植物化石群による第三紀気温変化の推定
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概要
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Climatic history during the Tertiary has been studied more in detail than those of any other geologic age except for Quaternary time. Based on plant megafossils and microfossils (pollen/spore) a terrestrial paleoclimate has been inferred principally by three distinct methods. A method introduced from Quaternary palynology has been applied to Tertiary pollen floras; paleoclimate is inferred from the relative abundance of certain genera which are now distributed mainly either in warm or cold regions. Climatic requirements of Tertiary plants, however, are difficult to be determined only by generic level. The second method based on climatic requirements of the extant related taxa has been most commonly applied to megafossil floras. Paleotemperature and paleoprecipitation are estimated from climatic parameters of the region which shows a closest floristic affinity to fossil flora, or which has modern communities closely similar to fossil assemblage. This method depends on accuracy of taxonomic determination and assumption of unchanging ecologic torelance of plants through the Cenozoic. It is difficult to be applied to early Tertiary floras including many extinct genera. Misidentification of fossils also is apt to lead an incorrect paleoclimatic inference. The relative abundance of the Arcto-Tertiary and Paleotropical elements in Tertiary floristic sequence of the middle latitudes was used as an indication of climatic changes. These elements are determined also by the nearest living species. The best method, so far as we can apply to fossil leaf assemblage at the present time, is based on general correlation between some foliar physiognomic characters and climatic parameters (especially, between the percentage of entire-margined species and mean annual temperature). This is independent of taxonomy of a given fossil; it can afford the most reliable result for paleotemperature inference, although its application to fossil assemblage has been debated. To obtain more accurate estimates of Tertiary climatic changes, a further investigation is needed to resolve some fundamental problems : a thorough understanding of relationships between fossil assemblage and source vegetation, for instance by taphonomic study; validly determining paleoaltitudes of fossil flora; a further refinement of method in physiognomy/climate relation of the modern vegetation.
- 日本古生物学会の論文
- 1993-06-30
日本古生物学会 | 論文
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