## 5 Discussion
### Analysis of Basin Tectonic Evolution  
(1) Basin structure and sedimentary formation filling characteristics  
Figure 11: (**a**) Sedimentary facies map of the Shahezi Formation in Changling Graben; (**b**) interpretive seismic sedimentary facies profile of the Shahezi Formation in Changling Graben (see Figure 1 for profile location). Initial Stage of Graben--Huoshiling Formation Deposition: The remaining strata of the Huoshiling Formation reveal that the Changling Graben is composed of multiple independent residual depression groups, with individual grabens being relatively small in scale. During this period, the Shenzijing and Fulongquan areas exhibit the maximum depositional thickness and rate, with intense deposition concentrated in the central region, gradually decreasing towards the north and south. Intense Stage of Graben--Shahezi-Yingcheng Formation Deposition: During the Shahezi Formation depositional period, compared to the Huoshiling Formation, the scale of the Qianbei Trough expanded. In the Yingcheng Formation period, faults and strata acted simultaneously to promote the further development and strengthening of each subordinate graben, with significant tectonic subsidence in the Heidimiao area during this period. The depositional thickness and rate at this time show a pattern of weaker in the south and stronger in the north, indicating a northward shift in the depositional center compared to the Huoshiling period. Transition from Fault Depression to Uplift--Denglouku Formation Deposition: During this period, the strata underwent non-uniform subsidence, and by the end of this period, some grabens experienced tectonic inversion, leading to denudation on the eastern and western sides. The basin began to subside, and the depositional range started to expand, gradually evolving into a unified large depression lake basin, marking the initial stage of the Songliao Basin's subsidence. At this time, the Qianbei area exhibited strong deposition, while the Heidimiao area experienced relatively strong deposition. In contrast, the depositional thickness and rate in the Shenzijing area during the Denglouku period were notably weak. This reflects the controlling influence of the structural deformation differences in the Changling Graben on the thickness and rate of depositional strata. (2) Basin tectonic evolution  
Based on the geological background of the Changling Graben area, the characteristics of basin sedimentation and filling, and the patterns of geological structures, combined with the research findings of previous studies, the tectonic evolution of the Changling Graben is divided into three stages(Figure 12): the graben stage, the sag stage, and the inversion stage. This study adheres to the principle of cutting through the main tectonic units with key profiles, dividing them into five representative horizontal and three vertical structural framework profiles. Through the analysis of the basin's structural framework, it is determined that the Changling Graben has a characteristic structure of being divided into eastern and western zones and northern and southern sections. This study selects the profile passing through the Shenzijing, Hashituo, and Fulongquan areas as a typical profile. By integrating regional geological background analysis, seismic profile structural interpretation, regional unconformities, and the restoration of denudation volumes, the tectonic evolution process of the Changling Graben is analyzed. The Huoshiling-Yingcheng Formation period (145 Ma-124 Ma) represents the graben stage. During the depositional period of the Huoshiling Formation, following the formation of the basin's base, the basin experienced NNW-directed compression from the Izanagi Plate to the east, accompanied by large-scale volcanic activity. This led to the formation of several NNE- and NNW-oriented major faults within the basin.