北海道士別市北西,湖南から産出する中期中新世植物化石群

抄録

A late Middle Miocene megafossil flora (Konan Flora) is preserved in lacustrine deposits in the Konan Tuffaceous Sandstone and Mudstone Member of the Bifuka Formation in Shibetsu City, Hokkaido, the northernmost island in Japan. The Konan Flora is composed of 38 taxa in 17 families and 24 genera and includes 4 evergreen conifers, 1 monocotyledonous perennial herb, 33 deciduous dicots, and 2 seeds of unknown affinity. The most dominant species in the flora is Fagus palaeojaponica, followed by Acer subcarpinifolium, A. protojaponicum, Picea sp., Salix sp., Cercidiphyllum crenatum, Betula protoglobispica, and Cladrastis chaneyi. The vegetation inferred from the Konan Flora is broad-leaved deciduous or mixed northern hardwood forest which is typical in northern Japan at the Middle Miocene. The composition and components of the Konan flora are similar to those of the Late Miocene Mitoku-type floras in Hokkaido. The leaf physiognomy and quantitative climate analysis based on the CLAMP (Climate Leaf Analysis Multivariate Program) revealed that the prevailing climate was a wet cool temperate climate similar to modern Hokkaido or northern Honshu. Compared with Sakipenpetsu flora (early Middle Miocene), Shanabuchi flora (Late Miocene) and Rubeshibe flora (Early Pliocene), there were no great differences between the Konan flora and those three floras in terms of climatic conditions.