Abstract
The Middle Pleistocene Terabayashi Formation around Mt. Ibuki, in Terabayashi, Maibara City, Shiga Prefecture, central Japan, interbeds the Terabayashi I and II volcanic ash layers that were laid down about 248-247ka ago (Late Middle Pleistocene) and which lie above the Aso-1 volcanic ash layer. The sediments correspond to oxygen isotope stages 8 to 7, a cold period leading to a warm period.
We reconstructed the paleovegetation and paleoclimate based on plant macrofossils, fossil pollen, and insect fossils from these sediments. 1) The vegetation of Mt. Ibuki and its surroundings was a mixed evergreen coniferous and deciduous broadleaf forest containing Pinaceae, Betulaceae, and Rosaceae, including such dominant trees as Pinus koraiensis, Tsuga diversifolia, Abies homolepis, Betula ermanii, B. platyphylla, B. grossa, Malus toringo, and Rubus. At present these species inhabit the upper cool temperate to subarctic zone. 2) The paleoenvironment was reconstructed in the Terabayashi area as follows : a small swamp in which Potamogeton octandrus and Chara grew and where insects such as Lithochlaenius noguchii and Bembidion subsisted and lived ; wetlands covered with Alnus japonica, Rubus, Cyperus, Carex, Polygonum, and Potentilla, and where insects such as Chrysosplenium and Plateumaris lived ; and sun-loving plants such as Kummerovia striata, Artemisia, and Solanum grew and the forest which was composed of Betula grossa, B. platyphylla, and Abies homolepis existed. In the adjoining mountains, Tsuga diversifolia grew on the ridges ; Abies homolepis, Corylus heterophylla, Malus toringo, and Phellodendron amurense grew on the more gradual slopes ; and Pterocarya rhoifolia and Juglans mandshurica var. sachalinensis grew on the valley sides. Herbs such as Melandryum, Coptis, Thalictrum, Impatiens textori, Angelica acutiloba, and Cornus cf. chamaepericymenum grew on the forest floor, where Carabus beetles also lived. In the upper parts of the mountains a mixed evergreen coniferous and deciduous broadleaf forest dominated by such trees as Pinus koraiensis, Tsuga diversifolia, and Betula ermanii existed. 3) The plant fossil assemblages from the lowermost part to the lower middle part of the Terabayashi Formation demonstrate a dry and cool temperate to subarctic paleoclimate. Fossil pollen shows a change from this dry and cold climate to wet and temperate conditions, with a decrease in Abies, Tsuga, Picea, and Betula but an increase in Fagus and Quercus subgen. Lepidobalanus, when the upper middle strata in the sequence were deposited.
