## 5 Interpretation
This lateral mineral distribution changes reflect an increasing degree of evaporation, creating a sedimentary environment dominated by sand and salt deposits. Core analysis reveals a rise in chloride concentration with shallower burial depths [39], indicating a vertical increase in evaporation intensity in the area. Monsoon winds from the northeast during the dry season and from the southwest during the rainy season govern dune orientation in the region, which typically trends northwest-southeast. In the brackish lakes (Figure 9(a)) located in the flooded interdunal corridors near Lake Chad, water is semi-restricted with higher salinity than the freshwater of Lake Chad. Figure 9: Image of Lake Chad **(a)**, Bristol Dry Lake **(b)**, and Abu Dhabi sabkha **(c)** to show eolian, fluvial-lacustrine, and marine dominated sabkha, respectively. [PERSON], 2016 [17]; [PERSON], 2020 [37]; [PERSON], 1997 [36]. Within the saline lakes, halite and sylvite may precipitate, forming small (tens of meters in diameter) polygonal structures in the southwestern parts of the lake (Figure 11). In the central areas, larger polygons (up to 100 m in diameter) are observed, likely caused by sand bridges or evaporite buildups. As evaporation intensifies, a saline lake eventually transforms into a dry saline pan when all brine water evaporates completely (Figure 12). Despite some vegetation planted near a village in the central region, the landscape is almost entirely covered with silt or mixed with evaporite deposits. Figure 11: Image of a saline lake in interdunal corridors northeastern Lake Chad. Figure 10: Image of brackish lake (**a**), saline lake (**b**), and dry saline pan (**c**) in interdunal corridors northeastern Lake Chad. Based on the sedimentary environment variations observed in Lake Chad and its northeastern area, we interpret the evaporite facies in Taidong area using the saline pan evolution model proposed by [PERSON] and [PERSON] and [PERSON] (2019) (Figure 13a). This model describes the development of saline pans through three key stages: freshwater flooding in a brackish lake, evaporative concentration in a saline lake, and desiccation in a dry saline pan where surface crusts break into sub-circular polygons. In an eolian-dominated setting (e.g., in Lake Chad, Figure 13b), silt can cover these polygons, further influencing the morphology of the sedimentary environment. Sedimentary process varies in the three stages. During stage 1, the water level is high, and older saline crusts are dissolved by the influx of fresh water. This leads to the deposition of mud and/or eolian silt in the brackish lake. During stage 2, as evaporation intensifies, the water level descents, coincided with saline concentration increases. In the saline lake, subaqueous crystallization occurs, leading to the formation of salt crystals, including syntaxial saline overgrowths and nucleated rafts and hoppers at the water surface. During stage 3, with the completion of the lake water evaporation, a dry saline pan forms. Diogenetic salt growth within the pan and beneath the crust leads to the formation of pressure polygons, exhibiting sub-circular geometries. In an eolian-dominated sabkha (desert lake), the process continues with ongoing salt growth, fissuring, and dissolution. Eolian silt infiltrates cracks, deforming the crust surface into knobs and ridges. Clays beneath the crust may also be pushed upward through the fractures ([PERSON], 2019). Given the generally drying and cooling environmental conditions in the Sanhu area over the past 1.51 million years, an eolian-dominated lacustrine sabkha serves as the geological background for the sedimentary facies observed in the three RGB-fused stratal slices from K2, K1, and K0 in the Taidong area (Figure 13c). Figure 12: Image of a dry saline pan in interdunal corridors northeastern Lake Chad. Slice 1 (Figure 13c left): the western part (I) is interpreted as a freshwater lake, while the eastern part (II) is a brackish lake, with embryonic sub-circular geometries in kilometer scale.