CHARACTERISTICS OF SEDIMENT GRAIN SIZE AT YALU RIVER ESTUARY AND IMPLICATIONS FOR DEPOSITIONAL ENVIRONMENT

Ten cores are collected along the Main Branch of the Yalu River estuary. Dating and grain size analysis are made for the cores layer by layer. The data of grain size is used in this paper for revealing the evolution of depositional environment. Hydrodynamic conditions, source input and depositional events are discussed as major topics. The results indicate that the influence of tidal current increased from land to sea spatially, and the runoff influence weakened gradually with time. The fine fractions of sediments came mainly from the runoff of the Yalu River, and most of the coarse fractions were from the coarser suspended load and saltation load, and few of them came from tidal ridges offshore. Nine depositional events are identified, among which four were directly related to flooding, and the others related to changes in environment and/or drainage. The 1960 event was certainly a significant one which led to the changes in landform pattern, including the formation of secondary branching, and three outlets towards the sea. The deltaic deposits at the Yalu River are well correlated with the tidal flat deposits on the west bank. Depositional events in 1970, 1988 to 1992 and 1995 are all recognizable in the profiles of the West Branch as well as the tidal flat in the west bank, and could be used as marks for sequence classification and correlation.