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Volume 45 (2006)
- Issue 6 Pages 423-
- Issue 5 Pages 315-
- Issue 4 Pages 263-
- Issue 3 Pages 151-
- Issue 2 Pages 67-
- Issue 1 Pages 1-
Volume 45, Issue 2
Displaying 1-7 of 7 articles from this issue
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Original Articles
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Yukihiko Kamoi, Satoshi Tanaka, Satoshi Yasui2006 Volume 45 Issue 2 Pages 67-80
Published: 2006
Released on J-STAGE: July 27, 2007
JOURNAL FREE ACCESSTen rows of sand dunes ranging parallel to the present coastline are identified in the Echigo Plain, northern Japan. The timing of sand dune formation is determined by the dating of organic matter from the sand dune itself, peaty sediments of interdune lowlands, and basement sand dune sediments. When the sea level was highest, in the Jomon transgression, about 8,000 years ago, a barrier island system associated with lagoons was established along the innermost zone of the Echigo Plain. When the sea level was stable or a little lower then the peak sea level, about 6,000 years BP, the fluvial plain expanded quickly, due to high sediment supply from large rivers such as the Shinanogawa River.
Coastal dunes developed intermittently in response to halts in the advance of the coastline, resulting in the formation of the sand dune rows named Dunes I-1, I-2, I-3, I-4, II-1, II-2, II-3, II-4, III-1, and III-2. The formation ages of the sand dunes were confirmed in detail as follows : Dune I-1 in about 6,000 years BP, Dune I-2 in 6,000-5,500 years BP, Dune I-3 in 5,000 years BP, Dune I-4 in 4,500 years BP, Dune II-1 in 4,000 years BP, Dune II-2 in 3,500 years BP, Dune II-3 in 3,000 years BP, Dune II-4 in 2,000-1,700 years BP, Dune III-1 in 1,700-1,100 years BP and Dune III-2 in 1,100 years BP.View full abstractDownload PDF (2790K) -
Takeyuki Ueki2006 Volume 45 Issue 2 Pages 81-97
Published: 2006
Released on J-STAGE: July 27, 2007
JOURNAL FREE ACCESSThe fluvial Kamikayama and Sayama surfaces with the Kamikayama and Imokubo Gravel Formations on the western side of the Kanto Plain, central Japan, underlie the air-laid 580- to 690-ka Kaisho-Kamitakara tephra (KMT). Paleomagnetic and rock-magnetic samples were taken from a flood loam facies at the uppermost strata of the Kamikayama Gravel Formation, tephric loess beds on the Kamikayama and Imokubo Gravel Formations, and the KMT. All the Kamikayama and Sayama samples hold normal paleomagnetic polarity. The magnetic carrier of primary remanence of these samples is titanomagnetite. Formation ages of the Kamikayama and Sayama surfaces are estimated to be the earliest Brunhes Chron.View full abstractDownload PDF (2699K) -
Tetsuya Sakai, Tomohiro Takagawa, Ananta P. Gajurel, Hideo Tabata, Nob ...2006 Volume 45 Issue 2 Pages 99-112
Published: 2006
Released on J-STAGE: July 27, 2007
JOURNAL FREE ACCESSSediments indicating a rapid fall in lake level have been discovered in the late Pleistocene Gokarna Formation, Kathmandu Valley, Nepal. The indicators are observed along a widely traceable erosional surface in this formation, and is characterized by (1) gently inclined (ca. 10°) tabular cross-stratified sand beds of delta front deposits consisting of coarser material and showing gradual decrease in elevation of its top to the progradation direction, (2) an antidune cross-laminated sand bed that interfingers with the delta front deposit, and (3) an approximately 5m-deep erosional depression filled with convolute laminated sand beds and recognized at a location distal to that where deposits (1) and (2) were found.
The early phase of rapid lake level fall caused minor erosion of the delta plain deposits by fluvial processes, introducing a higher rate of progradation of the delta front and resulting in the accumulation of deposit (1). The delta emerged as dry land due to further lowering of the lake level. The antidune cross-laminated sand bed shows evidence of having accumulated from a high-velocity stream that may have formed as the lake water drained from the delta front during the lowering of lake level. When the lake level fell below the level of the topographic high created by delta accumulation prior to the fall, incised valleys may have formed and part of them may have been filled with sediment at that time.
