日本中部北陆地区大陆架松任市水下森林的孢粉学研究

松任市水下森林于1998年发现，位于日本中部北陆地区松任市Hama-sogo和Kurabe附近手取河现代冲积扇2-3km外的20-30m水下，中树桩，树根或直立的树干保存。这一发现证明在早全新世当地有森林发育，森林的主要成分有Alnus,Quercus,Morus,Fraxinus,14C年代为距今8000-10000a，孢粉分析显示沼泽植物，如Alnus,Salix,Cryptomeria,Gramineae,Numphaceae丰富，Lepidobalanus,Castanea,Fraxinus常见，而Fagus ef.crenata Pinus少见，硅藻表明其在森林发育暑期当地为淡水或小湖泊。因此，当时森林生长在古手取河冲积扇边缘的沼泽地区，寒温带的Sasa-Fagetum crenate群丛（Association)的Alnus japonica群落（Community)广泛分布，推测年均温比现代要低几度，水下森林的形成时间和冰期后气候变暖所引起的海平面上升相一致，推测可能由于海水水位上升，古手取河洪水从上游冲下的碎屑物掩埋了当时的森林形成了现在的水下森林，因为日本海沿岸的洋流冲刷而使得这些化石森林显露出来，当前的水下森林和Nyuzen水下森林是目前世界上已知仅有的两处大陆架上的水下森林。

PALYNOLOGICAL INVESTIGATION OF THE MATTO SUBMERGED FOREST ON THE CONTINENTAL SHELF IN THE JAPAN SEA OFF THE TEDORI-GAWA ALLUVIAL FAN, THE HOKURIKU REGION, CENTRAL JAPAN

The Matto submerged forest was found in spring of 1998 as stumps, roots and erect trunks from the continental shelf at depth between 20 and 30 m, and in 2 to 3 km off the recent marginal area of the Tedori-gawa alluvial fan at Hama-sogo and Kurabe, Matto City, the Hokuriku region, Central Japan. This discovery proves the development of ancient forest in the early Holocene. Main tree remnants of the forest are Alnus, Quercus (Lepidobalanus), Morus and Fraxinus, the most commonly preserved genera. These trees had grown on the now submerged seaward margin of the old Tedori-gawa alluvial fan. An age of the submerged forest determined by the C-14 method is about 10 000 to 8 000 years B.P. According to pollen analyses, such marshy plants as Alnus, Salix, Cryptomeria, Gramineae and Nymphaceae are abundant, Lepidobalanus, Castanea and Fraxinus are common, and Fagus cf. crenata and Pinus are rare. Diatom remains give some indication of fresh water such as a bog and/ or small lake at the age of the forest development. Therefore, it is inferred that the forest had grown in back marshy area on the margin of the old Tedori-gawa alluvial fan. On the basis of tree composition in the submerged forest, it is estimated that Alnus japonica community of Sasa-Fagetum crenate association in the cool temperate climatic zone was fundamentally widely distributed, and an annual mean temperature at that age was a few degrees in centigrade lower than that of the Recent. The submerged forest shows the rising of sea-level coinciding with the warming of climate during the early Postglacial epoch. Remnants of an ancient forest were probably overwhelmed by a rise of the water table caused by a rise of sea-level, and preserved in the overlying flood debris derived from the upper stream of the ancient River Tedori. The present exhumation of the remnants is the result of a submarine erosion by the present coastal current along the coast of Japan Sea. This and the Nyuzen submerged forests are the only two existing submerged forests on the continental shelf throughout the world, where was once land area.