本邦産玄能石とアメリカ西部Pyramid Lake産チノライト : 特に酸素・炭素安定同位体比

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Since a large euhedral ikaite crystal was discovered in sediment of the Antarctic Shelf (Suess, et al., 1982), ikaite has been considered to be the precursor mineral of calcite pseudomorphs such as gennoishi and thinolite. The δ^<13>C value of thinolite from Pyramid Lake in Nevada shows positive value +3.28‰ in contrast to the negative values (-11.9〜-10.9‰) of gennoishi from Shunkushitakara in eastern Hokkaido. The positive values of thinolite and calcite after Shiowakka ikaite are concordance with the spring water origin and the fresh water environment where the latter was formed. The light carbon isotopic compositions of calcite after modern ikaite from deep sea ikaite (-22.9〜-18.8‰) and gennoishi suggest that CO_2 derived from organic matter in sedimentary sequences. The δ^<18>O values of calcite after Shiowakka ikaite (-3.69‰) and the calcareous sinter (-2.09‰), and the high saline water chemistry of Shiowakka cold spring water suggests that the origin of cold water derived from fossil sea water, and that δ^<18>O values should be raised by the isotope exchange reaction of water and calcareous rocks at low temperatures.
北海道教育大学の論文
2004-09-30