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Objective Yuncheng Salt Lake, located within the core area of the Fenwei Graben System in the south-central part of the North China Craton, is the earliest known salt lake in China and worldwide. The formation and evolution of the Yuncheng Salt Lake are closely related to the Cenozoic tectonic domains of the coastal Pacific in eastern China and the Qinghai-Tibet Plateau in western China. However, there are many debates regarding the spatiotemporal processes and key timing associated with these two domains in the Yuncheng Salt Lake. Additionally, the salt lake is rich in sodium, magnesium, chloride, and sulfate ions; however the sources of these saline ions remain unclear. Methods This study investigated the major changes in the Cenozoic tectonic geomorphology of the Yuncheng Basin and its surrounding areas, focusing on the evolution of the Cenozoic river-lake system to establish the formation and evolution stages of the Yuncheng Salt Lake. This study combined the tectonic background and geochemical element analysis of typical strata in the adjacent Zhongtiao Mountains to identify the main sources of saline ions in the Yuncheng Salt Lake. Results At the boundary between the Paleogene and Neogene, there was a widespread angular unconformity across the central and eastern parts of the North China Craton. This unconformity affected the Weihe Basin in the Fenwei Graben System to the west, and not the northeastern edge of the Qinghai-Tibet Plateau, which connects to the western North China Craton. This indicates that the tectonic forces during this period originated mainly from the coastal Pacific tectonic domain of the eastern North China Craton. In the mid-Miocene, a widespread unconformity along the northeastern edge of the Qinghai-Tibet Plateau connect to the western North China Craton. The northeastward uplift and expansion of the Qinghai-Tibet Plateau affected caused the Ordos Basin to rotate counterclockwise, initiating the formation of the Shanxi Graben System within the Fenwei Graben System. The Cenozoic evolution of the Yuncheng Salt Lake is the result of the interaction between the two major tectonic domains of eastern and western China. Before the mid-Miocene, the coastal Pacific tectonic domain predominantly controlled the region. Subsequently, the long-distance effects of northeastward uplift and expansion of the Qinghai-Tibet Plateau began to influence the Yuncheng Salt Lake. The Jixian System Longjiayuan Formation in the Zhongtiao Mountain area is composed of marine carbonate deposits that is the primary source of magnesium ions for the salt lake, with an average magnesium oxide content of 20.92%. The Paleogene Pinglu Group, an arid lake basin deposit rich in gypsum layers, provids sodium, chloride, and sulfate ions to the salt lake, with an average sodium oxide content of up to 2.6%. Conclusion This study suggested that approximatedly 700000 years ago, during the transition between the early and middle Pleistocene, the Yellow River flowed eastward into the sea through the Sanmenxia Gorge, leading to the disappearance of the Sanmen paleolake and the initial formation of the Yuncheng Salt Lake. Approximately 70000 years ago, during the mid-late Pleistocene, the Fen River changed its course and left the Yuncheng Basin, transforming the salt lake from an open to a closed system, ultimately forming the Yuncheng Salt Lake. Subsequently, under the continuous influence of the fault at the northern edge of the Zhongtiao Mountains, a large sedimentary depression formed, accumulating a large amount of saline minerals. Natural salt lake is formed over long periods of precipitation and evaporation. Currently, the saline ions of the Yuncheng Salt Lake mainly originate from adjacent sedimentary strata in the Zhongtiao Mountains and deep mineralization layers. The major fault controlling the salt lake provides the upward migration and injection of saline substances from deep mineralization layers into the salt lake. The marine high-magnesium dolomite of the Longjiayuan Formation of the Mesoproterozoic Jixian System in the Zhongtiao Mountains is a major source of magnesium ions for the salt lake. Significance The research findings provide fundamental geological evidence for the implementation of an ecological protection strategy to restore the lake by reducing salt levels in Yuncheng Salt Lake.

Desertification and drought in inland Asia are closely related to human habitation and social sustainability in western China. The climate in western China has experienced multiple shifts in temperature and aridity since the Late Pleistocene. Investigating this region's Late Pleistocene paleoclimatic changes contributes to predicting future climate trends. This study analyzes the pollen records from the Qingshuihe Basin in southern Ningxia during the middle to late Late Pleistocene, revealing four distinct pollen assemblage zones from bottom to top. These zones reflect paleovegetation and paleoclimate changes during the middle to late Late Pleistocene. The results indicate that during the middle Late Pleistocene (75-50 ka B.P.), the region featured a predominantly Artemisia-dominated steppe landscape with a cool and relatively dry climate. In the late Late Pleistocene (25-15 ka B.P.), the area experienced alternations between desert-steppe or steppe and forest-steppe, transitioning gradually to desert-steppe. During this period, the winter monsoon strengthened, leading to progressively cooler and drier conditions, with the climate shifting from cool and slightly moist to cold and arid. The further study of the palynological records during the middle and late Late Pleistocene in the Qingshuihe Basin of southern Ningxia holds significant implications for a proper understanding of the natural environmental history of the Loess Plateau and informs decision-making for its management.

