Brightness of pollen as an indicator of thermal alteration by means of a computer-driven image processor: statistical thermal alteration index (stTAI)

The brightness, or gray level, of pollen of Pinus, Podocarpus, Abies, Picea and Tsuga from the Neogene sediments in northern Japan was measured using a transmitted-light microscope with a computer-driven digital image processor. The mean value of the modes for the complete array of the indigenous pollen in a rock sample was called here “the statistical thermal alteration index” (stTAI). In the present investigation an inverse relationship between stTAI and vitrinite reflectance (RO) in sediments was found. The application of stTAI to samples from three boreholes indicated a decreasing trend with depth. By using this trend, threshold values of intense oil generation can be evaluated (145–110). Therefore, stTAI can be a useful parameter for determining organic maturation and for identifying the threshold zone of intense oil generation.