In conformity with their features

overthrust belts in northwest China can be divided into two basic types such as Karamay decollement-thrust type and Kuqa piedmont decollement-fold type.As for their origin

the former is a nappe structure formed mainly by gravity sliding

its root is a normal fault or a fault trough composed of high dip thrusts

the main body is relatively simple and the forefront is imbricated;the later is formed maily by lateral compression

the root of it is commonly not clear and usually occurs as a com-pressed belt

the main body is a complicated fold belt resulted from slide andoverthrust and is characterised by wide variation in formation thickness anddecollement.Due to the different iae of the above mentioned overthrust belts

a properpetroleum trap can only exist in a specialized belt.These overthrust belts thuscan be divided into ten kinds.It is considered that the overthrust belts have resulted in a new

special kind of source rock-reservoir-cap assemblage.Because of overthrusting

the pe-troleum exploration of Karamay oilfield in recent years has yielded gratifyingachievements.Besides

a large amount of petroleum will be exploited in someother thrust belts.