Eocene source-to-sink links between the Tibetan Plateau and East China Sea Shelf Basin from detrital zircon U-Pb dating

Abstract:

The Yangtze River, which links the Tibetan Plateau to the East China Sea, is one of the most important sediment routing systems in East Asia. However, the timing of its inception and full integration remain controversial. Here we report 666 new concordant detrital zircon U-Pb ages from the Eocene Pinghu Formation and the Oligocene Huagang Formation in the East China Sea Shelf basin (ECSSB), the primary sink for this system during much of the Cenozoic. The new data come from core samples obtained from twelve deep boreholes in the ECSSB that provide insights into the early development of this river system. Detrital zircons in the Pinghu Formation range in age from 34.9 ± 0.7 to 2800 ± 42 Ma, with major clusters at 100–300 Ma and 1,600–2,200 Ma and small early-middle Paleozoic, Neoproterozoic, and Paleoproterozoic to Archean peaks. A similar age range (33 ± 0.4 to 2842 ± 43 Ma) and nearly identical age peaks are documented for the stratigraphically younger Huagang Formation. The maximum depositional age, based on the youngest grains in our samples, is 34.9 ± 0.7 Ma for Pinghu Formation and 33 ± 0.4 Ma for Huagang Formation. Statistical comparison of the new data with published detrital zircon age data for the major tributaries and segments of the Yangtze River suggests the provenance of our samples is similar to samples from the modern river, near its outlet, but with a larger contribution of 1700-2100 Ma zircons, likely sourced from the Songpan Garze terrane. Our analysis also indicates the youngest age group (<50 Ma) in our samples is only recognized in samples from the upper reaches of the modern river. The high degree of similarity between our samples from the ECSSB and the modern Yangtze suggests the river and source-to-sink system were established by the late Eocene or perhaps earlier, and may point to early topographic adjustments linked to uplift Tibetan Plateau.