ISOTOPIC STUDIES OF CARBONATES FROM CIROS-1 DRILLHOLE, WESTERN McMURDO SOUND, ANTARCTICA

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概要

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• Carbonates from core samples from the CIROS-1 drillhole, western McMurdo Sound, Antarctica, were analyzed for isotopic, chemical and mineralogical compositions. Carbonates occur as both cement (Mg-calcite and aragonite) and vein filling (aragonite). Samples are generally depleted in ^<18>O to a level that is consistent with pore-water chemistry and downhole temperatures as high as 67℃. However, the samples from the upper part of the hole (<300m sub-bottom depth) contain extremely ^<18>O-depleted aragonite, suggesting precipitation from glacier- or ice-sheet-source meteoric water. Carbon isotopic rations of aragonite are enriched in ^<13>C relative to the neighboring Mg-calcite. Low δ^<13>C values of Mg-calcite may be ascribed to precipitation under the sulfate reduction layer where ^<13>C-depleted carbon dioxide might be released. It is plausible, however, that the high δ^<13>C values of aragonite are due to precipitation under the methane fermentation layer or CO_2 reduction layer, which underlay the sulfate reduction layer and produced ^<13>C-enriched carbon dioxide. Semi-micro scale isotopic analyses along two transects of aragonite veins revealed that δ^<13>C values vary from 3 to 5‰ within a vien. Near the bottom of the drillhole, δ^<18>O values in pore water remained constant during the aragonite precipitation. At shallow depths about 260m below the sea floor, δ^<18>O values in pore water were variable, probably owing to the different contribution of glacier or ice-melt water during the precipitation.

• 国立極地研究所の論文

著者

• Wada Hideki

  Institute of Geosciences, Shizuoka University

• Wada Hideki

  Institute Of Geosciences Faculty Of Science Shizuoka University

• OKADA Hakuyu

  Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University

• Okada Hakuyu

  Department Of Earth And Planetary Sciences Faculty Of Science Kyushu University

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