Palaeoenvironment of the Holocene deduced from Palaeontological Evidences in Nagoya Harbor, Central Japan1) Norio FUJI2), Yoshiaki MATSUSHIMA3), Shoji

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1 Palaeoenvironment of the Holocene deduced from Palaeontological Evidences in Nagoya Harbor, Central Japan1) Norio FUJI2), Yoshiaki MATSUSHIMA3), Shoji FUJII4), Hiroshi KITAZATO5) and Shinobu MORI6) To elucidate the changes of the environment such as sedimentary basin, climate, sea-level and vegetation during the Holocene epoch, the core samples obtained from Nagoya harbor and its adjacent area, Yatomi, in the coast of Ise Bay, Central Japan, were analyzed from the viewpoints of molluscan assemblage, foraminiferal and diatom analyses, and palynology. The change of the environment throughout the Holocene epoch is divided into some periods as follows: (1) About 10,000-8,500 years ago: In the early age of this period, the sea-level had been about -40 to -45m in the present altitude. Fresh and brackish water diatom assemblage, and Corbicula cf, japonica, living under a brackish water near the mouth of a river, were found from the sandy deposit (MMo). In the late age of this period, the open sea water reached rapidly into the ancient Ise Bay. As Ammonia beccarii was abundant with Pseudononion grateloupi and Elphidium subgranulosum, it is estimated that the bay had been about 10-30m deep. The molluscan assemblage such as Pingicula doliaris and Niotha liversens etc. had lived under an inner bay formed by a muddy bottom. According to the pollen assemblage, Fagus, Pinus, and Lepidobalanus are abundant, and it indicates that the climate had been as the Cool Temperate zone. (2) About 8,000-2,500 years ago: The sea had been extended to the inner part of the present Nobi plain. Judging from the abundant benthonic foraminifera E. subgranulosum, and Uvigerinella glabra etc., the sea-level in about 7,500 years ago had been about -30-0m in the present altitude, and the muddy deposit had been sedimented on the bottom of 10-50m deep in the center of the bay. On the other hand, diatom such as Cyclotella striata which lives under a low salinitic water dominated. As Pinus, Abies, Fagus, and Lepidobalanus were abundant around the bay, the climate of that time had been cooler than that of the present-day. After that time, during the about 7,000-5,000 years ago, marine water diatoms and the molluscan assemblage as Alvenius ojianus, Venemolpa micra, Raeta pulchella, Theora lubrica, and Ringicula doliaris, wihch have lived in the inner part of a bay or an inlet, increased gradually, and the sealevel reached gradually the higher level. On the land near the bay, the deciduous broad-leaved trees such as Fagus, and boreal conifers such as Abies and Tsuga decreaseed, and instead of them the evergreen broad-leaved trees such as Cyclobalanopsis and Castanopsis increased. The climatic optimum and the highest sea-level appeared in 14C-age the middle age of this period, about 5,000-4,000 years ago, in the western part of Nagoya

2 154 The Quaternary Research Vol. 21 No. 3 Oct harbor, the upper and middle parts of the Middle mud layer (MM) were sedimented under the high sea-level and the warm climatic condition as the present Warm Temperate zone. According to the diatom analysis, the sea-level reached the highest level during time between about 4,000-2,500 years ago. This warm and high sea- (3) The last 2,500 years: The Upper sand layer (US) was sedimented during this period. From this layer the mollusca such as Meretrix lusoria, Tapes japonica, Umbonium sp., and Proclava kochi living in a sandy bottom of the littoral area is yielded abundantly, and the fresh water diatom increases gradually in frequency upward this layer. Therefore, judging from these results, it is inferred that there was a minor regression or sedimentation by an advancement of delta. This phenomenon agrees chronological- mentation of sand, the diatom living in the sea water is yielded from the upper part of the Upper send layer (US), and indicates the minor transgression estimated to be about years B.P..

5 Fig. 2 Distribution map of molluscan assemblage from the Holocene series at the Nagoya Harbor. A: Corbicula japonica, B: Meretrix lusoria-tapes japonica-umbonium moniliferum-proclava kochi assemblage, C: Alvenius ojianus-venemolpa micra-raeta pulchella-theora lubrica assemblage, the other addreviations are shown in Fig. 1. Fig. 1 Frequency diagram of mollusks from the Holocene deposits at the Nagoya Harbor, Central Japan. 1: buried soil, 2: coarse sand, 3: medium sand, 4: fine sand, 5: silty sand, 6: sandy silt, 7: silt, 8: clayey silt, 9: clay, At: Atsuta Formation, No: Nobi Formation, MM0: sand bed in the lower part of the Middle Mud Member of the Holocene deposits, MM1: mud bed in the upper part of the Middle Mud Member, US0: silt bed in the lower part of the Upper Sand Member of the Holocene deposits, US1: sand bed in the upper part of the Upper Sand Member.

