Environmental change based on diatom assemblages from Lake Yamanaka at the northern foot of Mt, Fuji, Central Japan

概要

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Environmental history in Lake Yamanaka was investigated based on diatom assemblages obtained from the 17.5m length borehole core in the lake center. Lake Yamanaka (surface area 6.89km²; maximun depth 14.3m; mean depth 9.4m; altitude above sea level 978m) is one of the Fuji Five Lakes and located at the northern foot of Mt.Fuji. Although this lake had been considered formed by the lava flow from Mt.Fuji about 1850 years ago, results of this research suggested that the formation age more old stage on account of the presence of planktonic diatoms mentioned below. The borehole core sample has mainly consists of unconsolidated silts and scoria fall deposits associated with sandstone layers. According to the composition of diatoms contained in silts, the geohistory of this lake was divided into 4 periods;i.e., 1) The 1'st swamp or river period (11.4-9.2m borehole core in depth); Epiphytic or benthic diatomes such as Flagiralia spp. or Epithemia sp. were dominant in these samples. 2) The 1'st lake period(9.2-6.0m borehole core in depth): Planktonic diatoms such as Aulacoseira sp. or Cyclotella sp. were dominant in these samples. 3) The 2'nd swamp or very shallow lake period(6.0-2.5m borehole core in depth): Epiphytic or benthic diatoms became dominant again. 4) The 2'nd lake period (2.5m-surface borehole core): Planktonic diatoms were dominant again.
信州大学の論文
2004-02-28