Keywords: 
• argillaceous rock /
• organic matter /
• occurrence /
• sealing ability /
• Jiyang depression

Abstract: Occurrences of organic matter in Paleogene argillaceous rock of Jiyang depression are primarily studied by means of fluorescent microscopy. The occurrences of organic matter in Paleogene argillaceous rock are classified into three types which are named as “enrichment type、dispersion type and part-enrichment type”, respectively. “Enrichment type” means that the organic matters are distributed plentifully along bedding plane in the rock, which deposited mainly in moderate depth—deep lake facies and is rich in organic matter; “Dispersion type” means that the organic matter are scattered randomly in the rock that deposited mostly in fluvial-delta facies or shore -shallow lake facies or turbidity current deposist, which is various in abundance of organic matter; (c) “part enrichment type”is intermediate one with the property of both “ enrichment type" and “dispersion type”. Combined with part quantitative analysis data about seaing ability of argillaceous rocks, three different composition properties are concluded as follows : (1) The sealing ability of the argillaceous rock was worse when organic matters were rich and occurred with “enrichment type” in the argillaceous rock， (2) The argillaceous rock had a certain sealing ability when organic matters were rich and occurred with “dispersion type”in the argillaceous rock， (3) The sealing ability of the argillaceous rock was better when organic matters were poor and occurred with “dispersion type” in the argillaceous rock. Thus,the effect caused by occurrence of organic matter no the sealing ability of argillaceous rock should not be ignored. It can be one of the important basis for us to evaluate sealing ability of argillaceous rock over oil-gas reservoir.