## 5 Discussion
### Analysis of Paleogeomorphic Features of Basin  
During the Huoshiling Formation epoch (Figure 13a), the Changling Graben was characterized by low-amplitude, scattered troughs, with the more significant ones located along the central and eastern trough belts. The basin's prototype at this time exhibited a classic graben structure, featuring a pattern of alternating depressions and uplifts, with the Shenzijing Trough as the central subsidence point and a notably high sedimentation rate. Figure 13: Protolithic basin of the Huoshiling–Denglouku Formation in Changling Graben. Notes: (**a**) Huoshiling Formation; (**b**) Shahezi Formation; (**c**) Yingcheng Formation; (**d**) Denglouku Formation. As the Shahezi Formation period progressed (Figure 13b), the impact of tectonic uplift transformed the previously scattered small troughs into more expansive regional troughs. Notable examples include the Heidimiao Trough in the southwest, the Qianbei Trough in the center, the Shenzijing Trough, the Hashituo Trough, and the Fulongquan Trough in the southeast, effectively defining the distribution range of Troughs within the Changling Graben. The general low-lying paleotopographic areas were concentrated in the central band of the Changling Graben, indicating that the primary subsidence region during the Shahezi period was likely centered on the Qianbei-Shenzijing-Chaganhua-Hashituo axis [64]. During the Yingcheng Formation period (Figure 13c), troughs were mainly located in the Qianbei Trough and the Heidimiao-Longfengshan Trough, while the paleotopography of the Da'an Graben, Fulongquan, and Gudian Trough was relatively higher. The slope development areas for the Yingcheng Formation were identified in the southern part of the Da'an Graben, along the eastern and western flanks of the Qianbei Trough, between Chaganhua and Hashituo, in the eastern portion of the Gudian Graben, and in the southern reaches of the Heidimiao Trough. The regions experiencing rapid subsidence and significant deposition in the Changling Graben at this time were primarily concentrated in the Qianbei Trough and the Heidimiao-Longfengshan Trough. During the Denglouku Formation period (Figure 13d), troughs were primarily distributed across the Qianbei-Shenzijing northern part, Hashituo Trough, Heidimiao, and Longfengshan Trough. The area between Shenzijing-Chaganhua and Fulongquan stood as a high paleotopographic area, while other areas were characterized as slope zones. Throughout this period, the paleotopographic troughs, slopes, and uplifts in the Changling Graben developed in tandem. The structural analysis of the Changling Graben's prototypical basin (as illustrated in Figure 13) reveals a strong inheritability in the development of troughs throughout the graben phase. The Qianbei Trough, which has consistently served as a tectonic subsidence center since the Huoshiling Formation's depositional phase, stands out as the most deeply incised structural trough on an extensive scale. During the Huoshiling period, the epicenters of subsidence were located in the Shenzijing and Fulongquan areas. subsidence in the Qianbei area began to intensify from the Shahezi period, reaching its peak during the Yingcheng period, with Qianbei being the most significant and Heidimiao being the secondary center. By the Denglouku period, the Qianbei area had become a robust subsidence zone, while Heidimiao maintained a stable, albeit weaker, subsidence pattern. In the early stages of the tectonic graben, the Shenzijing area was notably active, with the Shenzijing Trough transitioning from a deep to a shallow configuration from the Huoshiling to the Denglouku period. This shift indicates a gradual decline in tectonic subsidence at the Shenzijing Trough over time. In the later stages, the Qianbei area exhibited strong activity. Stratigraphically, this is reflected in the thickness variations, with the Shenzijing area displaying thick deposits in the early stages and thinner layers in the later stages, while the Qianbei area showed the opposite pattern [33; 34].