It is well known that the Plio-Pleistocene marine sediments in the Boso Peninsula, namely the Kazusa Group, are remarkably thick and continuous. Many investigations on the stratigraphy and the fossils contained within them have been made in detail. The age of the Kazusa Group has recently become clear by means of some biostratigraphic and geomagnetic works. On the other hand, the Miura Group distributed over the Tama Hill adjacent to the Boso Peninsula has been poorly investigated. It was believed that the age of the Group was the Late Pliocene. In this paper, the writers described the stratigraphy and the geologic structure of the Miura Group in addition to the review of previous works on the Plio-Pleistocene formation in the Southern Kanto region. The results must offer some data on the restoration of the paleo-geography of this area. (1) An indistinctive anticlinal structure was found about the upper reach of the Tsurumi River. It seems that the structure is based on the original sedimentary basin structure. (2) The sedimentary facies of the Miura in the western region of the Tama Hill are characterized by the deposits of relatively shallow sea. In the lower part of the Miura, there are six sedimentary cycles due to the osillation of the sea level of the time. (3) From some plant fossils, such as Metasequoia, Juglans, the age of the Miura is estimated to be the Early Pleistocene.
In Kinki and Tokai districts, the eastern part of southwest Japan, there are three Plio-Pleistocene sedimentary basins, where are the Osaka, Kobiwako and Tokai Groups, respectively. The Osaka Group is composed of the cyclic sediments of lacustrine and bay in the upper part, and of lacustrine in the lower. The other Groups are composed of lacustrine sediments only. In the upper part of Osaka Group, the cyclic sedimentation caused by transgression and regression corresponding to climatic change. The stratigraphical summary of the three Groups was figured in terms of tephrochronology, paleomagnetic chronology, fission-track and K-A ages and fossil ranges. Then the climatic changes of Plio-Pleistocene age were introduced. The ages of cold climate were determined as follows. Terasho 3-3.1m.y. Saidera 1.2±m.y. Shimakumayama 2.3-2.4m.y. Gokenya 0.75-0.8m.y. Kamimura I 1.5+m.y. Manchidani 0.45±m.y. Kamimura II 1.5-m.y. In the Manchidani cold age, the coldest climatic age among them, the annual mean temperature was estimated to be about 10°C. The warmest climatic age of Pleistocene is the Shinkori warm age, 0.35m.y.. The climate of that time was mild in winter and had sufficient rainfall as in the southern part of Kyushu, being about 17°C in annual mean temperature.
Progress in the tephrostratigraphy in Kantô and Kinki for years made it possible to correlate the Plio-Pleistocene Kazusa group in South Kantô with the Osaka group and its correlatives in Kinki. In this paper the writer tried to correlate both groups by fossil elephants, fossil plants and paleomagnetic polarity of the deposits. Both Kazusa and Osaka groups lying below the biozone of Elephas naumanni yield Stegodon orientalis in the upper part. On the other hand, Stegodon shodoensis akashiensis is reported from the Lower part of the Osaka group, and molars of Parastegodon cf. aurorae which is an allied species of S. akashiensis were found at the middle and upper horizon of the Umegase formation (middle part of the Kazusa group) in Tama Hills. Moreover, in the Boso Peninsula the Umegase formation yields some specimens of Parelephas proximus which is thought to be closely related with Elephas shigensis from the Lower part of the Osaka group. Based upon these facts the correlation between the Kazusa and the Osaka groups is shown in the Table 1. As for the plant remains the Lowest part of the Osaka group is characterized by many species belonging to the Metasequoia flora. In South Kanto the Metasequoia flora has been reported from several horizons of the Kazusa group in Tama Hills which are correlated with the Umegase (or partly Otadai) horizon in Boso. According to the ONISHI's investigation into the pollen flora of the Kazusa group in Boso the group is divided into six pollen zones, and the correlation by the pollen zones of the Kazusa group with those of the Kinki district was carried out (Table 2). Paleomagnetic stratigraphy was investigated through successive measurements of DRM of the late Cenozoic formations of Boso and of NRM of the volcanic ash layers interbedded in the Osaka group and its correlatives together with fission-track dating of some ash layers. The boundary between the Brunhes and Matsuyama epochs is correlated with the middle horizon of the Kokumoto and the lowest horizon of the Upper part of the Osaka group. The Jaramillo event corresponds either to the middle Kokumoto or to the upper horizon of the Lower part of the Osaka group. Moreover, the Olduvai event is correlated with the middle horizon of the Umegase and with the boundary between the Lower and Lowest of the Osaka group. The correlation by the paleomagnetic polarity is shown in Table 3.
