The symposium of“Sea level changes since the Postglacial age in the Japanese Islands and some problems around them”was held on 25 August 1981 in commemoration of the annual meeting of the Quaternary Research Association of Japan at Toyama-shi, Central Japan. The purpose of this symposium is to discuss three thema as follows: The first theme is open discussions on the result of the study of studies IGCP 61 in Japan. The result of“Study on the recognition and dating of Holocene sea level in Japan Islands”was comprised. This study was investigated from 1977 to 1979 as a grant-in-aid for co-operative research, B and A the Ministry of Education, and was also related with the study of the world-wide sea level change; International Geological Correlation Program 61. The second theme is the depth of the sea level around the Japanese Islands during the Maximum Würm age. There are two opinions about the sea level of the Maximum Würm age. One is that it's more 100m deeper than the present sea level and the other, 80±5m deeper than the present sea level. These two opinions are discussed on the basis of the submarine features and the depth of the alluvial deposits around the river mouths in the Japanese Islands. The third theme is humidity changes at the Japan Sea side since Postglacial age. A heavy snow zone is along the Japan Sea. What age does heavy snow along the Japan Sea date back to? This problem relates with the time when cirques on the Japan Alps built, and whether Tsushima warm current flowed into Japan Sea or not in the Maximum Würm age, in other words, whether the Korean straight was closed or not in the Maximum Würm.
The Japanese Working Group of IGCP Project 61 (Holocene sea-level change) has published“Atlas of Holocene Sea-level Records in Japan”in 1981, which is chiefly based on already published data in the last twenty years up to March, 1981. It is written in English in order to introduce Japanese works internationally. The atlas consists of the following three parts: Part I (p. 1-100); All sea-level curves or relative sea-level curves known to the compilers are shown together with important data, diagrams and tables for constructing the curves. Part II (p. 101-165); Some papers, which seem to be significant to understand the geologic or geomorphologic evolution of the coastal areas related to Holocene sea-level changes, are introduced. Part III (p. 166-186); List of 14C results which are regarded to have close relation to Holocene sea-level records. In addition, bibliography of Holocene sea-level study is listed (p. 187-195). Based on the collected data in the atlas, we compilers tried to summarize the results of recent researches and some problems on the Holocene sea-level change in Japan. The number of papers has increased as a result of the increase in 14C data. Especially many papers were published at the time of publication of the three special issues on this subject (Fig. 1). The studies are chiefly concentrated on the areas of large coastal plains such as Kanto, Nobi and Osaka, where sufficient bore-hole data for constructing the sea-level curves were available. Uplifting areas fringed by the Holocene marine terraces, such as South Kanto, the Ryukyu Islands and others where sea-level records were found on the land, have been also intensively studied (Fig. 2). Holocene sea-level records are summarized in Table 1. Fig. 3 shows examples of relative sea-level curves from selected areas. Most Japanese sea-level curves are characterized by higher sea-level of ca. 6, 000y.B.P. (Jomon transgression), which followed rapid sea-level rise accompanying the deglaciation. Since then, the sea-level has lowered to the present level with minor fluctuations. Sea-level lowering is found three times during the last ca. 10, 000 years (1, 2 and 3 in Table 1). Number and time of sea-level lowering are, however, sligthly different place to place. The magnitude of fluctuations in sea-level curves is also different locally (Table 1 and Fig. 5). For instance, the maximum stage of the Jomon transgression occurred at ca. 6, 500y.B.P. in the areas which are characterized by high rate of uplift. In contrast, it is ca. 5, 000y.B.P. or younger in rather stable or subsiding areas (Fig. 4). Examples of heights and ages of the Holocene marine terraces are listed in Table 2. They are usually subdivided into several steps in the areas of high rate of uplift. Subdivision of the terraces was probably caused by co-seismic uplift in association with large earthquakes, judging from the differences in the number and age of each step, although there are no enough 14C age data on the lower steps of the terraces. However, some features of small steps, such as width of step or thickness of deposits overlying steps, seem to be attributed to minor sea-level fluctuation.
