Origin of dolomite in lake Lop Nur and its paleoclimatic implications since 7Ma

Western China experienced progressive aridification during the Late Cenozoic, yet the development of large lakes in the Tarim Basin indicates intervals of enhanced hydrological conditions, creating an apparent paradox. Here, we analyze carbonate mineralogy and oxygen isotope compositions from the LS2 drill core in Lop Nur to constrain the origin of lacustrine dolomite and the hydrological evolution between ∼7 and 4.9 Ma. Dolomite abundance covaries with bulk carbonate δ 18 O values, with higher dolomite contents corresponding to isotopic enrichment. This relationship, together with pronounced stratigraphic variability, indicates that dolomite formed predominantly during deposition or early diagenesis under the control of lake-water chemistry, rather than through late-stage burial diagenesis. Although this pattern is consistent with evaporative concentration, the absence of a clear δ 13 C–δ 18 O correlation and the lack of quantitative constraints on detrital carbonate input introduce uncertainty in attributing evaporation as the dominant control. Our results reveal a shallow saline lake system characterized by strong hydrological fluctuations superimposed on a persistently arid background. The environmental evolution can be divided into two stages: (1) 7.0–5.7 Ma, characterized by a shallow, reducing saline lake under generally warm and arid conditions, with intermittent cooling and humid episodes; and (2) 5.7–4.9 Ma, marked by continued shallow lacustrine conditions with higher-frequency hydrological variability, showing alternations between relatively warm–dry and cool–wet conditions, superimposed on an overall arid background with intensified evaporation and increasing salinity. Comparison with regional records suggests that Late Miocene lake expansion in Central Asia does not necessarily indicate sustained humid conditions, but instead reflects complex interactions among evaporation, basin hydrology, and climate forcing.