The Sea Level Changes And Response Of Sedimentary System On The ECS And YS Shelf After The Last Glacial Maxmium

The shelf of Yellow Sea (YS) and East China Sea (ECS) is one of the widest shelves around the world. The Yellow River and the Changjiang Rriver transports huge amount of terrigenous sediments to the sea. Under the tectonic subsidence background, the continental shelf of the ECS and the YS, from the inner shelf to the trough, has preserved detailed records of the Quaterary. The shelf was the natural laboratory to study the Quaterary paleo-environment and the high frequency sea level changes, especially the varierty of the paleo-environment due to the sea level changes of the Last Glacial Maximum (LGM) which makes the shelf become one of the global favorite regions to study paleoenvironment and paleo-sea level changes. This thesis synthesis the geological and geophysical data obtained in the past decades from the study area, to analyse the sedimentary system and sequence stratigraphy of the ECS and the YS and to rebuild the evolvement history of the sea level changes after the LGM, to study the response of the sedimentary system to the sea level changes.There happened four transgressions and regression cycles in the shelf of ECS and YS since the late pleistocence and developed four transgression and regression sedimentary sequences on the shelf. The sea level changes of the LGM was the greatest one of the Quaternary, it reached up to 120m lower than today. After LGM, the sea level rised rapidly. The Holocence sea level rise of the ECS and YS presented stepped trend, approximately it can be divided into four Rapid Rise periods and three Slow Rise periods and one falling period. During the Rapid Rise period, the sea level rise rapidly, erode and rebuilde the late Pleistocence terrigenous sediments on the shelf. The eroded sequence could be tracked all over the shelf. It was"transgression boundary layer". During the slow rise period, the sea level rise slowly or stand still, beach sedimentary system and tidal sand ridges developed on the shelf. Around 7ka B.P., the sea level reached 4～5m higher than today. Afterward sea level fell and stayed stabilization as today. Around 6ka B.P., the Changjiang River delta began to develop, and shoreline moved towards the sea. With the development of current circulation on the ECS and YS shelf, the mud sediment system began to develop in the middle and inner shelf. With the revolution of the industrial and the greenhouse gas emission rapidly, the climate of the world warmed up. The sea level rise continuously, the coastal and the delta area are under erosion. Sea level rise becomes a global issue.In this thesis, the researches depend on the former data to analyze the sea level changes on ECS and YS shelf after the LGM. The sea level changes on ECS and YS shelf after Last Glacial Maximum presented as stepped model. It can be divided into five periods and eight phases. The paleo landform of the shelf during the LGM was rebulided according to the thickness of holocence sediments and modern landform of the shelf. The flutuation of the shoreline on the shelf after the LGM was redrawn based on the sea level change history and related geological and geophysical evidences. Corresponding to the sea level changes after the LGM, several sedimentary systems had been developed on ECS and YS shelf, which includes paleo-shoreline, tidal sand ridges, transgression boundary layer, highstand mud deposite and the estuary delta system. The paleo-shoreline and tidal sand ridges were developed during the period of sea level rise paused. The transgression boundary layer was the eroded interface when the shoreline retreated quickly across the shelf. The mud sediment and the Changjiang River delta were developed during highstand period. The study of the environment and the sea level changes on ECS and YS shelf after the LGM was depended on the data of collected from the study area, and combine the core data with seismic data to analyse the record of sea level changes in the sediment. The studies on ECS and YS shelf have obtained great achievement. There were many scarcities for the lacking of the adequacy detailed core data and dateing data and high resolution seimic data. The work on this study should be continued.