Abstract: In the shale of the Wufeng-Longmaxi Formation in the southeastern Sichuan Basin, there are several sets of bentonite beds, which keeps records of key information about numerous geological events. In order to clarify the characteristics of bentonite development and its significance for shale gas, core observation, thin section identification, SEM observation, whole rock X-ray diffraction have been carried out for the core of several shale gas evaluation exploration wells and typical sections in neighboring areas in southeastern Sichuan, and the following results have been obtained. 1) In the standard well of bentonite in southeastern Sichuan Province, 59 bentonite layers are identified, and were further divided into 6 sets of bentonite development segments. 2) In the process of volcanic ash deposition, the alkaline water environment chemically destroys the hard protein structure of graptolite, resulting in the phenomenon that graptolite does not develop in the surrounding rocks above and below the bentonite. 3) There are alteration phenomena in the bentonite, and the products are mostly pyrite. 4) Low-frequency and high-intensity development of bentonite often indicate high-quality shale, and high-frequency and high-intensity, highfrequency and low-intensity development of bentonite often indicate subprime-quality shale, while low frequency and low intensity development of bentonite is regarded as ordinary organic shale.

Key words: southeastern Sichuan Basin, Wufeng-Longmaxi Formation, bentonite, alteration occurs, significance for shale gas