An east-west structural belt which extends from Ertuok Bannerin the northto Dinbian Jingbian in the south developed in middle Shaan-Gan-Ning Basin.It was a shallow platform depressionin early middle stage of Early Paleo zoic

a karst depression during the formation stage of Ordovician top weathered crust

a sea land transitional zone in mid late stage of Late Paleozoic

a lake landtransitional zone in the Mesozoic

and the boundary line between north and south Shaan-Gan-Ning in the Cenozoic.The typical characteristics of the belt is lower amplitude

that is

the lithofacies and strata thickness of the belt are similar to the adjoining area

the difference of strata thickness is only several hun dred merters.This property made it difficult to find the belt.Along this belt

two centers of source rocks and multi deltaic sedimentary systems of Upper and Lower Paleozoic widely developed and connected there.The sand bodies that stacked are good reservoir rocks.Five gas fields (gas accumulation zone)

i.e.

Hengshanpu

Changqing

Tianchi

Zhenchuanpu have been discoveried.