The geochronology of the Pliocene-Pleistocene deposits in the Aizu Basin, which are represented by the Izumi and Nana-orizaka Formations in ascending order, is presented from the stratigraphical, palaeomagnetical and palaeobotanical view points. Three major normal and reversed polarity sequences are confirmed by the palaeomagnetic data. The polarity sequences are correlated with the Brunhes normal, the Matsuyama reversed and the Gauss normal epochs proposed by Cox and Dalrymple (1967). Five short polarity events are also recognized, and they are correlated with the Jaramillo normal, the Gilsa normal, the Olduvai normal, the Kaena reversed and the Mammoth reversed events. The floras from the Pliocene deposits contain the extinct species such as Metasequoia japonica, Pseudolarix kaempferi, Juglans megacinerea and Pterocarya paliurus. The floras from the early Pleistocene deposits during the age represented by the Olduvai event contain the subalpine species such as Picea maximowiczii and P. jezoensis in addition to the extinct species mentioned above. While, the floras from the early Pleistocene deposits during the age represented by the Jaramillo event are dominated by the subalpine species such as Pinus koraiensis, Picea maximowiczii, P. jezoensis and Abies veitchii, but do not contain the extinct or exotic species. Moreover, the floras dominated by the subalpine species are found again in the middle horizon of the upper part of the Nana-orizaka Formation deposited during the Brunhes normal epoch.
It is generally said that the Ikeda formation distributed at the Oribe Upland in the north east part of Tokachi Plain is Pliocene-Early Pleistocene age. Besides, some unsettled problems have been left intact. For the purpose of re-examination, the writers have made some field investigations about the Ikeda Formation. The results are as follows.
1. The Uonuma Group (2250m+) at Oguni Region, can be divided into four parts. It has concordant synclinal structure with Neogene system, which axis runs NNE-SSW through the center of the Oguni basin. 2. The sedimentary facies of the Uonuma Group are shown in Fig. 1. The thirteen key horizons (SK 010-SK 130), which are made up of several kinds of tuffite beds, are proved to be remarkable for their correlation. 3. As the result of analysis of fossils from Uonuma Group (Fig. 2, Table 2) it is assumed that the paleoclimate during the stage of the Uonuma Group gradually changed from warm to cool, and that Metasequoia flora may have been extinct by the top stage of the Middle part. The sedimentary environments are considered to have changed from marine water (the Lowest stage) to brackish water (Lower to Middle stage) and then to fresh water (Upper stage). 4. In conclusion the Uonuma Group may be roughly correlated to the Osaka Group in the Osaka District.
The Uonuma Group is typical deposits with quite thickness of early Pleistocene Period in the area along the Japan Sea. The distribution of the Uonuma Group in Niigata Prefecture is shown in Fig. 1. In the present paper, the litho-stratigraphy, floral change and paleo-magnetic stratigraphy of the Uonuma Group are summarized as shown in Fig. 2. Furthermore, some important problems concerning the Uonuma Group are discussed.
This paper deals with the nature of the boundary between the Omma formation and the Utatsuyama formation and the correlation of the Plio-Pleistocene formations developing around Kanazawa City and Osaka district. As the results of the stratigraphical research concerning the interface between the Omma and the Utatsuyama formation, it seems that the Utatsuyama formation overlies on the Omma formation with conformable relation. However, considering each geological age of both formations by means of the biostratigraphy and paleo-magnetic stratigraphy, it seems to be considered that the stratigraphical relation of the formations is unconformity and that the Utatsuyama formation is correlated with the upper part of the Osaka group and the Omma formation do with the unconformity blank between the Osaka and the Nijio group.
