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Late Cretaceous (Campanian) provenance change in the Songliao Basin, NE China: Evidence from detrital zircon U-Pb ages from the Yaojia and Nenjiang Formations
文摘
In order to define the provenance change across the nonconformable boundary between the second and the third members of the Upper Cretaceous Nenjiang Formation (Campanian) in the north-central area of the Songliao Basin, two sandstone samples above (sample a-1 from the fourth member of the Nenjiang) and below (sample z-1 from the first member of the Yaojia Formation) the nonconformity were collected from core holes. U-Pb dating was performed on detrital zircons separated from the three sandstone samples. Detrital zircons from sample a-1 have dominant age populations of 100-110 Ma, 190-220 Ma, and ~ 1800 Ma, and sample z-1 has dominant ages of 130-150 Ma and ~ 350 Ma. This paper demonstrates that the provenance of the fourth member of the Nenjiang Formation is significantly different from the first member of the Coniacian Yaojia Formation. The provenance above the nonconformity became much more complex and the eastern source increased significantly, while the western source sharply declined. The main source areas of the fourth member of the Nenjiang Formation are mainly the Zhangguangcai Range, the eastern Lesser Xiang'an Range and the southeast of Songliao Basin. The dominant provenance of the first member of the Yaojia Formation is the northern, the central and the southern Great Xing'an Range. According to the depositional ages and combining the latest seismic stratigraphic profiles in the Songliao Basin, the tectonic inversion of the eastern Songliao Basin began between 73 Ma and 87 Ma, which differs from the previous age of 73 Ma.
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