The Akan-Kutcharo Uplift Zone of eastern Hokkaido is the geological extension of the Kuril arc volcanic zone, and it divides the Neogene terraines into the inner Tsubetsu-Abashiri Basin and the outer Konsen Basin. K-Ar ages were determined for Neogene volcanic rocks of these terranes. In the Tsubetsu-Abashiri Basin, the Abashiri Formation, uncomformably overlying the Lower Miocene, is composed mainly of andesitic to basaltic hyaloclastite, and gives K-Ar ages of 9.96 to 11.19Ma. The Upper Miocene to Pliocene volcanic rocks are locally distributed in the Kamisato area of the southwestern part of the Tsubetsu-Abashiri Basin, of which the Mito Formation gives K-Ar ages of 6.25 and 6.49Ma. The Neogene system in the Akan-Kutcharo Uplift Zone consists mainly of neritic to terrestrial deposits. The Pliocene Formations, uncomformably overlying the Middle to Upper Miocene in the Uplift Zone, are represented by shallow marine to terrestrial effusive rocks, and show K-Ar ages of 2.50 to 3.98Ma. Neritic finer grained sediments become dominant and the Pliocene Formations thicker toward the southeast of the Konsen basin. On the basis of lithology and thickness of the Cenozoic system, the formation of the Akan-Kutcharo Uplift Zone is considered to has commenced at the Paleogene and its most extensive development have been apparent in the Middle Miocene.

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Although the latest Early to early Middle Miocene sediments in the Southwest Japan arc are mostly of terrigenous and volcanic origin, small limestone masses with common lithological and paleontological properties occur within an intra-arc basin of the arc. This paper elucidates the formative process of the limestone bed intercalated in the Namigata Formation in Okayama Prefecture, at the northern margin of the intra-arc basin, and infers the regional paleoenvironment of the intra-arc basin. The Namigata Formation, ca. 120m thick, consists of well-sorted sandstone with conglomerate and limestone, and is a sediment on a transgressive rocky coast bordering the northern margin of the intra-arc basin. The basal unconformable surface of the formation shows that the rocky coast had a staircase geomorphology consisting of three-stepped wave cut terraces and an elevated peneplain behind. The limestone layer (ca. 15m thick) intercalated at the middle horizon of the formation comprises biosparudite (grainstone) which is a mixture of skeletal fragments of molluscs, bryozoans, cirripeds, echinodermata, foraminifera, brachiopoda and algae, and of terrigenous sands with various contents (42% on an average), without any other calcareous grains and lime-mud. These sedimentological features indicate that the limestone is classified as "non-tropical shelf carbonates", particularly "bryomol". The predominance of sessile benthos and suspension feeders, the remarkable fragmentation of the skeletals (except for non-worn benthic foraminifera tests), and the abundance of intergranular pore space show high water energies in both the carbonate factory and accumulation site for the "bryomol" limestone. The staircase rocky coast buried beneath the Namigata Formation is a product of intermittent rises of relative sea level. Benthic foraminifera in the "bryomol" bed show that it accumulated in the inner to middle sublittoral zone and the sea level at that time rose up to the altitude of the elevated peneplain behind the rocky coast. Hence we concluded that the "bryomol' bed is a condensed section formed under the following environmental conditions; 1) the marked reduction of terrigenous supply due to trapping on the drown elevated peneplain, and 2) the slow but exclusive supply of skeletals from the carbonate factory on the highest wave cut terrace lowered below "surf base". Extensively occurring in the intra-arc basin of the southwest Japan arc are limestone masses similar to the "bryomol" bed in the Namigata Formation and molluscan faunas preferring rapid water circulation. This suggests that high water energy is characteristic of the regional maritime environment of the intra-arc basin and that the intra-arc basin was a coastal open sea.

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Over 500 specimens of fossil ophiuroid were collected from the Early to the Middle Pleistocene Ichijuku Formation of Kazusa Group in the Ichijuku area, Kimitsu City, Chiba prefecture, Central Japan. They belong to same species to living Ophiura sarsii Lutken. The outcrop yielding the ophiuroids composed mainly of very coarse sandstone intercalated with some lenticular beds of siltstone and very fine sandstone. Based on the mode of their occurrence and their size-frequency histogram, it is inferred that small individuals with disk diameter less than 4mm lived on the floor of silt and very fine sand, and some of them moved onto very coarse sand floor as they grew up. Judging from the associated molluscan fossils, the sedimentary setting in which these ophiuroids lived is inferred to be the outer sublittoral zone dominated by the warm current with a slight influence of cold water. Provided also is a comparison, with regard to inhabited depth and density of fossil as well as living populations of Ophiura sarsii.

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Regional correlation in the Niigata sedimeneary basin were attempted in respect to the Pliocene volcanic ash markers in the Nobegawa route, Ojiya City. The correlation of volcanic ash markers were made based on their horizon, unit association, lithofacies, petrographic characteristics of components, and chemical composition of glass shards. Among the ash markers in the Nobegawa route, the following ashes were regionally correlated over more than 50km with those in the Higashikubiki and Uonuma Hills, and Hachikoku, Chuo and Nishiyama Oil Fields; that is NA3-NA5 with the Suganuma allanite-bearing ash zone (SAZ) such as Sec and OKIII ashes, NA7 with Chw and Isgp-A ashes, NA9 with Fup and OKII ashes, NA10 with Tsp, OKI and Kag ashes, NA11 with Sgs ash, and NA13 with Hap-2, Isg-g and Kap ashes. On the basis of the result of ash correlation, regional contemporaneous heterotopic facies relation was revealed. Upper shallow marine to fluvial environments initially appeared in the southern Higashikubiki and Uonuma areas in late Pliocene while lower shelf to slope environment contemporary existed in the central part of the basin. The basin was progradated by progressive extension of upper shallow marine to fluvial environments.

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