【摘要】 南沙群岛南永2井的红色沉积层和黑色沉积层标志着两次异常事件,简称为“红色事件”和“黑色事件”。这两个特殊沉积层的主要特征是磁化率为正值、锰铝(黑色沉积)和铁铝(红色沉积)含量高。关于它们的成因主要有两种观点:一种是火山喷发或地震活动,另一种是气候突变。将红色沉积层和黑色沉积层与南海其它珊瑚礁钻井资料、南海及其周缘火山活动和深海沉积中的微玻陨石进行详细对比,并综合分析几种成因的可能性大小。“红色事件”和“黑色事件”在南海其它珊瑚礁钻井中的反映不明显或无反映,表明两事件的影响范围很有限。尽管南海周缘的一些火山活动期次、全球气候变化的一些代用指标和深海沉积中的微玻陨石层在时间上与“红”、“黑”两事件有较好的对比,成岩作用也能使某些沉积层位形成铁富集或锰富集,但综合考虑各个因素可以排除周缘火山喷发、气候突变、撞击事件及成岩作用等4种成因。火山或地震活动引起的铁或锰热泉上涌可以对“红”、“黑”两事件作出较好的解释,是可能性较大的成因。更多还原

【Abstract】 The second drill core at the Yongshu Reef(core Nanyong-2) of Nansha Islands in the South China Sea is located at 9°33′N,112°52′E.It has been drilled down to 413.69 m,penetrating through the whole Quaternary into the upper Miocene. In this core,red-colored and black-colored sedimentary rocks are found at the depths of 195.96—196.26m and 96.59—99.69m,respectively.These unusual rocks are dominantly characterized with positive susceptibility and very rich in Mn-Al(black-colored sediments) and Fe-Al(red-colored sediments).They imply two abnormal events suddenly taking place during the accumulation of coral reefs,which are called "Red Event" and "Black Event" for short,respectively.At present,two explanations for their formations have been proposed—volcanic activity and sudden climate change.We try to correlate detailedly these unusual rocks with other reef drill cores,microtektites from deep-sea sediments and volcanic activities occurring in the South China Sea and its vicinity.Further more,all possible origins of the "Red Event" and "Black Event" have been systematically analyzed.These two events have only little reflection in core Nanyong-1,which is only 100m away from core Nanyong-2,and no reflection in other reef cores.That means the coverage of these two events is very limited.Therefore,volcanic activity and sudden climate change seem unlikely to be the origins of the "Red Event" and "Black Event".Although the red-colored and black-colored sediments can be correlated well with the microtektites from deep-sea sediments in age,they are greatly different in distribution,shape,configuration and other characteristics.Accordingly,celestial body impacts as the origins of these two events also should be eliminated.Diagenesis may lead to the concentration of Fe or Mn in certain sedimentary layers;however,the properties of such concentration are quite different from those of the studied layers.In the end,we come to the conclusion based on available data that Fe(Fe-rich hydrothermal fluid) and Mn plumes(Mn-rich hydrothermal fluid) are more favorable for explaining the formation causes of the red-colored and black-colored sedimentary rocks in core Nanyong-2.更多还原