涠洲岛北港海滩岩的铀系年代及其海平面指示意义  

Uranium-series ages of Beigang beachrock at Weizhou Island and their significance in recording sea level variations

作　　者：刘文会 余克服[2,3,4] 王瑞 颜廷礼[2,3,4] Liu Wenhui;Yu Kefu;Wang Rui;Yan Tingli(College of Resources,Environment and Materials,Guangxi University,Nanning 530004,Guangxi;Guangxi Laboratory on the Study of Coral Reefs in the South China Sea,Guangxi University,Nanning 530004,Guangxi;Coral Reef Research Center of China,Guangxi University,Nanning 530004,Guangxi;School of Marine Sciences,Guangxi University,Nanning 530004,Guangxi)

机构地区：[1]广西大学资源环境与材料学院,广西南宁530004 [2]广西大学广西南海珊瑚礁研究重点实验室,广西南宁530004 [3]广西大学珊瑚礁研究中心,广西南宁530004 [4]广西大学海洋学院,广西南宁530004

出　　处：《第四纪研究》2020年第3期764-774,共11页Quaternary Sciences

基　　金：国家重大科学研究计划项目(批准号:2017YFA0603300);广西科技计划项目(批准号:AA17204074和AD17129063)共同资助。

摘　　要：海滩岩是古海平面高程的重要标志。本文利用高精度铀系测年技术对北部湾涠洲岛北港海滩岩中保存完好的珊瑚枝进行了测年,得出珊瑚枝的年龄分布范围介于距今(2017 A.D.)1780~836年,表明涠洲岛北港海滩岩是晚全新世时期的产物。电子探针元素含量分析得出该海滩岩的胶结物是低镁方解石,其成岩环境为大气淡水环境,但相对高含量的锶则指示其成岩过程中经历了海水的冲刷作用。综合铀系年代、海滩岩的高程及邻近区域的古海平面数据,涠洲岛北港晚全新世时期的海滩岩指示出距今1780~836年海平面高于现今海平面约为0.91~1.16 m,为晚全新世时期高海平面提供了新的信息。Beachrock is an important indicator of the sea level in the past period.This paper studied the age and sedimentary feature of the beachrock at Beigang Village,Weizhou Island.Weizhou Island,which is located in the middle of Beibu Gulf,northern part of South China Sea,is at an elevation of 20~40 m.The coastline around the island is about 20 kilometers long,and coral reefs distribute in the north,east and southwest of the island at a depth of 2 m to 14 m.This paper examined the beachrock's sedimentary structure,clastic composition,organic components and relative elevation,and measured its contents of main elements(Mg,Na,Fe,Sr and Mn)using EPMA(Electon Probe MicroAnalysis)technology.The results showed that the cement of the beachrock is LMC(low magnesium calcite),indicating that it was primarily formed in atmospheric fresh water.However,the relatively high content of strontium indicated that seawater also contributed to the diagenetic process.This paper also collected four well-preserved coral branches from the beachrock,and dated them with U-Tu technology.Although the U-Tu age of coral branches represents the age of coral growth,the well-preserved surface structure of the coral branches indicated a series of process growth,breakage,transportation to beach,sedimentation to intertidal zone,and cementing in the beachrock would not last long.Therefore,the ages of coral branches in the beachrock of Weizhou Island can approximately represent the maximum age of the beachrock formation.To avoid any possible interference factors,the coral branches were finely polished before being dated with U-Tu technology.The results showed that the ages of these coral branches-and thus the approximate maximum age of the beachrock-ranged from 1780 a B.P.to 836 a B.P.(years before 2017 A.D.),in the Late Holocene.The elevation of the beachrock was surveyed relative to the modern sedimentary zone,where beachrock is most likely to form.The results showed that the bottom and top layers of the beachrock are 0.91 m and 1.16 m above the modern sed

关 键 词：海滩岩 铀系年代 海平面 新构造 晚全新世 涠洲岛 

分 类 号：P722.7[天文地球—海洋科学] P731.23