武蔵野台地成増における関東ローム層の植物珪酸体分析

Abstract

Opal phytolith analysis of the Kanto Loam Formation (the tephra layers) composed of the Shimosueyoshi Loam, the Musashino Loam, the Tachikawa Loam and the Kuroboku Soil (in ascending order) at Narimasu Geological Exposure, Itabashi, Tokyo, was carried out. Five local opal phytolith zones can be roughly distinguished. The Kuroboku Soil (A zone) was characterized by the dominance of Pleioblastus with Paniceae, suggesting a warm temperate climate. The Tachikawa Loam (B zone) was dominated by Sasa, indicating a cool temperate climate. This zone was subdivided into two subzones, B1 and B2. Zone B1, the upper part, contained more panicoid phytoliths than Zone B2, the lower part. The Musashino Loam was divided into two zones, C and D, with the boundary between the two situated over the tephra TP (4.9×104F.T.y.B.P.). Zone C was characterized by Pleioblastus, indicating a warm temperate climate, which may correspond to the Middle Pleniglacial in Europe. An increased number of Festuceae and Paniceae were found in zone D which probably means that zone D was in the cooltemperate to subarctic climate. This cold age is correlated with the Murodo Glacial Substage of Mt. Tateyama and the Lower Pleniglacial in Europe. The Shimosueyoshi Loam (zone E) contained much more weathered phytoliths than the other zones. The vegetation at E zone, therefore, unfortunately could not be reconstructed.