Recognition And Reconstruction Of Event Deposits From The Mud Area In The Inner Shelf Of The East China Sea In The Past 100 Years

This study base on the research of high resolution deposition records which sampling from the Yangtze River estuary and the inner shelf of East China Sea (ECS), some common method, such as Grain size method, Elements method, Biological silicon method et al has been used on five cores. In consideration of the time series of Yangtze River floods and typhoon storms in this area. Recognition the event deposition in each core. Describes the process and characteristics of event deposition. Reconstruction typhoon and flood deposition in the past 100 years. The study is provide the scientific support for the continental shelf sedimentary processes and the formation of sequence since high sea level.First, this research use the typhoon data (1949-2013) of CMA tropical cyclone datasets, according to the experience formula to calculate the scope of typhoon’s tenth level wind, which area within wind radius at ten levels as the typhoon influence, last to calculate the frequency of typhoon which influence the inner shelf of ECS. The Conclude indicate that, the frequency of typhoon in the inner shelf of ECS are between 7-61 times in these 65 years, and an average of about 29 times, most of the area (almost 85%) 10-40 times. The frequency of the Yangtze River estuary the minimum area affected by the typhoon is 7-27, an average of about 18 times. The largest frequency is 20-61 which area are south Fujian and Zhejiang, an average of 36 times; Fujian and Zhejiang north somewhere is among them, the typhoon frequency is 14-45, an average of 28 times. In summary, the characteristic of frequency affected by the typhoon is a phenomenon which north low south high, near shore low open sea high.At the same time, in order to confirmed the Yangtze flood time series for decades, this study chase the Yangtze flood peak flow which record by Datong Hydrometric Station as the reference standard and combined with the historical documents. Between 1951-2010, a total of 26 times flood events are produced, the biggest flood occurred in 1954,1998 and 1999, during the flood, the flood peak flow is more than 80000 m3/s.Core 18, C0702, DH6-1, C0803, DH7-2 sampling from the inner shelf mud area of the ECS, the study of sedimentary characteristics and the comparison of the typhoon and flood time series shows as follow. Flood and typhoon events are characterized by the characteristics of the sediment granularity coarsens, the way of sediment transport is suspended transport, and the suspended transport can be divided into two way. Two kinds of event deposits differences reflected in the different sedimentary sequence, the flood event deposits characterized by particle size increases gradually upward, then gradually become smaller; Storm event deposits show the upward gradually reduced after suddenly become bigger. In addition, the gray value of the core can response event well, and the element.Yangtze river flooding events affect only 18 station and the area close to the Yangtze river estuary, the mud area of Zhejiang and Fujian coastal are not recorded. Although the typhoon frequent transit the inner shelf of the ECS, but the storm event sedimentary records affected by the water depth and distance offshore. The typhoon event deposits mainly in the shallow water of the north sedimentary center of Fujian and Zhejiang coastal mud area are more clear than Yangtze river estuary mud area and the south sedimentary center of Fujian and Zhejiang coastal mud area. The study also found that a single typhoon’s influence scope is limited, and the space comparative of typhoon event sedimentary is bad.