Through the multiple discipline methods of petrology, mineralogy and geochemistry, the authors try to elucidate the forming mechanism of carbonate cements at different phases, distribution and main controlling factor as well as reservoir effects in the Triassic Yanchang Fm. sandstones, which were deposited in the lacustrine center of Ordos Basin, NW China. The tendency of mixing of organic carbon in the carbonate cements at different phases indicates that the quantity of organic carbon would gradually enhance with increasing distance from the ancient lacustrine center.oft-com:office:office" />