The rapid fall in lake level is interpreted to have been the result of lake-wall failure, which would have occurred at the gorge outlet as the only discharge path for the basin. The initial rise of lake level causing accumulation of terrace sediments may have been due to the formation of a plug at this outlet, attributable to mass movement along the gorge.View full abstractDownload PDF (5642K) -
Ken-ichi Nakao2006 Volume 45 Issue 2 Pages 113-121
Published: 2006
Released on J-STAGE: July 27, 2007
JOURNAL FREE ACCESSThe uppermost part of the lower Pleistocene Kazusa Formation is a marine deposit which is characterized by Thalassinoides isp., lenticular-wavy-flaser bedding, and marine mollusks. At the Tsubami outcrop, an upward shallowing sequence from mid-bay or lower intertidal zone to tidal flat and salt marsh was observed. The Theora association, which is composed of many fossils of Theora fragilis, occurred from the lowermost clay bed, while the Scapharca-Volachlamys association which mainly consists of Anomia chinensis, Ostrea denselamellosa, Volachlamys hirasei, Scapharca kagoshimensis, and Meropesta capillacea, were collected from the upper sand bed. All species from the Kazusa Formation are now living. V. hirasei and M. capillacea are well-known relict species now restricted to the Chinese continent and the Ariake-Seto Inland Sea faunas, and are the oldest records in Japan. Thus, the molluscan assemblage from the Kazusa Formation is the oldest tidal flat to embayment fauna that includes some relict species of the Chinese continent, which appeared in Japan during the Early Pleistocene.View full abstractDownload PDF (2573K)
Short Articles
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Hidetsugu Yoshida, Toshihiko Sugai, Hiroo Ohmori2006 Volume 45 Issue 2 Pages 123-129
Published: 2006
Released on J-STAGE: July 27, 2007
JOURNAL FREE ACCESSThis paper explains how the debris originating from the sector collapse of Asama volcano at 24ka, traveled longer than 90km as a kind of “plug flow” with a thin laminar boundary layer. At 3 outcrops at distances of 45km, 75km, and 90km from the origin, vertical changes in the chemical composition throughout the debris avalanche deposits and underlying fluvial sediments were examined employing the energy-dispersive X-ray spectroscopic method. 57 samples were classified into two groups with different chemical compositions. The chemical composition of the debris avalanche block with fragile internal structures at the 90km site, is almost the same as those of the debris avalanche matrix. This indicates that the debris avalanche matrix originating from the collapsed volcanic body was partly produced from the debris avalanche blocks and that almost all portions of the debris avalanche deposits consist of the plug part. The lowermost part of the debris avalanche deposits at the 45km site, however, expresses a chemical composition similar to that of the fluvial sediments. This indicates that the debris avalanche, having a laminar boundary layer with strong shear stress working at the base, was flowing down. The geochemical result and lithofacies of the deposits suggest that the sediments have traveled rapidly at least 90km, as a single debris avalanche.View full abstractDownload PDF (2073K) -
Takashi Ogami, Toshihiko Sugai2006 Volume 45 Issue 2 Pages 131-139
Published: 2006
Released on J-STAGE: July 27, 2007
JOURNAL FREE ACCESSThis study revealed the subsurface geological structure under the flexure scarp of the Yokkaichi Fault, based on arrayed boring cores with their radiocarbon dates, to evaluate the paleoseismicity of the fault since the late Pleistocene.
The Holocene sediments can be divided into 5 units, and cumulative fault displacement was recognized. The average vertical slip rate of the fault is 1.2-1.8mm/yr during the last 10,000 years. This rate is equivalent to that of the Yoro-Kuwana Fault. The timing and vertical offset of the last three faulting events are probably the same as those of the Kuwana Fault, as has been shown in recent studies.
Those results support the idea that the Yokkaichi Fault played the same behavioral segment as the Yoro-Kuwana Fault during the Holocene.View full abstractDownload PDF (2552K)
Note
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A. Kitamura, T. Kase, S. Umino, N. Yamamoto, S. Ohashi, M. Hiramoto, N ...2006 Volume 45 Issue 2 Pages 141-144
Published: 2006
Released on J-STAGE: July 27, 2007
JOURNAL FREE ACCESSDownload PDF (1207K)
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