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要对沉积层的形成方式有个基本了解,就必须把颗粒的沉积和聚集区别开来。沉积指的是颗粒在海底的暂时停置。聚集则是指沉积物多期沉积和迁移的净和。沉积速率与聚集速率间的差异,影响着环境纪录沉积事件的能力。在海底范围内可分别用~(234)Th和~(210)Pb放射性核素来确定100天的沉积速率和100年的聚集速率。在长江口附近的陆架上,短期沉积速率约为每月4.4厘米,而一个多世纪以来的聚集速率则小一个数量级,约为每年5.4厘米。
To have a basic understanding of the formation of the sedimentary layer, it is necessary to distinguish between the sedimentation and the accumulation of particles. Sedimentation refers to the temporary rest of the particles on the seabed. Aggregation refers to the net sediment deposition and migration. The difference between deposition rate and accumulation rate affects the ability of the environment to record sedimentary events. The ~ (234) Th and ~ (210) Pb radionuclides can be used to determine the 100-day deposition rate and the 100-year accumulation rate in the seabed range, respectively. On the shelf near the Changjiang Estuary, the short-term sedimentation rate is about 4.4 centimeters per month, whereas for more than a century the rate of aggregation is an order of magnitude smaller, about 5.4 centimeters per year.