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  [in Japanese] Taphonomy of large-scale oyster shell beds : examples from the Pleistocene Shimosa Group around the Lake-Kasumigaura area, Ibaraki Prefecture, Japan  [in Japanese]

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Author(s)

    • 安藤 寿男 ANDO Hisao
    • 茨城大学理学部地球生命環境科学科 Department of Environmental Sciences, Faculty of Science, Ibaraki Univ.
    • 橋本 聡子 HASHIMOTO Satoko
    • 茨城大学理学部地球生命環境科学科:(現)埼玉県警察 Department of Environmental Sciences, Faculty of Science, Ibaraki Univ.:(Present address)Saitama Prefectural-Police

Abstract

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.

Journal

  • Fossils

    Fossils 76(0), 32-45, 2004

    Palaeontological Society of Japan

References:  52

Cited by:  1

Codes

  • NII Article ID (NAID)
    110002704322
  • NII NACSIS-CAT ID (NCID)
    AN00041606
  • Text Lang
    JPN
  • Article Type
    Journal Article
  • ISSN
    0022-9202
  • NDL Article ID
    7105762
  • NDL Source Classification
    ZR1(科学技術--生物学) // ZM41(科学技術--地球科学)
  • NDL Call No.
    Z18-838
  • Data Source
    CJP  CJPref  NDL  NII-ELS  J-STAGE 
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