Journal of the Sedimentological Society of Japan

Cover Story

Hot spring travertines in the Rapolano Terme area, Toscany, central Italy

Hiroki Matsuda

2008 Volume 72 Issue 2 Pages 108
Published: December 20, 2013
Released on J-STAGE: March 05, 2014

DOIhttps://doi.org/10.4096/jssj.72.108

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Articles

Tsunami-induced gravity currents generated in an experimental flume

Satoru Niitani, Fujio Masuda, Hajime Naruse

2008 Volume 72 Issue 2 Pages 109-113
Published: December 20, 2013
Released on J-STAGE: March 05, 2014

DOIhttps://doi.org/10.4096/jssj.72.109

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As a result of sediment entrainment by the experimental tsunami waves on the wave-dominated shallow marine geomorphology, a sediment-gravity flow occurred at the lower foreshore to the upper shoreface by tsunamigenic oscillatory flows in the experimental flume. Collision of run-up currents on the subaerial region and ebb currents with submarine erosion cyclically occurred by the tsunami, providing suspended sediments continuously to the downslope-migrating sediment gravity flow on the shoreface. Considering the recurrence intervals of the large tsunamis, the tsunamigenic turbidity currents could be significant as an origin of widely distributed turbidites in the regions of active plate margins.

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Tenma spit deposit in the Holocene of the Osaka Plain: Distribution and stratigraphy

Fujio Masuda, Younosuke Nakagawa, Takahiko Sakamoto, Yuka Ito, Minao S ...

2008 Volume 72 Issue 2 Pages 115-123
Published: December 20, 2013
Released on J-STAGE: March 05, 2014

DOIhttps://doi.org/10.4096/jssj.72.115

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Distribution and stratigraphy of the Holocene Tenma spit deposit in the Osaka Plain were firstly clarified using by borehole database and previously reported ¹⁴C ages. The deposit within the middle marine clay part of the Holocene sediments was deposited 8000 to 5000 years ago during the transgressive and maximum flooding periods. The deposit is characterized by a long and narrow platform, a progradational upward-coarsening sediment sequence, and signs of emergence at its top. The deposit extends continuously from a lower offshore to an upper landward end. It includes depositional structures generated by storm-waves and marine fossil shells. The deposit is most extensively developed in the area of the paleo-wave cut cliffs and benches on the northwestern margin of the Uemachi Upland. These features strongly support an origin from coastal sand and sandy gravel spit systems. The Tenma spit developed in two stages, bounded by the rapid rise of sea level 8000 to 7000 years ago. This final developed spit was 7-8 km long and less than 100 m wide from Tenma through Nagara to Awaji in 6000 to 5000 years ago. After 5000 years ago during the highstand period, the spit evolved into a wide strand-plain system with long sand or sandy gravel beaches.

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Research Report

Ripples under partially standing waves for different reflection coefficients: a laboratory experiment

Naofumi Yamaguchi, Tomohiro Sekiguchi

2008 Volume 72 Issue 2 Pages 125-134
Published: December 20, 2013
Released on J-STAGE: March 05, 2014

DOIhttps://doi.org/10.4096/jssj.72.125

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A series of wave-flume experiments was performed to examine ripple geometry, development, and migration under partially standing waves for five different intensities of wave reflection. The present experiments showed the cross-shore variation of the development and geometry of bedforms corresponding to the position of nodes and antinodes. The ripple field tended to initiate under nodes and spread from nodes to antinodes. The local-mean ripple spacings were the largest under nodes and the smallest under antinodes. The difference of the ripple development and the ripple spacing between nodes and antinodes became more pronounced with increasing the intensity of wave reflection. The local-mean ripple spacings in the present experiments correspond approximately with those predicted by Nielsen’s (1979, 1981) empirical formula. The trend of sediment transport predicted by ripple migration is consistent with the bed profiles at the end of each run. The geometry, development, and migration of ripples are a possible clue for understanding the cross-shore variation in local hydraulic conditions and mass sediment transport under partially standing waves.

