Abstract: Field geological investigation, petrology and geochemistry study showed that three oil shale groups in Kazuo basin were developed in Member 1,2,3 of the Jiufotang Formation of Lower Cretaceous, the third oil shale group located in 3rd member have the greatest industrial significance. Oil shale always has the accompanying relationship with overlying sedimentary tuff or other tuffaceous strata.The oil shale(ore) of this area have four types, including mudstone, calcareous mudstone containing silty band, marlite and shale, and the former two are main types. The recoverable oil shale composed of 50% low-grade, 42% middle-grade and 8% highgrade oil shale. All of them are high-ash oil shale. Based on this, the authors discussed that the organic matter type of oil shale is humic-sapropel, and originated from the lower plants. The type of oil shale (ore) which formed in shallow-semi-deep lake environment is calcareous mudstone, and that in deep lake is mudstone. Mother rock types of provenance controlled the characteristics of chemical composition and types of ash component of oil shale. The volcanic eruption of the catastrophic event terminated the mineralization of the oil shale.

Key words: Kazuo basin, Jiufotang Formation, oil shale, ore-controlling condition, sedimentary environment, volcanic event