Abstract:

 Hailar Basin is a MesoCenozoic basin which superimposed on the Paleozoic collision orogenic belt of Inner MongoliaGreater Hinggan Mountain. The basin, trending northeast, consists of five firstorder structural units (three depressions and two uplifts), they are, from west to east, the Zhalenuoer Depression, Cuogang Uplift, Beier Lake Depression, Bayanshan Uplift and Huhe Lake Depression, respectively. Wuerxun  and Beier Sags are two secondorder structural units in the south of Beier Lake Depression. The research indicates that in the Early Cretaceous, WuerxunBeier Sag underwent two longterm compressions: NWSE trending during Damoguaihe Period to early Yimin Period, and near EW trending during late Yimin Period, respectively. The compressions led to the inversion of some depressioncontrolled normal faults in the extensional faulted depression, and formed new faultpropagation fold, faultband fold, imbricate structure, duplex structure, popup structure, triangular zone etc. Because of the differences in geometric and kinematic features and the variance in the ratio of the uplift rate of compressional structures to the deposition rate of isostructurally growing strata in space, the syncollision strata sequences show different sedimentary features in different structural positions. These structural features are very similar to those of orogenic belt. The discovery of two phases of compressional structure in WuerxunBeier Sag proved that the crust of Northeast China was not always in the state of extension and thinning in the Early Cretaceous, but showed the features of superimposition and thickening during the two compression periods, and thus formed structural framework of alternative distribution of compressiondepression basins and intracontinental (intraplate) orogenic belt in space.

Key words:

Key words: compressional structure; structural feature; faultrelated fold; growing strata; Early Cretaceous; geological significance; WuerxunBeier Sag; Hailar Basin