Determining the provenance of sedimentary basin fill in the northern Qaidam Basin is a key step toward understanding the sedimentary system dynamics and mountain-building processes of the surrounding orogenic belts in Tibet. The exceptionally thick (average of 6-8 km) Cenozoic fluvio-lacustrine deposits in the northern Qaidam Basin were once thought to have been eroded from the nearby northern Qaidam Basin margin and the southern Qilian Shan and to reflect the prolonged thrust-related exhumation of these orogenic belts. However, several recent studies, based mainly on paleocurrent and detrital zircon U-Pb age data, suggested that they were derived from the distant East Kunlun Shan to the south, or the Qimen Tagh to the southwest (at least 200 and 350 km from the northern Qaidam Basin, respectively). That model assumed that the East Kunlun Shan and Qimen Tagh formed significant topographic barriers during the earliest sedimentation of Cenozoic strata (e.g., the Lulehe Formation) in the northern Qaidam Basin. Therefore, the tectonic significance of the provenance of the Lulehe Formation remains a fundamental problem in understanding the postcollisional uplift history of the northern Tibetan Plateau. To address this issue, we conducted sedimentological and paleocurrent analyses of the Lulehe Formation and detrital zircon U-Pb dating of Mesozoic strata in the northern Qaidam Basin. The results, in combination with existing paleocurrent and seismic reflection data, collectively indicate that although the source area cannot be specified by matching zircon U-Pb ages in sedimentary rocks with crystalline basement source rocks, other evidence points consistently to a unified proximal northerly source area (the northern Qaidam Basin margin and the southern Qilian Shan). Our results emphasize that noncrystalline basement rocks (e.g., Mesozoic sedimentary rocks) in fold-and-thrust belts should be taken into consideration when seeking potential source areas by correlating zircon U-Pb ages of siliciclastic detritus with related basement rocks. In addition, this study strongly supports the claim that variations in the proportions of age populations should be used with caution when determining source terrane by comparisons of age distributions.
Global cooling and/or Tibetan Plateau uplift have long been regarded as the principal drivers of late Cenozoic central Asian aridification and the resulting widespread accumulation of eolian deposits in eastern Asia. However, these two factors are unable to form large source areas of fine-grained sediments enhancing eolian deposition synchronously from northern Tibet to North Pacific. Here we provide magnetostratigraphic and detrital apatite fission-track evidence for a major sediment recycling event in northern Tibet at ∼8 Ma, coeval with a sudden increase in eolian deposition, which we ascribe to syntectonic erosion of uplifted friable fluvio-lacustrine sediments and selective entrainment by the westerly winds during basin deformation. Our results emphasize the importance of widespread and persistent occurrence of fine-grained sediments along the pathway of westerlies to produce voluminous dust deposits. These findings suggest that the onset of eolian deposition may not be directly related to global cooling or uplift of mountain ranges.
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