| In the present paper a study is done on the Permian gas rocks, the Shanxi Formation and Shehezi Formation, in the Ordos Basin by integrated use of the data of outcrops, cores, well logs, and seismic profile, and the following conclusion is drawn: (1). According to lithology and log response of various sedimentary facies, 3 kinds of sedimentary facies: flurial facies, delta facies and lacustrine facies, 6 kinds of subfacies: river bed, dike, flood land, delta plain, delta front and prodelta, and 15 microfacies may be recognized in the the Shanxi Formation and Shehezi Formationof of the Ordos Basin. (2) Delta deposits is the main sedimentary system in the sq8-sq9, and both river system and delta system occur together in the sq10-sq12. (3) In the Ordos Basin lacustrine transgression takes place at the sq8, and lacustrine regression starts in the sq9 and continues until the sq12. (4) ) Based on log facies analysis, the borderline between fluvial facies and delta facies and regional distribution of main sand bodies may be ascertained during sq8-sq12. (5) There are multiple-directions of material sources in the Ordos Basin. The main material source comes from the north, and there are 4-5 former material sources nearly parallel to each other in the northern part of the basin. In the southern part and eastern part of the basin secondary material sources exists and form small-scale deltas. (6) The sedimentary system in the sq8-sq12 is characterized by river and delta deposits formed under shallow water environment with strong fluvial effect and weak influence of lake, and distributary channel deposits are well-developed and widespread.
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