Sedimentation Rate Research In Guangxi Beibu Gulf

Coastal zone, the intersection of land and sea,is strongly affected by human activities and environmental. Sedimentation rate is a critical indicator in sedimentary evolution research, as well as a significant method to coastal sedimentary factor analysis on marine research. Typical sedimentary columns were sample in Guangxi Beibu Gulf (including Fangchenggang, Qinzhou and Beihai).137Cs and 210Pb specific activity in sediments from Nanliu River 3# and Sanniang Bay SN2 were measured, meanwhile grain size distribution of sediments were measured. According to the above results, sedimentation rate of Guangxi Beibu gulf were discussed with 137Cs and 210Pb dating. The main result of the thesis is as follows:(1)Sedimentation rate of Nanliu River 3# are 0.964 cm/a by 137Cs dating and 0.930 cm/a by 210Pb dating respectively, the deviation is less than 3.5%. It’s obviously on 137Cs vertical distribution characteristic, and easy to identify the time scale, but not on 210Pb due to the distribution in a swing.(2)Sedimentation rate of Sanniang Bay SN2 are 0.429 cm/a by 137Cs dating and 0.458 cm/a by 210Pb dating respectively, the deviation is less than 6.3%. It’s obviously on 137Cs vertical distribution characteristic, but the content is less; It’s obviously on 210Pb vertical distribution characteristic showing a good agreement with exponential decay rule.(3) Nanliu River 3#’s sedimentation rate is higher than Sanniang Bay SN2’s, since sedimentary environment of river is more intense than the sea in Guangxi Beibu Gulf. Both columns shows that sedimentation rates are reduced along with the time changing.(4) Powder sand and clay are main composition in Nanliu River sediments, of which the average ratio of both are 89.54% and 11.46% respectively. Powder sand are dominated, clay content is less. The vertical distribution characteristics of sediment grain size shows a 4 stages of erosion series; Fine powder sand and clay are main composition in Sanniang Bay sediments, of which the average ratio of both are 61.09% and 38.91% respectively. The clay content is decreased from bottom to surface layer, the sediment grain size is more concentrated, only has fluctuated in the surface layer with the range of 10 cm.