Diagenetic Illite K-Ar Age Analysis and Its Significance

The timing of hydrocarbon generation is of particular concern in resource exploration. When were the solid organic matters heated to form oil and gas? Because illite forms in rocks in response to heating in the same temperature range as oil formation, its K Ar age is an important parameter. Illite in reservoir sedimentary rocks is a mixture of detrital and diagenetic components. Defining reliable diagenetic ages of illitization in sedimentary rocks still remains a formidable challenge because separation of the diagenetic component is impossible, even if it is carried out down to the grain size as small as 0.02μm. Illite age analysis (IAA, Pevear, 1992) provides a methodology for estimating the diagenetic ages of illite. This paper describes this method and its application in interpreting the K Ar age of illite for a sample from the depth of 2772 m in the Talimu basin. The diagenetic age of illite was determined at 408 Ma. It demonstrates that the maximum geothermal regime was reached in the early Silurian epoch.