The Noroshi Flora of Note Peninsula, Central Japan

Abstract

The beautiful abundant fossil plants are preserved in the lagoonal beds of the Yanagida formation in Noroshi area locating at the northeastern extremity of Noto Peninsula, sea-coast of central Japan. The Yanagida formation is mainly composed of dacite tuffs resting conformably on the Anamizu formation which consists mainly of andesites and makes a basal part of the Miocene in this part of the Green Tuff Region. The overlying Suzu formation has a rich fauna in the lower part, indicating the Middle Miocene age. The fossil plants of the Yanagida formation, the Noroshi flora, are obtained from tuffaceous shales about 10 m thick intercalated in the dacite tuffs of about 200 m in thickness. The Noroshi flora is composed of 84 species which have living equivalents of 69 species in China, 51 in Japan, 15 in western North America, and 22 in eastern North America. The living equivalents of the Sub-element are found mostly in the warm temperate forests of southwest Japan. Many species of the Chinese Sub-element are found living in central China and Taiwan. Three associations are discriminated in the Noroshi flora, that is, lake border or flood plain and valley slope association. The former association consists of 41 species occupying 54.62% of the total number of specimens. Main species are Comptonia, Elaeocarpus, Liquidambar, Quercus, Rhus and Zelkova. A valley slope association includes 58 species attaining 74.60% in quantity. Representative species are Acer, Elaeocarpus, Keteleeria, Libocedrus, Perrottetia, Quercus, Rhus and Zelkova. A mountain association, such as Picea and Pinus palaeopentaphylla, is rather poor, represented by only 13 species, 0.81% of the all. The annual precipitation of the Noroshi flora is assumed to have been at least 1, 600 mm, presumably even as much as 2, 000 mm. The coldest monthly mean temperature, the warmest mean temperature and the annual mean temperature are estimated to have been about 4-5℃, 26-27℃ and 14.5-15.0℃, respectively. Autumn was the rainiest season, and even drier months have a precipitation of over 100 mm. Comparing with the correlative Middle Miocene floras along the coast of the Sea of Japan, such as, those of Noto-nakajima in central Japan, of Utto in northeast Japan and of southwestern Hokkaido, the southern limit of the deciduous forest zone in Japan Sea side must have been nearly two degrees further north than the present position.