## 3 Databases and Methods
### Restoration Method of Formation Denudation
These unconformities, characterized by truncation and onlap contact relationships on seismic profiles, indicate that the strata underwent tectonic deformation prior to denudation. The study area exhibits two distinct types of denudation (Figure 7), with the strata beneath the unconformities displaying clear truncation features. Figure 6: Schematic diagram of denudation recovery using the acoustic wave time difference method. Notes: (**a**) acoustic wave time difference curve of well Changshen 39; (**b**) basic principle of the acoustic wave time difference method. By carefully analyzing the orientation of the residual strata and the convergence patterns at internal layer interfaces, we can identify areas that have remained unaffected by denudation. By measuring the degree of thinning over equivalent horizontal distances, we can extend our findings to eroded zones, reconstructing the eroded thickness by adhering to the principle of a uniform rate of thinning. This method allows us to estimate the extent of denudation in the affected areas, as illustrated in Figure 8.  
The specific process for denudation restoration calculations is as follows:  
Step One: Precisely locate two denudation reference points, A and A\({}^{\prime}\), within the sedimentary layers. Given the constraints of seismic profile lengths, the exact denudation points may not always be identifiable. Consequently, the reference points selected are generally the apparent denudation points A\({}^{\prime}\) and A, which are positioned closest to the basin's center on the profile [62]. Figure 8: Schematic diagram of the principle of calculating denudation thickness using the stratigraphic trend extrapolation method. Figure 7: Denudation types of Changling Graben. (**a**) Fold denudation type; (**b**) marginal uplift denudation type. H represents the residual stratigraphic thickness, and h\({}^{\prime}\) represents the denudation thickness. Step Two: Compute the thinning rate \(K\). This is achieved by identifying a strata segment (BA\({}^{\prime}\)) that exhibits a relatively stable thickness change towards the basin from the apparent denudation reference point A\({}^{\prime}\). Designate the distance between BA\({}^{\prime}\) as \(L\) and the apparent thickness of the strata segment at points A\({}^{\prime}\) and B as \(H^{\prime}\) and \(H\), respectively. With these values, the thinning rate \(K\) can be derived using Equation (1). \[K=(H-H^{\prime})/L\times 100\%. \tag{1}\]  
Step Three: ascertain the pristine thickness of the strata, denoted as \(H_{\rm i}\). Commencing from the apparent denudation reference point A\({}^{\prime}\), delineate the calculation points C\({}_{1}\), C\({}_{2}\), C\({}_{3}\),..., C\({}_{n}\) across the eroded region and ascertain the respective distances from these points to point B, labeled as \(L_{1}\), \(L_{2}\), \(L_{3}\),..., \(L_{n}\). By applying Equation (2), one can deduce the original thickness of the strata at each designated point. \[H_{\rm i}=H-K\times L_{\rm i}. \tag{2}\]  
In this context, i equals 1, 2, 3,...,\(n\). Step Four: Calculate the denudation thickness, \(H_{\rm b}\). By subtracting the remaining strata thickness (\(h_{\rm i}\)) from the original strata thickness (\(H_{\rm i}\)) at each point, the denudation thickness (\(H_{\rm b}\)) at each point can be determined. Formula (3) is as follows:  
\[H_{\rm b}=H_{\rm i}-h_{\rm i}. \tag{3}\]  
Step Five: Determine the actual thickness of the eroded strata.