Pollen diagrams are represented from core samples taken from five boreholes in the Tenma Formation (lower terrace deposits) and the Nanba Formation (Alluvial deposits) in the Osaka plain. On the basis of pollen stratigraphy the diagrams are divided into two local pollen assemblage zones (E and F) including 11 sub-zones (E 1-5 and F 1-6). The forests characteristically inferred from the pollen assemblage are Castanopsis-Quercus (Cyclobalanopsis) Forest, Abies firma-Tsuga sieboldii Forest, Fagus Forest and Subalpine coniferous Forest. A considerable number of pollen grains preserved are thought to be derived from catchment areas of each river as the deposits accumulated. The forest history of the area is as follows. E1-E3 sub-zone; Subalpine coniferous Forest and Fagus Forest were extensive to cover the area from about 30, 000y.B.P. to 20, 000y.B.P.. E4 sub-zone; Subalpine coniferous Forest was the most widely spread over to the area between 20, 000y.B.P. and 18, 000y.B.P. (?). F1-F2 sub-zone; Fagus Forest was widely expanded to the lowland area in the early Holocene (10, 000y.B.P.-7, 500y.B.P.). F4 sub-zone; Castanopsis-Quercus (Cyclobalanopsis) Forest was widely developed in the lowland area in the middle Holocene (6, 000y.B.P.-2, 500y.B.P.) F6 sub-zone; These forests were replaced by a secondary forest in the latest Holocene (since 1, 500y.B.P.).
In this paper we discuss processes of slope denudation during the Holocene in the hilly area near Sendai. We gave it our general consideration of the history of local geomorphic environments and hillslope development based on the analyses of sediments located in isolated depressions, including pollen analyses, radiocarbon datings and plant communitical data. The main results are as follows. 1. Three periods of hillslope instability are identified: 1) before 9, 000y.B.P., 2) between 6, 000 and 2, 500y.B.P., with a prominent period between 6, 000 and 5, 000y.B.P., and 3) after 1, 000y.B.P. The unstable period between 6, 000 and 5, 000y.B.P. is contemporaneous with the Hypsithermal epoch (Fig. 4). 2. It is not yet certain that the unstable period after 1, 000y.B.P. can be wholly attributed to soil erosion caused by human impacts on natural vegetation. 3. Palynological analysis is useful for the clarification of slope conditions at various in time, for increases and decreases of pollen grains of certain plants which reflect geomorphological conditions, (especially Zelkova, Ulmus, Carpinus, Fraxinus and Fagus), enable one to determine micro-topographical changes on hillslopes. 4. Different kind of denudation process on hillslope, i.e. soil creep on crest slope in the stable period (Fig. 7a) and small surface failure of slump type on side slope in the unstable period (Fig. 7b), has characterized present hillslope morphology.
An active fault, by which middle Jomon dwelling site was displaced, was found at the Kojinyama Site constructed on a small fan in the southeastern side of Lake Suwa, Nagano Prefecture. This fault has NW-SE direction with vertical displacement of 60cm at the maximum, and a small displacement of left lateral sense. Judging from the situation and direction of the fault, it is most probably a part of the Itoigawa-Shizuoka Tectonic Line. As the fault cuts the dwelling site of the middle Jomon age (ca. 4, 500y.B.P.), the formation of the fault was just after the construction of the dwelling or later in age. The latest movement of the Itoigawa-Shizuoka Tectonic Line near Lake Suwa, is more dominated by vertical sense than lateral movement, judging from the displacement of dwelling as well as that of the nearly fan surface (correlated to the Tachikawa surface in Kanto).
A rhyolite lava flow near Mt. Haneyama, Central Kyushu, gives the age of 0.53m.y. by the fission track method. This lava belongs to so-called “Haneyama lavas” which are widely distributed in Central Kyushu and have been considered to have erupted from several volcanic centres for their scattered distributions. Another Haneyama lava near Sakanashi at about 30km south of Mt. Haneyama was dated 0.41-0.50m.y. by K-Ar and fission track method (KANEOKA & SUZUKI, 1970). The radiometric ages of these two lavas suggest that Haneyama lavas nearly simultaneously erupted from the several volcanic centres. The fission track age reported in this paper will also contribute to determining the age of the upper part of Oita Group and the age of activities of the Haneyama graben.