Journal of the Sedimentological Society of Japan

Modelling of motion of and deposition from turbidity currents

Yu'suke Kubo

2001 Volume 54 Issue 54 Pages 1-7
Published: December 25, 2001
Released on J-STAGE: May 27, 2010

DOIhttps://doi.org/10.4096/jssj1995.54.1

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A review of the examples to model a motion of and deposition from turbidity current is presented, with applications of the models to natural settings. Empirical relationship and some equations derived from simple descriptions of energy and momentum balance are used to describe a steady motion of turbidity current. A turbidity current generated by the lock-exchange method in laboratory flume can be considered as lateral extension of a heavier fluid along the floor. Based on empirical formula giving the speed of the lateral extension, velocity variation and deposit distribution can be predicted. In natural settings, turbidity current is divided to two types; short-lived, surge-type flow and sustained, continuous type flow. A surge-type turbidity current can be modelled as a cloud of suspension and its motion can be described by a simple momentum equation. This model has an advantage to evaluate effects of variation in slope in a simple form. A sustained turbidity current is usually described by Navier-Stokes equation, which requires numerical computation to give detailed information on flow conditions and deposit distribution.

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Two relative sea-level changes recorded in the “Miwa Formation”, Shimosa Group

an example in the Ishioka-Hokota area, Ibaraki Prefecture, Japan

Yoshiharu Yokoyama, Hisao Ando, Shinzo Ooi, Yoshitaka Yamada

2001 Volume 54 Issue 54 Pages 9-20
Published: December 25, 2001
Released on J-STAGE: May 27, 2010

DOIhttps://doi.org/10.4096/jssj1995.54.9

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Two sedimentary cycles can be recognized from the late Pleistocene “Miwa Formation” of the Shimosa Group in the Ishioka-Hokota area, Ibaraki Prefecture, by analyzing depositional facies, tephra key beds and erosional surfaces. The lower cycle consists of an incised-valley fill depositional system, which is limited in the western part in distribution and the overlying shoreface-beach system distributed throughout the studied area. The upper cycle is characterized by a widely-distributed back-barrier system, which has thickly been preserved in the western part, whereas had been much eroded by an overlying shoreface-beach system in the eastern part. The following Joso Formation is composed mainly of fluvial deposits, though marine beds are found in the lower part of the eastern area. The two sedimentary cycles in the “Miwa Formation” correspond to two depositional sequences determined by the upper and lower sequence boundaries (SB1, SB2 and SB3). The two depositional sequences include transgressive and highstand systems tracts, and contain two erosional surfaces: bay ravinement surface and wave ravinement surface.

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An implication of depositional environments with reference to maceral compositions from the Miocene to Pleistocene sediments in the Chuo Oil Field, Niigata Prefecture, central Japan

Akiko Omura, Takeo Nimura, Toshiyuki Sato, Koichi Hoyanagi

2001 Volume 54 Issue 54 Pages 21-36
Published: December 25, 2001
Released on J-STAGE: May 27, 2010

DOIhttps://doi.org/10.4096/jssj1995.54.21

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Maceral compositions of kerogen in various sedimentary environments of the Upper Miocene to Pleistocene strata distributed in the Chuo Oil Field, Niigata back arc basin in Japan are examined. NFA and vitrinite of terrestrial origin are abundant in the sediments deposited in the outer shelf, lower slope and basin floor submarine fans. In the outer shelf environment vitrinite increases with the decrease of NFA content toward the shore. The outer shelf sediments not always contain abundant amount of vitrinite comparing with the submarine fan sediments. Maceral distribution pattern is explained by the sedimentary facies analysis to have been controlled by not only the distance from the shore but also the transportation processes of the sediments.

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Flume experiments on the migration rate of wave-formed ripple marks

Sachiko Mori, Tomohiro Sekiguchi, Tsuguo Sunamura

2001 Volume 54 Issue 54 Pages 37-43
Published: December 25, 2001
Released on J-STAGE: May 27, 2010

DOIhttps://doi.org/10.4096/jssj1995.54.37

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The migration rate of wave-formed ripple marks was investigated using a two-dimensional wave flume. Well sorted fine-grained sand (0.2mm in diameter) was placed on a 1/20-fixed slope and an adjacent part of the horizontal flume bottom. The onshore migration rates of ripples and near-bottom orbital velocities were measured at three sites along the slope with different water depths and at one site on the horizontal bed. Ripples which developed fully and reached the steady state migrated at constant rates. The ripple migration speed generally increases as the maximum bottom velocity becomes higher. Ripples in the lowest part of the slope migrated more slowly than those on the horizontal bed although the maximum velocities were nearly equal. A detailed comparison of velocity data between these areas indicated that the time-variation pattern of the bottom velocities slightly differed from each other. Considering sediment transport on ripples, such a slight difference in the velocity patterns was found to give an influence on the ripple migration rate. A comparison using mobility number between the results of this study and the previous data suggested that ripple migration is much more complex in the field where irregular waves are dominant.

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Founders of sedimentology (2)

Hakuyu Okada

2001 Volume 54 Issue 54 Pages 45-48
Published: December 25, 2001
Released on J-STAGE: May 27, 2010

DOIhttps://doi.org/10.4096/jssj1995.54.45

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A method to make solid columnar samples from unconsolidated sandy sediments

Yoshihiro Kontani

2001 Volume 54 Issue 54 Pages 49-51
Published: December 25, 2001
Released on J-STAGE: May 27, 2010

DOIhttps://doi.org/10.4096/jssj1995.54.49

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Report on AGU Chapman Conference on the Formation of Sedimentary Strata in Continental Margins at Puerto Rico (June 17-19, 2001)

Yoshiki Saito

2001 Volume 54 Issue 54 Pages 61-65
Published: December 25, 2001
Released on J-STAGE: May 27, 2010

DOIhttps://doi.org/10.4096/jssj1995.54.61

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Report on 2001 Annual Meeting of the Sedimentological Society of Japan Field Trip

Toru Nishikawa

2001 Volume 54 Issue 54 Pages 67-69
Published: December 25, 2001
Released on J-STAGE: May 27, 2010

DOIhttps://doi.org/10.4096/jssj1995.54.67

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Report on the IAS 2001 21st Meeting

Akiko Omura

2001 Volume 54 Issue 54 Pages 71-78
Published: December 25, 2001
Released on J-STAGE: May 27, 2010

DOIhttps://doi.org/10.4096/jssj1995.54.71

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