有孔虫と非生物的環境の復元

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Foraminifera are used extensively for reconstruction of paleo-abiotic environment on the basis of the data accumulatedon their ecology and distribution in modern seas and oceans. In current studies some problems as undermentioned are involved. Weakness inherent to the uniformitarian method may be covered by multiple comparison among independent species. Dead assemblages appear more informative than live ones for paleo-ecological application. Discrimination of allochthonous elements (as individuals, species, assemblage) from autochthonous ones is still difficult, though accomplished to some degree. Considerations should be given to the biotic environment which had been almost neglected in current studies. The necessity of statistical analyses is emphasized for the ecological investigations of Foraminifera. Three analytical methods recently introduced to this field are critically reviewed. Vector analysis is useful for faunal comparison, and the results may be mappable by proportional contributions of each end member. Objective choice of the end members has, however, not yet been clearly demonstrated. Each proportional contribution by a member represents only apart of the characteristics of a given fauna. Even employing many end members, another statistical examination will be needed for synthetic interpretation of the results. The clustering method promises to excel in classifying faunas with the consideration of every faunal constituents. So far as each fauna yields a sufficient number of species, the method just mentioned is also applicable to a smaller number of faunas or ones which are remote from each other. The facts that should be subjected to reconsiderations are that no objective and universal criteria have been set for choice of similarity level, and that this method itself does not involve clues for the mechanism of a biotic environment. In this respect the factor analysis may provide a more advanced analytical method. Communality of this analysis represents a synthetic and detailed but simple measure of the faunal composition. It is quite effective in the case of closed ecosystem, but not for periodically changing environments and open ecosystems. Correlation between test morphology and some environmental factors is discussed and illustrated by examples of bolivine variations in basins off southern California. It is generally accepted that benthonic Foraminifera are advantageous for reconstruction of paleobathymetry on the one hand and the planktonic ones for paleotemperature on the other. Recent investigations on planktonic forms, however, suggest that specific association or wall structure of some groups may be also informative for paleobathymetry. For example, the occurrence of a Globorotalia truncatulinoides population without the crust layer from the Nekoya Formation is considered to indicate that the formation was formed in water shallower than 350 m.
日本地質学会の論文
1968-12-28

有孔虫と非生物的環境の復元

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