# Lithium Concentrations in Saline Brines of the Shu-Sarysu Depression
## 2 Geological Characteristics of the Study Area  
The research area (Figure 1) encompasses over 1500 square kilometers and is situated within the administrative boundaries of Kazakhstan's Turkistan and Kyzylorda regions. Geomorphologically, the study zone is characterized by a relatively undulating topography, featuring a combination of low gentle hills and extensive flat lowlands. These lowlands are dominated by vast takyrs and salt flats, some of which extend over a distance of 30 to 40 km. The territory of the Shu-Sarysu Depression, due to the low annual precipitation and high aridity of the climate, belongs to the semi-desert and desert regions with a very poorly developed hydrographic network, featuring two relatively large rivers, the Shu and the Sarysu. The number of sunny days per year in the region exceeds 3000 h and the amount of precipitation is less than 100 mm per year [10; 11]. The Shu and Sarysu valley comprises a gently undulating plain, spanning up to 40 km in width. Across its surface, there are isolated areas of aeolian sands, numerous salt flats, lakes, and dry beds of seasonal watercourses. During periods of water flooding, the river's water exhibits a slightly increased salinity relative to fresh water, while in the summer, as it lingers in the reaches, its total dissolved solids (TDSs) exceed 10 g/L. The alluvial plain consists of mixed-grained sands with gravel and pebbles, sandy loans, and, in the downstream, Ioams, fine-grained sands, clays, and lacustrine sediments, often covered with salt deposits. The thickness of these deposits ranges from a few meters to over 40 m. The watered portion extends between 2 and 15 m in depth. The water table fluctuates between 1 and 5-9 m, with an amplitude of 0.6-1 m. Flow rates at water points vary from 2 to 86 m\({}^{3}\)/day, occasionally reaching 172 m\({}^{3}\)/day (2 L/s). Within the river's floodplain region, the waters tend to be predominantly salty, with only slight brackishness in some areas. On terraces and near the river's mouth, TDS can reach 10-50 g/L or even higher [10]. The chemical composition of groundwater is predominated by sodium sulfates and chlorides. Groundwater is replenished by filtration of the Shu and Sarysu river waters and atmospheric precipitation. Water is lost through transpiration by vegetation and evaporation, which is many times greater than the annual amount of precipitation. In the study area, the following formations are identified: (1) Middle Quaternary sediments are present on the valley sides, comprising fine-grained sands with interlayers of Ioams, measuring 0.7-0.9 m in thickness. The total sediment thickness amounts to 8.0 m. (2) Middle-Upper Quaternary formations occupy the channels of temporary streams and the broad valleys of the ancient hydrographic network. These formations consist of poluvial Ioams, sandy Ioams, and sands, with a total deposit thickness of 5.5 m. (3) Upper Quaternary sediments constitute the takyr terrace of the Syrdarya River, overlaying the eroded surface of the Upper Cretaceous and Paleocene. These sediments are  
Figure 1: Salt flats investigated in the Shu–Sarysu Depression (Base map from Google Earth). composed of sandy loans, loans, and fine-grained sands, with a thickness ranging from 3.8 to 7.0 m. (4) Present-day Quaternary sediments are extensively distributed and predominantly consist of takyrs and salt flats, ranging in size from several hundred meters to several kilometers. Proluvial takyrs consist of loans and clays, occupying depressional landforms. Within the depressions between the hills, which are composed of reddish Upper Cretaceous sediments, loam and clay are prevalent. The lower strata of the takyrs consist of clays, with the upper part containing a mixture of sandy material.