SEDIMENTARY INFORMATION OF TIDAL FLAT OF THE YELLOW RIVER DELTA AFTER LAST GLACIAL MAXIMUM AND ITS ENVIRONMENTAL IMPLICATIONS

The Yellow River is the sediment supplier for building up the vast Norht China Plain. It swings frequently on the plain and finaly pours into the Bohai Sea after the River cut through the Sanmenxia about 150 kaBP. The annual average sediment charge of the Yellow River into the sea reached (11~12)×10⁸t since 1 000 aBP, most of which deposited at the river mouth to form deltaic lobes, and the modern Yellow River delta was formed in 1855. According to the vertical variations in sediment grain size of the YDZ1-core of the Yellow River delta, in connection with the AMS¹⁴C dating and historical data, this paper analyzed the sedimentary information and the evolution of sedimentary environment of the Yellow River delta after the last glacial maximum. The main types of sediment are sand, silty sand, sandy silt, silt and clayey silt. From top to bottom, the mean size and sorting coefficeint show trends from decrease to increase, then coming back to decrease, while the skewness and kurtosis exhibit contrary trends in a increase-decrease-increase pattern.The sequence shows a facies succession of flood plain facies, fluvial facies, delta-front facies, shallow marine facies, tidal flat facies and fluvial facies from bottom to top. It means that the dynamic environment varied from strong (continental facies) to weak (marine facies), then to strong (continental facies) again.