Grain fabric of Bouma A and B divisions deposited from surge-like turbidity currents: an example from the Plio-Pleistocene Kakegawa Group, Japan

島根大学地球資源環境学研究報告 Volume 22 Page 173-178 published_at 2003-12-27
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Title
Grain fabric of Bouma A and B divisions deposited from surge-like turbidity currents: an example from the Plio-Pleistocene Kakegawa Group, Japan
Creator
Source Title
島根大学地球資源環境学研究報告
Volume 22
Start Page 173
End Page 178
Journal Identifire
ISSN 13439774
Descriptions
The grain fabric of the massive Bouma A division of a turbidite bed from the Plio-Pleistocene Kakegawa Group,Shizuoka,Japan is analyzed in detail.The bed is interpreted as having been deposited on the levee of a small submarine channel,and consists of a T_<a-d> Bouma Sequence thinning in the down-current direction in a ~15 m-wide outcrop.This feature indicates that the flow waned rapidly away from the channel.
The grain fabric of the A and B divisions analyzed in horizontal intervals of 0.4 mm and 0.2 mm,respectively,can be characterized as follows:(1)The lower part of the A division is dominated by down-current imbricated intervals,and the
corresponding rose diagrams have large circular variance.(2)The upper part of the A division is characterized by both down−current and up−current imbricated intervals,although the latter is dominant,and highly inclined grains tend to be less common.(3)The B division is represented only by up-current imbricated intervals.These results are similar to those derived from fabric analysis of experimental gravity flow deposits,except for the dominance of down-currrent imbricated intervals in the lower part of division A.The down-current imbricated intervals are interpreted as having being formed by shear oscillation in the basal high-density flow layer(i.e.,a quick bed),as observed in flume experiments.The prominence of the down-current imbricated intervals in the natural turbidite beds compared to those seen in experiments is probably due to the larger flow scale.These results also suggest that paleoflow analysis based on the grain fabric of division A may give incorrect flow directions in some turbidites.For improved reliability of paleoflow analysis,flow directions should be determined from a combination of paleoflow indicators.
Language
eng
Resource Type departmental bulletin paper
Publisher
島根大学総合理工学部地球資源環境学教室
Department of Geoscience, Interdisciplinary Faculty of Science and Engineering, Shimane University
Date of Issued 2003-12-27
Publish Type Version of Record
Access Rights open access
Relation
[NCID] AA11455176
Remark 12-14,16+ / 1993+