西沙群岛西科1井晚中新世-上新世生物礁沉积的磁性地层学初步结果  

Preliminary results of rock magnetism and magnetostratigraphy for Late Miocene to Pliocene biogenetic reefs in the Xisha Islands,South China Sea

作　　者：王振峰 张道军 刘新宇 尤丽 罗威 易亮[2,3] 祝幼华[4] 秦华峰[2] 谢强[5] 车志伟[6] 李忠权[8,9] 邓成龙[3,7] 朱日祥[3] WANG Zhen-Feng ZHANG Dao-Jun LIU Xin-Yu YOU Li LUO Wei YI Liang ZHU You-Hua QIN Hua-Feng XIE Qiang CHE Zhi-Wei LI Zhong-Quan DENG Cheng-Long ZHU Ri-Xang(Zhanjiang Branch, China National Offshore Oil Corporation, Zhanjiang Guangdong 524057, China State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China Institute of Deep sea Science and Engineering, Chinese Academy of Sciences, Sanya Hainan 572000, China Haikou Marine Environment Monitoring Central Station, State Oceanic Administration, Haikou 570311, China University of Chinese Academy of Sciences, Beijing 100049, China State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu 610059, China Key Laboratory of Tectonic Controls on Mineralization and Hydrocarbon Accumulation, Ministry of Land and Resource, Chengdu University of Technology, Chengdu 610059, China)

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 [5]中国科学院深海科学与工程研究所,海南三亚572000 [6]国家海洋局海口海洋环境监测中心站,海口570311 [7]中国科学院大学,北京100049 [8]成都理工大学,油气藏地质及开发工程国家重点实验室,成都610059 [9]成都理工大学,国土资源部构造成矿成藏重点实验室,成都610059

出　　处：《地球物理学报》2016年第11期4178-4187,共10页Chinese Journal of Geophysics

基　　金：国家科技重大专项(2011ZX05025-002);中国海洋石油总公司(CNOOC-2013-ZJ-01);国家自然科学基金(41402153,41272014,41030426)联合资助

摘　　要：本文对西沙群岛西科1井钻孔岩心晚中新世-上新世生物礁沉积进行了详细的岩石磁学、磁性扫描与磁性地层学研究.结果显示,西科1井生物礁相沉积中的载磁矿物主要是磁铁矿.我们推测,这些磁铁矿的微小颗粒主要来自海水中含有的陆源物质,在生物生长过程中通过珊瑚体或其它寄生生物对海水的过滤与吸附作用保存在生物礁沉积中.进一步的磁性地层学研究及其与地磁极性年表的对比发现,在上新统莺歌海组、上中新统黄流组内部可获得多个年龄控制点,并对莺歌海组和黄流组的底界位置给出了初步制约.其中,莺歌海组记录了C2An.3n和C3n.4n,黄流组记录了C3An.2n至C5n.2n.虽然这一对比方案存在一定不确定性,但是在现阶段生物地层年代及其它年代学资料相对匮乏的情况下,我们认为本项研究的磁性地层学结果能为西沙群岛晚中新世以来的生物礁沉积提供更多可靠的年龄控制点,并为今后的区域地层对比提供磁性地层年代学依据.The South China Sea（SCS）in West Pacific Ocean is the largest marginal sea in Asia.Due to the unique location,its Cenozoic evolution has been attracting great attentions during the past decades.As one of the most debated issues,geochronological frameworks of the SCS basin have been widely investigated mainly based on geophysical data or regional unconformities.As one of two major types of depositions（terrigenous and marine biogenic）in this critical region,numerous coral reefs have been developed on the Xisha-Zhongsha terrain since the early Miocene.Previous studies of the Xisha carbonate platforms have mainly focused on the analyses of sedimentology,tectonics,and modern ecology,but little geochronological work,which ought to be an important component of such researches,has been performed.This lack of geochronological information significantly hinders our understanding of the initiation and development of these biogenic reefs.Herein, multi-parameter rock magnetic measurements,including isothermal remanent magnetization（IRM）acquisition,hysteresis loops and magnetic scanning,were performed on typical samples collected from Borehole XK-1in the Xisha Islands.The results suggest the predominance of ferrimagnetic phases in the XK-1biogenic reefs,and the average sizes of magnetic mineral grains are relatively coarse,falling within the pseudo-singledomain to multidomain-like grainsize region.Further mathematical partitioning demonstrates the predominance of low-coercivity component（mainly magnetite）.Considering that the study area is far away from the East Asian continent and the growing process of the biogenic reefs,it is inferred that the main magnetic mineral in biogenetic reefs is magnetite,which is from terrestrial detrital materials and absorbed or filtered into the reef with its growth.Further magnetostratigraphic study shows that the identified normal and reverse magnetozones can be correlated with geomagnetic polarity time scale（GPTS）,providing several reliable age constraints for thosereefs.It

关 键 词：南海 西沙群岛 生物礁沉积 岩石磁学 磁性地层学 

分 类 号：P318[天文地球—固体地球物理学]