By means of the analysis of many boring cores collected by the Authority of Nagoya Port, the authors studied the geology and stratigraphy of recent alluvial deposits and made clear the buried topography beneath the southern part of the Nobi Plain. As a result, following conclusions were induced. The basal topography beneath the recent alluvial deposits is classified into four buried geomorphological surfaces in descending order, 1) the buried wave-cut platform (shallower than -15m), 2) the buried surface of the Atsuta terrace, 3) the buried surface of the Toriimatsu terrace and 4) the buried valley bed. Recent alluvial materials upon the basal gravel beds are divided into four beds in acending order, 1) the Lower Sands, 2) the Middle Muds, 3) the Upper Sands and 4) the Top Muds, The Lower Sands (a so-called Nobi Formation) were deposited in the late glacial time as the foreset bed of delta, their ages are about 18, 000 to 13, 000y.B.P, by 14C dating. The Middle Muds (20 to 10m thick) were deposited as the bottomset bed of delta in the extended Ise Bay of the Holocene transgression time and their 14C dating ages are about from 9000 to 5000y.B.P. containing the Akahoya volcanic ash layer (Ah). The Upper sands were deposited as progressing foreset bed of delta after the age of the maximum sea level of Holocene transgression. The age of this deposition around the Nagoya harbour is 2500 or 2000y.B.P. The Top Muds along the coastal district are the artificial earth materials on reclaimed lands.
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 such as Pseudononion grateloupi, “Elphidium” somaense, Ammonia beccarii, Elphidium advenum, 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 sea-level 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 of 7, 000-6, 000 years B.P. corresponding to the “Jomonian Transgression”. During the middle age of this period, about 5, 000-4, 000 years ago, in the western part of Nagoya 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-level period was followed by a low sea-level age corresponding to the “Yayoian Regression”, and by a slightly cool climate age, a little ice age. (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.
Three embayment-sediment cores were taken from the bottom of west Nagoya harbor situated in Ise Bay on the coast of the Pacific Ocean, Central Japan. Three cored columns (B2, B3 and B18) obtained in lengths of 43.4, 52.5 and 51.5m were dated by 14C-method to be 9, 000 and 9, 400 and 9, 500 years B. P. at the deepest horizon, respectively. To study the environmental changes such as the climatic and sea-level fluctuation in the past geologic time, cored sediment samples were sampled approximately at intervals of 1m along each column and analyzed for the stable carbon isotopic composition (13C/12C) and C/N ratio of sedimentary organic materials and pyrite (FeS2) contents. Total organic materials in cores have a δ 13C-range from -22.1 to -27.1‰ relative to PDB-standard and a C/N ratio-range from 10 to 40 in the weight ratio, and sediments have a pyrite contents-range from 0.0 to 9.0mg of S/g. Large ranges of δ 13C values and C/N ratios are due to the past depositional history affected primarily by the relative contribution of terrestrial- and marine-derived organic materials to the bottom sediments. Besides a difference in the source of organic materials, δ13C value is affected by the sedimentary environment, temperature conditions. The large range for pyrite contents of sediments is due to a change of the source SO=4 concentration because authigenic pyrite is produced mainly by a bacterial reduction of SO=4 to sulfide. From a difference in source organic materials due to the depositional environments and the temperature dependence of kinetic isotope effects in the production process of organic materials by the photosynthesis, one can expect the tendency towards larger δ13C values and smaller C/N ratios (large contribution of marine planktons) of organic materials deposited during warmer and higher sea-level periods. On the contrary, small δ13C values and larger C/N ratios (large contribution of non-marine planktons and terrestrial plants) can be expected in the sediments deposited during colder and lower sea-level periods, glacial ages. Pyrite contents of sediments must be higher for warmer and higher sea-level depositional conditions, because sea water contains 1, 000 times of SO=4 in concentration as high as that of fresh water. Based on the above-mentioned principles which have been verified by studying the present bottom surface sediments from a river and Ise Bay near Nagoya harbor, vertical profiles of δ13C values, C/N ratios and pyrite contents of sediment columns have been examined. Fluctuations of δ13C, C/N and FeS2 versus depth and the 14C-age showed the completely same climatic and sea-level change patterns for three cored columns, and as expected an inverse correlation can be found between δ13C and C/N. From the fluctuation pattern of δ13C, C/N and FeS2, we can find the following feature indicating the sea-level and the climatic (temperature) changes during the end of the last glacial age (Wurm or Winsconsin) and the Holocene. A low sea-level and a cold climate can apparently be seen at the deepest horizon of sediment columns in the 14C-age of 8, 800 to 9, 000 years B. P.. After this period, the sea-level gradually rose, and the highest sea-level and climatic optimum appeared in the 14C-age of 6, 000 to 6, 700 years B. P. corresponding to “the Marine Transgression of Jomon Age”. This warm and high sea-level period is followed by a low sea-level and a cold climate corresponding to a small scale“Marine Regression of Yayoi Age”, a little ice age. After the little ice age, 1, 000 to 1, 500 years B. P., the sea-level gradually rose again toward the present.
