Qilian-Zoulang-Helan Region developed into a large depressed basin in Carboniferous Period.The main sedimentary facies were delta

shore and shoal sea facies.The basin underwent considerable reformation in the late stage of Carboniferous

it shrank in the end of Variscan Period

but its tectonic framework didn't change much;in Indo- Chinese Epoch

the basin was denuded seriously

Permian System was completely denuded due to strong fold

and Carboniferous System was also denuded in different degrees;in Yenshen Period

the basin began to disintegrate

but the Mesozoic distribution areas were favourable for preservation of Carboniferous System.The residual basins were deeply buried in Himalayan Period

and the Carboniferous System was piecemeal distributed in the depressed belts of orogenic zone.In eastern and southern depressions of Bayanhott Basin

the remained Carboniferous System is larger and thicker

and has more types of hydrocarbon source rocks with higher hydrocarbon generation potential

it should be taken as target area for oil exploration.