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Notes

Relationship among the deformation of river bed, river level, discharge, and groundwater level

Kazuhisa Suzuki

2008 Volume 72 Issue 2 Pages 135-140
Published: December 20, 2013
Released on J-STAGE: March 05, 2014

DOIhttps://doi.org/10.4096/jssj.72.135

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Intra-arc tectonics in the Early to Middle Miocene in Northeast Japan

Jun Hosoi, Makoto Okada, Tomohiro Gokan, Kazuo Amano

2008 Volume 72 Issue 2 Pages 141-146
Published: December 20, 2013
Released on J-STAGE: March 05, 2014

DOIhttps://doi.org/10.4096/jssj.72.141

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Geometry and internal organization of hyperpycnites formed in front of a shelf-margin delta system, a Middle Pleistocene Chonan Formation on the Boso Peninsula, central Japan

Masaya Fuse, Keisuke Nakamura, Makoto Ito

2008 Volume 72 Issue 2 Pages 147-151
Published: December 20, 2013
Released on J-STAGE: March 05, 2014

DOIhttps://doi.org/10.4096/jssj.72.147

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This study investigated downslope variations in vertical changes in grain sizes and sedimentary structures within sandstone and sandy siltstone beds, which are interpreted to have formed as hyperpycnites in front of a shelf-margin deltaic system. An example of this study is from the Middle Pleistocene Chonan Formation on the Boso Peninsula, Japan. In general, the hyperpycnites show an overall convex-up lenticular geometry and downslope decreases in grain sizes and thickness, except for medium- to very thick-bedded massive sandstones, which are associated with some bypass zones in a proximal area. Thin- to medium-bedded hyperpycnites in a proximal area are characterized by single or multiple inversely-to-normally graded bedding in association with tractinal structures, which pass upward to normally graded sandstones and sandy siltstones. In contrast, normally graded sandstones, which are gradationally overlain by sandy siltstones with local concentrations of plant fragments and can be described by the Bouma model, are more common in a distal area as a response to both the decrease in the density of hyperpycnal flows and the sedimentation from lofting plumes.

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Evaluation of the effect of turbidity currents in the formation of hemipelagic siltstones: An example from the lower Pleistocene Kazusa Group on the Boso Peninsula, Japan

Shiho Kurosawa, Mayu Mitsui, Makoto Ito

2008 Volume 72 Issue 2 Pages 153-157
Published: December 20, 2013
Released on J-STAGE: March 05, 2014

DOIhttps://doi.org/10.4096/jssj.72.153

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This study investigated downslope variations in sedimentation rate, grain size, magnetic susceptibility, and clay mineral composition of hemiplelagic siltstones in the Kd8 (ca. 1.2 Ma) and O7 (ca. 0.9 Ma) volcanic ash key bed horizons in the Pleistocene Kazusa Group on the Boso Peninsula, Japan. In general, sedimentation rates decrease in the downslope directions in association with the decrease in grain size, except for local increases in sedimentation rates and grain size as a response to additional supply of fine-grained sediment particles from turbidity currents. In contrast, although the magnetic susceptibility shows a downslope variation in harmony with that in grain size in the O7 volcanic ash key bed horizon, it is also influenced by local development of authigeneic magnetic minerals in the Kd8 volcanic key ash bed horizon. Regardless of the spatial variations in sedimentation rates, grain size, and magnetic susceptibility, clay mineral composition does not show any distinct spatial variation and can be used as a proxy of temporal variation in hinterland geology and paleoclimates in a one-dimensional stratigraphic record.

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Basin evolution reconstructed from reflected turbidite: an example from the Plio-Pleistocene Kakegawa Group, Western Shizuoka, Japan

Kenta Kitahori, Tetsuya Sakai

2008 Volume 72 Issue 2 Pages 159-164
Published: December 20, 2013
Released on J-STAGE: March 05, 2014

DOIhttps://doi.org/10.4096/jssj.72.159

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Conference Report

A report on the Western Pacific Sedimentology Meeting

Megumi Seki

2008 Volume 72 Issue 2 Pages 165-172
Published: December 20, 2013
Released on J-STAGE: March 05, 2014

DOIhttps://doi.org/10.4096/jssj.72.165

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