Charging time of mantle CO

2

in sedimentary basins is a basis for studying interaction of CO

2

-sandstone and CO

2

-crude oil.Generally

eruption age of volcanic rocks near CO

2

reservoirs is supposed to be the charging time of mantle CO

2

but this approach is obviously not suitable to hydrocarbon basins with multi-stage volcanic eruption.Two hydrocarbon charging phases and one CO

2

charging phase have been identified in the dawsonite-bearing sandstone by the systematic observation and determination of diagenetic sequence and fluid inclusions in Southern Songliao Basin.The first and second hydrocarbon charging were recorded by the liquid hydrocarbon inclusion and gas-liquid hydrocarbon inclusion within fractures of authigenic minerals and detrital minerals

while the mantle CO

2

charging by the dawsonite and CO

2

-bearing inclusion within fractures of detrital minerals.The charging time of mantle CO

2

is slightly latter than or approximately the same as the second phase of hydrocarbon charging.According to the analysis of diagenetic sequence and liquid inclusions in dawsonite-bearing sandstone

and in combination with the timing of hydrocarbon accumulation and structural fractures development

the charging time of mantle CO

2

leading to dawsonite formation in Songliao Basin might be from the end of Cretaceous (the end of Mingshui period) to Paleogene.