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Volume 43, Issue 1
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Akira Inada, Takeyoshi Saito, Kazuko Ohama, Shizuko Kaneko, Kenji Shim ...2004 Volume 43 Issue 1 Pages 1-14
Published: February 01, 2004
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSPlaeo-environmental transitions since ca. 4, 500yrs BP were clarified through pollen and diatom analyses in and around a lowland along the Shinkawa River (Shinkawa Lowland) in Yachiyo City, Chiba Prefecture.
From pollen analysis, we recognized three pollen zones for regional vegetation changes of the hill area around the lowland. The vegetation of KaP-I pollen zone (ca. 4, 500 to 3, 400yrs BP) shows a deciduous broadleaved forest mainly of Quercus (Lepidobalanus). The KaP-II pollen zone (ca. 3, 400 to <1, 400yrs BP) is characterized by the increase of Cryptomeria, Abies and Tsuga in the deciduous broadleaved forest. The KaP-III zone (<1, 400yrs BP to the present) occurred with the establishment of the Pinus secondary forest.
Environmental transitions in the Shinkawa lowland are shown as follows.
KaD-ib diatom zone and KaP-IA pollen zone: At ca. 4, 500yrs BP, sedimentation took place under terrestrial environments. The vegetation was an open grassland composed of Compositae, Gramineae, and Cyperaceae plants.
KaD-ic diatom zone and KaP-IB pollen zone: These grassland turned to shallow swamp, and aquatic Cyperaceae and Gramineae plants lived around it.
KaD-iia diatom zone and KaP-IC pollen zone: Swamp forest of Fraxinus and Alnus expanded, probably due to the lowering of the groundwater level.
KaD-iib diatom zone and KaP-IIA, C pollen zone: Terrestrial conditions occurred again in this diatom zone. The vegetation was characterized by the expansion of a Ulmus-Zelkova forest.
KaD-iiia diatom zone and KaP-IID pollen zone: The occurrence of planktonic diatoms indicates swamp or lacustrine conditions. Emerging communities of Cyperaceae, Gramineae, and Typha expanded.
KaD-iiia, b diatom zone, and KaP-III pollen zone: The zone is characterized by the establishment of modern paddy fields in the low-land.
In the KaP-IIB pollen subzone (ca. 3, 000yrs BP), Pinus and Gramineae pollens occurred in high percentage abundances, accompanied by Fagopyrum, Sagittaria, Alisma, Monochoria, Xanthium, and Aneilema. Plant opals of Oryza sativa were also found in the subzone. These facts suggest the short-term expansion of the Pinus secondary forest and the existence of paddy rice fields. These vegetational changes may have been caused by cultural activities in and around the lowland during the late to latest Jomon Periods.View full abstractDownload PDF (2797K) -
Major Element Composition of the Glass Shards Using EDS AnalysisYoshitaka Nagahashi, Shusaku Yoshikawa, Chihiro Miyakawa, Takashi Uchi ...2004 Volume 43 Issue 1 Pages 15-35
Published: February 01, 2004
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSEnergy dispersive Xray Spectrometry (EDS) was applied to measure the major element composition of volcanic glass shards. One hundred three analytical tephra samples were collected from the Takashima-oki drilling core sample on Lake Biwa, as well as some representative drilling core samples in the Osaka coastal area and Middle Pleistocene tephra layers at the foot of the Yatsugatake Mountains. The ages of the principal tephra layers were estimated from the correlation between the biostratigraphic horizons from the core samples and the oxygen isotope stratigraphy. The estimated ages of the Kg, K-Ah, U-Oki, AT, Aso-4, K-Tz, Aso-3, BT44, BT51, Ata-Th, Aso-1, Ng-1, Kkt and BT72 tephra layers are 3.1ka, 7.3ka, 10.7ka, 29ka, 87ka, 91ka, 133ka, 203ka, 216ka, 238ka, 249ka, 294ka, 334ka, and 349ka, respectively. These principal tephra ages provide the estimated ages of other tephra layers using the sediment accumulation rates in the Takashima-oki core. Consequently, this study has reconstructed the tephrostratigraphy and chronology during the past 430ky. Furthermore, it is pointed out that caldera forming eruptions have occurred at low sea level periods just before the maximum high sea level.View full abstractDownload PDF (3544K) -
From the Analysis of Fracture WingsJun Takakura, Masami Izuho2004 Volume 43 Issue 1 Pages 37-48
Published: February 01, 2004
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSThis paper discusses the theoretical framework of identification of flaking techniques based on the fracture mechanics of brittle solids, and presents the results of a series of experiment which examined a criterion of identification applicable to the archaeological records. The term ‘flaking technique’ is used in conjunction with knapping materials (stone, metal, antler, wood) and knapping techniques (direct percussion, indirect percussion, and pressure).
To address this issue, we focus on fracture wings, which are microscopic markings found on the fracture surfaces of a wide range of brittle solids including obsidian. Fracture wings are ubiquitous and very reliable registers of crack velocity. Identification of flaking techniques is divided into two processes: (1)identification of crack velocity based on the model of fracture mechanics, (2) a strong correlation between crack velocity and flaking techniques that is experimentally recognized. Our several experiments demonstrate that a strong association between crack velocity and flaking techniques does in fact exist. Through the analyses of fracture wings, we establish three groups of flaking techniques (I: pressure, II: indirect percussion, direct percussion using antler or wood, III: direct percussion using stone or metal), which are strongly dependent on the difference in crack velocity. This result makes it possible to identify the flaking techniques in the archaeological records, and should contribute to the understanding of the processes involved in flaking formation.View full abstractDownload PDF (2639K) -
Guangbiao Wei, Yoshinari Kawamura, Changzhu Jin2004 Volume 43 Issue 1 Pages 49-62
Published: February 01, 2004
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSNumerous remains of a bamboo rat from the Early Pleistocene of Renzidong Cave are described systematically. The morphological characters of the remains indicate that they are assignable to a new species of Rhizomys, which is named R. fanchangensis here. Rhizomys is an extant genus, but the new species is extinct and shows such primitive characters as being small-sized and bearing brachydont molars as a species of Rhizomys. It is chronologically the oldest one among the species of Rhizomys. Thus, the new species is important for bridging the Pliocene species of the ancestral genus, Brachyrhizomys, and Rhizomys species from the later stages of the Quaternary, chronologically and morphologically. Additionally, in this paper, we follow the chronological division of the Pliocene and Pleistocene generally adopted among Chinese geologist, in which their boundary lies at the Matuyama/Gauss geomagnetic boundary.View full abstractDownload PDF (2355K) -
Akihisa Kitamura, Yoshitaka Sakaguchi2004 Volume 43 Issue 1 Pages 63-68
Published: February 01, 2004
Released on J-STAGE: August 21, 2009
JOURNAL FREE ACCESSThe youngest graded gravel to sand bed in Hakodate Bay was discovered to contain abundant glassy spheres 0.5-2.0mm in diameter. The stratigraphic distribution and the processes of formation and supply of the glassy spheres, and the history of natural and anthropogenic events influencing Hakodate Bay, lead to the following conclusions:
1. The glassy spheres may have been formed by explosions of large steamships in the east head of the bay during World War II (July, 14, 1945).
2. During Typhoon Toyamaru in 1954, the storm surge and associated currents could have carried abundant sediment, including the glassy spheres, seaward and deposited them as the youngest graded bed in Hakodate Bay.
The storm bed may be useful as a key bed that can be used to understand depositional processes and environmental changes in Hakodate Bay.View full abstractDownload PDF (1491K)
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