山形県小国町の中部中新統からマングローブ(メヒルギ属)花粉の産出

概要

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Molluscan and pollen fossils in the mangrove swamp are known from the upper Lower-lower Middle Miocene sediments in Southwest Japan. Pollen analysis was performed for the purpose of finding a fossil mangroves in Northeast Japan. Sixteen samples were collected from two sites of the Middle Miocene Myozawabashi Formation in the Oguni area, Yamagata Prefecture, Northeast Japan. As a result, evergreen Quercus occurred dominantly in the pollen composition of both sites, which is characteristic for the NP-2 zone of the Neogene pollen zones. In particular, mangrove pollen (Kandelia sp.) fossils were found in an oyster fossil bed. This is the northernmost record of fossil mangroves in Japan. The living mangrove Kandelia candel (L.) has a northern limit at South Kyushu (Kiire, Kagoshima Prefecture), and so the average winter (January) temperature of Oguni town in the early Middle Miocene period is estimated to have been at least 9℃ higher than today. Since a mangrove swamp-dwelling bivalve Geloina was recently found in northern Iwate Prefecture, the mangrove pollen may be found in more northern places than the Oguni area.
2008-05-15