A practical method to evaluate maximum temperature of mudstone is examined based upon the biomarker maturation parameters. Progresses of these reactions in sedimentary rocks are closely concerned not only with paleotemperature but also with the reaction time (geologic age). However, a numerical analysis indicates that it is possible to correlate directly a biomarker maturation level to a maximum temperature with an acceptable degree of error in the restricted sedimentary basins where similar apparent heating rates of sedimentary rocks can be expected. Using following biomarker maturation parameters; hopane epimerization, sterane epimerization and sterane cracking, we can evaluate a relatively wide paleotemperature range (70 to 180°C) in the Japanese Neogene Tertiary Sedimentary Basin. An example of thermal and subsidence histories assessment based upon biomarker geothermometers in the Nishiyama and Chuo Oil Fields, Neogene Tertiary Japan is also described in this paper.

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Gas-hydrates are ice-like compounds consisting of water molecules and guest gas molecules such as methane. Gas-hydrates are formed at temperatures well above 0°C if the gas pressure is enough high to stabilize gas-hydrates. Therefore, organic-rich continental margin sediments provide favorable conditions for the formation of methane hydrate.
Authigenic carbonates formed during burial in the non-hydrated sediments off northeast Japan demonstrate V-shaped pattern in the variation of carbon and oxygen isotopic composition, whereas those in the hydrated sediments of the Blake Outer Ridge off Florida provide quite different pattern with extraordinary heavy oxygen siderites. This anomaly is likely to have been related with decomposition of methane hydrate at the depth of 500 to 600 meters.

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