## 2 Materials and Methods  
### Regional Geological Setting  
Basin A is a passive continental margin basin formed by the separation of the South American and African plates as a result of the rifting of the Gondwana continent (Figure 1); it mainly experienced two stages of evolution, the Jurassic-Cretaceous to Aptian rift and the passive marginal stage since the Albian, and developed the NW-SE Early Cretaceous high-angle tensile fractures parallel to the shelf, the stratigraphy of the basin is relatively continuous, and mud shale, deep-water turbidite sandstone, carbonate rocks, etc., are well developed (Figure 2) [30].  
The overall seismic pattern of the basin is a typical passive margin that evolves upward during the sag and thermal cooling phase from a ramp to prograding geometries. These geometries are controlled mainly by accommodation created by eustacy and extensional tectonics with strike-slip influence from the Guyana Transform (Figure 3). These geometries are mainly controlled by regulating extensional structures affected by subduction and strike-slip [31]. Based on the tectonic interpretation, three stages of tectonic development can be identified: (i) Triassic-Jurassic Rift Phase. (ii) Lower Cretaceous Strike Slip Influenced Passive Margin Phase. (iii) Upper Cretaceous-Recent Passive Margin Phase [32].  
The Triassic-Jurassic Rift Phase is characterized by the active development of half grabens and synrift terrestrial facies related to the initial stages of the extensional grains related to the proto Central Atlantic opening (Figure 3A). The second phase is related to an extended flooding of the Guyana Craton and the development of a ramp setting dominated by carbonates during the Lower Cretaceous. Synchronally, the development of a NW-SE transform controlled the subsequent opening of the proto-South Atlantic and the separation of the Deremara Rise from the Guinea Plateau. The transform activity created a series of structured inverted features until the Upper Cretaceous (Figure 3B). The third  
Figure 1: Location map of Basin A.  
stage is a typical passive margin, Africa drifted away from South America, which formed the main extensional geologic regime in the Guyana Basin and caused a general collapse of the unstable shelf edge and slope (Figure 3C). This predominantly transcurrent movement occurred mostly from the Albian to the Eocene, but is still active at present  
Figure 3: Plate tectonic evolution of Basin A (**A**) Triassic-Jurassic Rift Phase. (**B**) Lower Cretaceous Strike Slip Influenced Passive Margin Phase. (**C**) Upper Cretaceous-Recent Passive Margin Phase.  
Figure 2: Stratigraphic column of the Late Cretaceous in Basin A.  
The Late Cretaceous Maastrichtian Formation possesses good physical characteristics, abundant drilling and seismic data, and lacks fracture zones. Through the observation and statistics of the core, it is found that high-angle structural tension fractures develop, and oil and gas are shown in the fractures. Through the examination of the logging data, it is evident that the natural gamma curve displays funnel, bell, low-amplitude micromoth, and box-funnel composite shapes. The sedimentary phases progress from west to east, consisting of the shallow tableland phase, submarine fan phase, and deep-sea in-situ deposition. Within the sedimentary submarine fan phase are three subphases: the upper fan, middle fan, and lower fan subphases (Figure 4). The lithologies consist of sandstone and siltstone, including silt, sandy siltstone, sandy marl, marl, mudstone, and sandy mudstone.