High-resolution chronostratigraphic framework and spatiotemporal evolution of Carboniferous-Permian source rocks in the Junggar Basin and its periphery

Prolific Carboniferous-Permian source rocks in the Junggar Basin and adjacent regions record critical information on the final closure of the Paleo-Asian Ocean. This succession reflects a transitional marine-to-continental setting and is characterized by a scarcity of marine index fossils, causing significant uncertainty in chronostratigraphic correlation. The lack of precise temporal control has long challenged the correlation of hydrocarbon-bearing strata and the reconstruction of the basin’s tectonostratigraphic evolution. In this study, we conducted comprehensive zircon U-Pb geochronological analyses of volcanic ash layers from key Carboniferous-Permian sections and drill cores across the northwestern, southern, and eastern margins of the Junggar Basin and the adjacent Turpan-Hami, Santanghu, and Yili basins. Using high-precision CA-ID-TIMS, SIMS, and LA-ICPMS dating techniques, we successfully obtained 53 U-Pb ages from ash beds, providing the first robust chronostratigraphic constraints for multiple key source rock intervals. The results show that: (1) The principal source rocks in the Junggar Basin’s Mahu Sag (Fengcheng Formation) were deposited from the late Carboniferous (Kasimovian) to the earliest Permian (Asselian); (2) The main source rocks in the southern Junggar, Turpan-Hami, and Santanghu basins (Lucaogou/Tarlong Formation) were deposited during the Sakmarian to Artinskian (Cisuralian, early Permian); (3) The key source rocks in the Yili Basin’s Yining Sag (Tamuqisayi Formation) were deposited during the early Kungurian (late Cisuralian); and (4) The Pingdiquan Formation in the eastern Junggar Basin is most likely Wuchiapingian (Lopingian, late Permian) in age. These data define three major source rock development intervals: Kasimovian-Asselian, Sakmarian-Kungurian, and Wuchiapingian. This refined chronostratigraphic framework reveals a pronounced diachroneity in the marine-terrestrial transition, which becomes progressively younger from the northwest (Kasimovian) to the east (Gzhelian). This temporal pattern provides new evidence supporting the “scissor-like” closure model for the Paleo-Asian Ocean. This new, robust Carboniferous-Permian chronostratigraphic framework for the Junggar Basin and its surrounding regions provides a solid foundation for hydrocarbon exploration and basin evolution studies in northwest China.