上部中新統土岐口陶土層堆積盆地とその周辺の古地形変化に伴う古植生の変化

Species composition of plant macrofossil assemblages from the Tokiguchi Porcelain Clay Formation in Tajimi City，central Japan are compared on a stratigraphic basis．The formation was deposited in a fluvial environment in a sedimentary basin at about 10 Ma（early Late Miocene）．The fossil assemblages always contained subtropical elements indicating warm climate．Cool temperate elements increased in the upper hodzon，along with herbaceous taxa including annuals．This change is thought to reflect topographic changes in and around the sedimentary basin．During deposition of the lower horizon，plant macrofossils were derived from wetland vegetation and forests between the distal end of the fan and uplands along the sedimentary basin．The forest there was composed mainly of deciduous broad-leaved trees mixed with conifers and evergreen broad-leaved trees，and the herb layer was less developed．During deposition of the upper horizon，the drainage basin of the river expanded to include higher mountains，from which the cool temperate elements were derived．Active tectonism at this time increased disturbance，creating the habitat which enabled herbaceous plants（including annuals）to grow on the deposits of a large gravelly rivers．