It is of great significance to clarify the formation mechanism of carbonate cementation and its influence on reservoir physical properties. By means of petrology and geochemistry

the occurrence characteristics and formation mechanism of carbonate cements in Cegai slope of Junggar Basin are analyzed. The results show that the distribution range of

δ

13

C

PDB

val

ue is -29.6 ‰~6.7 ‰

that of

δ

18

O

PDB

value is -12.5 ‰~19.2 ‰

and it has a large span. All those indicate the material source of carbonate cementation and the complexity of water-rock interaction.

δ

13

C

PDB

value has a positive offset with the typical marine or lacustrine phase of carbonate

while

δ

18

O

PDB

value has the negative offset. The positive offset of

δ

13

C

PDB

value is mainly affected by the carbon isotope fractionation of mixed hydrothermal fluid and the dissolution of a small amount of sedimentary carbonate. The negative deviation of

δ

18

O

PDB

value may be caused by the mixing of various fluids—such as precipitation and deep hydrothermal—and the rise of diagenetic temperature. The material source of carbonate cements in Che-Guai slope is related to the CO

2

produced by the decarboxylation of organic acids

compaction and drainage of clay minerals

the dissolution of feldspar debris and the release of a large amount of plasma like Ca

2+

Fe

3+

and Mg

2+

by conversion among clay minerals. Under the microscope

it is found that the carbonate cements are metasomatic to detrital particles and accompanied by asphaltene appearance

and appear in the form of crystal powder to macrocrystalline grain among the closely arranged clastic particles

as a product of late diagenetic stage

which destroy the physical properties of reservoirs.