The Tsunozu Group is developed in the western part of San-in district facing the Japan Sea. In the hilly-land neighbouring Gotsu and Tsunozu (the stratotype), it is composed of loose sediments of gravels, sands and muds which belong to five sedimentary cycles. Each cycle, with the exception of uppermost one, has a marine clay bed that is called M1, M2, M3 and M4, respectively, in ascending order. As the uppermost cycle consists of wethered gravels, it is named the Upper Gravel Bed. In the hills around Mt. Ôe-takayama, the pyroclastic flow and fall deposits are embedded in the clastic sediments in which M4 and aeolian sand beds (ancient dune deposits) are included. As Stegodon elephantoides(?) and plant remains, such as Pseudolarix, Glyptostrobus, Sequoia, Liquidambar, Nyssa, and Paleodavidia, are found in M1 cycle, the lower part of the Tsunozu Group is correlated to the Pliocene age. Some elements of the Mesasequoia flora, such as Picea koribai, Metasequoia, Cunninghamia, and Juglans megacinerea, are found in M4 cycle, so the upper part belongs in the Pleistocene. Though much parts of depositional surface of the Tsunozu Group suffer the erosion and the lowering of hight, some parts are well presarved. The Tsunozu Surface (the summit level of the hills consisted of the Tsunozu Group) is the depositional surface of the early Pleistocene in age. Relict red soils are formed at least two periods, that is, pre-Tsunozu or Tsunozu (late Pliocene) and post-Tsunozu stage (early Pleistocene).
The Oita Group and its equivalent strata, extensively developed in the middle Kyushu, are documented with the tremendous volcanic products and Villafranchian to early classical Quaternary fauna and flora. Regional geologic evidence shows that the strata occupy a part of the Second Setouchi basin, which represents the final collapse of the axial zone of the Honshu geanticline at the last phase of the geosynclinal cycle. However the strata in the middle Kyushu markedly differ from those of other parts of the Setouchi by the extensive volcanism and great thickness. The basin of the middle Kyushu is divided into two parts by the Kunizaki-Chikugo upheaval zone of NEE-SWW trend. The southern part is a half graben bordered by the Oita-Kumamoto fault line at the south. The half graben and its north and south upheaval areas are corresponded respectively with the area of negative and positive Bouguer anomaly. This fact suggests that the early Pleistocene events have the relation to the geophysical character of present time in the middle Kyushu. Hence the early Pleistocene basin is examined in regard to the present geophysical features. There is a distinctive zone of the negative isostatic anomaly along the east coast of Kyushu, where the crust is still sinking with deeper MOHOROVICIC plane. The focal plane of the medial- and deep-focused earthquakes intersects with the earth surface in this zone and the intersection coincides with the zero line of the Bouguer anomaly. It should be noted about the earthquake that the more north the position, the shallower the foci. These features seem to be the expression of the Ryukyu arc at its northern extremity. Thus the overlap of the activities of the younger Ryukyu arc to the final collapse of the Honshu geosyncline results the unique geologic events in the middle Kyushu.
