*2.2. Stratigraphy*

Basement rocks in the Jizhong Sub-Basin are developed in the Archean, Proterozoic, Paleozoic, and Mesozoic from bottom to top (Figures 2 and 3) [19,37]. The Archean and Paleoproterozoic are composed of metamorphic rocks, while the Changcheng, Jixian, and Qingbaikou systems, which are developed in the Mesoproterozoic and Neoproterozoic, are a set of sediments made up of marine carbonate rocks. The Lower Paleozoic develops the Cambrian and Ordovician, which are typical sediments dominated by carbonate rocks of neritic platform facies. The Carboniferous and Permian in the Upper Paleozoic are clastic rocks of continental and transitional facies, where coal-bearing strata are relatively abundant. The Mesozoic is mainly Jurassic and Cretaceous, which are continental clastic rocks containing volcanic rocks. Due to the erosion and intermittent deposition caused by multistage structural uplifts, the Jizhong Sub-Basin strata are absent from the Silurian, Devonian, Early Carboniferous, and Triassic periods [29]. The Cenozoic strata consist of a set of interbedded depositions that are mainly sandstone and mudstone of lacustrine and deltaic facies [38].

The target layer in this study is the basements of carbonate rocks in the Mesoproterozoic, Neoproterozoic, and Lower Paleozoic periods. These basement rocks have undergone complex sedimentation, diagenesis, and tectonism, forming various reservoirs with proven economic hydrocarbon accumulations [39]. Source rocks are mainly dark mudstones of lacustrine facies in the Paleogene, along with coal and dark mudstones of transitional facies in the Carboniferous and Permian periods [40]. These source rocks are often adjacent to the basements, where hydrocarbons have migrated into the reservoir through faults and unconformities [34,41]. It should be noted that these coal and dark mudstones are also good regional caprocks for the carbonate basement reservoirs in this sub-basin. Additionally, many interlayers with high argillaceous content exhibit high-quality caprocks in the inner reservoirs of these basements [36,42]. As a result, combinations of source rocks, reservoirs, and caprocks have created a suitable petroleum system in the carbonate basements of the Jizhong Sub-Basin and have provided grea<sup>t</sup> potential for oil and gas exploration and development in this area [9].
