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Based on grain size analysis and high-resolution elemental scanning of core YD0901, taken from the subaqueous Yangtze River delta, a 600-year flood history was reconstructed for the Yangtze River drainage system. Zr/Rb ratios were chosen as a proxy for Yangtze River floods. Zr resides mainly in the coarse-grained minerals, and Rb is found in the fine-grained minerals. When floods occur, the discharge of the Yangtze River increases, which carries more coarse-grained minerals into the East China Sea. Therefore, deposition of coarse-grained minerals significantly increases relative to fine-grained minerals on the subaqueous delta, and subsequently the Zr/Rb ratios also increase. The higher the Zr/Rb peaks, the greater number of coarse particles deposited by saltation processes. Zr/Rb peaks correlate very well with historical records for Yangtze River floods. Especially at about AD 1870, the Zr/Rb ratio reached a maximum value over the last 600 years, which is consistent with "the extreme flood event" in the upper and middle reaches of the Yangtze River in AD 1870, as indicated in the historical records. Results show that floods have occurred at a relatively high frequency over the last 600 years, which is consistent with historical records when, during the Ming-Qing Dynasty, floods occurred once every 4 years. In addition, spectral analysis of the Zr/Rb ratio showed that there is close link between the Yangtze River floods and ENSO intensity. [ABSTRACT FROM AUTHOR]

Detrital zircon grains of Late Cenozoic sediments dated back to ca. 3.6 Ma from core DY03 in the Yangtze delta were dated by LA-ICP-MS, in order to investigate the sedimentary provenance and to find some clue for the evolution of the Yangtze River. Most of the detrital zircon U-Pb ages are distributed at 100-300 Ma, 350-550 Ma, 600-1000 Ma, 1400-2000 Ma and 2200-2800 Ma, which correspond well with the main tectonic and magmatic events in the Yangtze drainage. The detrital zircon age patterns show distinct difference between the 3 samples below 189.8 m and other 6 above 189.8 m. 43%-55% zircons in the 3 samples below 189.8 m fall within Cretaceous, while ages from 150 to 2800 Ma are distributed with no obvious peaks, which indicate the sedimentary provenance may be limited to the lower Yangtze drainage. The 6 samples above 189.8 m show similar age patterns, and the ages are relatively evenly distributed, indicating the sedimentary provenance broadened distinctly. All 6 samples deposited later than ca. 3.2 Ma show age information from the upper Yangtze drainage (including the Emeishan large igneous province), indicating that the Three Gorges may have already been cut through by then. [ABSTRACT FROM AUTHOR]