Abstract：[Objective] The Qaidam Basin is the largest Cenozoic continental intermountain basin in the northeastern Qinghai-Tibet Plateau. The continuous and complete lacustrine sedimentary sequence recorded in the Miocene provides a good carrier for the accurate reconstruction of the paleoenvironment and the ecological evolution process of the lake basin. The purpose of this study is to reveal the control mechanism of climate-tectonic coupling process on the evolution of lake basin ecosystem in Qaidam Basin during the Miocene, and to clarify the covariation relationship between climate change and the evolution of lake basin and basin ecological environment. [Methods] In this study, the JS-2 well in the Yiliping Sag of the Qaidam Basin was taken as the research object. By comprehensively applying technical methods including elemental logging, rock pyrolysis, and saturated hydrocarbon chromatography analysis, the evolutionary characteristics of the lacustrine basin ecological environment during the Miocene sedimentary period were systematically analyzed from the perspectives of organic matter types, paleoclimate, and sedimentary environment. [Results] The research results indicate that during the sedimentary period from the lower segment of the Lower Youshashan Formation to the Upper Youshashan Formation, the climate of the basin exhibited obvious alternations between arid and humid conditions. Meanwhile, the lacustrine sedimentary environment gradually became hypoxic, with multiple synchronous fluctuations occurring in salinity and water depth, and the organic matter was dominated by aquatic plants and terrestrial higher plants. In contrast, during the sedimentary period of the Shizigou Formation, the basin climate was persistently arid, the lacustrine basin shrank significantly, and the lake water column developed salinity stratification. The sedimentary environment was characterized by a strong reducing state, the input of terrestrial organic matter increased remarkably, and herbaceous plants further became the dominant vegetation type. [Conclusion] During the Miocene, tectonic evolution and climatic fluctuations were the key drivers of changes in the lacustrine environment and vegetation communities in the Qaidam Basin. The aridity during the deposition of the lower Xiayoushashan Formation resulted from the initial uplift of the East Kunlun Mountains, which blocked moisture transport into the basin. During the deposition of the upper member of the Xiayoushashan Formation, global warming and the periodic melting of ice sheets enhanced moisture transport by monsoons into the basin, resulting in a warm and humid climate during this period. From the deposition of the Shangyoushashan Formation to the Shizigou Formation, the climate shifted to cold and dry, with pronounced aridification across the basin. This was primarily driven by global cooling—marked by the establishment of a permanent Antarctic ice sheet—coupled with the accelerated uplift of the Tibetan Plateau and its surrounding ranges, which effectively obstructed moisture transport into the Qaidam Basin. Based on geological fundamentals, climate fluctuations drive the transformation of the lake aquatic environment, regulate the basin's productivity and ecological space, and ultimately control the succession of vegetation communities.
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