## 2 Geological Background  
The Changling Graben is located in the southern part of the Central Depression Zone of the Songliao Basin, extending in a northeasterly direction [29, 30, 31]. Controlled by the basement master faults formed during the Late Jurassic to Early Cretaceous period, multiple secondary grabens were formed, such as the Da'an Graben, Qibei Trough, Gudianzi Graben, Shenzijing Trough, Hashitu Trough, Chaganhua Trough, Fulongquan Trough, Heidimiao Trough, and Longfengshan Trough, etc. (Figure 1). Above the Cretaceous basement, the graben period strata mainly include the Huoshiling Formation, Shahezi Formation,Yingcheng Formation, and the Denglouku Formation during the fault subsided transition period (Figure 2). During the deposition period of the Huoshiling Formation, influenced by the rapid oblique subduction of the Izanagi Plate in a NNW direction toward the Eurasian continent, the Changling Graben was subjected to a sinistral transpressive tectonic stress field. This led to the development of a series of NNE-trending sinistral transpressive faults and relatively smaller-scale NW-trending extensional faults within the basin [32; 33]. Under the control of these faults, multiple graben and half-graben secondary depressions formed, laying the foundation for the later development of fault depressions and preliminarily establishing the basic structural framework of the fault depression basin. The overall pattern was characterized by a wider and deeper northern part and a narrower and shallower southern part. Building on the previously eroded and leveled Jurassic strata, the basin entered the fault depression stage, with strata widely distributed and relatively thick within the basin. By the end of the Huoshiling Formation deposition period, significant  
Figure 1: Location map of the Songliao Basin. Figure 2: Geological location of the Changling Graben (**a**) and the division of the secondary troughs within the Changling Graben (**b**). volcanic activity caused topographic variations, leading to localized denudation of the Huoshiling Formation and the formation of the T\({}_{4}\)2 unconformity surface [34; 35; 36]. The Shahezi Formation deposition period marked the intense fault depression stage of the basin. The activity of the fault-controlled depressions was strong, governing the sedimentation and filling of the depressions and promoting the development and expansion of secondary sags. The basin continued to extend and subside [37; 38]. By the end of the Shahezi Formation deposition period, localized areas experienced some degree of compressional inversion, resulting in the denudation of the top strata and the formation of the T\({}_{4}\)1 unconformity surface [39; 40; 41]. During the Yingcheng Formation deposition period, the basin entered the waning stage of fault depression. The sedimentary characteristics of the strata were mainly characterized by infilling and leveling, accompanied by volcanic eruptions, which caused localized structural inversion and the formation of the T\({}_{4}\) unconformity surface [42; 43]. In the deposition period of the Denglouku Formation, the fault-controlled depressions continued to be active in the early stage, with non-uniform crustal subsidence. During this stage, the scale of the faults decreased, primarily manifested as a reduction in fault displacement. This resulted in the lower Denglouku strata being significantly controlled by faults, exhibiting fault depression characteristics [44; 45; 46]. However, the subsidence range of the Denglouku Formation was notably larger than that of the lower fault depression layers, also displaying characteristics of a depression. By the end of this period, a brief tectonic inversion occurred, forming the T\({}_{3}\) unconformity surface(Figure 3). From this point onward, the Changling Graben entered the depression stage, exhibiting a typical fault depression superimposed structure in cross-section.