琼东南盆地深水区钻井岩屑稀土元素地球化学特征及其对沉积物源和环境的指示

The sedimentary environment and provenance analysis based on geochemical characteristics of rare-earth elements in deepwater well core of the Qiongdongnan Basin

对琼东南盆地深水区YL19A钻井岩屑样品进行了稀土元素(REE)地球化学特征分析,旨在研究琼东南盆地深水区的沉积物源及古环境变化。钻井岩屑样品的球粒陨石标准化REE配分模式总体呈轻稀土(LREE)富集、重稀土(HREE)亏损的右倾式,但在各时代地层之间表现出一定的差异。崖城组和陵水组岩屑呈明显的Eu正异常,而梅山组、三亚组和黄流组岩屑呈Eu的弱负异常,指示了沉积环境和沉积物源上的变化。在早渐新世时期,研究区物源以来自周边凸起的火山碎屑和陆源碎屑为主,沉积环境为海陆过渡相;自渐新世晚期开始,随着琼东南盆地全区发生海侵,研究区水深逐渐加大,沉积环境由海陆过渡相变为浅海相,物源变为远源陆源物质,并具有红河与海南岛多物源混合的特征,红河沉积物对物源的贡献相对较大,基性火山物质对物源的贡献减弱。YL19A钻井岩屑的REE地球化学特征在距今30、28.5、25.5和23.8Ma等地层界面处均发生明显的突变,对区域性构造运动事件有明显的响应。

The geochemical characteristics of rare-earth elements(REE)in samples collected from the deep-water well core YL19A of the Qiongdongnan Basin were analyzed to reveal the changes in sedimentary source and paleoenvironment.The chondrite-normalized REE partitioning patterns in the core samples exhibit the relative enrichment of light rare earth elements and a stable content of heavy rare earth elements on the whole.However,there are differences between the different formations.The samples of the Yacheng and Lingshui formations exhibit significant positive Eu anomaly,and the samples of Meishan,Sanya,and Huangliu formations exhibit weak negative Eu anomaly.This indicates the changes of sedimentary source and paleoenvironment.The provenance in the study region mainly resulted from the volcanic materials and terrigenous debris of the peripheral uplift areas,and the sedimentary environment was continental-marine transitional environment in the early Oligocene.Since the late Oligocene,with the Qiongdongnan Basin transgressions,the sea level increased gradually.The sedimentary environment transformed from continental-marine transition into shallow marine environment,and the provenance expanded from the proximal to the distal realm,exhibiting a characteristic of multi-source sedimentation.The provenance was from the Red River and the Hainan Island,and the sediment coming from the Red River contributed more to the provenance.The basic volcanic materials in provenance decreased.In the strata of well YL19A,30,28.5,25.5,and 23.8 Ma,the REE geochemical characteristics have undergone significant saltations,reflecting the impact of tectonic movements.