基于古地磁与^(230)Th定年的西沙西科1井乐东组生物礁沉积年代的初步研究  

Magnetostratigraphy and ^(230)Th dating of Pleistocene biogenic reefs in XK-1 borehole from Xisha Islands,South China Sea

作　　者：王振峰 张道军 刘新宇 尤丽 罗威 易亮[2,3] 谭亮成[4] 祝幼华[5] 秦华峰[3] 程海[6] 李忠权[7] 谢强[8] 车志伟[9] 邓成龙[3,10] 朱日祥[3] 

机构地区：[1]中海石油(中国)有限公司湛江分公司,广东湛江524057 [2]同济大学海洋与地球科学学院海洋地质国家重点实验室,上海200092 [3]中国科学院地质与地球物理研究所岩石圈演化国家重点实验室,北京100029 [4]中国科学院地球环境研究所黄土与第四纪地质国家重点实验室,西安710075 [5]中国科学院南京地质与古生物研究所资源地层学与古地理学重点实验室,南京210008 [6]西安交通大学全球环境变化研究院,西安710049 [7]成都理工大学地球科学学院,成都610059 [8]中国科学院深海科学与工程研究所,海南三亚572000 [9]国家海洋局海口海洋环境监测中心站,海口570311 [10]中国科学院大学,北京100049

出　　处：《地球物理学报》2017年第3期1027-1038,共12页Chinese Journal of Geophysics

基　　金：国家科技重大专项<南海北部深水区潜在富生烃凹陷评价>(2011ZX05025-002);中国海洋石油总公司<西沙生物礁古地磁学;古环境磁学与白云岩化形成机制研究>(CNOOC-2013-ZJ-01);973项目(2013CB955902);国家自然科学基金(41402153;41272014)联合资助

摘　　要：生物礁是重要的自然资源,在全球气候变化与碳循环中扮演了重要角色.磁性地层学是建立年代框架的有效手段,但是,由于生物礁沉积物中天然剩磁强度弱,南海地区生物礁的磁性地层学研究尚未很好展开.为此,本文利用西沙群岛西科1井乐东组生物礁沉积样品进行了详细的岩石磁学和磁性地层学研究.结果显示,西沙群岛乐东组记录了布容正极性时、奥杜维尔正极性时和松山负极性时.通过对比已有的钻孔资料,本文认为应基于岩石地层特征这一标准将西沙地区的乐东组埋深予以统一.在此基础上,综合磁性地层与^(230)Th定年结果,本文将乐东组的底界限定在~2.0 Ma.Biogenic reefs and carbonate platforms are valuable natural resources, which play a role in modulating global climate and carbon cycle through biological processes. In this study, by combining paleomagnetic data and ^230Th dating with lithostratigraphic characters for the XK-1 biogenic reef sequence from the Xisha Islands, northern South China Sea, new insights into the regional geochronology since the early Pleistocene are obtained. The main results are as follows： （1） Paleomagnetic findings suggest that the sequence records the Brunhes normal chron and the Matuyama reverse chron, including the Jaramillo and Olduvai normal subchrons. （2） The studied biogenic reef sequence named as the Ledong Formation has two subunits, i. e. , upper and lower sections, which can be correlated to the middle and late Pleistocene, and the early Pleistocene, respectively. By comparing our results with those for previous long cores from the Xisha area, we conclude that the previous debate on the position and age of the Ledong Formation around the Xisha area mainly arose from inadequate absolute dating and use of different criteria for lithostratigraphic boundary determination. After determining the lower lithological boundary of the Ledong Formation, we set the age of the boundary as -2.0 Ma.

关 键 词：磁性地层 ^230Th定年 生物礁 南海 更新世 

分 类 号：P318[天文地球—固体地球物理学]