Secular variation of carbon isotopic compostition of the Phanerozoic shallow marine carbonates.

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The purpose of this research is to ellucidate the secular variation of the oceanic cabon isotopic composition throughout the Phanerozoic era, based on the fact that the carbon isotopic composition of shallow marine carbonated reflect the oceanic carbon isotopes. Geologic survey and sampling were made in the first year, and isotopic analysis was made in the second year.1, Limest one from the Carboniferous Onimaru and Nagaiwa Formations of South Kitakami were measured and sampled. Visean dolomite and calcite are relatively depleted in 13-C compared with the Namurian and Westpharian carbonates, however, most of the data are plotted within the range of 2 to 5 permil.2, Travertine limestone of Shirahone Spa were analyzed to show the variatin witin inland lake. Carbon isotopic values are mostly enriched in 13-C,ranging from 0 to 6 permi.3, Cambro-Ordvician carbonates of the Chosen Group of Korea were observed to show strong negative anomaly at the Middle to Upper Cambrian strata. The Ordvician section is characterzed by lighter signatures.4, Devonian-Carboniferous sections of northeran Iran were measured and sampled. Carbon isotopic values range between 1 and 3 permil for the Devonia section, but the Visean section show a general decreasing trend as observed in Kitakami massif.