## 6 Comprehensive Analysis of Hydrocarbon Source Rock Development Factors
### Hydrocarbon Source Rock Development Model  
In North Africa and the Middle East, current research on the genesis of Silurian hydrocarbon source rocks primarily revolves around two theoretical perspectives. The first viewpoint attributes the genesis to glacial valley erosion, supported by the evidence of the discontinuous planar distribution of the hydrocarbon source rocks. This discontinuity is interpreted as geological evidence of glacial activity, where glacial valleys were formed on the earth's surface due to ice erosion. The second viewpoint suggests that these hydrocarbon source rocks were formed in shallow marine shelf environments. The evidence supporting this theory lies in the variability and discontinuity of the source rock distribution, which is closely associated with changes in sedimentary facies. This interpretation emphasizes the significant role of the sedimentary environment in the formation of hydrocarbon source rocks, particularly how changes in sedimentary facies influence the distribution patterns of these rocks.  
During the Silurian period, both the Yangtze Platform in South China and North Africa and the Middle East regions were situated on the northern edge of Gondwana [81]. They shared a fundamentally similar tectonic and sedimentary background. The characteristic feature of the Silurian hydrocarbon source rocks in these regions is black graptoilitic shale. The research indicates that the Silurian hydrocarbon source rocks on the Yangtze Platform in South China have a broad distribution and are typical of shallow marine shelf deposits.  
Given their similar tectonic settings and concurrent stages of tectonic evolution, coupled with largely consistent stratigraphic and lithological traits, as well as similar paleobiological types and assemblages, it is believed that the Silurian hydrocarbon source rocks in North Africa and the Middle East follow a shallow marine shelf depositional model [33].  
The glacial valley genesis model for hydrocarbon source rocks suggests that Silurian hydrocarbon source rocks were deposited in erosion valleys formed by glacial erosion during the late Ordovician period [82]. With the warming climate of the early Silurian, widespread marine transgressions flooded these erosion valleys, leading to the deposition of dark graptoilitic thermal shales within the valleys. In contrast, the elevated regions outside these valleys lacked hydrocarbon source rock deposition. A developmental model of hydrocarbon source rocks is shown in Figure 11.  
During the late Ordovician regression, the rapid marine transgression in the Early Silurian led to the inundation of the northern shelves of the Gondwana continent, resulting in the widespread shelf sedimentation characteristic of the maximum flooding period. In this context, the paleogeomorphology of the shelf exhibited significant undulations, particularly in the low-lying areas. Due to the stagnant, low-energy hydrodynamic conditions in these deeper waters, an anoxic environment was prevalent, favoring the preservation of dead accumulations of graptoolites, chitinozoans, marine algae, and  
Figure 11: Silurian hydrocarbon source rock ice-eroded valley model in North Africa and the Middle East.  
tating the formation of high-quality hydrocarbon source rocks. The dark graptolitic shales in these regions are relatively pure in mud content, exhibiting high amplitudes in natural gamma ray log profiles. In contrast, the shallower shelf areas with stronger hydrodynamic energy had relatively poorer organic matter preservation, resulting in hydrocarbon source rocks of average quality with lower mud purity and correspondingly lower natural gamma ray readings. The thermal maturity characteristics of these rocks were less pronounced compared to those in deeper water settings. The depositional model of hydrocarbon source rocks in shallow marine shelves is illustrated in (Figure 12).