象山近海表层沉积物特征及成因

Characteristics and Sedimentary Origin of the Surface Sediment in the Xiangshan Offshore Area

摘要: 根据象山近海沉积物现场地质采样和粒度分析成果，对其特征和成因进行了探讨。结果表明，研究区表层沉积类型以粘土质粉砂为主，砂、粉砂和粘土粒级含量分别为5%~10%、65%~75%和20%~25%，平均粒径大多数在6.00 φ~7.00 φ (0.016~0.008 mm)之间，分选较差。沉积物由近岸到外海呈现粗–细–粗的总体分布格局，西北近岸海域沉积物类型变化稍大，东南侧外部海域沉积物较为统一。频率曲线呈弱正偏态到常态，峰态较宽平的单峰型为主，峰值在4 φ~7 φ之间。概率曲线可分2~4段。沉积动力分区图显示水动力条件较弱。粒级–标准差曲线识别出四个峰值区，6 μm和29 μm附近峰值突出，说明研究区沉积物主要来源于长江入海物质向南输运沉积；460 μm和1 μm附近峰值较弱，分别代表本地海岸岛屿侵蚀物质和外海物质漂移的影响。

Abstract: According to the data of grain size and characteristics of the surficial sediments in the Xiangshan offshore sea area, the type, distribution pattern and possible origin of the surface sediments are discussed. Surface sedi-ments are mainly clayey silt, in which the sand, silt and clay particles portions weight 5%~10%, 65%~75% and 20%~25%, respectively. With mean diameter of about 6.00 Φ~7.00 Φ (0.016 mm~0.008 mm, fine silt), stand deviation coefficient of about 1.60 Φ~2.10 Φ, frequency analysis displays poor sorting and weak-positive skewness with one-dominant peak value (4 Φ~7 Φ) curve. Probability distribution may be discerned 2~4 sections represented as rolling, skip and suspended sediment transportationpatterns. The Pejrup ternary diagram for sedimentary environment classi-fication shows a weak dynamics condition. Distinguished the environmental sensitive groups from the sediments by particle size standard deviation method, the dominant deposits is silt which is widespread in subaqueous delta and adjacent sea areas transported by modern coastal currents systems, while the coarse sandy and fine muddy components show the influence of local lands-islands erosion and marine transportation.