institute of Geological Survey of Hainan Province,Haikou 570206,China;Comprehensive Institute of Geological Investigation of Hainan Province,Haikou 570206,China)

机构地区：[1]海南省海洋地质资源与环境重点实验室,海口570206 [2]海南省地质调查院,海口570206 [3]海南省地质综合勘察院,海口570206

出　　处：《科学技术与工程》2023年第10期4079-4090,共12页Science Technology and Engineering

基　　金：海南省海洋地质资源与环境重点实验室自主课题(ZZ[2020]2019256-02);2019年海南省基础与应用基础研究计划(自然科学领域)高层次人才项目(2019RC346,2019RC348)。

摘　　要：海滩岩是形成于潮间带,由碳酸盐胶结海滩沉积物而成的一种海岸带碳酸盐胶结岩,对于研究古海平面变化、海岸带演化以及古气候变化等海陆相互作用过程具有重要意义。对海滩岩的岩石学、地球化学特征进行了研究,结果表明:海滩岩主量元素与上部陆壳(upper continental crust,UCC)的平均含量比较,显著富集MgO和CaO,略富集MnO,其他均亏损,其中Na_(2)O亏损最大。6件海滩岩稀土元素(rare earth element,REE)总体呈微弱的右倾轻稀土富集型曲线,轻、重稀土分异不强,以Eu弱负异常,Ce弱负异常及La弱正异常为特征;从早到晚,Al_(2)O_(3)/MgO比值变小和陆源碎屑组分SiO_(2)、Al_(2)O_(3)、Na_(2)O、K_(2)O、TiO_(2)等含量逐渐下降共同反映陆源的化学风化减弱,气候越来越干旱。古盐度Z值、Sr/Ba、Rb/K、V/Cr、V/(V+Ni)和稀土元素判别研究区为弱氧化-氧化的海陆交互环境,古地理格局为半封闭边缘海。根据δ^(18)O计算出的晚更新世古水温平均温度为28.22℃,与前人用浮游有孔虫壳体Mg/Ca比值计算出的古海水温度相吻合,显示为热带海洋环境。Beach rock is a kind of coastal zone carbonate cement rock formed by carbonate cement beach sediments in intertidal zone,it is of great significance to study paleo-sea level change,coastal zone evolution and paleoclimate change.This research studies petrological and petro-geochemical characteristics of late Pleistocene beach rocks in Paipu area of Danzhou City,northwestern Hainan Island.Results show beach rocks are enriched in MgO and CaO,slightly enriched in MnO,while others are depleted,of which Na_(2)O is significantly depleted,compared with UCC(upper continent crust).The REE(rare earth element)distribution patterns of six beach rocks are similar after normalization by PAAS(post-archean australian shale),and generally show a weak rich-dipping light rare earth element curve.The light and heavy rare earth elements are not strongly differentiated.Elements are characterized by weak negative Eu,Ce and weak positive La.SiO_(2),Al_(2)O_(3),Na_(2)O,K_(2)O,TiO_(2)gradual decline and the ratio of smaller of Al_(2)O_(3)/MgO reflected that the Land-based chemical weathering lessens and the climate becomes increasingly arid.Paleosalinity Z,Sr/Ba,Rb/K,V/Cr and V/(V+Ni)ratios and rare earth elements discriminate the study area as a sea-land interaction environment,dominated by an weakly oxidized-oxidized environment.The palaeogeographical environment is a semi-closed marginal sea.The calculated average paleo-water temperature is 28.22℃in the late pleistocene based onδ^(18)O,which is consistent with the paleo-water temperature calculated by the predecessors using the Mg/Ca ratio of planktonic foraminifera shells.Results indicate the study area is a tropical marine environment.

关 键 词：海滩岩 地球化学特征 古环境 晚更新世 海南岛 

分 类 号：P595[天文地球—地球化学] P534.63[天文地球—地质学]