Abstract Sodium-bicarbonate HCO3–Na (sodic) groundwaters exist throughout southeastern West Siberia at approximate depths from 50–300 m to 1.0–2.3 km in Mesozoic-Cenozoic sediments. They belong to five main types of fresh (I), brackish (II), high-pH low-saline (III), coal-related saline (IV), and carbonated (V) waters that differ in composition, as well as in depth and lateral extent. Waters of types I and II are of regional extent and common chemistry, while those of three other types have specific compositions and are restricted to local areas. Isotope data (δ18O, δD, δ13C) indicate that waters of all five types originated by the infiltration mechanism; type IV water has an enriched oxygen isotope composition; all water types except V have biogenic carbon sources. As shown by thermodynamic calculations, all HCO3–Na waters are nonequilibrium with many primary aluminosilicate minerals bur are equilibrated with carbonates and clay minerals. The number of minerals equilibrated with these waters increases progressively from type I to IV with salinity and pH. The obtained data allow reconstructing the formation of sodic waters of different types in the context of the evolution in the system ‘water – rock – gas – organic matter’. The formation scenario is the same for all types of water: dissolution of sedimentary aluminosilicate minerals which are not in equilibrium with the waters and concurrent precipitation of carbonates. Waters in the zone of slow water exchange at depths from 100 to 300 m acquire the HCO3–Na compositions, with TDS >0.7–0.8 g/L and рH >7.6. The diversity of the waters results from difference in their residence time, even during the formation of HCO3–Na chemistry (types I and II), and from environment effects: presence of inorganic CO2 (V) and organic carbon (IV) sources or their absence (III).

中文翻译：

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俄罗斯西西伯利亚东南部的碳酸氢钠地下水：成分、类型和形成条件

摘要 碳酸氢钠 HCO3-Na（钠）地下水存在于整个西西伯利亚东南部的中、新生代沉积物中，深度约为 50-300 m 至 1.0-2.3 km。它们属于五种主要类型的淡水 (I)、微咸水 (II)、高 pH 低盐水 (III)、与煤有关的盐水 (IV) 和碳酸 (V) 水，它们的成分不同，并且深度和横向范围。I类和II类水具有区域范围和共同化学成分，而其他三种类型的水具有特定的成分并仅限于局部区域。同位素数据（δ18O、δD、δ13C）表明五种类型的水都是由渗透机制产生的；IV 型水具有富氧同位素组成；除 V 外的所有水类型都具有生物碳源。如热力学计算所示，所有 HCO3-Na 水都与许多原生铝硅酸盐矿物不平衡，但与碳酸盐和粘土矿物平衡。与这些水平衡的矿物质数量随着盐度和 pH 值从 I 型到 IV 型逐渐增加。获得的数据允许在“水-岩石-气-有机质”系统演化的背景下重建不同类型钠水的形成。所有类型的水的形成情况都是一样的：与水不平衡的沉积铝硅酸盐矿物的溶解和碳酸盐的同时沉淀。在 100 至 300 m 深度的缓慢水交换区的水域获得 HCO3–Na 成分，TDS > 0.7–0.8 g/L 和 рH >7.6。水域的多样性源于它们停留时间的不同，