Abstract
The writer summarizes some features of the Quaternary volcanic ash layers in the Kanto and Hokuriku regions of central Japan from palynological point of view. He intends to aquire informations of the difference in the contents of pollen and spore grains between the volcanic ash layers and the normal sediments above and below them.
(A) Pollen and spore grains found in volcanic ash layer sedimented in the sea.
1) The absolute quantity of pollen and spore grains is generally less in the volcanic ash layer than in the overlying and underlying deposits.
2) In the case of a thin ash layer, about 5 to 20cm in thickness, the relative frequency of pollen and spore grains in the ash layer is similar to that in normal sediments.
3) In the case of a thick volcanic ash layer, about 20 to 50cm in thickness the contents of pollen and spore grains are not uniform throughout the layer.
4) Even in the case mentioned in 3), the relative frequency of pollen and spore grains included in the normal sediment above the volcanic ash layer is similar to that in normal sediment below the ash layer.
(B) Pollen and spore grains found in volcanic ash fall deposits on the land.
1) Although many pollen of such needle-leaf trees as Pinus, Picea, and Abies and pollen of such broad-leaved trees as Alnus, Betula, Fagus and Quercus are found in the lowermost and uppermost parts of volcanic ash layer, they are scarcely found in the middle part.
2) The absolute quantity of pollen and spore grains found in normal sediment below the ash layer is always more than that in normal sediment above the ash layer.
3) The relative frequency of pollen of such woody plants as Pinus, Picea, Abies, Quercus and Alnus is higher than that of herbaceous plants.
4) In the normal sediments above and below the volcanic ash layer, the relative frequency as absolute quantity of the pollen of such needle-leaf trees as Pinus, Picea and Abies is higher than those of such broad-leaved trees as Quercus and Alnus.
5) Concerning the amount of spore grains, they are frequently found in the underlying normal deposits, but are hardly found in the volcanic ash layer and in the overlying normal sediment.
The information about the difference in the contents of each layer mentioned above are summarized in the text-figure.
These data may give a hint as to the influence of volcanic ash fall on the land flora in the environs of a volcano and the floral change after the fall of volcanic ash.
