## 1 Introduction  
Biogenic gas, characterized by its high methane content, represents a more environmentally friendly energy source compared to oil, coal, and other fossil fuels. It has been discovered in several basins worldwide, including the Cook Inlet Basin in Alaska [1], the West Siberian Basin in Russia [2], the Central Pannonian Basin in Hungary [3], and the North Papua Basin in Indonesia [4]. Over 20% of global gas reserves are of biogenic origin [5], with several giant biogenic gas fields, such as Agostino-Porto Garibaldi in Italy [3.5 trillion cubic feet (Tcf) original gas in place], Sebei-1 in the Sanhu Depression (China, 95 Tcf), and Urengoy in Russia (220 Tcf) [3]. Due to its \"green energy\" attributes, widespread distribution, and shallow burial depth, biogenic gas is becoming an increasingly important resource. In the Sanhu Depression, Qaidam Basin, NW China, biogenic gas has been produced continuously for 13 years, with an annual output of 0.18 Tcf [6]. The primary moderate-buried (1000-1500 m) gas-bearing zones in the Sanhu Depression are sealed by mudrock rather than hydrostatic pressure [5,7]. However, compared to mudrock and hydrostatic pressure, halite possesses superior sealing capacity. In the Sanhu Depression, where loose sediments are prevalent, the presence of an effective sealing cap rock is a key factor controlling biogenic gas accumulation. Evidence from outcrops and groundwater tests reveals the presence of evaporite lithologies, such as halite and anhydrite, in shallow layers (less than 800 m) in the region. The global decline in temperature and precipitation since the Late Quaternary aligns with the evaporite environment observed in the Qaidam Basin [8,9]. Numerous wells have confirmed the presence of biogenic gas in shallow layers, ranging from tens to several hundred meters in depth, likely sealed by evaporites. The distribution of evaporites, particularly halite and anhydrite, has become a critical issue for biogenic gas exploration and development as well as for evaporites mining in the Sanhu Depression. However, due to the influence of gas chimney or gas cloud, traditional P-wave seismic data cannot be used to set up stratal framework, let alone to predict lithology distribution. Halite may precipitate in restricted areas such as marine basins, inland seas, nonmarine brine lakes, and salt pans [10,11]. Salt pans have been investigated primarily through outcrops, satellite images, and modern sediment studies [12,13]. Seismic and well data are proved to be effective to quantitatively investigate evaporite sequence [14]. However, few studies have utilized S-wave 3D seismic data [15], which has superior vertical resolution than P-wave data in shallow layers to investigate evaporite facies (i.e., distribution of evaporite environment and evaporite lithologies) because of the lacking of S-wave data. Taidong area is located in the northwest of Sanhu Depression, and is covered by a newly acquired S-wave 3D seismic data. Considering the superior vertical resolution of S-wave seismic data and the decent lateral resolution of stratal slices (e.g., a meandering channel is tens of meters deep that is beyond of seismic vertical resolution; but several kilometers long that can be interpreted easily on slices), this paper applies seismic sedimentology to the S-wave 3D seismic data, revealing unique sub-circular features on RGB-fused slices generated from the Quaternary strata in the Taidong area, west of the Sebei-1 gas field, for the first time. Considering the geological context and modern analogs, these features are interpreted as saline pans [16], formed in continental lacustrine and eolian interdunal playa environments [17]. The morphological and structural features observed in the geophysical (seismic) data, combined with geochemical evidence (salinity data), confirm the existence and evolution of salt pans in the area.