# Geometry and Kinematics of the Central Fault Zone, Fula Sag, Central Africa Shear Zone
## 2 Geological Setting  
The basins in the CASZ, namely the Central African Rift System (CARS, Figure 1a), are Mesozoic-Cenozoic intracontinental passive rift basins [44]. They experienced three rifting cycles, driven by the expansion of the Atlantic Ocean, the northward movement of the Indian Plate, and the openness of the Red Sea. The first rifting was primarily influenced by the Atlantic opening, resulting in a right-lateral strike-slip CASZ [45; 46; 47; 48]. As the shear movement extended northeastward from the Congo Craton, the CASZ transformed from a shear stress field to an extensional stress field [21]. The second rifting was mainly influenced by the rapid opening of the Indian Ocean, causing a weakening near-NE-striking stress field in central Africa [49]. The third rifting was associated with the separation of the Red Sea, leading to an east-to-west weakening and near-NE-striking extensional stress field within the African plate [50; 51]. Furthermore, they also exhibit characteristics of a pull-apart basin, which are evident in the distribution pattern of major highs and lows, the shifting of the depocenter over time, the thermal regime of the basin, and the formation of traps [52; 53; 54]. The Fula sag, as a part of the Muglad Basin, is located in the middle portion of the CASZ, covering an area of about 5000 km\({}^{2}\). The sag as a whole has sub-N-S longitudinal spreading, while the internal structure is NW-SE trending. Based on the sag structure and fault characteristics, the Fula sag can be divided into seven sub-technic units from north to south, including the northeastern fault-array-and-ramp zone, the northern sub-sag, western steep-slope zone, the southern sub-sag, the CFZ, the eastern ramp zone, and the southwestern fault-array-and-ramp zone (Figure 1b) [55]. The Fula sag is a graben controlled by two boundary faults (1 and 2 in Figure 1b) in the east and west, but fault 1 is more active, and the western deposits are thicker, with a thickness reaching up to 11,400 m. The sag as a whole is an \"asymmetric graben\", with thicker strata in the west. The main faults of the CFZ have an overall NNW strike with a diagonal distribution, and the basement of the CFZ rises upward, separating the depocenter of Fula sag into two, namely the northern sub-sag and the southern sub-sag. There are three main faults here,  
Figure 1: (**a**) Location of study area, (**b**) division of structural units in Fula sag, and (**c**) comprehensive stratigraphic column of Fula Sag (Modified after [20, 23, 46, 55]). Noted that (**a**) The Fula sag, as a part of the Muglad Basin, tectonically situated in the middle CASZ. (**b**) The CFZ of the Fula sag have three main faults with similar NWW strike. (**b**) Since its formation in the Early Cretaceous, the Fula sag has experienced three phases of rifting cycles, each of which consists of a syn-rift as well as post-rift thermal subsidence. Tectonic units: I-VII. are the northeastern fault-array-and-ramp zone, northern sub-sag, west-arm steep-slope zone, southern sub-sag, CFZ, eastern ramp zone, and southwestern fault-array-and-ramp zone, respectively; 1 and 2 are boundary faults of the Fula sag; the CFZ faults depicted in (**b**) represent F1, F3, and F2 from south to north. CASZ = Central Africa Shear Zone. named F\({}_{1}\), F\({}_{3}\), and F\({}_{2}\), from south to north (Figure 1b). The dip of the northern two main faults is eastward, while the dip of the southern one is westward. Since its formation in the Early Cretaceous, the Fula sag has been influenced by tectonic events such as the Atlantic opening, the rapid opening of the Indian Ocean, and the opening of the Red Sea rift, forming a large number of high-angle normal faults and experiencing three phases of rifting cycles [17; 18; 19; 20]. Each rifting phase consists of a syn-rift as well as post-rift thermal subsidence (Figure 1c). The Abu Gabra Formation (referred to as the AG Formation) and the Bentiu Formation constitute the syn-rift phase and post-rift phase of the first rifting, respectively.