Abstract: Kaolinite subgroup is found in Tarim basin as kaolin and dickite pieces, both have individual feature and forming con-dition. The authigenic kaolinite occurred in Lower Jurassic, Triassic, Carboniferous sand-shale member and Kela No.2 gas struc-tural zone (Palaeogene and Lower Cretaceous), allothigenous kaolinite appeared in Lower Ordovician limestone cracks. The dickite is found in Carboniferous sandstone of Mincan No.1 Well in southern Tarim. According to mineral features of kaolinite and dick-ite, the sedimentary environments of these horizons and water media at stage of hydrocarbon accumulation are analyzed. The re-sults suggest that Lunnan Well 59 to Cao-2 Well Block in period of Late Devonian Donghetang formation was smothered bay en-vironment, Donghe-1,2 and 4 Well Blocks were inshore deposition. The dickite is transformed from kaoline crystal under the condition of structural geotherm at 500°C.

Key words: Tarim basin, clay mineral, kaolinite, dickite, origin