Both the Nantun Formation in the Wuerxun Sag of the Hailaer Basin and the Quantou Formation in the Gudian CO2 Gasfield in the southern Songliao Basin contain abundant dawsonitebearing sandstones. The petrologic characteristics of these sandstones including the framework clastic composition，cements and authigenic minerals and diagenetic paragenesis succession are investigated through polarizering microscope，scanning electron microscope，alizarin redstaining，Xray diffraction，electron probe and INCA energy spectrum analysis etc. The results show that these sandstones are finegrained or finetomediumgrained，poorly to moderately sorted arkoses and lithic arkoses. The dominant cements are secondary quartz overgrowths，authigenic quartz，dawsonite，ankerite and clay minerals. The amount of dawsonite is higher(up to 22％ of the total volume of the sandstones)，either as cements，filling intergrain pores as radial，bunchy，rosette，intricately trichoid，spheric and platy collectives，or as replacement of feldspar and lithic grains with bunchy and platy shapes. Dawsonite is mainly composed of elements such as Na，Al，O，and C according to electron probe and INCA energy spectrum analyses. The paragenetic sequence includes(1)clay mineral coatings;(2)secondary quartz overgrowths，authigenic quartz，authigenic kaolinite;(3)petroleum charging;(4)CO2 charging;(5)dawsonite;and (6)ankerite. The authigenic minerals formed before CO2 charging include secondary quartz overgrowths，authigenic quartz and authigenic kaolinite，while the main cements formed after CO2 charging are dawsonite and ankerite.