The Magnetic Characteristics And Environmental Implications Of The Short Columnar Sediments In The Yellow Sea And East China Sea

The Yellow Sea and East China Sea are located in the western Pacific Ocean, and between the Chinese continent and the Western Pacific fringe island arc. It is an important part of China’s eastern shelf seas. As two worldwide rivers, the Yangtze river and the Yellow river delivered plenty of sediments deposited in this area. Under the complex conditions of its ocean dynamic system, a plurality of mud depositions formed. There are many pieces of geological history information contained in these mud depositions. They have important significance to reveal environment change of seabed, detect resource of ocean, and investigate the interaction of human activities, marine environment and climate change.This paper is based on analysis of particle size parameters, magnetic parameters and 210Pb dating parameters of 188 short columnar sediments from south Yellow Sea mud area, southwest Jeju mud area and Zhe-Min coastal mud area which are located in the Yellow sea and East China sea, summarizes the vertical and horizontal changes of various parameter characteristics. It has analysed the situation of magnetic minerals’type, domain and content from short columnar sediments in the Yellow Sea and East China Sea mud areas, and investigated the relationship between magnetic characteristics and depositional environment in the study area. Obtains the main knowledge as follows:1. Particle size analysis of sediments in the study area shows:Main of the sediments of South Yellow Sea mud deposition, southwest Jeju mud deposition and Zhe-Min coastal mud deposition are silts. Their median diameters are between 0.005 to 0.013 mm with a higher sorting coefficient and poor sorting. Sediments from South Yellow Sea deposition and Zhe-Min coastal deposition main show negative skewness. Their average particle sizes are coarser than median diameter with more fine grains. The kurtoses are moderate, nearly normal. Sediments from Jeju mud area main show positive skewness. Their average particle sizes are finer than median particle size with more coarse grains. The kurtoses are very narrow and their particle sizes are outstanding principal. All of the three areas have weak hydrodynamic conditions and stable sedimentary environments.2. Magnetic analysis of sediments in the study area shows:There is little difference in sediments’magnetic characteristics of 3 areas. Main of their magnetic minerals are ferrimagnetic minerals and the major magnetic domains are single domain and quasi single domain. However, magnetic domains of sediments in Zhe-Min coastal mud area are larger than other two areas with more MD and SP grains. The content of three mud areas display a trend of increase from north to south, southwest Jeju deposition is larger than South Yellow Sea deposition and smaller than Zhe-Min coastal deposition. Magnetic characteristics of sediments in these three areas have little relationship with their particle size and early diagenesis.3. 210Pb specific activities analysis of sediments in the study area shows:The deposition rate of the southern Yellow Sea mud area is 0.12～0.14 cm/yr, southwest Jeju deposition is 0.3 cm/yr, and Zhe-Min coastal deposition is 0.46 cm/yr. The relevance between specific activities and depth is good. The specific activities show exponential decrease with depth increase which indicates stable sedimentary environment and continuous deposition in these areas.4. Comparative analysis of sediments’magnetic properties in the study area shows:There are stably and weak hydrodynamic conditions depositional environments in the three depositions. The sediments of south Yellow Sea deposition are mainly from Yellow river. Both of Yellow river and Yangtze river grains are deposit at southwest Jeju mud area. The major source of Zhe-Min coastal deposition is Yangtze river. The difference of sediments’ source is the principal reason of their difference of magnetic characteristic.