Abstract
The Tokusa Basin is situated at an elevation of 300m in the northeastern part of Yamaguchi Prefecture in the western Chugoku Mountains, western Japan. A 68m long core containing silt, peat, volcanic ash and clay, which accumulated in the old lake Tokusa during Pleistocene, was sampled at Tokusa-Sadayuki, Ato-cho, in the Basin.
In the study reported in this paper, a part of the 68m long core: 10.6m were palynologically examined at intervals of 20cm. Three samples were measured by 14C dating method: the age of the middle samples (390-395cm) was 46, 110±1, 050y. B. P. The volcanic ash inbedded between 500 and 520cm was estimated as Aso-4 ash which accumulated in the old lake ca. 70, 000 years ago.
From the results of pollen analysis from the Tokusa Basin and the Ubuka Basin (HATANAKA and MIYOSHI, 1980), seven pollen zones could be recognized; in order from the surface to the lower part, they are as follows:
L zone (10, 000-15, 000y. B. P.) with subarctic pollen types (Pinus, Abies, Picea, Tsuga, Betula)
P-I zone (15, 000-25, 000y. B. P.) with subarctic pollen types (Pinus, Abies, Picea, Tsuga)
P-II zone (25, 000-45, 000y. B. P.) with subarctic pollen types (Pinus, Abies, Picea, Tsuga, Betula)
P-III zone (45, 000-70, 000y. B. P.) with temperate pollen types (Cryptomeria)
P-IV zone (70, 000-80, 000y. B. P.) with cool temperate pollen types (Fagus, Quercus, Tsuga, Picea)
P-V zone (80, 000-120, 000y. B. P.) with cool temperate pollen types (Fagus, Quercus, Carpinus, Ulmus)
P-VI zone (120, 000-?) with temperate pollen types (Cryptomeria, Tsuga, Pinus, Carpinus) L and P-I zones are from the Ubuka Basin, P-II and P-VI zones from the Tokusa Basin.
The six pollen zones from L to P-V cover approximately the 110, 000 years of the last glacial period, while the P-VI zone is a part of the last interglacial period.
