The Characteristics Of Seismic Stratigraphy And Evolution Of The Tectonic-sedimentary Environment In The South Yellow Sea Since The Middle Pleistocene

The South Yellow Sea(SYS) is a semi-closed shallow continental shelf. Land based sources were carried into the sea and deposited here by Yangtze River and Yellow River which was an important part of the deposition process of from source to sink. Thick sedimentary strata is important for the study of sediment dynamics, land and sea interaction, quaternary climate change. Meanwhile, the SYS is located on the eastern margin of Eurasian Plate which is affected by the Pacific subduction obviously. A lot of tectonic deformation developed in the Late Cenozoic sedimentary strata. So the SYS is an ideal laboratory of researching the new tectonic movement.Based on the high-resolution reflection seismic profiles collected in central SYS, the tectonic and sedimentary environment was analyzed by seismic stratigraphy method.Profiles can be identified shallow marine faceis, deltaic estuarine faceis, channel fill phase faceis according to reflective appearance, internal reflecting structure, reflecting strength and continuity characteristics. These four sedimentary faceis are the most common faceis in eastern China continental shelf. These four sedimentary faceis vertically presented periodically, showing that the sedimentary environment cyclical changes with the sea-level change.Based on the reflection termination mode, the reflective layer and internal structure of the reflective layer, the profiles divided into 11 seismic stratigraphic sequences(DS1~DS11) in the identified depth. Most sequences includes the channel filling and shallow marine or deltaic deposits. Sometimes there is trangressive faceis between the channel filling and marine deposits. They represent the LST, HST and TST of the same period of sea level change, which compose a complete cycle. The boundaries between these sequences include the high amplitude erosion boundary or the land exposed boundary which reflect the regression period.Using the published drilling data, the seismic stratigraphic sequences are dating. There are seven seismic sequences developed since the middle Pleistocene. The Holocene strata is shallow sea faceis which average 5.7 m. The late Pleistocene strata average 25 m including the channel fillings at the last glacial and the marine deposits at the last interglacial period.Development of the strata is influenced greatly by tectonic activities. Before late Pleistocene Fujian-Lingnan uplift influenced the development of strata through blocking the seawater intrusion. The central uplift of South Yellow Sea through not completely submerged in the seawater and continued to rise slowly which affecting the formation of strata. To the end of the middle Pleistocene, the central uplift stopped to rise. Later, a large number of ancient river channels were developed in the late Pleistocene strata which indicated that the ancient rivers had been able to flow through the central uplift. The lifting movement of the continental shelf in the South Yellow Sea region also affects strata development. Compared with the MIS cycles, the stratigraphic sequences lack more than ten cycles.