## 4 Results  
### Petrography of Mixed Siliciclastic-Carbonate Rock  
#### 4.1.1 Classification of MSR  
The classification scheme for MSR follows a three-endmember classification combined with the tertiary nomenclature of sedimentary rocks [31]. Six lithofacies of MSRs were identified: dolostone-bearing sand, sandy dolostone, sandstone-bearing dolomite, dolomitic sandstone, sandy limestone, and argillaceous dolomite-bearing sand. The siliciclastic components are predominantly quartz, with minor feldspar. The first four are the main types of MSRs in the Member B of the Asmari Formation. In this study, the classification of MSRs is based on the mineral composition identified by X-ray diffraction data. Dolostone-bearing sand contains approximately 10-25% sand. The sand is fine-grained, sub-angular to sub-rounded, with low sphericity and a long ellipsoidal shape. Dolomite content is about 75-90%, predominantly microcrystalline (accounting for 80% of all samples) with fine crystals (accounting for 10% of all samples) that are subhedral to euhedral (Figure 3a). Sandy dolostone contains on average approximately 30% sand. The sand is medium- to fine-grained, sub-rounded to rounded, with high sphericity and a long ellipsoidal shape. Dolomite content is about 70%, predominantly fine-crystalline (Figure 3f). Sandstone-bearing dolomite contains on average approximately 85% sand. The sand is fine-grained, with traces of medium-grained sand, sub-rounded to rounded, with high sphericity and a spherical shape. Dolomite content is about 15%, predominantly microcrystalline (Figure 3d). Dolomitic sandstone contains on average approximately 65% sand. The sand is medium-grained, with traces of coarse-grained sand, sub-rounded, with low sphericity and an ellipsoidal shape. Dolomite content is about 10%, mainly fine-crystalline. In some cases, gypsum cements account for approximately 10-25% in these sandstones (Figure 3e,g). Sandy limestone contains approximately 15% sand. The sand grains are coarse, angular to sub-angular, and the calcite content is approximately 80% (Figure 3c,h). Figure 3: Thin section images of the lithofacies of MSRs. (**a**) Well BF, 3152.8 m, fine-crystalline dolostone-bearing sand. (**b**) Well BF, 3110.4 m, granular dolostone-bearing sand with some bioclastic debris. (**c**) Well BF, 3202.5 m, dolomitic sandstone. (**d**) Well BF, 3170.5 m, dolomitic sandstone with some gypsum cement. (**e**) Well BF, 3135.7 m, very fine-crystalline dolostone-bearing sand. (**f**) Well BF, 3138.4 m, sandy dolostone. (**g**) Well BF, 3151 m, sandy limestone. Note that calcite is stained red by alizarin red; (**h**) Well BF, 3154.95 m, dolomitic sandstone. Argillaceous dolomite-bearing sand contains on average approximately 12% sand. The sand is fine-grained, sub-angular to sub-rounded, with high sphericity and a long ellipsoidal shape. Dolomite content is about 60%, predominantly microcrystalline, with an argillaceous content of 25-50% (Figure 3b). The different mixing of carbonate and siliciclastic materials was deposited in different sedimentary environments. Based on thin section observations, in the vertical section, the MSRs lithofacies sequence is sandstone-bearing dolomite, dolomitic sandstone, and dolostone-bearing sand, from bottom to top. This sequence indicates a transformation from sedimentary environments dominated by sandstone to those dominated by carbonate rocks. Element indices were used to explain the differences in sedimentary environments. Al and Rb are mainly derived from terrigenous clasts and can indicate provenance effects. Vi/(V+Ni) is widely used to infer redox conditions, while Mn/Fe can be used to indicate ancient water depth [31]. As shown in Figure 4a,b, as the terrigenous element content (Al and Rb) decreased, the Mn/Fe ratio increased [32]. Meanwhile, according to the element indicators, the MSRs were deposited in transitional sedimentary environments. As shown in Figure 4a, the depositional environments of sandy dolostone differs from that of other MRSs.