Molluscan fossil assemblages and sedimentation of the Holocene marine clay deposits : results of Shimonada core in Iyonada Sea, Seto Inland Sea, Southwest Japan

• Yokoyama Yoshiharu

  Graduate School of Science and Technology, Waseda University

• Nanayama Futoshi

  Institute for Marine Resources and Environment, Advanced Institute Science and Technology

• Ando Hisao

  Department of Enviromental Sciences, Faculty of Science, Ibaraki University

• Otsuka Kazuhiro

  Kawasaki Geological Engineering Co., Ltd.

Bibliographic Information

Other Title

• 完新統海成粘土層中に産出する軟体動物化石群と堆積過程 : 瀬戸内海伊予灘海域, 下灘沖海上ボーリングコアの解析結果の例
• カンシントウ カイセイ ネンドソウ チュウ ニ サンシュツ スル ナンタイドウブツ カセキグン ト タイセキ カテイ セトナイカイ イヨナダ カイイキ シモナダオキ カイジョウ ボーリングコア ノ カイセキ ケッカ ノ レイ

Abstract

Holocene marine clay deposits from the Shimonada core in Iyonada Sea are examined by an integrated analysis of molluscan fossil assemblages, sand content, sedimentation rate and radiometric ages. The Shimonada core lithostratigraphically consists of five depositional units, A to E in upward sequence : A) gravel, B) massive sandy clay with rootlet and brackish molluscs, C) bioturbated sandy clay with thin very fine sand layers, containing brackish and tidal-flat molluscs, D) bioturbated clay with inner-bay stagnant-water molluscs, and E) bioturbated sandy clay with two very fine sand layers and inner-bay mud-bottom and nearshore sandy mud-bottom molluscs. Five molluscan fossil assemblages are recognized through species composition as follows : 1) brackish, 2) tidal flat, 3) inner-bay stagnant-water, 4) inner-bay mud, and 5) nearshore muddy sand assemblages. Tide-influenced salt marsh and estuary environments represented by B with assemblage 1) appeared before 12, 000-11, 000 cal. yBP. Tidal flat environment [C with 1) and 2)] was prevailing during 11, 000-10, 000 yBP. After rapid sea-level rise at about 10, 000 yBP, possibly resulting from subsidence by an event of the Shimonada-oki-minami and Shimonada-oki-kita faults, inner-bay stagnant environment [D with 3)] had appeared in the graben off Shimonada, Iyonada Sea during 10, 000-8, 000 yBP. Inner-bay muddy environment [E with 4) and 5)] have continued since the graben had filled by mud with high sedimentation rate until 8, 000 cal. yBP. While mud sedimentation rate decreased, sand content relatively increased at about 8, 000 cal. yBP, possibly reflecting muddy sediment bypassing. This seems to have resulted from tidal currents and transgression associated with the formation of Seto Inland Sea.

Journal

• Fossils

  Fossils 74 (0), 7-17, 2003

  Palaeontological Society of Japan

Keywords

• molluscan assemblage
• sedimentary process
• marine clay deposits
• Holocene
• Iyonada Sea
• Seto Inland Sea

Details

• CRID: 1390282679412571648
• NII Article ID: 110002704300
• NII Book ID: AN00041606
• DOI: 10.14825/kaseki.74.0_7
• ISSN: 24242632
• ISSN: 00229202
• NDL BIB ID: 6714597
• Web Site: https://ndlsearch.ndl.go.jp/books/R000000004-I6714597
• Text Lang: ja
• Data Source:
  • JaLC
  • NDL
  • CiNii Articles
  • KAKEN
• Abstract License Flag: Disallowed