長野県中部における小坂田ローム層降灰期の古気候
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概要
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The Ono Peat Bed (36°N. Lat.; 850 m above sea-level), and the Nakayama Peat Bed (36°10' N. Lat.; 750 m above seal-level), both in central Nagano Prefecture, represent a nearly equal time range with that of the Osakada Loam, the late Quaternary volcanic ash beds, though a short hiatus intervenes between the two peat beds. The results of pollen analyses together with some cones, fruits and leaves reveal such palaeoclimatic fluctuations in central Nagano Prefecture as mentioned below. (1) The lower part of the Nakayama Peat Bed (corresponding to the horizons from Pm-lA Pumice Bed to Pm-2B Pumice Bed of the Osakada Loam) During this stage it was fairly cool in summer, but was not so cold in winter. The main element of the coniferous forests around the Matsumoto Basin was Picea maximowiczii REGEL, while deciduous broad-leaved trees were rather rare in those forests. There were shallow marshes in the lowland of the Matsumoto Basin. In the clear waters with high content of silica such diatoms as Diploneis Yatukaensis Okuno and others flourished. As a whole the climate of this stage was fairly cold. (2) The upper part of the Nakayama Peat Bed～ the lower part of the Ono Peat Bed (corresponding roughly to the horizons from Pm-2B Pumice Bed to a horizon a little above Pm-3F Pumice Bed of the Osakada Loam) It was rather warm in this stage. Both in the Nakayama and Ono areas coniferous forests, with Picea maximowiczii REGEL as the chief element, declined, while deciduous broad-leaved trees gained prosperity with coniferous Cryptomeria and such broad-leaves as Pteracarya, Alnus, Ulmus (or Zelkova), Corylus and Castanea. A short period of a warm climate intervened in the last phase of this stage (a horizon near the top of the lower part of the Ono Peat Bed), when the climate as a whole was becoming cool. (3) The middle part of the Ono Peat Bed (corresponding to the horizons from Pm-3F Pumice Bed to the uppermost part of the Osakada Loam; or from the horizon a little below the bed of 35,700 ± 1,400 ^<14>C y. B. P. to the bed of 30, 000 y. B. P) It was very cold in this stage. In the environs of Ono, Coniferous forests were flourishing consisting mainly of such subalpine flora as Picea maximowiczii REGEL, Pinus koraiensis SIEB. et ZUCC., Abies veitchii LINDL., Tsuga (probably Tsuga diversifolia MAST.) and Larix leptolepis MURRAY. Deciduous broad-leaved trees largely faded away. The height of the zone of Picea jezoensis CARR. var. hondaensis REHD. fell to a level a little higher than the area of the Ono Peat Bed. During this stage and also in the stage 2, the flat lands, for instance the river terraces, were covered with such grasses as of the Cyperaceae. Probably the volcanic ash fall hindered trees to grow. (4) The upper part of the Ono Peat Bed (from approximately 30,000 y. B. P. to approximately 27,000 y. B. P.) It was rather cool temperate in this stage but was ameliorating. The coniferous trees declined, while such deciduous broad-leaved trees as Alnus, Betula, Ulmus (or Zelkova) and Pterocarya increased as compared with the preceding stage.
- 信州大学理学部の論文
- 1973-10-01
信州大学理学部 | 論文
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