中太平洋铁锰结壳灰度序列中米兰柯维奇周期的识别及结壳生长速率的演化

The Identification of Milankovitch Cycles in the Gray-Level Series of Fe-Mn Crust from the Central Pacific Ocean and Its Growth Rate Evolution

利用数字图像处理方法提取中太平洋海山铁锰结壳(CB14)生长剖面的灰度序列,运用功率谱分析方法揭示出结壳由表及里5个亚层中分别存在多级序的显著周期,它们均能够分别与地球轨道周期(偏心率周期、黄赤交角周期和岁差周期)的级序很好匹配,根据匹配结果获得CB14第1至第5亚层的生长速率分别为2.15、2.70、2.43、2.75、2.67mm/Ma,各亚层的界面年龄分别为1.3、2.5、5.9、6.7、7.5Ma。表明晚中新世以来,结壳的生长速率呈现波动变化,最近1.3Ma以来,结壳的生长速率明显减慢。认为通过识别结壳灰度序列中存在的米兰柯维奇周期可以有效获得结壳各生长阶段的高分辨率生长速率,可以为研究中新世以来古海洋环境的演化提供重要信息。

A Fe-Mn crust sample（CB14）from a seamount in the central Pacific Ocean was studied in detail.According to the micro-texture of the growth profile of the crust,its outer layer（18.7mm in thickness）can be divided into 5 sub-layers,no hiatus observed between the adjacent sub-layers.Using the technique of digital image processing,the gray-level variation series of the reflectivity of the growth pattern were obtained.The power spectral analysis revealed that most of the prominent cycles identified from gray-level series are corresponding to Milankovitch cycles（eccentricity,obliquity and precession）.Through matching and tuning to the Milankovitch cycles,we obtained that the growth rates of sub-layer 1 through sub-layer 5 are 2.15,2.70,2.43,2.75 and 2.67 mm/Ma,respectively.Their corresponding ages are 1.3,2.5,5.9,6.7 and 7.5 Ma,respectively.Our results show that since late Micocene,the growth rates of Fe-Mn crust changed alternatively,since recent 1.3 Ma,the growth rate of the Fe-Mn crust slowed down significantly.It is considered that the gray-level series of the growth profile of Fe-Mn crusts can be used as a paleo-environmental indicator,and the application of orbital pacing method on gray-level series is an effective approach to determine the high resolution growth rates of Fe-Mn crust and hence provide important information on paleo-environmental change.