## 1 Introduction  
China's oil and gas exploration is increasingly shifting from conventional to unconventional resources, with a primary focus on tight sandstone reservoirs, leading to substantial achievements [1]. The Jurassic Shaximiao Formation in the Sichuan Basin is of particular interest, as over 80% of the basin's reserves are located in tight sandstone formations [2]. The Shaximiao Formation in the Shunan region of the Sichuan Basin reaches a significant thickness of up to 1500 m [2]. However, this region has historically received limited attention in exploration efforts, leaving substantial gaps in our understanding of its geological characteristics [3]. Therefore, in-depth studies of sandbody genetic types influenced by the depositional environment, sediment supply, and hydrodynamic conditions, are critical for predicting reservoir quality in tight sandstone formations [4; 5]. As an important component of sedimentary rocks, sandstone has always been a core topic in sedimentology research, focusing on its depositional processes, structural characteristics, and sedimentary environments. [PERSON] and [PERSON] proposed the \"Turbidite Facies Model\", which systematically describes the depositional characteristics of sandy turbidites and divides them into several facies zones, including coarse-grained sandstone facies, parallel-laminated sandstone facies, ripple cross-laminated sandstone facies, and mudstone facies [6; 7]. In subsequent research, [PERSON] further explored the depositional dynamics of sandstone, particularly the mechanisms of sediment gravity flows and their impact on sandstone structures [8]. [PERSON] proposed a classification of sediment gravity flows and revealed the intrinsic relationships between grain size distribution, bedding structures, and depositional environments in sandstone. In recent years, [PERSON] et al. introduced the concept of \"Hybrid Depositional Systems\", emphasizing the influence of interactions between turbidity currents and bottom currents on sandstone deposition [9; 10]. This research provides new perspectives for understanding sandstone distribution patterns in complex depositional environments. Through detailed analysis of Cenozoic basins in the Mediterranean region, [PERSON] revealed the dynamic relationship between sandstone deposition and tectonic activity [11]. These research findings provide significant guidance for the study of marine and continental sandstone deposition. Sand bodies have diverse genetic types and are primarily controlled by factors such as the sedimentary environment, sediment supply, hydrodynamic conditions, and tectonic activities [12; 13; 14; 15]. Based on differences among sedimentary environments and hydrodynamic mechanisms, the genetic types of sand bodies can be classified into the following categories: (1) Fluvial Sand Bodies: Fluvial sand bodies are mainly formed by river transport and deposition, commonly found in alluvial plains and river valleys. Bedding structures are dominated by cross-bedding and parallel bedding [16]. (2) Deltaic Sand Bodies: Deltaic sand bodies form in the interaction zone between rivers and oceans or lakes. Bedding structures are primarily characterized by cross-bedding [17]. (3) Coastal Sand Bodies: Coastal sand bodies are mainly developed in coastal zones, including beaches, barrier islands, and tidal flats. Bedding structures are dominated by low-angle cross-bedding [18]. (4) Turbidite Sand Bodies: Turbidite sand bodies are primarily formed by sediment gravity flows (e.g., turbidity currents) in deep-sea or deep-lake environments, exhibiting typical Bouma sequences. Bedding structures include graded bedding, parallel bedding, and ripple cross-bedding [6; 19; 20]. (5) Lacustrine Sand Bodies: Lacustrine sand bodies form in lake environments, including littoral, shallow-lake, and deep-lake subfacies. Ripple marks and cross-bedding are characterized by littoral sand bodies, while deep-lake sand bodies may include turbidites and slump deposits [21].