Abstract
The Upper Permian to Triassic sedimentary successions of the southern Junggar Basin and western Turpan Basin are characterized by widespread unconformities. However, the origin of these unconformities remains highly controversial. Three sections, namely the Jimsar section in the southern Junggar Basin and the Aiweiergou and Yuergou sections in the western Turpan Basin, have been systematically studied using detrital zircon U-Pb geochronology, heavy mineral assemblages, and whole-rock geochemical analyses. Detrital zircon ages show that both Upper Permian and Triassic samples from each section have similar age distributions, with a major age group at 250–380Ma, a subordinate age group at 380–540Ma, and sporadic Precambrian ages, suggesting that the main provenance areas were the North Tian Shan and the northern margin of the Yili-Central Tian Shan, with a secondary source area in the Yili-Central Tian Shan. REE distributions and trace element crossplots also indicate that Upper Permian and Triassic samples display similar characteristics in both basins; all were sourced from felsic or mixed mafic/felsic rocks, with only a minor component of ancient or recycled sediments. Detrital provenance and geochemical analyses agree in showing no significant changes in the source-to-sink sediment transport system from the Late Permian to the Triassic. However, field observations, heavy minerals analysis, and geochemistry do suggest that both the southern Junggar Basin and western Turpan Basin experienced an arid climate during this interval. Both Upper Permian and Triassic sediments in the two basins contain abundant hematite, display low CIA values and Th/U ratios, and have mudcracks, redbeds, and other indicators of arid climate. Therefore, we suggest that the regional unconformities in the two basins were not generated by regional tectonic uplift, but most likely resulted from an increasingly arid climate.
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