Abstract: Rectorite, a clay mineral, was discovered in Silurian sandstone strata in Tarim basin by means of XRD, SEM, DTA, etc. Because the rectorite is not composed of 1:1 alternate arrangement of illite-montmorillonite layers, it could be named "pararectorite". The study indicates that the pararetorite belongs to K-rectorite transformed by Ca-rectorite, and sedimentation-diagenesis origin in weak acidic aqueous media with pH value ranging from 4 to 5 and under 120℃ or more. The results from the pararectorite research will be of great significance to the stratigraphic classification or comparison, the reservoir rock feature and the formation of the hydrocarbon reservoirs in Tarim basin.

Key words: Tarim basin, rectorite, clay mineral, stratigraphic comparison, oil-gas reservoir