大規模カキ化石密集層のタフォノミー : 茨城県霞ヶ浦周辺の第四系更新統下総層群を例に

• 横山 芳春

  早稲田大学大学院理工学研究科

• 安藤 寿男

  茨城大学理学部地球生命環境科学科

• 橋本 聡子

  茨城大学理学部地球生命環境科学科:(現)埼玉県警察

書誌事項

タイトル別名

• Taphonomy of large-scale oyster shell beds : examples from the Pleistocene Shimosa Group around the Lake-Kasumigaura area, Ibaraki Prefecture, Japan
• ダイキボ カキ カセキ ミッシュウソウ ノ タフォノミー イバラキケン カスミガウラ シュウヘン ノ ダイ4ケイ コウシントウ シモウサソウグン オ レイ ニ

抄録

Large oyster shell beds are contained in incised-valley fill deposits of the Cycle 1 of the Miwa Formation, Shimosa Group, Lake Kasumigaura area, Ibaraki Prefecture . This paper describes taphonomic processes of large oyster shell beds well exposed in three localities . Six shell bed types can be recognized on the basis of their lithology, sedimentary facies, mode of fossil occurrence and associated fossils : 1) autochthonous aggregated, 2) autochthonous scattered, 3) parautochthonous aggregated, 4) cross-bedded aggregated, 5) crossbedded scattered and 6) shell-fragment aggregated types. The large oyster shell bed higher than 5 m and wider than 30 m at east Hama (Loc. 1) is characterized by type 1 with two layers of type 3 five to 20 cm thick that seem to have formed by sudden storm events. The second shell bed at west Hama (Loc. 2) shows two mounds 3 m high and or wider than 7-10 m composed of type 1 and covered by massive muddy sediments. This means that the oyster banks were buried under estuary mud. The last example at Sakihama (Loc.3) is the largest oyster shell bed in this area with height of 5m and width of 70m. It can be divided into three unit bounded by two erosional surfaces. The unit I is composed mainly of type 1 representing in situ oyster reefs, and subordinately of 3 formed by reworking through tidal current. The unit II composed of types 4 and 5 forms a shallow channelfilled structure that seems to have been formed as a tidal channel. The overlying unit III above a flat erosional surface mostly consists of type 6. Reworked oyster shell fragments might have concentrated intermittently and condensed through muddy sediment bypassing within tidal flat to embayment.

収録刊行物

• 化石

  化石 76 (0), 32-45, 2004

  日本古生物学会

キーワード

• Oyster
• Shell bed
• Taphonomy
• Bivalvia
• Pleistocene
• Shimosa Group

詳細情報

• CRID: 1390001204435216000
• NII論文ID: 110002704322
• NII書誌ID: AN00041606
• DOI: 10.14825/kaseki.76.0_32
• ISSN: 24242632
• ISSN: 00229202
• NDL書誌ID: 7105762
• Web Site: https://ndlsearch.ndl.go.jp/books/R000000004-I7105762
• 本文言語コード: ja
• データソース種別:
  • JaLC
  • NDL
  • CiNii Articles
  • KAKEN
  • Crossref
• 抄録ライセンスフラグ: 使用不可