The Holocene sea level changes are investigated based on the environmental analysis of boring cores from 16 sites at the west part of Nagoya harbour. As the result of the investigation, the sea level which was 42-43m deep below the present sea level in 9, 000y.B.P. rose to 25m deep in 8, 000y.B.P. Several fossils and coastal feature which supported higher sea level than that of the present were unable to be found in this district. Because alluvial plains in Japan are subsiding generally, the Nobi plain including the Nagoya harbour is no exception. The evidences which supported the higher than the present sea level in the Holocene transgression time are found in the strata around the Nobi plain.
The sea-level changes since the Postglacial ages in the Hokuriku region are investigated by means of studying emerged topography, shell beds, submerged forests, sand dune and their ages. As the result of investigation, the sea-level was higher than that of the present between 4, 500 and 5, 500y.B.P. along the east side of the Noto Peninsula and the Toyama Bay. While the present sea level is the highest at the Kahoku lowland on the southwestern side of the Noto Peninsula. This controversial result has been solved by following considerations. The coastal areas along the Toyama Bay consist of rock coasts and alluvial plains. The rock coast is uplift zone and the alluvial plain is subsidence zone generally in the order of 104-6 years. If uplift is severe in this region, emerged sea shells of older ages must be in a high place and sea level of younger ages must be in a low place. But the emerged sea shells clustered between 2 and 6m and higher than the present sea-level and their ages clustered in between 4, 500 and 5, 500y.B.P. This evidence shows that the rate of eustatic sea-level changes is quicker than that of the uplift in the order of 103 years. Elevation of the boring site becomes the highest point of the sea-level so long as discussion was done about the boring cores. The present sea-level is the highest since the Postglacial age, because the altitude of the lowland is the same latitude of the present sea-level.
This paper deals with the method to determine the upper limit of Holocene marine facies. The example for the Holocene sediments is given by Tamatsu Bed developed in the mouth of the Akashi River, Hyogo Prefecture. The Tamatsu Bed consists chiefly of unconsolidated sand (lower), marine clay (middle) and silt (upper), and the age being from 9, 000y. B. P. to 2, 000y. B. P. We have examined the Tamatsu Bed on marine molluscan fossils, marine diatom assemblages, trace fossils of marine animals and lithofacies especially formation of pyrite crystals. The altitude of the upper limit above the present sea level is as follows: Marine molluscan fossils +0.5m Marine diatom assemblages +2.2m Trace fossils of marine animals +1.6m Pyrite crystals formation +2.2m Among them diatom assemblages, especially Terpsinoe americana which inhabits at the intertidal zone of the mouth of a river may be the best indicator of sea level. It is noticed that the fine crystals of pyrite formed on the surface of the outcrop show the same upper limit as that of diatom assemblage.
