The Arakawa Lowland is situated in the western part of the Kanto Plain. Diatom analyses of a large number of boring core samples obtained from the Lowland have been performed, and marine clay deposits on the US (Holocene upper sand bed) have been found in the Arakawa Lowland. Holocene sediments of the Arakawa Lowland can be divided into five diatom zones, of which the fourth is subdivided into subzone A, B, and C. The marine clay deposits roughly correspond to subzone A of the fourth diatom zone. This subzone is characterized by euhalobous species, dominant among them Actinocyclus normanii and Melosira sulcata. The marine clay deposits lie horizontally from Akabane in the Tokyo Lowland to the JR Kawagoe Line in the Arakawa Lowland, and spread vertically from 0m to 3.0m above sea level. The author has investigated the problems of the marine clay deposits using data obtained through diatom analyses and 14C dating. In consequence, the geomorphological history of this area in the Holocene period is inferred as follows. (1) Between about 7, 970y.B.P. and 4, 860 to 3, 130y.B.P., fluvial valleys were drowned by Jomon transgression and were filled with marine sediments. (2) From about 5, 270 to 4, 570y.B.P., the US (Holocene upper sand bed) was formed in this area. (3) Around 3, 990y.B.P., marine clay deposits accoumulated on the upper sand bed. (4) After the period 4, 450 to 3, 130y.B.P., the uppermost alluvial deposits were formed.
Opal phytolith analysis using A horizons of present and buried soils at Te Ngae Road Tephra Section in Rotorua Basin, New Zealand, was carried out to clarify the relationship between vegetation and volcanic ash soils during the last 20, 000yrs. Silica bodies in some New Zealand native trees were also examined. The results are summarized as follows. 1) For the period between 20, 000 and 11, 250y.B.P. grass was the main source of phytolith. The very low amount of phytolith in soils formed before the deposition of the Rerewhakaaitu Ash (14, 700y.B.P.) indicates that these soils developed under scattered grassland or in forests poor in phytolith-supplying trees. During the formation period of soil in the Waiohau Ash (11, 250-7, 330y.B.P.) the main sources of phytolith were grasses and trees. The clear rise of cauliflower-head-like phytolith originating from trees suggested that the climate was wetter and milder than at an earlier stage. Between 7, 330 and 930y.B.P. tree-origin phytolith was dominant. This indicates that forest vegetation completely covered soils. After the deposition of the Kaharoa Ash (930y.B.P.), grass, trees, and ferns were sources of phytolith. The increase of grasses and ferns was due to Polynesian settlements with a resultant reduction in forest cover and increase in fernland and grassland. 2) Holocene volcanic ash soils buried beneath the Kaharoa Ash contain very low amounts of humus because these soils developed under forest vegetation without grasses and ferns. After the deposition of the Kaharoa Ash, widespread grassland and fernland introduced by Polynesian settlements provided the volcanic ash soils with a black humus horizon. 3) It is said that volcanic ash soils with thick black humus horizons (Koroboku soils) were formed under grass vegetation and slow tephra deposition of slow rate. The fact that few Kuroboku soils are distributed in New Zealand might be explained by the fact that until the deposition of the Kaharoa Ash (930y.B.P.) there was little human activity which destroyed forests and induced grass vegetation. 4) Small cauliflower-head-like phytoliths were found in the leaves of Rewarewa (Knightia excelsa) and the wood of Kohekohe (Dysoxylum spectabile). These trees seemed to be one of the sources of tree-origin phytolith (small grain type) in the soils of New Zealand.
The Ohachidaira is a small caldera 2km across in Daisetsu Volcano, central Hokkaido, which was formed by a series of pyroclastic eruptions about 30, 000 years ago. Electroconductivity measurements and pollen analysis of the lake deposit in the caldera has been conducted to obtain information about thickness, facies changes, vegetation, and climatic condition during the deposition. a) The fine-grained lake deposit is more than 60m thick below the bottom of the caldera; its total thickness is more than 80 to 90m if the deposit exposed at the terrace-shaped cliff inside the caldera is included. b) The deposit exposed at the terrace-shaped cliff and buried in the caldera bottom is subdivided into 4 pollen zones (OH-I, OH-II, OH-III, and OH-IV) in ascending order. Each zone is characterized by high pollen percentages as follows: OH-I: Betula OH-II: Betula and Alnus OH-III: Picea Betula and Pinus. OH-IV: Picea and Butala Based on the present vegetation and the pollen transportation mechanism in the alpine region of Daisetsu Volcano, the climatic condition of 4 pollen zones is estimated to be cold; the OH-II zone in particular is very cold.
This paper describes the palynological study of a core from Yanohara Bog, Fukushima Prefecture, northeastern Japan. Four marker tephras laid down during the Last Glacial Period are recognized in the core: Pm-1, Aso-4, DKP, and AT. The pollen diagram obtained is divided into five pollen zones. The ages of the boundaries between the pollen zones are calculated from the depositional rate of the marker tephra. YH-I (about 8-5.7m.y.B.P.) corresponds to the early Last Glacial Age. Both YH-IIa (about 5.7-5.0m.y.B.P.) and YH-IV(2.6-1.4m.y.B.P.) correspond to cold stages. YH-V corresponds the Holocene. It is clear that there were two cold stages and one relatively warm stage during the Last Glacial Period. From pollen analytical data, it is found that the earlier cold stage(YH-IIa) was colder to than the later stage(YH-IV).
A thin volcanic ash intercalation was found in a 0.2 to 1.4m thick peat layer in the basal part of the sedimentary layer, provisionally named the Hakoi Formation, unconformably overlying the Katanishi Formation; this formation yielded warm, near-shore marine and brackish water fauna and flora and has been correlated with the Last Interglaciation in the glaciated regions. The refractive index of glass shards of the ash (1.499-1.501) coincides with the Aira-Tn ash (AT), and the glass has almost the same major element composition as the AT detected in Dekizima, western Aomori Prefecture. The carbon-14 age of fossil wood from a horizon slightly above the ash is 15, 470±620y.B.P. (I-14, 646). These characteristics indicate that the ash is Aira-Tn ash, ejected from the Aira Caldera, southern Kyushu, the most prominent marker tephra of the Late Pleistocene in Japan. The pollen assemblage of the peat indicates a cold climate during the time of deposition of the ash.