WEATHERING CHARACTERISTICS AND PROVENANCE OF THE SURFACE SEDIMENTS IN THE OFFSHORE OF NORTHERN FUJIAN
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摘要:
通过对闽北近岸海域的229个表层沉积物样品和周边河流的54个表层沉积物样品进行粒度和常量元素测试，分析了研究区常量元素分布及粒度控制效应，并运用成分变异指数(ICV)和化学蚀变指数(CIA) 2种风化指标，结合(A-CN-K)-(A-CNK-FM)三角图，探讨了其风化特征及物源指示。研究表明，闽北近岸海域从岸向海表层沉积物粒径变粗，底质类型表现为明显的条带状，依次为泥-粉砂-砂质粉砂-砂。分析认为，形成这种条带状的主要原因是其物源及动力机制的不同，近岸主要为长江及周边河流物质输送，分布在50 m水深以浅，而在70 m以深的粗砂主要为残留沉积，50～70 m表现为过渡类型。风化程度研究表明，在空间分布上，从岸向海化学风化程度逐渐增强，70 m以深的异常区是以石英为主的残留沉积，抗风化能力强，黏土矿物含量低，表现为弱化学风化程度。长江、瓯江、闽江沉积物的风化程度表现为随着地理纬度的降低而增强，气候效应明显，研究区与长江沉积物风化趋势更为接近，所经历的形成环境最为相似，受物源效应影响。
Abstract:The analysis of grain size and major elements was carried out for 229 surface sediment samples collected from the coastal area of northern Fujian and 54 surface samples from the surrounding rivers. The factors controlling the distribution patterns of the major elements and grain size are studied. Two weathering indicators, the component variation index (ICV) and the chemical alteration index (CIA), are used together with the (A-CN-K)-(A-CNK-FM) triangle chart to reveal the weathering characteristics and provenance indicators. Results show that the surface sediments along the coast are distributed in a quite regular pattern. From the coast to the sea, the deposits are getting thicker, and spatially in a banded manner. Sands occur near the land followed by mud-silt-sand silt-sand towards the sea. It is believed that the banded distribution pattern depends on sediment source and water dynamics. The near shore sediments are mainly coming from the Yangtze River and surrounding rivers, and deposited in the area less than 50 m in water depth. The coarse sands found in the area under 70 m of water depth are mainly residual sediments. In the area between 50～70 m in water depth, there occur the mixed sediments of the above two. Research of weathering degree suggests that chemical weathering becomes stronger off shore. The sediments below 70 m are mainly the residual sands dominated by high quartz and low clay mineral content, indicating a weak chemical weathering. The weathering degree of fluvial sediments in the Yangtze River, Oujiang River and Minjiang River shows an increase trend with the decrease in geographical latitude, and the effect of climate is obvious. The weathering status of the study area is rather similar to the Yangtze River sediments, and thus the environments are also similar and both affected by sediment sources.
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表 1 表层沉积物常量元素含量统计
Table 1. Contents of major elements in surface sediments
元素含量/% 区域 参数指标 SiO2 Al2O3 Fe2O3 MgO CaO Na2O K2O CIA 平均粒径（Mz） 研究区（n=229） 最大值 66.04 18.96 14.58 4.21 19.21 3.91 3.56 64.74 7.83Φ 最小值 29.73 6.85 4.36 1.81 2.82 1.36 1.21 44.80 1.26Φ 平均值 55.62 15.99 6.19 2.59 4.19 2.68 3.09 56.14 6.42Φ 标准偏差 4.23 1.86 1.05 0.35 1.61 0.61 0.30 3.40 1.19 变异系数 0.07 0.12 0.17 0.13 0.39 0.23 0.10 0.07 0.19 上陆壳 平均值 66.00 15.20 5.00 2.20 4.20 3.90 3.40 47.92 \ 长江（n=13） 最大值 72.42 16.10 6.62 2.83 8.84 1.79 2.89 73.76 \ 最小值 49.16 8.36 3.38 1.81 3.62 0.82 2.08 52.09 平均值 61.28 12.68 5.27 2.32 5.66 1.38 2.39 62.78 瓯江（n=17） 最大值 77.08 17.13 6.84 2.41 1.44 2.85 5.01 70.79 \ 最小值 58.79 11.45 2.02 0.28 0.33 0.82 3.15 48.15 平均值 69.14 14.27 3.88 1.03 0.83 1.58 3.91 63.43 闽江（n=28） 最大值 87.78 24.06 7.69 1.00 1.09 1.19 4.24 91.15 \ 最小值 51.49 6.12 1.29 0.16 0.15 0.13 1.72 50.83 平均值 68.67 16.58 4.21 0.58 0.49 0.64 3.01 74.68 注：上陆壳数据引自文献[22]。 
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表 2 主要常量元素与平均粒径的相关性
Table 2. Correlation coefficients of grain size and main elements
X Y 方程 R2 Mz SiO2 y = −2.985 2x + 74.945 0.771 8 Mz Al2O3 y = 1.472 8x + 6.609 8 0.921 8 Mz CaO y = −0.740 8x + 8.786 5 0.647 5 Mz MgO y = 0.247 6x + 1.003 6 0.752 7 Mz K2O y = 0.221 7x + 1.677 3 0.822 4 Mz Na2O y = 0.293 1x + 0.799 0 0.299 5 Mz Fe2O3 y = 0.748 0x + 1.321 4 0.871 4
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