广西防城港海域沉积物特征及输运趋势

Sediment Characteristics and Transport Trends in the Sea Area of Fangcheng Port, Guangxi

通过对2010―2011年在广西防城港海域表层沉积物所取样品进行粒度实验,并利用二维沉积物粒径趋势分析模型进行了粒径输运趋势分析。结果表明,研究区海域底质沉积物类型主要为砂、粉砂质砂、砾石质砂、砂-粉砂-黏土、黏土质粉砂和砂质粉砂等6种。粒度参数在空间分布上,沿岸和西部海域中值粒径较粗,分选中等或较好,偏态呈正偏或极正偏,在海湾口处呈负偏或极负偏;东南部海域粒径较细,分选系数差,偏态呈负偏或近对称。根据沉积物输运趋势方向不同,将研究海域分为3个区:沿岸海域主要离岸输送,方向由北向南;东南部海域的沉积物输运趋势向中间汇聚,形成一个沉积中心;西南部海域,沉积物输运方向偏北。

Sediment characteristics are important for understanding of hydrodynamic processes and sedimentary environments. In the present study, 200 surface sediment samples were collected from December 2010 to April 2011 in the sea area of Fangcheng Port in the Beibu Bay, China. The samples were analyzed by using a MasterSizer 2000 Laser Analyzer and by sieving （for particles with a diameter of＜2 mm and＞2 mm, respectively） to obtain grain size data. Three grain size parameters （ median grain size, sorting coefficient and skewness ） were then calculated by a moment method （Folk-Ward, 1957）. The results showed that 6 types of sediment were presented according to the sediment classification scheme proposed by Shepard （1954）, including Sand, Silty Sand, Gravelly Sand, Sand-Silt-Clay, Clayey Silt and Sandy Silt. Median grain size and sorting coefficient for the sediment in the study area was-0.5～7.5Φand 0.3～5.2, respectively. The coarse （＜4Φ） and well sorted （＜0.35） sediment was located over the nearshore and western parts of the study area, where the sediment was positively skewed. The sediment in the southeastern area was finer （＆gt;4 Φ） and poor sorted（＆gt;1） , with negatively skewed（-1～0.3） or nearly symmetrical（-0.1～0.1）. Good correlation between the distribution pattern of the grain size parameters in Fangcheng Port sea area and the sediment types （and hydrodynamics processes） was presented. The two dimensional model for grain size trend analysis proposed by Gao and Collins （1992） was adopted to identify sediment transport pathways in the study area. Grain size trends were then obtained by using this model with the maximum characteristic spatial sampling interval adopted. Based on the difference of the sediment transport trends,the study area was divided into three subareas：1） the sea area along the coastline where the major direction of the sediment transport was offshore（from north to south）;2） the southwest area where the direction was northward; 3） the southeast area where the sediment converged toward the center of the area, forming a deposition center. Such patterns were highly consistent with those of current velocities, geomorphologic information and heavy mineral movement.