东太平洋锰结核中叠层石纹层周期信号的谱分析及其意义

Spectral Analyses of Rhythmic Laminae of Stromatolite in Manganese Nodules from the Pacific Ocean and their Significance

利用光学显微镜对一取自东太平洋的光滑型锰结核中的叠层石纹层进行分级统计,得到纹层带、纹层组和纹层对的韵律周期分别约为500μm、50～42.8μm和11～9.0μm。利用电子探针线扫描分析获取了锰结核磨光面上一生长剖面(长0.7mm)的Si、Al、Fe、Mn元素的含量变化序列,运用功率谱分析方法识别出上述4种元素序列具有111.3μm、46.5～40.6μm、24.9～28.1μm、23.1～23.9μm和11.7～13.4 μm的显著振荡周期。除了纹层带周期由于受剖面长度限制没有出现外,显微镜下统计得到的叠层石的纹层组和纹层对周期在元素序列的功率谱分析结果上均得到了反映。通过对锰结核生长速率的讨论,认为锰结核的纹层韵律很可能与地球轨道参数的周期性变化有关,纹层组周期可能对应地球轨道的黄赤交角变化周期,纹层对周期可能对应地球轨道的半岁差周期,所研究剖面叠层石的生长速率约为1.134mm/Ma。

Sample 1783 is a smooth-typed manganese nodule that was collected from the eastern Pacific Ocean. Its stromatolite laminae in the growth direction were counted under the reflected light microscope. A profile of 700μm long without hiatus was analyzed by line scanning of the electron microprobe to yield geochemical strati graphic series. The power spectral analysis method was used to distinguish the oscillation periodicity of Si, Al, Fe and Mn series. The study results show that both the lamina thickness and geochemical stratigraphic series display conspicuous cyclicity: the average thickness of lamina band, lamina group and lamina pair are about 500 μm, 50-42. 8 μm and 11 - 9. 0 μm respectively. The Fast Fourier Transform (FFT) of Si, Al, Fe and Mn series gives principal spectra peaks at 111. 3, 46. 5 - 40. 6, 24. 9 - 28. 1, 23. 1 - 23. 9 and 11. 7 - 13. 4 μm. The cycles of lamina group and lamina pair are revealed and reflected in the Si, Al, Fe and Mn series. Since the studied profile is too short, the cycle of lamina band does not appear. Based on the discussion of the nodule growth rate it is considered that the rhythmic laminae of manganese nodules are most probably associated with the periodic variations of earth's orbital parameters. The cycle of lamina group probably corresponds to the period of obliquity, and that of lamina pair probably corresponds to the period of a half precession. The net growth rate of the studied profile is about 1. 134 mm/Ma.