日本海沿岸の鮮新世貝形虫群集と海洋環境との関係(<特集>日本海の生物相の変遷と環境変動-過去,現在そして未来へ向けて)

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Previous studies of Pliocene ostracode assemblages have been compiled and reanalyzed. Three ostracode associations were identified in the fossil ostracode assemblages from the middle Pliocene Sasaoka Formation, Akita Prefecture, northeastern Japan. Association A is abundant in the lower part, dated before 2.75 Ma, and is composed of warm-to-mild-temperate water species. Species belonging to Association B are common throughout the sequence. Association C is abundant in the upper part, dated after 2.75 Ma, is composed of species living in subarctic to cool-temperate shallow marine areas, and contains extinct cryophilic species. Fossil ostracode assemblages from the middle Pliocene Kuwae Formation, Niigata Prefecture, central Japan, show that temperate intermediate water species were abundant or common in most interglacial periods. Moreover, shallow warm-temperate and cool-temperate species occurred together before ca. 2.75 Ma but, thereafter, their relative abundances became inversely related. Extinct shallow cryophilic species greatly increased during the glacial periods of the marine oxygen isotope stages G4 (ca. 2.7 Ma) and 104 (2.6 Ma). These results prompt the following conclusions. 1) Temperate intermediate waters entered the Japan Sea during most of the interglacial periods at least during the period ca. 3.0-2.6 Ma and water temperatures were higher in the lower sublittoral to upper bathyal zones during those periods than they are today. 2) The differences between surface water temperatures during the interglacial periods and those during the glacial periods became great at ca. 2.75-2.6 Ma. 3) Many cryophilic species migrated from northern seas during each glacial period after 2.75 Ma.
2007-10-15

日本海沿岸の鮮新世貝形虫群集と海洋環境との関係(<特集>日本海の生物相の変遷と環境変動-過去,現在そして未来へ向けて)

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