For the Osaka group and its allies, fossiliferous deposits of Plio-Pleistocene which are widely distributed in Kinki district, five zones are discriminated biostratigraphicaly basing upon mammalian fossils. These are as follows ascendingly: 1. Stegodon cf. elephantoides Zone >3.0m. y. 2. Stegodon insignis sugiyamai Zone ca. 2.5m. y. 3. Stegodon shodoensis akashiensis Zone ca. 2.0-1.5m. y. 4. Elephas shigensis Zone ca. 1.5-0.6m. y. 5. Stegodon orientalis Zone ca. 0.6-0.3m. y. The age determination is estimated to take DRM, fission-track method and K-A chronology into consideration. Besides them, with due regard to the results of palynological investigation and floral change, they should be correlated with Villafranchian division of Perrier hill, Auvergne in southern France by Azzaroli (1967), such as Zone 1 to Lower-, Zone 2 to Middle-, Zone 3 & 4 to Upper Villafranchian and Zone 5 to post Villafranchian with each other. Remarkable faunal gaps exist between Zone 1 and Zone 2 and also between Zone 4 and Zone 5. Faunal turnover from Zone 1 to Zone 4 is characteristic and its procedure advanced from warm forest fauna of Indo-Malayan Faunal Complex to temperate and/or cool forest-steppe fauna of Sino-Siberian Faunal Complex. At the time of Zone 5, warm forest fauna revived again as Sino-Malayan Faunal Complex. In the process to analyse those faunas in turn, it is also stated as to the Pliocene-Pleistocene boundary that the concept of Haug's Line is invalid from paleobiogeographical and paleoecological view point, because the faunal complex, like as Sino-Siberian, Indo-Malayan, Villafranchian (European), Blancan (North American) and African, was already established in Pliocene time and went on with their own faunal turnover independently. Therefore, in order to notice the pattern of faunal gap and turnover, it is important not only to treat some selected taxa but also faunal complex as a whole. Those complex had been disassembled from time to time in relation to intra-complex change, like as change of population density or population pressure brought about by habitat change, i. e. from forest to steppe or from steppe to desert. As a result of such diversity in complex, many faunal facies or sub-facies had been formed and localized. When the blend of those facies occured, resulted mix facies reacted to mother complex to reveal the faunal gap and faunal turnover. In such a way, Pliocene-Pleistocene gap, Villafranchian turnover and Villafranchian-post Villafranchian gap may be explained.
Three problems on the early Pleistocene molluscan fauna are discussed in this paper. 1. Fresh water molluscan fauna in Paleolake Biwa and its environs The fresh water molluscan fauna in Lake Biwa consists of 43 species and bears 19 endemic species. A part of the fauna occurs in lacustrine sediments of the Paleo-Biwa, Osaka and Tokai groups. It seems that the speciation and changes in distribution correspond to the geologic development of the lakes. 2. Continental coastal mollusks Continental coastal mollusks are now living in inner bay in Japan. They are on the decline in number and distribution. Some of the elements of the continental coastal fauna are found in early Pleistocene formations. Considering the vertical and geographical distribution of the fauna in age from early Pleistocene to Recent, same problems as the fresh water molluscan fauna occur in this case. 3. “Omma-Manganzi” fauna There is a problem on the cold sea water type “Omma-Manganzi” fauna in the Pliocene Wakimoto stage. In comparison with the Pliocene faunas and floras in Kamchatka and Alaska which indicate environment warmer than now, it needs to check the age and the features of the “Omma-Manganzi” fauna. Conclusion on this problem is postponed because of the synthesis of various data makes possible to solve the problem.
In this paper, the changes of floras between the Pliocene and Pleistocene are considered through the evidences, that are recognized in the plant fossils from the Late Pliocene and Early Pleistocene sedimentaries, Those sedimentaries are developed in Western Carpathians and Dutch-Prussian border of Central Europe and Osaka, Niigata and Aizu areas of Japan. The changes of floras gradually progressed as a whole in each area, but some phases that made rapid change of flora were inserted. Those changes are characterized by the disappearance of numerous extinct and exotic elements and the first appearance of the authochtonous and boreal elements.
Combined paleomagnetic and biostratigraphic works have been carried out on the Cenozoic sedimentary rocks of Japan, chiefly in the Boso Peninsula (Nakagawa et al., 1969) and Choshi Peninsula (Sakai et al., 1970), Chiba Prefecture, Kinki District (Ishida et al., 1969), Shiga, Kyoto, Osaka, and Hyogo Prefectures, Uonuma area (Nitobe and Yamanoi, 1970), Niigata Prefecture, and Aizu Basin (Manabe et al., 1969), Fukushima Prefecture. Many reports have been published on the geomagnetic and biostratigraphic frameworks made on the deep-sea sediment cores (for example, Hays et al., 1969). On the other hand, a preliminary paleomagnetic and biostratigraphic investigation was made on the rocks from the proposed strasotype of the lower limit of the Pleistocene in Southern Italy by Nakagawa et al. (1970). The results of these investigations made it possible to correlate the Lower Pleistocene of Japan with those in Southern Italy and with the deep-sea sediment cores of the equatorial Pacific. A tentative correlation of the Lower Pleistocene is shown in Fig. 1.
