The nature of shell beds in the inner-shelf deposits. A case study of the upper Miocene to lower Pliocene Horokaoshirarika Formation in central Hokkaido.
Bibliographic Information
- Other Title
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- 内側陸棚相の貝化石層の解析 北海道沼田町に分布する上部中新統～下部鮮新統幌加尾白利加層の例
- ウチガワ リクダナソウ ノ カイ カセキソウ ノ カイセキ ホッカイドウ ヌマタマチ ニ ブンプ スル ジョウブ チュウ シントウ カブ センシントウ ホロカオシラリカソウ ノ レイ
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Abstract
Fossil shell beds of the shelf can be used as the good tools in the analysis of paleoenvironments because they include many features clearly associated with sedimentary processes. Thier usefulness, however, has not been evaluated adequately. The upper Miocene to lower Pliocene Horokaoshirarika Formation is distributed in central Hokkaido. The upper part of the Horokaoshirarika Formation is composed mainly of sandy and fossiliferous deposits and is interpreted to be deposited in the inner-shelf. Analysis of the sedimentary facies suggests it as a successive upward-shallowing sequence. Based on the shell arrangement in the deposits, the shell beds of the upper part of the formation can be divided into two types. Type 1 shows regularly arranged shells which are stacked, imbricated, and arranged parallel to the bedding plane and is formed by physical reworking. Type 2 represents randomly arranged shells and is formed by bioturbation. We subdivide the upper part of the formation into even stratigraphic unit I to IV. Number of both types increases gradually from I to III, but abruptly decreases from III to IV. The ratio between Types 1 and 2 does not change from I to IV. The increase of the type 1 from I to III reflects the increase frequency of storm reworking in ascending order, and its abrupt decrease from III to IV reflects severe amalgamation of the shell beds. The constant ratio of Types 1 and 2 indicates the constant extent of bioturbation in each unit. Thus, in the inner-shelf deposits of the Horokaoshirarika Formation, the physical reworking increases upward with shallowing, while extent of biological reworking is almost the same throughout the successtion.
Journal
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- The Journal of the Geological Society of Japan
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The Journal of the Geological Society of Japan 106 (2), 136-150, 2000
The Geological Society of Japan
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Details 詳細情報について
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- CRID
- 1390282681210651648
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- NII Article ID
- 110003013099
- 10004494553
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- NII Book ID
- AN00141768
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- ISSN
- 13499963
- 00167630
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- NDL BIB ID
- 5298102
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- Text Lang
- ja
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- Data Source
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- JaLC
- NDL
- Crossref
- CiNii Articles
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- Abstract License Flag
- Disallowed