Fourier Analysis of Growth Pattern of a Precambrian Stromatolite for Palaeo-Geochronology

概要

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The growth pattern of Infra-Cambrian (ca.650-800Ma) stromatolite is studied by means of the personal image analyzing system (PIAS). Between the strong dark-colored rings, more than ten finer dark-colored stripes are visible on the polished surface. The CCD image of these concentric ring pattern is then Fourier analyzed. The number of these stripes should give palaeo-astrometric information, if the annual and monthly ring formations could be identified. Two types of image analyses are employed for counting the number of finer rings between the consecutive strong dark-colored rings. In one case, only the intermediate scale corresponding to finer stripes in the direction parallel to them are taken into account in the inverse Fourier transform, minimizing disturbances from smaller scales on the counting of finer rings. In another approach, the edge enhanced image is traced in the direction perpendicular to the ring structure at several positions. The tracings are analyzed in the fast Fourier transform (FFT), giving the representative wave number of the finer ring structure. The results of both types of analysis show that the average number of finer stripes (months) between consecutive strong dark-colored rings (one year) to be surely exceeding twelve. Thus, the periodicity of the primitive plant life in Infra-Cambrian era is estimated to be about 13 months per year. The moon was about 5 per cent closer to the earth than today.
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