Thermal history of selected sedimentary basins in an island arc: evidence from organic matter and fluid inclusions

Abstract

The thermal history of sedimentary basins affects the genesis of hydrocarbon deposits, hence it has become of interest in recent years. Traditional geothermometers such as vitrinite reflectance (Karweil, 1956), level of organic metamorphism (Hood et al., 1975), conodont colour alteration index (Epstein et al., 1977), transformation temperatures of authigenic minerals (Aoyagi and Kazama, 1980; Daniels et al., 1990), SEM-EDX observation of associated minerals (Kwieciñska et al., 1992) and FT-IR analysis of coal (Ibarra et al., 1994) for studies of diagenesis and low-grade metamorphism are based mainly on pyrolysis experimental results or thermodynamic calculations. Therefore, they may not always be representative of actual geological systems. In most sedimentary basins, maximum temperatures and heating duration during diagenesis are considered to be below one hundred and several tens degrees Celsius and up to several millions of years respectively, therefore a practical geothermometer effective at lower temperatures is needed. The aim of this study is to clarify the increasing vitrinite reflectance value with actual temperatures under geological systems in some sedimentary basins in Japan using fluid inclusions as a quantitative geothermometer. On the basis of the results, thermal regimes in Japanese Islands are proposed.