Detailed surveys on the submarine topography and geology have been carried out in the environs of Tsushima, Ishikari Bay and Wakasa Bay in the Japan Sea. Especially the most detailed survey was done in the west coast of Tsushima where following submarine terraces were recognized; I (0-15m), II (20-35m), III (40- 50m), IV (60-70m), V (75-85m), VI (90-110m) and VII (110-130m) Terraces. These are distributed in the east coast of Tsushima, Ishikari Bay and Wakasa Bay also. As the results of continuous seismic profiling surveys, the buried channels on continental shelves are pursued to deeper than 90m in the west coast of Tsushima, 105-110m in the east coast of Tsushima and deeper than 80m in Ishikari Bay. These buried channels are continuous to the buried valleys on the coastal land area and the bottom of the valleys is correlated to the basal plane of Alluvium. The buried channels and valleys were formed in the stage of the lowest lowering of sea level during the last Glacial Age. The shelf edge ranging 130 to 140m around Japanese Islands is also formed in this stage. After then, the sea level has risen rapidly up to the present sea level intercalating long pauses of sea level upheaval at VI (90m) and V (80m) Terraces and short pauses at IV and III Terraces.
The problem of the maximum depth, down to which the sea level dropped during the last glaciation, is even more difficult and obscure than that of the high sealevels. Some evaluations have been proposed, being based on the estimations of depth of the Holocene sediments base in the coastal plain or on the consideration of submerged sediments or geomorphological features now found on the continental shelf. Many Japanese geologists estimate -100m to -140m for the last glacial low stand sealevel, but some doubt is cast on their data and opinions. Our estimate, -80±5m, was a conservative interpretation based on dates of shells and peat obtained from the shelf and coastal plain of Japanese Islands. From the detailed survey of the submarine topography in the Tsugaru strait between Honshu and Hokkaido, six submarine terraces were found on the sill. It is noteworthy that the depth of those terraces on both areas of Honshu and Hokkaido is nearly the same. This fact suggests that there have been no distinct crustal movements after the building of those terraces on the sill of the strait. Among the submarine valleys developed on the continental shelf, one of which continued to a valley on land can be detected on the eastern part of the sill. From those circumstances of submerged terraces and valleys about 80m depression of sealevel at the last glaciation is deduced. In most Pleistocene, the Japanese Islands was connected with the Korean Peninsula, and present major islands themselves were tied to each other. It is sure that large mammals such as elephants migrated into the Japanese islands through land bridges. In the early Shimosueyoshi transgression (Riss-Würm interglacial period), when the sealevel was about -100m, the Japan Sea connected with the Pacific through narrow passages located in the Korean and Tsugaru straits. At the time of maximum Würm when the sealevel was depressed to -80±5m, the land bridges between Honshu and other lands were never formed.
The eolian sand members along the coast of the Japan represent at least five major periods of accumulation. These deposits include well-defined paleosols which divide individual eolian sand members into five parts. The five major periods of eolian sand accumulation can be found as follows: 4, 000-5, 000y.B.P. (the youngest); 18, 000-20, 000y.B.P.; 30, 000y.B.P.; 50, 000y.B.P.; and 70, 000y.B.P. (the oldest). Among these eolian sand members, members of 70, 000y.B.P., 50, 000y.B.P., and 4, 000-5, 000y.B.P. cover a wide area. These periods of accumulation are correlated with the early stage of regression phase during the period of the Last Glacial Age and Holocene. On the other hand, the distribution patterns of eolian sand members of 30, 000 and 18, 000-20, 000y.B.P, are limited in a few coastal areas. As coast lines in two periods were located more than 50km apart from the present coast line, sand could not be transported by the prevailing wind to the position of the present coast line. Two sand members are reaccumulation deposits which stem from older eolian sand members. Loess which comes from China had deposited on the upland in Kyushu and Ryukyu Islands. Loess had been much mixed in the paleosols during the Last Glacial Age. The accumulation ratio of loess is estimated 2.1-3.3g/cm2/1, 000 years in Kyushu.
