Fingerprinting sedimentary source of Yangtze deltaic deposits through
using single detrital zircon geochronology
Daidu Fan1, Shaohong Chen1, Yangyang Wang1, Yongsheng Liu2, Juan Zhao1
1 State
Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China (ddfan@tongji.edu.cn)
State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan
430074, China
Sedimentary sequences, heavy-mineral assemblages, geochemistry and geochronology of riverine
sediment in the onshore/offshore basins can be used as a critical link to decipher history of
drainage evolution, tectonic activities and climate change in the drainage basin. Great progress has
been recently achieved with single-grain micro-probing techniques in improving dating precision
and minimizing sample preparation. Such advances make it possible to generate large amounts of
zircon age data within reasonable timeframes and cost. We employed detrital zircon LA-ICPMS
U-Pb age data to fingerprint different sediment source provinces, and vertical variations in zircon
U-Pb age populations were used to discuss the timing of Yangtze formation and the impact of
glacial cycle on sediment yield and transport processes in the Yangtze drainage basin.
The youngest (<50 Ma) zircon grains are inferred only from the Tibetan Plateau. The early
Cretaceous (125-150 Ma) grains should mainly source from the lower Yangtze block and the
Cathaysia block; the late Permian (~260 Ma) grain predominantly derived from Emeishan flood
basalt. Other age groups of zircon are usually attributed to more than two source provinces. Zircon
structure and trace elemental composition can be used to distinguish the different provenance
zircon with the same age.
Downhole the PD-99 core, 11 sand samples were selected for provenance study. 3 samples from
the Gauss chronozone have completely different zircon age populations with others from the
Matuyama and Brunhes chronozones. The Gauss chronozone is characterized by a single age peak
at 125-150 Ma without any Himalayan zircon grains, indicating that the Yangtze was relatively
small and only drained the present lower and middle reaches at that time. Above the
Gauss-Matuyama boundary, zircon age populations are characteristic of multiple peaks with the
consistent presence of the Himalayan grains sourcing from the Tibetan Plateau. It is therefore
indicated that the Yangtze similar with the present system should have been formed since then.
Compared with LGM river sediment, Middle Holocene deposits have higher content of
Early-Proterozoic grains and less abundance in Late-Proterozoic and Triassic grains. It is inferred
that strong summer monsoon during Middle Holocene should have drain more sediments from the
Upper Yangtze drainage basin (i.e. Songpan-Ganzi terrane). Weakened summer monsoon at
present is, however, not observed to decrease the input from the Songpan-Ganzi terrane. It can be
interpreted to suffer from human impact on sediment yield patterns over climatic cycle.
Acknowledgements: This research was jointly funded by the National Natural Science Foundation of China (Grant
Nos. 40576030, 40876021, 40830107), Program for New Century Excellent Talents in University (Grant No.
NCET-07-0619), and GPMR200709.