Early Pleistocene refers to the period from Pre-Günz to either the end of Mindel or the end of Günz glaciation, the latter being rather widely adopted in the field of geology and palaeontology. The most important man-like creatures so far known from the period are Australopithecines which accompany with the Villafranchian fauna in Africa. According to the finds at their living sites, it seems out of question that they had already acquired the bipedal locomotion and reached the level of tool-making. In 1931 Dr. N. Naora discovered a human coxal bone imbedded in an earth lump which he believed to have been dislocated down from the upper Lower or lower Middle Pleistocene deposit at a cliff on the coast of the Inland Sea near Akashi, Hyogo Prefecture. The bone was destroyed by fire in 1945, but a few years later its cast was studied by Dr. K. Hasebe, who found primitive characteristics of the bone and proposed a tentative name Nipponanthropus akashiensis. Besides the bone, Dr. Naora discovered crude stone implements from the layer comparable to that of Nipponanthropus. However, it remains controversial as yet whether the Pleistocene deposit had actually yielded the bone in question.
Massif central in France may be one of the best territories for the Villafranchian studies because of its wealthy occurrence of fossil beds and associated volcanic products available for determining their absolute ages and magnetic polarities. More informations from this territory will afford a possibility that the Auvergne section would standardize the nature of the progress of the Villafranchian age, which is presumed to be a transitive period between Pliocene and Pleistocene times, Recent informations from the Le Puy basin seem to prove the difficulty in attempting to draw a single borderline across a period from the so-called pre-Quaternary to the early Quaternary. Apart from this sort of problem on the demarcation, volcanostratigraphic studies comprising the dating and magnetic measurement have afforded much workable clues for global correlation.
Since the first Palaeolithic site (Iwajuku in Honshu) was excavated in Japan twenty one years ago, some five hundred sites between the ages of 30000 and 10000 years BP have been inevestigated. Vertical stratifications of assemblages are present at some twenty of the sites, and thirteen radiocarbon determinations have now been obtained. On the basis of these materials, which are of course by no means sufficient, it is possible to suggest a general outline for the chronological sequence of the Late Palaeolithic cultures in Japan. In this paper, the writer wishes to discuss problems of the human occupation of Japan prior to 30000 BP. A radiocarbon determination in excess of 31900 BP has been obtained for Cultural Horizon 7 of Fukui Cave, and lithic artifacts are being recovered from the Musashino and Shimosueyoshi loam deposits which predate 30000 BP. As an example, Fig. 4 shows some columnar sections at the famous Iwajuku site in Honshu. Two assemblages named Iwajuku I and Iwajuku II were obtained from Locality A during excavation in 1949. The dark zone in which Iwajuku I occured is dated to 24000 BP. Recent re-investigation of the site have revealed the existence of another artifact-bearing horizon at Locality D: the artifacts are made in quarzite and the horizon is clearly below the Hassaki pumice layer. These artifacts, therefore, should predate to be 30000 BP (Fig. 5). These older assemblages include choppers, chopping-tools, pointed tools, proto-handaxes, flakes, cores, and hammer-stones. The ratio of flake tools to core tools is approximately 5:5 or 4:6. Frequently the implements are made on chert, quartz vein or quarzite. It is possible that Lower Palaeolithic peoples of mainland Asia reached Japan during the time of the last major sea transgression, and that, they or their descendants left the assemblages which we are now recovering. As to the feasibility of the entry, some geologists are now suggesting that the area of the Korean Strait was probably dry at the time of the transgression; therefore, human and faunal movements from the Asiatic mainland were not entirely impossible.
This short paper deals with the two important problems concerning lower Pleistocene deposits in Japan from the viewpoint of applied geology; the one is the water balance problem in the basin of these deposits and another is the land subsidence occurred in association with the withdrawal of confined water.