Abstract
Trace amounts of Cd, Ni and Cu in Permian, Carboniferous and Silurian limestone samples from South Kitakami Terrane were determined by flame atomic absorption spectrophotometry combined with the ammonium pyrrolidinedithiocarbamate (APDC) -4-methyl-2-pentanone solvent extraction system. The geometric means of Cd contents of these limestone samples from Kusayamizawa (n = 9, Silurian), Onimaru (n = 5, Early Carboniferous), Roukando Cave (n = 5, Carboniferous), Nagaiwa Mine (n = 12, Early Permian) and Iwaizaki Coast (n = 12, Middle Permian) were 0.04, 0.31, 0.78, 0.32 and 0.43 ppm, respectively. The Cd contents of Permian and Carboniferous limestones tend to be relatively higher than those of the other geological ages (i.e., before Devonian and after Triassic). Most of the Cd in Permian and Carboniferous limestone samples can be dissolved with 1 mol dm-3 acetic acid, suggesting that a large portion of Cd2+ is incorporated from marine waters into calcite by replacing Ca2+ during the formation and deposition of precursory carbonate minerals of the limestones. The high Cd contents of Permian and Carboniferous limestones are independent of sedimentary environments in the ocean, such as distance from continents, which controls the amounts of land originated detrital materials. This fact implies that the concentration of Cd was high in worldwide throughout the ocean during Parmian and Carboniferous periods.