The snowfall on the Japanese high mountains is supplied by the winter monsoon wind from the Japan Sea. The environmental change of the Japan Sea during the Last Glacial Age, caused by the lowering of sea level, would have certainly affected the amount of snowfall which nourished mountain glaciers in Japan. The purpose of this paper is to reconstruct the amount of snowfall during the Last Glacial Age by the glacial landforms, in order to evaluate the amount of the lowering of sea level. Major glacial advances during the Last Glacial Age in the Japanese high mountains occurred in the two glacial periods which is separated by an interstade around 30, 000y.B.P. The glacial extension and the paleoclimate of each glacial period, reconstructed from glacial, periglacial and fluvial landforms, are as follows (Fig. 1): 1) Period about 60, 000-40, 000y.B.P.: Glaciation attained to its maximum extension. Lowering of summer temperature and the southern shift of polar front could be referred. The drop of the amount of snowfall which was not so great as in the younger period, would suggest the inflow of the Tsushima Current into the Japan Sea. 2) Period about 25, 000-10, 000y.B.P.: In spite of the lower air temperature, the glacial extension was much more limited than in the former period. The amount of snowfall should have decreased the most, reflecting on the drop of surface water temperature of the Japan Sea, in which the Tsushima Current ceased to enter in this period, because of the lowering of sea level. The amount of snowfall is reconstructed by using the glacial landforms at Mt. Kurobegoro (2, 840m) in the Northern Japanese Alps. At first, the extension and the shape of a cirque glacier (named Kurobegoro Glacier) at the stage II (ca. 25, 000y.B.P.) is reconstructed, based on the topography of lateral moraines of this stage (Figs. 2 & 3). Then, the mean air temperature during the ablation season on the Kurobegoro Glacier is calculated from the estimated air temperature at Toyama in the Last Glacial Age (Tab. 1), by using the decreasing rate of air temperature of 0, 6°C/100m (Tab. 2). The total ablation of each altitude on the glacier is calculated by the formula (1), and finally, the net accumulation (ablation) on the glacier, by the formula (5). The result of the calculation (Tab. 3) shows that the mass balance of the Kurobegoro Glacier was realized when the degree-day factor (f) is between 0, 3 and 0, 8. The probable decrease of the value of f during the Last Glacial Age leads to the conclusion that the amount of snowfall at this stage should have been less than 50-70% of the actual value. The estimation of the amount of the lowering of sea level which caused this diminution of the amount of snowfall will be an interesting subject of studies in future.
Recently some of palynologist, ecologist and also climatologist have suggested that in Japanese islands it was dry in the Last Glacial Age and wet in late- and post-Glacial Ages. This climatic change was considered to have been mainly brought by the turning into heavy snow. In this paper the author investigated this hypothesis from the viewpoint of climatic geomorphology. He examined especially the age and environments of the formation of fossil periglacial slopes, nivation hollows and mountain oligotrophic bogs. Results are summarized as follows: 1. On high mountains in central Japan, except the northernmost part of the Northern Japan Alps there are developed wide fossil periglacial slopes which are covered with coarse blocks and vegetation. They are thought to have been formed in the Last Glacial Age under the cold climatic conditions. If it was snowy in Glacial Age, the formation of these slopes might have been impossible. So it is considered that there was little snow in the Last Glacial Age except the northernmost part of the Northern Japan Alps. 2. In the snowy high mountains of the Japan Sea side, there are many nivation hollows. They are divided into two types. One, wide and shallow type and the other; narrow and deep type. Though the latter is now being formed, the former is fossil type and the latter is situated in the former. From this fact the author guessed the change of snowfall from little to heavy. Perhaps during the Last Glacial Age it snowed little, but under the cold climatic conditions shallow and wide nivation hollows were formed. However, since late Glacial Age it became warmer and warmer, and snow melting was accelerated. So nivation hollows became fossil. But on account of increasing snowfall, deep snow banks were born on a part of fossil nivation hollows. Such parts were thought to have been developed into new nivation hollows. This estimation supports the above-mentioned hypothesis. 3. To know the age of the beginning of heavy snowfall, the author examined the age of the beginning of deposition of peat in mountain oligotrophic bogs which were located around the present nivation hollows. The ages center in 12, 000-7, 000y.B.P. and 4, 100-3, 300y.B.P., Peats of the latter age are thought to have been deposited owing to the delay of snow melting caused by the little lowering of temperature. But peats of the former age are thought to have been born on account of heavy snowfall. Perhaps in the mountainous region of the Japan Sea side snowfall increased since 12, 000y.B.P. and became as present in about 7, 000y.B.P., 4. On Mt. Kisokomagatake in the Central Japan Alps, there exist small nivation hollows which were born on fossil periglacial slopes. This means possibility of increasing of snowfall on the high mountains of Pacific Ocean side in Holocene.
