More than 70 fault depressions of various scales occur in the Songliao Basin and they have significantly different levels of development and hydrocarbon enrichment.Study of the characteristics of the fault depression and the associated volcanics shows that the subduction of the Pacific plate to the Northeast-Asia plate in different directions and speeds during the Late Jurassic and Early Cretaceous resulted in the development of fault depressions of various scales in different stages.In the Late Jurassic

the positive subduction of the Pacific plate to the Northeast-Asia plate caused the rising of the upper Mantle and the thinning of the earth crust

and resulted in the characteristics of fault depression distribution similar to "triple junction".Influenced by the hysteretic effect of tectonic stress transmission

fault depressions near the triple junction are characterized by early development

strong extension

large scale and thick deposits.In contrast

fault depressions far from the triple junction are characterized by late development

weak extension

small scale and thin deposits.In the Early Cretaceous

the regional tectonic stress field converted from extension to transtension

with its influences limited to the eastern fault depression and the fault depressions on both sides of the central uplift.The continuous development of the fault depression in this region and the stagnant of the development of fault depressions in other regions further enhanced the unbalance of development of fault depressions.The continuously developed fault depressions are characterized by large scale

thick fault depression sequences

multiple sets of source rocks

high level of hydrocarbon enrichment

and large potential of exploration.The fault depressions developed in late stage have relatively smaller exploration potential.The fault depressions developed in early stage are characterized by small scale

thin sequence and the least exploration potential.