Environmental conditions of carbonates and chemosynthetic animal communities associated with cold seepage zones along the subduction zone in Sagami Bay, central Japan

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Other Title
  • 相模湾の沈み込み帯の冷湧水域に伴う炭酸塩類と化学合成独立栄養動物群集の環境
  • サガミワン ノ シズミコミタイ ノ レイユウ スイイキ ニ トモナウ タンサン

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Description

Methane (biogenic)-rich cold seepage zones are distributed along the N-S trend active fault off Hatsushima Island and NW-SE trend active fault along the foot of Okinoyama Bank Chain in the western and central parts of Sagami Bay, the depth ranging from about 800m to 1450m. The Philippine Sea Plate is subsiding beneath the North American Plate and lzu Peninsula along those active faults. Chemosynthetic animal communities and carbonates are widely distributed along the cold seepage zones. The δ^<13>C and δ^<18>O values of carbonates range from -27 to -38‰ vs PDB and from 3.24 to 6.42‰ vs PDB respectively. The CaCO_3 and MgCO_3 contents of carbonates range from 34 to 89% and from 13 to 16% respectively. The ^<14>C ages of two Calyptogena shells included in carbonates are 9710±100 and 37020±1060 yBP. High temperatures as much as 11.5℃ of bottom sediments about 20cm below the bottom surface were observed at the reddish brown colored bacteria mat area, whereas the temperature of bottom water is around 3℃. Temperatures of the bottom sediments about 20cm below bottom surface in Calyptogena communities are at about 2 to 3℃ higher than the temperature of bottom surface water. It is clarified that the environmental conditions of the reddish brown colored area and the area of Calyptogena communities differ in temperature, texture, pH, oxygen contents of bottom sediments, composition of carbonates and combination of chemosynthetic animals.

Journal

  • Fossils

    Fossils 60 (0), 13-22, 1996

    Palaeontological Society of Japan

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