The eastern region of the Myoko volcano group, Central Japan, is covered with thick tephra formations, and is called the“tephra region of Myoko volcano group”. A catalogue of Pleistocene tephra layers in this tephra region was presented by HAYATSU and ARAI (1980). This paper presents the additional descriptions about some marker tephra layers distributed especially at the southern half part of this tephra region. Petrographic characteristics of six marker tephra layers such as pumice, scoria and ash layers are described in detail.
In addition, the stratigraphic relations between marker tephras and non-volcanic sediments at the foot of volcanoes are shown. Some lake deposits (Sasagamine, Furuma, Mure and Nojiri lake deposits) are formed during the nearly same period respectively. Some of marker tephra, layers have their source in the volcanoes far away from the Myoko volcano group. They are usually found as very thin layers in the tephra formations, being well preserved only at the limited locations where settling of tephra proceeded rather rapidly.

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(1) 播磨灘表層堆積物の花粉分析の結果, 花粉・胞子は灘全域で検出されたが, 乾泥1g当たりの花粉・胞子数は, 明石海峡, 鳴門海峡, 備讃瀬戸を通過する潮流の影響を受ける海域で100×10²粒以下と少なく, 一方中南部および北西部の潮流の影響をほとんど受けない海域で200×10²粒以上となっている.
(2) 総花粉・胞子数の分布は堆積物の物理的特性である微細粒子率, 含水率, 比重の分布傾向と一致する. また, 総花粉・胞子数の対数値とφ6以上粒子の比率との間には高い相関が認められ (R=0.85), これらのことから, 花粉・胞子はおよそ16μm以下の微細粒子と挙動を共にする.
(3) 花粉・胞子の分布から, 花粉・胞子は主に恒流によって灘北部から中央部へ運搬され堆積することがわかる.
(4) Pinus, Cryptomeria, Fagaceae 花粉は総花粉・胞子の分布とほぼ一致するが, Pinus 花粉ではさらに南部沿岸と淡路西淡町沖に分布がみられる. Abies, Tsuga 花粉は西部海域に多かった. Gramineae 花粉は北部沿岸海域で多数検出された. シダ胞子は灘全域でほぼ均一に分布した. これらの分布決定の主要因は, 花粉・胞子の搬入経路と浮遊力である.

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In the present paper, a pollen analytical study was made on 55 samples obtained from the upper member of the Shimoabira Formation, and the lower and the upper member of the Shiomi Formation belonging to the late Pleistocene in SE Ishikari Plain, Hokkaido, and palaeoenvironmental changes were discussed, being based on three pollen zones or divisions recognized, which were comparable to the three geological divisions mentioned already.
Successive palaeoenvironmental changes are suggested from the pollen diagrams that the climatic condition have changed from warm to cool temperature condition. This thermal change, however, was considered to be a change within the Fagus crenata=Sasa Class in a phytosociological sense. Thus, the palaeoclimatic environments were possibly corresponding to the present climatic environments of the Kuromatsunai Area which is a significant demarcation area separating the Cool Temperate vegetation with Fagus crenata from the Cold Temperate vegetation with Quercus crispula, P. glehnii and P. jezoensis but lacking F. crenata in natural habitats in Hokkaido. The conclusion mentioned above was abstracted from the following: (1) gradual increasing of the ratio Picea/Abies from older periods to recent periods or from the pollen zone III to the zone I, although more or less irregular fluctuations were recognizable often in pollen diagrams, (2) conspicuous and nearly constant mixture of Picea, Tsuga, Abies, Cryptomeria, Pterocarya, Fagus, Quercus, etc. which was believed to be a proof of long existence of the Mixed forest, not pure boreal coniferous forests like the Taiga nor exclusive Temperate Summergreen forests, and (3) drastic decrease of maritime Chenopodiaceous pollen grains in the sample number just above the lowest sample number of the upper member of the Shimoabira Formation, showing palaeoenvironmental change from the high sea-level condition to low sea-level condition.
Two exceptional pollen diagrams were shown: Ka-II' and Ni-I'. The pollen diagram of Ka-II' was considerably different from diagrams of the remaining 4 diagrams and was characterized by a tendency with increased amount of pollen grains of Picea and Cryptomeria, even though a species list of pollen grains was very similar to the remainder. The diagram of the lower part of Ni-I' pollen zone was characterized by complete lack of conifer grains. Elucidation of these exceptional cases was not tried in the present discussion and remained to be solved.
Through the Shiomi Formation Period, it was supposed that bog vegetations were constantly developed; one is Picea-Sphagnum bog and the other is Alnus-Cyperaceae bog. As a result of the present study, it was shown that constant and extensive spreading of bog was considered to be the most characteristic palaeoenvironmental feature of the Shiomi Formation. Thus, the authors proposed that the Shiomi Formation Period should be called“Shiomi Bog Period”in pollen diagrams. This Period was contemporary with the Biraotori Bog Period and dated a period from the Riss-Würm Interglacial to W_I Subglacial Period.

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