The Characteristic Of Core Sedimentary And The Sediment Environment Of Beilun Estuary

The Beilun estuary is a limitrophe estuary between China and Vietnam. It is the west end of Guangxi coast. Few researches were carried in this area because of the hypersensitive location. In order to get the scientific information of how to do rational development and utilization, how to do ecological resources protection and the maintenance of Homeland Security, We took the drilling sample in the Beilun Estuary for the first time and got three cylindrical core sample. Then we did the analysis of the sediment particle size, detrital minerals, geochemical character, radiocarbon dating and 210Pb dating. We do the division and contrast of the Stratigraphic sequence since the late Pleistocene in Beilun estuary based on the data we got and tried to understand the evolution of the sedimentary environment since the late Pleistocene. The conclusions are as follow:(1) The deposition thickness of the three drilling KL1, KL2, KL3 was 2.9m, 1.0m, 2.6m respectively. The sedimentary layer was thin in the Beilun estuary. It meant that the hydrodynamic effect was strong and the deposition rate was slow.(2) The sediment type was silty sand, sandy silt, medium sand, fine-medium sand, silty sand from the bottom to the top in drlling KL1, the sediment was presented 2 deposition cycle from the bottom to the top (the size was varied from fine to coarse and then back to fine); the drilling KL2 had single sediment type, it was fine-medium sand; the sediment type was gravel, sand gravel, rough in the sand, silty sand, clayey sand, sand-silt-clay from the bottom to the top in drilling KL3, the sediment grain size was varied from coarse to fine from bottom to the top. The sorting of the sediment was hard in the three drilling because of the strong hydrodynamic effect.(3) The 14C dating data showed that the newest sediment layer was formed about 17522±53 years ago and it was belonging to the late Pleistocene glacial deposition. The bedrock was Jurassic sandstone, the sediment and the bedrock was unconformable contacted and the layer between the late Pleistocene and the Jurassic was missing.(4) The main heavy minerals were ilmenite, zircon and tourmaline in the research area, and the light minerals was quartz.(5) The deposition curve of the major Elements Fe2O3, P2O5, MnO and trace elements Co, Ni and Cu was basically the same: it had high value in 0～120cm and 207～ 235cm, low value in 120～207cm in core KL1.(6) Late Pleistocene sediments were found in the core of 2.07～2.90m in drilling KL1, the particle size was from rough to fine from the bottom to the top, the major elements and trace elements had high value. It was a transgression. The Holocene sediments were found between 0～2.07m in KL1,0～1.0m in KL2 and 0～2.6m in KL3, the particle size was from thick to thin. The major elements and trace elements had low value between 1.2～2.07m and higher value above 1.2m. It was a process from sea regression to sea intrusion.(7) The evolution of the sedimentary environment since the late Pleistocene was a cycling of transgression-regression -transgression:the transgression in the end of late Pleistocene, the regression in the early Holocene and the transgression in the mid-Holocene.