## 5 Discussion
### Analysis of Basin Tectonic Evolution
These faults have distinct graben and half-graben structural forms, laying the foundation for the later development of the graben and initially forming the basic structural pattern of the graben basin. At the end of the Huoshiling depositional period, fault activity weakened, the strata were uplifted as a whole, and the shrinkage of the lake basin at the end of the deposition led to extensive denudation of the early-deposited Huoshiling Formation in the Changling Graben, resulting in an angular unconformity with the overlying strata. During the Shahezi-Yingcheng Formation depositional period, the controlling depression faults continued to be active, governing the deposition and development of the strata, which mainly developed in the sag on the downtown side of the faults. The strata were thickest at the fault roots and wedged out away from the faults. In the Shenzijing Trough, it manifests as the stage of filling and compensation. At the end of the graben period, tectonic inversion occurred; the strata were uplifted and eroded, forming an unconformity interface. During the Denglouku Formation's (124 Ma-112 Ma) depositional epoch, which signifies the shift from fault-controlled depression to sag, the basin collectively entered a phase characterized by sag subsidence. The robust tectonic inversion and crustal uplift that marked the conclusion of the Yingcheng Formation's deposition evolved into a period of relaxation and elongation. The early continued activity of the controlling depression faults led to non-uniform crustal subsidence, with the strata beneath the Denglouku Formation being notably influenced by fault control, displaying graben traits [63]. However, Denglouku's subsidence area is significantly more expansive than the underlying graben layers, also reflecting sag features. Towards the end of the Denglouku Formation's deposition, certain grabens experienced tectonic inversion, with denudation affecting the eastern and western flanks. The basin commenced sinking, its depositional range broadened, and it progressively transformed into a cohesive large depression lake basin, thereby heralding the commencement of the Songliao Basin's sag phase. The Quantou-Nenjiang Formation's depositional interval marks the sag phase, characterized by widespread blanket sedimentation that extended across the entire region, connecting various troughs and showcasing a distinct, unified stratigraphic distribution pattern. At the end of the Nenjiang Formation's deposition, compressive folding movements occurred, with the graben's controlling faults reversing and thrusting, forming low-amplitude, broad-fold structures. However, during this period, inversion structures were minimal in the Shenzijing-Hashituo areas of the Changling Graben, with only slight stractal flexures evident near the principal controlling faults, suggesting a generally subdued degree of deformation. As the deposition of the Nenjiang Formation neared its end, the basin began a gradual contraction, entering the inversion phase, which coincided with the late-stage tectonic  
Figure 12: Results of structural evolution restoration of the typical profile in Changling Graben. inversion of the Songliao Basin. During this period, the Changling Graben also experienced regional tectonic inversion. Additionally, extensional activities were present, giving rise to a modest number of normal faults that interconnected segmentally with the underlying faults. This resulted in more substantial displacements in the upper sections and comparatively minor ones in the lower sections.