Pollen analytical examination is carried out using the 32.2m core taken from a bottom of the Lake Mikata which is located in Fukui Prefecture (35°33′32″N.L.. 135°53′40″ E.L.). From the result of pollen analysis, 10 local pollen zones can be distinguished that is from lower upward MG (I, II, III), FG (I, II, III, IV, V), L and R. Each local pollen zone is sub-divided into several sub-zones. MG I and II zones (ca. 50, 000-41, 000B.P. years) are characterized by stabilized high values of Cryptomeria and Alnus suggesting cool and damper climate. This period is correlated with Port Talbot Interstadial in North America. MG III zone (ca. 41, 000-35, 000B.P. years) starts with short cold epoch which is defined by temporal increase of Tsuga. After this temporal cold epoch, frequency values of Cryptomeria shows unstability decreasing upward, on the other hand, Tsuga increases upward. This period is a transitional period from Interstadial to Pleniglacial. FG zone (ca. 35, 000-15, 000B.P. years) is marked by a decline of Cryptomeria with increase of Tsuga, Abies, Picea, Pinus Haploxylon and grass pollen like Artemisia, Thalictrum, Polygonum and Compositae indicating cold and dry climate. This zone is roughly subdivided into three characteristic periods. FG I zone (ca. 35, 000-31, 000B.P. years) is characterized by high values of Tsuga and other sub-alpine coniferous trees suggesting cold and dry climate. FG II zone (ca. 31, 000-24, 000B.P. years) is defined by increase of pioneer trees like Betula, Salix and Alnus replacing Tsuga. This zone occupies a relatively warm epoch and correlates with Plum Point Interstadial in North America. FG III, IV, V zones (ca. 24, 000-15, 000B.P. years) are dominated by Tsuga, Picea, Abies and Pinus Haploxylon indicating cold and dry climate. But the climate at FG IV zone (ca. 20, 000-18, 000B.P. years) shows wetter condition than those of FG III (ca. 24, 000-20, 000B.P. years) and FG V (ca. 18, 000-15, 000B.P. years) zones. L zone is defined by the decrease of Tsuga, Picea, Abies and Pinus Haploxylon with increase of Quercus and Alnus suggesting a climatic ameriolation. The opening of this zone is dated at 15, 000B.P. years. R zone is characterized by the sudden decrease of Tsuga, Picea, Abies and Pinus Haploxylon with the sudden increase of temperate trees like Fagus, Quercus, Juglans and Carpinus. Grass pollen also decreases suggesting the development of dense temperate broad-leaved forest under warm and moist climatic condition. The opening of this R zone is dated in 10, 000B.P. years.
High correlation between the shell growth and the sea-water temperature has been indicated based on the multiple regression analyses of daily growth increments and environmental factors, and on oxygen isotope analyses using fossil shells of Meretrix lamarcki, suggesting that shell growth analyses will be available for an investigation of palaeo-environmental change. Geographical variations and chronological changes in shell growth in the Japan Sea were examined using fossil shells of Meretrix lusoria (Ruding) and Meretrix lamarcki DESHAYES collected from 4 localities of Holocene shell beds and from 4 stages of Jomon shellmound sites and compared with shell growth of recent specimens. Average shell heights against absolute ages were calculated by Walford's graphic method. Specimens from northern localities generally had low initial shell heights and relatively high growth rates, while specimens from southern localities had relatively high initial shell heights and low growth rates. Samples of the Hokuriku area had medium values of the initial shell height and slightly low growth rates. Growth of fossil shells of M. lusoria in the Hokuriku area was rapidder than that of recent specimens collected at the Hakata Bay and Ariake Sea. Daily growth increments of M. lusoria from Ariake Sea showed a tidal influence on shell growth, while the tide pattern did not appear in those from the Hokuriku area, suggesting that disturbance on shell growth during ebb tides had eliminated among shells of the Japan Sea where the tidal range is smaller than that of Ariake Sea. Changes in the shell growth during the Jomon transgression had a similar trend between specimens from the southern Kanto and the Japan Sea. Decrease of growth speed during the Middle Jomon period was recognized both in M. lusoria and M. lamarcki.