Research Of Quaternary Sediments And Neotectonic Movements Of The Dongguan Basin

Dongguan Basin is located in north eastern part of the Pearl River Delta in the direction of near east-west. Controlled by Shilong-Houjie fault in the south and Shougouling fault in the north, it was formed on the former Cretaceous-Eogene Period basin, and behaves as a Quaternary fault basin.Quaternary Standard Borehole Detection Project constructed 3 Quaternary boreholes (ZK1, ZK2 and ZK3) in the deposition centers in Dongguan Basin. The project recorded rock core information and sampled 14C and OSL in dating, with microfossil, sporopollen and grain size in deposition environmental analysis. The sample testing results of ZK3 borehole show well and are taken as main evidences analysis in this thesis.Dating data of ZK3 show that about 6000a ago the depositing environment suddenly changed or structural activity occurred. The continuity of sea-environmental microfossil sequence can preliminary define the 3.5-12.0m part of borehole as coastal and shallow sea facies and 13.0-26.5m as combination of shallow sea and river delta facies. The transition between two sporopollen combination belts indicates the weather turning to be cold, corresponding to the sub-North Cold Period in time. Both in glaciation and interglacial periods, a considerable area of water distributes around the borehole region. Climate change made very little influence to the depositing environment. Grain analysis of sample with less than 2mm in grain diameter shows the depositing environment above 10.5m in depth is river delta facies, and below 10.5m in depth is combination of turbidity sediment of shallow sea facies and river delta facies which show transgression-regression alternation.The adjacent belt of Dongguan Basin elevated and exposed terraces with height of 15-20m. The thickness of inner basin deposition since Quaternary Period reaches 10-30m. Dating data shows Shilong-Houjie fault was active in mid- Pleistocene and turned relatively stable since Holocene. It is estimated that only 0.19m of deposition was produced in the last 10,000 years. In the last 30,000 years the Shougouling fault formed a vertical relative displacement of 4.1m with a rate of 0.14mm/a showing it a low-middle active intensity. Since 1951, the Dongguan Basin and ajacent region have been in a uprising mode with speed of 2~4mm/a.In comparison with weather and sea level changes, with the summary of measured data, it is concluded that the Dongguan Basin has undergone three times of transgression-regression evolution which formed the alternation of land and sea facies stratum structure. The whole uprising trend of the Dongguan Basin and ajacent region caused the last regression movement. Neotectonics activities and climate changes make little direct contribution to the evolution of depositing.