海南岛西南部全新世海滩岩地球化学特征及其古气候意义

GEOCHEMICAL CHARACTERISTICS OF HOLOCENE BEACH ROCKS IN SOUTHWESTERN HAINAN ISLAND AND THEIR PALEOCLIMATIC IMPLICATIONS

对海南岛西南部东方地区的潮间带海滩岩以及新发现的高排村埋藏海滩岩进行了微区稀土元素与碳、氧同位素分析,结果表明:高排村海滩岩亮晶胶结物ΣREE值以及LREE/HREE比值在几种不同类型胶结物中是最低的,但与文石、微晶高镁方解石等胶结物相比,其差值并不明显,说明陆地渗流环境对胶结物的REE影响有限。不同类型胶结物具有类似的配分特征,表现为轻稀土亏损,重稀土曲线平缓,具有铈负异常特征,并且与二叠纪海水和现代东太平洋海水配分模式基本一致。根据胶结物碳、氧同位素计算的出的古盐度Z均值为130,古海水平均温度为27℃,显示为热带海洋环境,与海南岛西南部气候吻合,指示海滩岩胶结物可作为记录古气候的良好载体。

We report elemental geochemical data from beach rocks in the intertidal zone of Dongfang in western Hainan Island, and newly discovered buried beach rocks at Gaopai Village. The data show that EREE contents and LREE/HREE ratios of sparry cement in beach rocks at Gaopai Village represent the lowest among various types of cements, but the differences are small compared with aragonite and high- magnesium calcite cement. Thus, terrestrial seepage environment has had limited impact on REE geochem- istry of cement. Moreover, different types of cements have similar REE distribution patterns, character- ized by low LREE contents, a HREE plateau, and a negative Ce anomaly. The REE distribution patterns are similar to those of Permian seawater and modern eastern Pacific seawater. Based on the C and O isotope data of cements, the average paleosalinity Z is 130, and the average temperature of ancient seawater is 27 ℃, suggesting a tropical marine environment in southwest Hainan Island. Beach rock cement is a reliable archive of paleoclimatic records.