| SUN Zhipeng,ZHAI Shikui,XIU Chun,LIU Xinyu,ZONG Tong,LUO Wei,LIU Xiaofeng,CHEN Kui,LI Na. 2014. Geochemical characteristics and their significances of rare-earth elements in deep-water well core at the Lingnan Low Uplift Area of the Qiongdongnan Basin. Acta Oceanologica Sinica, 33(12):81－95 |
| Geochemical characteristics and their significances of rare-earth elements in deep-water well core at the Lingnan Low Uplift Area of the Qiongdongnan Basin |
| 琼东南盆地陵南低凸起深水钻井岩心的稀土元素地球化学特征及其意义 |
| Received:June 20, 2014 Revised:September 29, 2014 |
| DOI：10.1007/s13131-014-0578-3 |
| Key words:Qiongdongnan Basin deep-water well core rare-earth elements sedimentary source and environment response to tectonic movement |
| 中文关键词: 琼东南盆地 深水钻井 稀土元素 物源和沉积环境 构造运动响应 |
| 基金项目:The National Major Project of Science and Technology of China under contract No. 2011ZX05025-002-03. |
| Author Name | Affiliation | E-mail | | SUN Zhipeng | Zhanjiang Branch of China National Offshore Oil Corporation (CNOOC) Limited, Zhanjiang 524057, China | | | ZHAI Shikui | Key Laboratory of Submarine Geosciences and Technology of Ministry of Education, Ocean University of China, Qingdao 266100, China | zhaishk@public.qd.sd.cn | | XIU Chun | Key Laboratory of Submarine Geosciences and Technology of Ministry of Education, Ocean University of China, Qingdao 266100, China | | | LIU Xinyu | Zhanjiang Branch of China National Offshore Oil Corporation (CNOOC) Limited, Zhanjiang 524057, China | | | ZONG Tong | Key Laboratory of Submarine Geosciences and Technology of Ministry of Education, Ocean University of China, Qingdao 266100, China | | | LUO Wei | Zhanjiang Branch of China National Offshore Oil Corporation (CNOOC) Limited, Zhanjiang 524057, China | | | LIU Xiaofeng | Key Laboratory of Submarine Geosciences and Technology of Ministry of Education, Ocean University of China, Qingdao 266100, China | | | CHEN Kui | Key Laboratory of Submarine Geosciences and Technology of Ministry of Education, Ocean University of China, Qingdao 266100, China | | | LI Na | Key Laboratory of Submarine Geosciences and Technology of Ministry of Education, Ocean University of China, Qingdao 266100, China | |
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| Abstract: |
| A geochemical analysis of rare-earth elements (REEs) in 97 samples collected from the core of deep-water Well LS-A located at the Lingnan Low Uplift Area of the Qiongdongnan Basin is conducted, with the purpose of revealing the changes of sedimentary source and environment in the study region since Oligocene and evaluating the response of geochemical characteristics of REEs to the tectonic evolution. In the core samples, both ΣREE and ΣLREE (LREE is short for light-group REEs) fluctuate in a relatively wide range, while ΣHREE (HREE is short for heavy-group REEs) maintains a relatively stable level. With the stratigraphic chronology becoming newer, both ΣREE and ΣLREE show a gradually rising trend overall. The ΣREE of the core is relatively high from the bottom of Yacheng Formation (at a well depth of 4 207 m) to the top of Ledong Formation, and the REEs show partitioning characteristics of the enrichment of LREE, the stable content of HREE, and the negative anomaly of Eu to varying degrees. Overall the geochemical characteristics of REEs are relatively approximate to those of China's neritic sediments and loess, with significant “continental orientation”. The ΣREE of the core is relatively low in the lower part of Yacheng Formation (at a well depth of 4 207-4 330 m), as shown by the REEs partitioning characteristics of the depletion of LREE, the relative enrichment of HREE, and the positive anomaly of Eu; the geochemical characteristics of REEs are approximate to those of oceanic crust and basalt overall, indicating that the provenance is primarily composed of volcanic eruption matters. As shown by the analyses based on sequence stratigraphy and mineralogy, the provenance in study region in the early Oligocene mainly resulted from the volcanic materials of the peripheral uplift areas; the continental margin materials from the north contributed only insignificantly; the provenance developed to a certain extent in the late Oligocene. Since the Miocene, the provenance has ceaselessly expanded from proximal to distal realm, embodying a characteristic of multi-source sedimentation. In the core strata with 31.5, 28.4, 25.5, 23, and 16 Ma from today, the geochemical parameters of REEs and Th/Sc ratio have significant saltation, embodying the tectonic movement events in the evolution of the Qiongdongnan Basin. In the tectonic evolution history of the South China Sea, the South China Sea Movement (34-25 Ma BP, early expansion of the South China Sea), Baiyun Movement (23 Ma BP), late expansion movement (23.5-16.5 Ma BP), expansion-settlement transition, and other important events are all clearly recorded by the geochemical characteristics of REEs in the core. |
| 中文摘要: |
| 本文对位于琼东南盆地陵南低凸起的LS-A深水钻井岩心97个样品做了稀土元素地球化学分析,旨在揭示研究区渐新世以来的沉积物源及沉积环境变化,探讨稀土元素地球化学特征对盆地构造演化的响应.岩心样品中∑REE和∑LREE波动范围较大,而∑HREE相对稳定.随着地层年代由老变新,∑REE和∑LREE总体上呈现逐渐升高的趋势.从岩心下部崖城组(井深4207 m以上)至顶部乐东组∑REE较高,REE具有轻稀土富集、重稀土含量稳定、Eu具有不同程度负异常的配分特征,REE地球化学特征总体上与中国浅海沉积物和中国黄土较为接近,具有显著的“亲陆性”.崖城组底部(井深4207-4330 m)∑REE较低,表现为轻稀土亏损、重稀土相对富集和Eu正异常的REE配分模式,REE地球化学特征总体上接近于洋壳和玄武岩,所指示的物源以火山喷发物为主.结合层序地层和矿物学分析可知,渐新世早期研究区物源主要来自于周边凸起区的火山物质,北部陆缘物质贡献极小,至渐新世晚期物源区有所发展.自中新世以来物源区由近源向远源不断扩大,显示出多源沉积特征.在距今31.5 Ma、28.4 Ma、25.5 Ma、23 Ma和16 Ma的岩心地层处,REE地球化学参数及Th/Sc比值均发生显著跃迁,反映了琼东南盆地演化中的构造运动事件.南海构造演化历史中的南海运动(34-25 Ma BP,南海早期扩张)、白云运动(23 Ma BP)和晚期扩张运动(23.5-16.5 Ma BP)、以及扩张—沉降转换等重要事件在岩心沉积物REE地球化学特征上都有着明显的记录. |
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