The first excavation at Tategahana, on the shore of Lake Nojiri, was carried out in 1962; since then, excavations have been undertaken ten times. On the occasion of the 10th excavation season in 1987, the total number of excavated items reached 7, 872. They include 755 archaeological items, 1, 931 mammalian fossil items, 98 lithic artifacts and 23 bone artifacts which were mainly made of bones of the Naumann elephant (Palaeoloxodon naumanni). The Nojiri-ko Formation is divided into three members, Lower, Middle and Upper, with marked unconformities between them. Furthermore, each member is subdivided into three or four parts. On the basis of radiocarbon dating and both palaeontological and archaeological studies, the chronometric framework of the Nojiri-ko Formation can be attributed as follows: the Lower Member represents 50, 000-30, 000y.B.P., the Middle Member represents 30, 000-25, 000y.B.P., and the Upper Member represents 25, 000-10, 000y.B.P. The present paper focuses on bone tools including a cleaver, flakes, a spiral flake and chips made of Naumann elephant bones from Middle Member I (26, 100±2, 070y.B.P. 14C, GaK-7789), giving a description of morphological characteristics and attempting to reconstruct the manufacturing processes of bone tools. The most remarkable tool from this layer is a bone cleaver which coincides well morpho-typologically with the definition of a stone cleaver. Our discussion compares the cleaver with other examples of bone cleavers from Anaguni, Central Italy, and Lang/Ferguson, South Dakota. The characteristics of secondary flaking technique for the bone cleaver, together with a bone “point” excavated in the 5th excavation season, were discussed in comparison with the flaking technique expressed among lithic industries from Cultural Layers IX and X in the Musashino Upland area of Tokyo. The distribution pattern of the bone tool assemblage, including two refitted bone items, on the horizon of Middle Nojiri-ko Member I implies that the elephant hunters had also made bone tools in the process of kill-butchering.
Five distinctive tephra beds (A1Pm-A5Pm), carrying abundant biotite and quartz crystals, are widely distributed in central Japan. They are here collectively called Omachi APms or APms in short, and are petrographically identified by high refractive indices of hornblende (n2=1.685-1.696) and orthopyroxene (γ=1.728-1.737). One bed of the APms is found as far as 239km from the presumed source, Momisawadake in the Hida Mountains, where it is 4cm thick and composed mainly of silt-sized glass. No proximal deposit made up of coarse pumice fragments is found owing to unfavorable preservation of the mountainous landscapes; however, the eruption style is supposed to be of plinian type based on analyses of grain size along the dispersal axis. Assuming that the accumulation rate of loess soil has been constant at each locality, the age of APms is estimated 0.24-0.33 Ma by the overlying soil thickness. Moreover, in the south Kanto district, one of the APms is intercalated between two well-established marker-tephra: GoP (0.25-0.30Ma) and TE-5 (0.35-0.40Ma). It is very likely that the age of APms is 0.30-0.35Ma. The time interval between A1Pm and A5Pm eruptions is estimated to be less than 0.05Ma, because the thickness of the soil layer intercalatcd between APms does not exceed 106cm at any locality. The Omachi APms are found on the flanks and slopes of many volcanoes in central Japan, such as Azumaya, Yatsugatake, Kusatsu Shirane, and Takahara. They are also found among deposits forming fluvial terraces in north Kanto. The significance of APms as Middle Pleistocene time-markers will be established hereafter.
Recently, many widespread tephras have been discovered in Japan. However, researchers into local tephras have been puzzled by the fact that one tephra called by a local name may also be identified as a widespread tephra although some analytical data on the local one differ from those on the widespread one. The felsic plural tephras, which erupted about 1, 000 years ago, are distributed in the Tohoku district. One that covers Aomori prefecture and the northern part of Iwate prefecture is named Towada-a. Others found in other areas are named Ooyu pumice, Akita-Yakeyama pumice, Isawa volcanic ash and light gray-colored volcanic ash in the various areas where they are found. There are two theories about the origin of these tephras. One, that all of them erupted from Towada volcano, was advanced on the basis of the refractive indices of volcanic glass, orthopyroxene and plagioclase. The other theory is that these tephras originated from different volcanos, because the chemical composition of ferromagnetic minerals among these tephras especially the vanadium content, varied considerably. We investigated the major and minor elements of these tephras and their content of volcanic glass, magnetic minerals and pyroxenes, and concluded that all the tephras erupted from Towada volcano and that Ooyu pumice, Akita-Yakeyama pumice, Isawa volcanic ash and light gray-colored volcanic ash were same tephra, but Towada-a was a different fall unit tephra from the others. The V content of ferromagnetic minerals in tephra was higher in the smaller particles of titanomagnetite than the larger ones. The difference in V content of these minerals among tephras was due to the difference in the particle size; the farther it is from Towada volcano, the smaller was the particle size of the tephra. This result indicated that it is necessary to use the same-sized particles for the identification of tephra by the V-Zn belt of ferromagnetic minerals.
The tephra and peat beds distributed at Tokotan and Honbekkai in the eastern margin of the Konsen Plateau, Eastern Hokkaido, were investigated by tephra stratigraphy, pollen analysis, and 14C datings. The peat layers of Tokotan Loc. 1 were estimated to date from the late stage of the Last Glacial Age. Four pollen zones were discriminated there. The lowest zone, TK-I, about 36, 000y. B. P., is characterized by high pollen percentages of Picea coexisting with Larix and Abies. Zone TK-II is characterized by high Larix, Betula, Alnus, and herbs. Zone TK-III, a little older than 32, 000y. B. P. in age, is dominated by Picea. The uppermost zone, TK-IV, is estimated at about 32, 000y. B. P. based on the existence of Nl-a and Spfa-l, and it has high percentages of Larix, Picea and herbs. During the formation of these 4 zones, there could be subarctic forests (zones TK-I and TK-III) and subarctic open forests (zones TK-II and TK-IV) dominated by larch and/or spruce on bogs. Generally, the climatic conditions of zones TK-I-IV was colder and drier than at present, especially in zone TK-II, and less so in zone TK-III.
This paper discusses the relative Holocene sea level change in a small lowland of Takagami, located on the central part of the Choshi Peninsula, easternmost of Kanto district. Samples obtained by drilling machine and peat-corer were used for radiocarbon dating, sedimentary facies observation and analysis of molluscan, diatom and pollen assemblages. Our data, combined with our first report (OTA et al., 1985), reveal that the Postglacial transgression has started at c. 10, 000y.B.P. at the latest. A rapid sea level rise has continued till c. 7, 000y.B.P., followed by a decrease of water depth. The upper limit of marine deposits is about 4.0m above mean sea level. The culmination of relative sea level rise has occurred at about 5, 500y.B.P., judged by clustering of radiocarbon ages of the lowest terrestrial peat bed in c. 5, 000-5, 500y.B.P. Since then, sea level probably has lowered to the present position without any intermittent uplift.