定量化された新しい有機熟成指標

stTAI

抄録

The brightness, or gray level, under transmitted-light microscope was measured on numbers of pollen grains of Pinus, Podocarpus, Abies, Picea and Tsuga from Neogene sediments in Northern Japan by means of computer-aided digital image processor. The mode value of the brightness distribution was assigned as a brightness indicator for each pollen grain. The mean value of all the modes for the complete array of these pollen types which are interpreted as indigenous in each rock sample was labeled as “statistical Thermal Alteration Index” (stTAI) for the sample. The present investigation identified an inverse relationship between stTAI and vitrinite reflectance (Ro). The application of stTAI to samples from the MITI Yuri-oki-chubu borehole revealed a decreasing trend with depth, and the threshold of intense oil generation was identified at about 2, 000m. This is in harmony with the interpretation based on the trend of Ro, especially in sediments shallower than 1, 600m. The Ro trend in deeper sediments is disturbed probably by a lithological effect. Therefore, stTAI is a potentially useful parameter for determining organic maturity and identifying the threshold of intense oil generation.