东海内陆架EC2005孔沉积物粒度分形特征

Grain-Size Fractal Features of the Core EC2005 Sediments in the Inner Shelf of East China Sea

对位于浙-闽沿岸泥质带的EC2005孔沉积物粒度分形特征以及与平均粒径和分选系数的关系进行了探讨。EC2005孔沉积物粒度在累积含量5%～95%的无标度区间内,统计自相似程度高,具有分形特征。沉积物平均粒径与分维值既存在正相关,也有负相关关系。二者正、负相关关系的分界点表现为平均粒径7.0Φ左右,<7.0Φ时,平均粒径越大,分维值越小;>7.0Φ时,平均粒径越大,分维值越大。该孔沉积物粒度分选系数与分维值呈正相关关系,>7.0Φ较细粒沉积物中二者表现为高度正相关。这是由于沉积物分选系数越小,粒径相对越集中,其形成背景相对简单,自组织程度越高,导致分维值越小。作为重要分界点的平均粒径7.0Φ,实际上主要对应了EC2005孔泥质沉积段和非泥质沉积段的划分点。该孔28.06～0m较均一泥质沉积物具有较小的平均粒径、较低的分选系数以及相对较低的分维值,说明该沉积段自组织程度较高,形成背景相对简单。本文揭示的沉积物粒度分维值与平均粒径存在的正、负相关关系,与以往的研究结果存在不同,该方面研究有待于进一步开展。

This study discussed the fractal features of grain size distribution of the core sediments from the depocenter of the Zhejiang-Fujian mud wedge on the inner shelf of the East China Sea（ECS）,and the correlation between mean grain size and sorting coefficient.The EC2005 sediment grains falls within the fractal scaleless zone of cumulative percentage between 5% and 95%.The core sediment is characterized with high self similarity and（or fractal） grain-size distribution.The mean grain sizes of the sediments are in both positive and negative proportion to fractal dimension.The point dividing negative and positive relationship exhibits a mean grain diameter of 7.0 Φ：if the mean grain size is less than 7.0 Φ,the greater the mean grain sizes that correspond to the smaller the fractal dimension.Meanwhile,if the mean grain size is larger than 7.0 Φ,the greater the former and the larger the fractal dimension.The sediment grain size and fractal dimension exist not only positive but also negative relationships.The sorting coefficients are positively related to the fractal dimension,especially in the finer sediments（larger than 7.0 Φ）.This is because the smaller sorting coefficient of sediments indicates the accumulation of particles with same sizes in a relatively simple environment.Therefore,the sediments have a high self-organization degree,resulting in lower fractal dimension value.The mean grain-size value of 7.0 Φ,an important boundary point,actually corresponds to the boundary between upper muddy section and lower coarser sediment of core EC2005.The muddy sediments at the depth of 28.06～0 m have small mean grain sizes,low sorting coefficient and relatively low fractal values,indicating that this sedimentary section is of high degree of self-organization and deposited in a relatively stable environment.This study reveals the positive and negative correlations between mean grain-size and fractal dimension,and this is different from the previous studies to some extent.Therefore,much research needs to be further carried out.