西沙西科1井元素地球化学特征与海平面升降的关系  

ELEMENT GEOCHEMISTRY OF WELL XIKE 1 ON THE XISHA ISLANDS AND ITS BEARING ON SEA LEVEL FLUCTUATION

作　　者：刘新宇 邵磊[3] 史德锋 侍文芳 欧阳杰 LIU Xinyu;SHAO Lei;SHI Defeng;SHI Wenfang;OUYANG Jie(Hainan Energy Co.Ltd.of CNOOC,Haikou 570100,China;Zhanjiang Branch of CNOOC(China)Ltd.,Zhanjiang 524057,China;School of Ocean and Earth Science,Tongji University,Shanghai 200092,China)

机构地区：[1]中海油海南能源有限公司,海口570100 [2]中海石油(中国)有限公司湛江分公司,湛江524057 [3]同济大学海洋与地球科学学院,上海200092

出　　处：《海洋地质前沿》2021年第6期8-17,共10页Marine Geology Frontiers

基　　金：“十三五”国家科技重大专项(2017ZX05026-005);国家自然科学基金(41106064,41872114)。

摘　　要：以南海北部西沙群岛石岛碳酸盐岩台地为研究对象,对1 268件碳酸盐岩样品进行全岩元素地球化学特征分析,并结合早中新世以来沉积学特征,研究其与海平面升降的响应关系。实验结果显示,该地区常量元素(Na_(2)O/K_(2)O、Na_(2)O/SiO_(2)、P_(2)O_(5))及微量元素(B/Ga、Zr/Al、Li、V)分析的古盐度、古环境氧化还原状态和酸碱度及海平面变化,与岩石地层学和古生物学分析得到的结论基本一致,进而可应用于孤立海相碳酸盐岩台地的沉积层序划分;受限于复杂的白云岩化作用,Mg/Ca难以反映海平面变化。Na_(2)O/K_(2)O、Na_(2)O/SiO_(2)、P_(2)O_(5) B/Ga、Zr/Al、Li、V等指标表明,早中新世初期三亚组水深逐渐加深,有利于生物礁的发育;中中新世早期梅山组二段海平面第1次达到最高值,礁盘随之扩大,形成较深水环境下的碳酸盐岩台地,以潟湖相和内侧滩相为主;随后水体于中中新世晚期梅山组一段逐渐变浅,持续至晚中新世早期黄流组二段,生物礁受淋滤剥蚀形成礁-滩相沉积;晚中新世晚期黄流组一段海平面再次持续上升,于上新世达到第2次最高值,直至更新世水深才逐渐变浅。This study focused on major and trace element geochemistry of the carbonate platforms of the Xisha Islands, northern South China Sea(SCS), based on the sedimentary characteristics of the succession since earlyMiocene. A total of 1 268 carbonate samples are collected and analyzed by ICP-MS. Both the major elements of Na_(2)O/K_(2)O, Na_(2)O/SiO_(2), P_(2)O_(5), and the trace elements of B/Ga, Zr/Al, Li, V show perfect consistence with petrographic, stratigraphic and paleontological variations caused by the changes in paleo-salinity, Eh, pH and sea level fluctuation, which can be well applied for the study of depositional sequences of the isolated carbonate platforms. However, Mg/Ca are hard to be used as a proxy to reveal sea level changes, owing to the strong dolomitization. Na_(2)O/K_(2)O, Na_(2)O/SiO_(2), P_(2)O_(5) B/Ga, Zr/Al, Li, V suggest that the bioherms started blooming with the sea water invasion since early-Miocene. During early middle-Miocene, bioherms with lagoonal and beach facies were well formed when the sea level reached its first peak. Then the sea level dropped in late middleMiocene and early late-Miocene. In the late middle-Miocene, bioherms were strongly leached and eroded, as dominated by reef-beach facies. The sea level started to rise again during late late-Miocene and got to its second peak in Pliocene and then dropped for the second time during Pleistocene period.

关 键 词：西科1井 微量元素 常量元素 海平面变化 

分 类 号：P736.4[天文地球—海洋地质] P736.2[天文地球—海洋科学]