## 1 Introduction  
Deltas, as a crucial component of source-to-sink systems, act as key sedimentary units linking terrestrial environments with lakes or oceans. They capture and record information on the source material composition, transport processes, and environmental evolution from provenance areas. Deltaic sedimentation is governed by the combined effects of fluvial, wave, and tidal processes, with its transport and depositional evolution reflecting significant sediment-dynamic information [1; 2; 3]. Additionally, the formation processes and internal structure of deltas are influenced by multiple interacting factors including fluvial activity, paleoclimate, paleotopography, and lake-level fluctuations. The resulting deposits preserve detailed information on sediment supply, tectonic subsidence, climatic evolution, and sea/lake-level changes across geological history [4; 5; 6; 7]. Currently, delta sand bodies in several petroliferous basins (e.g., Songliao, Ordos, Junggar, and Bohai Bay Basins) are recognized as prolific hydrocarbon reservoirs, characterized by extensive distribution, large scale, and diverse types. These deposits have emerged as key targets for lithology-based hydrocarbon exploration and development [2; 8; 9; 10; 11; 12; 13; 14; 15]. Previous studies have shown that deltatic systems display distinct sand body distribution patterns across different water depth conditions [5]. As a result, researchers have categorized deltas into deep-water and shallow-water types based on sediment supply systems and basin depths [16]. Deep-water deltas, such as Gilbert-type deltas, exhibit a tripartite stratigraphic architecture consisting of topset, foreset, and bottomset beds [17; 18]. In contrast, shallow-water deltas lack a tripartite structure and typically develop in shallow epicontinental seas and large depression basins characterized by stable tectonics, low-gradient topography, and limited water depth [10; 16; 18; 19]. Several aspects of sedimentology in shallow-water deltas have been preliminarily studied, and certain achievements have been made including: (i) developmental settings and formation mechanisms [20; 21; 22; 23]; (ii) sedimentary architecture and depositional models [2; 10; 19; 24]; (iii) sand body geometry and geophysical responses [5; 25; 26]; and (iv) reservoir characteristics with their controlling factors [27; 28; 29]. The current research on shallow-water deltas primarily focuses on humid-climate settings, characterized by sustained water discharge, stable sediment supply, consistent depositional processes, and well-developed channelization. However, lacustrine basins in arid climates exhibit more restricted water distribution, pronounced lake-level fluctuations, and distributary channels extending farther basinward. Consequently, both sedimentary characteristics and depositional architectures differ markedly from those of deltas in humid climates. Currently, research on shallow-water deltas within arid lacustrine basins remains relatively scarce [26; 30; 31]. Research on their sandbody genesis, distribution patterns, and depositional models remains limited. Therefore, the sedimentary characteristics of shallow-water deltas in arid climates warrant detailed investigation. The study area was deposited in an arid, shallow-water paleoenvironment, characterized by alternating subaqueous and subaerial exposure conditions [32; 33]. Therefore, sediments in the Qigu Formation provide a rare case study for investigating how arid-hot climates influence depositional processes and internal architectures in shallow-water deltas. Several studies have investigated the seismic sedimentology and sedimentary characteristics of the Qigu Formation, interpreting the study area as dominated by braided river delta and littoral-shallow lacustrine depositional systems [34; 35]. However, detailed research on the lithofacies analysis, sedimentary microfacies distribution, evolution characteristics, and development models within the sequence stratigraphic framework remains limited.