The Cenozoic tectonic deformation and sedimentary processes in the arcuate tectonic belt along the northeastern margin of the Tibetan Plateau have been influenced by the remote effect of the subduction of the Pacific Plate as well as controlled by the northeastward extension of the Tibetan Plateau. Determining the sedimentary age of the Cenozoic strata is an essential prerequisite for understanding these tectonic deformation and sedimentary processes. However, the sequence and depositional age of the Cenozoic strata in the arcuate tectonic belt is still controversial. This paper systematically studied the Paleoproterozoic to Neoproterozoic sedimentary sequences and stratigraphic ages in the arcuate tectonic belt. The results show that the sedimentary ages of the Sikouzi Formation, the Qingshuiying Formation, the Zhang'enbao Formation, and the Ganhegou Formation in the arcuate tectonic belt are the Middle to Late Oligocene, the Late Oligocene–Early Miocene, the Middle Miocene–Late Miocene, and the Late Miocene-Pliocene, respectively. We systematically analyzed the two unconformities of the Paleocene to Neoproterozoic and refined their formation age as well as geotectonic significance. The first unconformity developed between the Qingshuiying Formation and the Zhang'enbao Formation in the Early-Middle Miocene, which indicates the appearance of the remote effect caused by the northeastward extrusion of the Tibet Plateau at about Early Miocene. The second unconformity developed between the Zhang'enbao Formation and the Ganhegou Formation, which implies the summit of tectonic activities caused by the northeastward extrusion of the Tibet Plateau at about the Late Miocene. It is concluded that the Cenozoic basins have evolved through three stages based on the coupling relationship between the sedimentary process and the tectonic evolution. From the Middle Oligocene to the Early Miocene, the tectonic stress field of the arcuate tectonic belt was controlled by extension under the remote effect of the rollback of the subducted Pacific Plate. The tectonic stress field changed into compression under the effect of the northeastward extrusion of the Tibet Plateau from the Middle to Late Miocene; Significant and sustainable tectonic uplift developed in the arcuate tectonic belt from the Late Miocene to Pliocene, and the Cenozoic basins were divided by the strike-slip fault systems.

The ancient Fen River diversion was a crucial earth's surface transformation in the Yuncheng Basin during the Cenozoic. The time frame for the diversion of the ancient Fen River is still characterized by two views: the middle Pleistocene and the late Pleistocene, which has yet to be finalized. This study investigated the late Pleistocene sedimentary sequence of the Kaolao Tableland in the Yuncheng Basin, and the critical time frame of the sedimentary sequence transition was determined based on optically stimulated luminescence (OSL) dating results. The causes of the late Pleistocene sedimentary sequence of the Kaolao Tableland and the geological factors that controlled the sequence were analyzed using detrital zircon U–Pb isotope dating. It is concluded that the late Pleistocene sedimentary sequence of the Kaolao Tableland in the Yuncheng Basin is characterized by a two-layer structure, with fluvial sands in the lower part and eolian loess in the upper part. Based on the OSL dating results, the formation time of the boundary between these two parts is between ~76–63 ka B.P. Comparative analysis of detrital zircon age sequences indicates that the early Pleistocene fluvial sands in the Kaolao Tableland and sediments in the ancient Fen River have similar age sequence characteristics. Therefore, it can be deduced that the regional tectonic uplift of the northeastern Emei Terrace in the middle of the late Pleistocene resulted in the diversion and exit of the ancient Fen River from the Yuncheng Basin and the sedimentary facies began to change from fluvial to eolian. The tectonic uplift in the middle of the late Pleistocene extensively developed around the Ordos Basin, and that indicates a significant tectonic uplift of the Tibet Plateau during this time, whose remote effect might be the major cause for the exit of the ancient Fen River from the Yuncheng Basin. This research provides new sedimentary evidence for the time frame of the ancient Fen River diversion in the Yuncheng Basin.

The Fen–Wei graben system is an essential Cenozoic extensional fault–depression belt in the central part of the North China craton. Previous research achievements mainly focused on its formation process and dynamic mechanism, but the initial time has been unresolved due to the lack of quantitative dating objects. This paper first reports the granite porphyry dikes in the andesite of the Majiahe formation in the Xionger group of the Zhongtiaoshan orogenic belt adjacent to the Fen–Wei graben system. The dating results of the granite porphyry dikes indicate that the age sequence concentrates mainly in two stages, 1769.8 ± 8.7 Ma and 69.14 ± 0.85 Ma. The former is consistent with the primary age of the volcanic rocks of the Xionger group, representing the characteristics of inherited zircons, and the latter represents the formation age of the granite porphyry dikes. The Ga/Al value ratios of granite porphyry dikes of the Qifeng samples are all greater than 2.6, characterized by enriched silicon, alkali, potassium, depleted calcium, and high magnesium. The rare earth elements are enriched in light and depleted in heavy rare earth elements. The Qifeng granite porphyrite dikes are I-type granites, indicating that the tectonic setting is extensional. The research provides new evidence for the initial time of the southern part of Fenwei graben in the Cenozoic.

The precise age of the strata at the northeastern margin of the Tibetan Plateau in the Paleogene-Neogene, and the initial time when the uplift of the Plateau affected its northeastern margin, have always been two main bone contentions among geologists. The Guanyindian section at the northeastern margin of the Tibetan Plateau is our research subject. We gain new insights to the two mentioned issues by using detrital zircon U-Pb dating in combination with the previous results concerning regional paleontological fossil identification and paleomagnetic dating. The dating results show, among the samples from the upper Paleogene Qingshuiying formation at the northeastern margin of the Tibetan Plateau, the youngest peak is 17.8 Ma. Two conclusions are drawn from the research results. Firstly, the deposition age of the Qingshui formation is from the late Oligecene to early Miocene, showing the characteristic of diachronism. Secondly, the northeastward extension and pushing of the uplift of the Tibetan Plateau has begun affecting the west of the Haiyuan-Liupanshan fault zone since the early Miocene with a coupling relationship among tectonics, sedimentation and climate in the area. The research findings provide a new time scale for determining the initial time when the northeastward pushing of the Tibetan Plateau began to affect its northeastern margin.