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Volume 45, Issue 1
Displaying 1-4 of 4 articles from this issue
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Original Articles
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Eisuke Ono, Akio Ohira, Kazunori Tanaka, Ikuo Suzuki, Kunio Yoshida2006 Volume 45 Issue 1 Pages 1-14
Published: 2006
Released on J-STAGE: July 27, 2007
JOURNAL FREE ACCESSThis study discusses landform development in the Central Echigo Plain in relation to change in depositional areas of fluvial sediment.
The plain is located on the Japan Sea side of the central Honshu Island, and it extends about 60 km from north to south and 50 km from east to west. The plain was formed by depositions of the Shinano River and its tributaries. The micro-landform of the plain can be divided into five components ; natural levees, back marsh, recent dunes, alluvial fans, and abandoned channels, based on the interpretations of aerial-photographs.
The authors obtained core samples from about 40 sites in the study area, measured their 14C ages, analyzed their electric conductivity, and referred to the existing boring data and archaeological data. These analyses indicate the following history of the sedimentary environment during the late Holocene.
A remarkable Holocene transgression (the Jomon transgression) occurred and formed a large lagoon around 6,000 yrsBP in the study area. After the Holocene transgression, fluvial deposits buried the lagoon gradually and center deposition moved the coast forward. After 4,000 yrsBP, sediment from the Shinano River rapidly formed the foreset bed and sand dunes on the coast side. Meanwhile the sedimentary environment of the floodplain became stable, and sediment from Shinano River gradually formed a topset bed. During 1,400-1,000 yrsBP, peaty soil was formed in a wide area of the floodplain. After 1,000 yrsBP, floodplain sedimentation became rapid, and natural levees on the present plain's surface were mainly formed during 1,000-800 yrsBP.View full abstractDownload PDF (3042K) -
Yasuo Miyabuchi, Shinji Sugiyama2006 Volume 45 Issue 1 Pages 15-28
Published: 2006
Released on J-STAGE: July 27, 2007
JOURNAL FREE ACCESSA 30,000-year record of vegetation change has been constructed using phytolith analysis from a tephra sequence located at the east of Aso caldera, central Kyushu, southwestern Japan. The sequence was divided into three zones : Zone 3 (ca. 32-30 cal ka), Zone 2 (30-13.5 cal ka), and Zone 1 (13.5-0 cal ka), in ascending order. Gramineae phytoliths were predominantly detected from most horizons, whereas a small amount of arboreal phytolith was observed at a few Holocene horizons. Zone 3 was dominated by a Sasa grassland (mainly Sasa sect. Crassinodi), suggesting a cool and dry climate. However, the Sasa grassland declined due to violent volcanic activity of Aso Volcano in Zone 2, which corresponds to the Last Glacial Maximum. During Holocene time (Zone 1) a Miscanthus grassland continued consistently for more than 10,000 years. The long continuation of the Miscanthus grassland might be related to artificial burning. In and around Aso Volcano, brownish soil layers were formed when the accumulation rate of soil parent materials (tephra) was high, whereas blackish humic soil layers were formed when the rate was low. The tephra discharge rate boundary between the formation of brownish and blackish soil layers is estimated at 0.1-0.2 km3/ky.View full abstractDownload PDF (5016K) -
Yasufumi Satoguchi, Chiyomi Yamakawa2006 Volume 45 Issue 1 Pages 29-39
Published: 2006
Released on J-STAGE: July 27, 2007
JOURNAL FREE ACCESSConglomeratic beds, whose depositional age is unknown, are distributed around the Terabayashi area at the foot of Mt. Ibuki. These beds are described as the Terabayashi Formation. This formation is divided into four parts : the Lowermost, Lower, Middle, and Upper parts, based on detailed discrimination of lithofacies. The Lowermost part rests on an irregular surface of the basement rock and is composed of varved mud, organic mud, and matrix-supported massive gravels. The Lower and Upper parts are dominated by matrix-supported massive gravel beds, which are deposited as debris-flows. The Middle part consists of lenticular sand beds intercalated in clast-supported massive gravel beds that were deposited as longitudinal bars or lag deposits within channels.
Three volcanic ash beds named the Terabayashi I, II, and III volcanic ash beds in the Lowermost part are described based on their lithofacies, petrographic properties, and chemical composition of volcanic glasses. The Terabayashi I and II volcanic ash beds are correlated with BT60 and BT59 volcanic ash beds in the Takashima-oki core, respectively, based on their characteristic properties. The Takashima-oki core, which was bored at Lake Biwa, represents the typical tephrostratigraphy and tephroclonology of the Kinki district. These correlations of volcanic ash beds show that the depositional age of the conglomeratic beds is around the boundary between oxygen isotope stage 8 and stage 7.View full abstractDownload PDF (1796K)
Short Article
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Miyuki Inagaki, Akio Omura2006 Volume 45 Issue 1 Pages 41-48
Published: 2006
Released on J-STAGE: July 27, 2007
JOURNAL FREE ACCESSThe uplifted Pleistocene marine terraces in Kikai Island have been investigated using radiometric dating since the 1960s. The highest terrace was called the Hyakunodai Terrace, which is divided into three blocks by faults, assigned in this study as Block C, Block B and Block A in ascending order of height. Previous studies indicate that Block A was formed during Marine Isotope Stage (MIS) 5e and that MIS 5c corals were distributed on the cliff between Blocks A and B based on Uranium-series dating. We carried out careful fieldwork and report more precise α-spectrometric U-series ages of Blocks A and B. Fossil corals showed eight Mid- to Late Pleistocene dates ranging from 154.8±6.4 to 97.7±3.0 ky (2σ) and three Middle Pleistocene ages (>450 ky). Mid- to Late Pleistocene dates are divided into three age groups, 154.8±6.4-142.7±5.8 ky, 122.1±3.8 ky and 108.2±3.2-97.7±3.0 ky, corresponding to MIS 6, 5e and 5c, respectively. While all age groups were obtained from Block A, Block B only contains MIS 5c and Middle Pleistocene corals. The MIS 5c outcrop at Block A contains clear reef structure (bindstone) and the coral assemblages indicate depositional depth ranging from 5 to 15 m. These facts suggest that the highest terrace was formed during MIS 5c. Exposure of MIS 5e or 6 corals is possibly due to erosional effect during MIS 5c transgression.View full abstractDownload PDF (725K)
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