Abstract: The Upper part of the Kongdian formation of the Paleocene-Eocene age consists mainly of fine to medium feldspathic sandstone. Samples analyzed are from depths of 1572.55 to 2298m, representing a temperature range of 60.5 to 88.5 °C. The authigenic clay minerals are composed of the following: illite-smectite mixed layer, illite, kaolinite, and chlorite (not detected in the samples). The dominant clay minerals are illite/smectite mixed layer, illite, and kaolinite respectively. The I/S mixed layer occurs as irregular flakes with short lath-like projection. The illite is also formed as irregular flakes with short lath-like projection. The authigenic kaolinite occurs as pseudohexagonal plates and pseudohexagonal-staked plates. The authigenic clays occur as pore linings and pore fillings. The major mineralogical change with depth takes place over the interval involving smectite conversion into illite or I/S mixed layer, increasing the amount of illite, and decreasing the amount of kaolinite.