Paleotemperature analysis in sedimentary basins is very important to petroleum exploration because generation of petroleum from kerogen is controlled mainly by temperature. Vitrinite reflectance generally is used for this analysis. A new technique of paleotemperature analysis depends on the relationship between transformation temperatures of authigenic minerals in diagenetically altered argillaceous sediments and their depth of first appearance in any specific well. Study of both the paleogeothermal gradient and porosity-depth relationships in a basin make possible predictions of hydrocarbon pools in the exploration area. For example, primary migration of oil in Neogene rocks of the Niigata basin in central Honshu, Japan, has occurred at burial depths between 2,260 and 3,950 m (7,410 and 12,960 ft). This corresponds to the analyzed paleogeothermal gradients of exploited oil and gas fields in the basin (3.0° to 4.0°C/100 m = 1.6° to 2.2°F/100 ft).