## 3 Materials and Methods
### Combination Styles  
Individual sand bodies interact and combine to form composite sand bodies. In the study area, the combination styles of single sand bodies include lateral amalgamation and vertical stacking [33]. 1. Lateral Amalgamation During delta sedimentation, multiple subaqueous distributary channels transport sediment to the basin in different locations within the same period. These distributary channels advance, forming widespread sheet sands. As a result, multiple underwater distributary channel sand bodies or sheet sand bodies laterally amalgamate within the same single layer [41; 42; 43; 44; 45]. Based on the architectural analysis results, four types of lateral amalgamation patterns for single sand bodies were identified in the study area (Table 1). 2. Underwater Distributary Channel-Underwater Distributary Channel Lateral Amalgamation: In the shallow-water delta front, limited accommodation space causes adjacent distributary channels to laterally migrate and amalgamate, forming contiguous sand bodies. This pattern is characterized by contact along channel edges, where channel boundaries intersect. Channel elevations are generally consistent, and erosion is minimal. 3. Underwater Distributary Channel-Sheet Sand Lateral Amalgamation: Sand material transported and modified by lake waves and distributary channels forms sheet sands on the channel flanks or in front of the channels. These sheet sands amalgamate with distributary channels to form continuous sand bodies. The boundaries between the two are often difficult to distinguish. 4. Underwater Distributary Channel-Underwater Distributary Channel Lateral Cutting and Overlapping: During lateral migration, one channel erodes and cuts into an adjacent channel, or a later-stage channel incises into a previously deposited channel. This results in a lateral contiguous but vertically overlapping pattern. 5. Underwater Distributary Channel Separated by Mudstone: When sediment supply is insufficient, underwater distributary channel sand bodies are laterally separated by mudstone, resulting in non-connected sand bodies. 6. Vertical Stacking [PERSON] et al. [33] analyzed the vertical stacking patterns of sand bodies within a short-term cyclic sedimentary period and concluded that the stacking patterns are primarily composite and isolated. Within the same sand group or layer, vertical stacking styles of subaqueous distributary channel and sheet sands are influenced by channel incision and lake-level fluctuations. In the study area, three main vertical stacking styles were identified (Table 1). 1. Underwater Distributary Channel-Underwater Distributary Channel Stacking: In environments with sufficient sediment supply and strong hydrodynamic forces, the incision of subaqueous distributary channels is significant. Later-stage channelscut into previously deposited channel sediments, forming vertically thick stacked sand bodies. * Underwater Distributary Channel-Sheet Sand Stacking: Similar to the channel-channel stacking type, later-stage channels stack on top of previously deposited sheet sands. As sediment transport advances downstream along the sediment source direction, hydrodynamic energy decreases, reducing the channel incision capability. This prevents complete erosion of the sheet sands, resulting in a combination that forms thick sand bodies. * Underwater Distributary Channel-Underwater Distributary Channel Vertical Separation: In the shallow-water delta front, channel sand bodies are separated vertically by thick lacustrine mudstones or thin mudstone interlayers within distributary channel accretion bodies. These separations cause flow barriers within the same sand body, leading to disconnected upper and lower sand bodies. As subaqueous distributary channels develop downstream, the types, sizes, and stacking patterns of channel sand bodies exhibit certain correlations.