石灰質ナンノ化石サイズ変化とDiscoaster生産量からみた新生代古海洋変動(<特集>後期新生代の環境指標としての微古生物学と古海洋学の進展)

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We discuss in detail the Cenozoic paleoceanograpy related to the sea surface stratification, nutrient, and sea surface temperature based on the relationship between the coccolith maximum size and Discoaster abundance. The positive correlation was recognized between these parameters in the sequence from Eocene to Pliocene. As Discoaster is likely a lower photic species as like Florisphaera profunda, abundant occurrence of Discoaster indicates the sea surface stratification and the oligotrophic condition. On the basis of the relationship between coccolith maximum size and Discoaster abundance found in the Cenozoic sequence of ODP sites 807 and 731, the intervals of the late Eocene, NN3 to NN4 zones in the early Miocene, and NN6 to NN9 zones in the middle Miocene, are interpreted as the oligotrophic conditions.
2009-10-16