地处华北北缘与中亚造山带交接部位的开鲁盆地奈曼凹陷，其九佛堂组下段的天然碱—盐岩等蒸发岩十分发育，形成了世界第二大天然碱矿床，成为东北亚地区早白垩世古气候与古环境的重要深时记录，然而天然碱的“源—汇”过程和成因尚不清楚。因此，开展了多尺度的沉积学研究，包括区域尺度盆山耦合、岩心尺度的沉积旋回以及微观薄片尺度的矿物共生组合等，分析了奈曼天然碱的物质来源、沉积相带分布、关键界面、沉积分异机制和天文旋回。研究表明，奈曼天然碱矿床类似于美国西部的绿河组碱矿，蒸发岩位于湖盆凹陷沉积中心的暗色泥岩层系内，具有陆源碎屑—碱土碳酸盐—天然碱—盐岩的“牛眼式”分带特征，沉积分异受溶解度和湖盆地貌高差的控制。奈曼天然碱矿床的形成主要涉及两个过程：首先，在气候湿润期湖盆周缘的大量中基性火山岩中淋滤出的Na⁺、Ca²⁺、Mg²⁺、HCO{}_{\mathrm{3}}^{-}和Cl^-，以稀溶液形式注入湖盆，富含Na⁺-HCO{}_{\mathrm{3}}^{-}的湖水大规模聚集，形成了碱土碳酸盐饱和的碱性咸水湖，为天然碱形成提供了物质来源；其次，湖盆在极端干旱气候条件下的高度浓缩，卤水达到天然碱—盐岩矿物的过饱和，最终在凹陷中心依次结晶析出。奈曼天然碱矿床具有泥页岩与蒸发岩互层的特征，反映了碱矿的发育具有多旋回性，湖平面存在多期波动。依据纹层尺度的蒸发岩沉积韵律和米兰科维奇旋回，推断主要的成碱期约为1.2 Ma，远小于九佛堂组下段的沉积时限（2.5 Ma）。奈曼凹陷天然碱矿床的“源—汇”沉积模式，将为类似Na-碳酸盐矿床的勘探开发提供借鉴。

The evaporites in the lower part of the Jiufotang Formation of Naiman Sag，Kailu Basin, were widely developed, forming the world’s second-largest trona deposits, which serve as important deep-time records of the Early Cretaceous palaeoclimate and palaeoenvironment in Northeast Asia. However, the genesis of the trona deposit and its source-to-sink processes are still unclear. In order to investigate the formation processes of soda ash, we carried out a multi-scaled investigation of the sedimentary route system, involving regional “basin-mountain coupling”, core-scaled sedimentary cyclothemes and thin section-scaled analysis of mineral assemblages. And the material sources, facies distribution, key interfaces and sedimentary differentiation mechanisms of the Naiman trona deposit were explored. The results show that the Naiman trona deposit is similar to the Green River Formation in the United States, and the evaporites were precipitated in the central depression where black shales were also widely developed. Evaporite facies conform approximately to a bull’s eye pattern with a zonation of terrigenous clasts, alkaline earth carbonate, surrounding a basin centre accumulation of Na-carbonate and halite, indicating that the depositional differentiation is controlled by the solubility and geomorphic elevation of the basin. The formation of Naiman trona deposits mainly involves two processes: firstly, the Na⁺-HCO{}_{\mathrm{3}}^{-} rich brine accumulated in the lake during the humid period with large amounts of Na⁺, Ca²⁺, Mg²⁺, HCO{}_{\mathrm{3}}^{-}, Cl^- leached from the intermediate-basic volcanic rocks around the periphery of the basin. Secondly, the lake basin was highly dried under extreme arid climate conditions, and the lake was saturated with trona-halite, which were precipitated sequentially in the center of the depression. The giant trona deposits are characterized by interbedded halite, trona, gypsum, and black shale, reflecting frequent fluctuations of the lake level and cyclicity of trona accumulation. The annual varves and Milankovitch cycle of evaporites in Naiman Sag indicate that the trona-accumulating period was about 1.2 Ma, much smaller than the depositional time of the lower part of the Jiufotang Formation (2.5 Ma). The source-to-sink depositional pattern of trona deposits in the Naiman Sag will provide a reference for the exploration and development of similar Na-carbonate evaporite deposits.