6 158 The Quaternary Research Vol. 21 No. 3 Oct. 1982

7 attached Foraminifera: Cibicides lobatulus, Rosalina vilardeboana, Gavelinopsis sp. Miliolinid: Macsilina spp., Miliolinella spp., Quinqueloculina spp., Triloculina spp. Fig. 3 Columnar section of the boring core at Inako, Yatomi-cho and frequency diagram of main species of foraminiferas. 1: gravel, 2: sand, 3: silt, 4: clay, 5: Akahoya tephra.

8 Fig. 4 Sedimentation ratio of the boring cores. Longitudinal axis: depth of boring core, transverse axis: radiometric age, a: sedimentation ratio of the boring core at Inako, Yatomi-cho, b: sedimentation ratio of the B2 boring core at the western part of the Nagoya Harbor.

10 Fig. 5 Frequency diagram of diatom from the B2 boring core at the western part of the Nagoya Harbor. a: marine diatom, b: Melosira sulcata (larger than 0.03mm in diameter), d: fresh water diatom, f: less than 2.0%.

11 Fig. 6 Pollen diagram of the B2 boring core at the western part of the Nagoya Harbor.

12 Fig. 7 Pollen diagram of the B18 boring core at the western part of the Nagoya Harbor.

13 Fig. 8 Climatic change by the pollen analysis of the B2 and B18 boring cores and comparison with those of the other districts.

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15 ISEKI, H. (1971) The erosional bases of the late Pleistocene buried valleys in the coastal region of Japan. Quaternaria, 14, p ISEKI, H, (1974) Sea level toward 2000yr. B.P. in Japan. Jour. Fac. Literature, Nagoya Univ., no. 62, p ITIHARA, M. (1954) Bottom Sediments of Osaka Bay, Part I Mechanical Analysis and Frustules of Diatoms. Jour. Inst. Polytec. Osaka City Univ, Ser. G, 2, p FLINT, R.F. (1971) Glacial and Quaternary Geology. KAIZUKA, S., Y. NARUSE, & I. MATSUDA (1977) Wiley, New York, 839 p. Recent formations and their basal topography in FUJI, N. (1965) Palynological study on the Holocene and around Tokyo Bay, Central Japan. Quatern- peat deposits from the Hokuriku region of ary Research, 8, p Central Japan. Bull. Fac. Education, Kanazawa Univ., Natural Sci., no. 13, p FUJI, N. (1975) The coastal sand dunes of Hokuriku district, Central Japan. Daiyonki Kenkyu (Bull. Jap. Quaternary Research), 14, p FUJI, N. (1980) Pollen analysis of the Postglacial deposits from Lagoon Kahoku-gata, Central Japan. Abstract of the 21st. Congress Inter. Assoc. Theoret. & Applied Limnol, 18. p MIYADI, D. (1941) Marine benthic communities of FUJI, N. (1982) Pollen analysis. In Lake Biwa (ed. the Ise-wan and the Mikawa-wan. Mem. Imp. by S. HORIE), Monografiae Biologicae, 42, p Mar. Obs., 7, p : Dr. W. Junk bv. Publishers, The Hague. FUJI, N. (1982) Chronostratigraphic Subdivision of the Postglacial Deposits in the Japanese Islands. Striae, 16, p FUJI, N. and L-K. KONIGSSON (1980) Palynological Evidence for Correlation of Holocene Climatic Changes in Japan and Oland of Southern Sweden. I. Bull. Fac. Education, Kanazawa Univ., Natural Sci., no. 29, p FUJI, N and L-K. KONIGSSON (1981) Palynological Evidence for Correlation of Holocene Climatic Changes in Japan and Oland of Southern Sweden OSHITE, K. (1959) Sedimentological Study of Diatoms II. Bull. Fac. Education, Kanazawa Univ. Natural in Marine Deposits from the Adjacent Seas Sci., no. 29, p of Japan. Jour. Hokkaido Gakugei Univ., 10, p. 416 FUJI, N. and M. MIYAMATSU (1981) Fossil Diatom Assemblage of the Latest Quaternary Deposits from Lagoon Kahoku-gata, Kanazawa, Central Japan. Bull. Fac. Education, Kanazawa Univ., Natural TANIMURA, Y. (1981) Late Quaternary Diatoms of Sci., no. 30, p the Sea of Japan. Tohoku Univ, Sci. Rep. 2nd. Ser. 51, p

194 The Quaternary Research Vol. 29 No. 3 Aug. 1990

194 The Quaternary Research Vol. 29 No. 3 Aug. 1990 The History of Straits around the Japanese in the Late-Quaternary1) Islands Kazuo OHSHIMA2) The problem of the maximum depth to which the sea level dropped during the last glaciation is even more difficult