分形方法在庐山第四纪沉积环境研究中的应用*

沉积物中Fe³⁺/Fe²⁺的值与形成时的古温度有益指数关系。假定Fe³⁺/Fe²⁺的值沿剖面的变化具有自相关性,那么它所反映的古温度变化是一条分形曲线。本文以庐山大校场剖面为例,根据孢粉和Fe³⁺/Fe²⁺的测试数据,建立了一个推算古温度的非线性公式。据此推算的古温度表明,本区中更新世以来共有3次明显的冷暖波动,最高年均温在22℃左右,最低达3℃左右,出现在末次冰期。未发现有低于0℃者。由粒度分数维的概念,推导出的计算公式可作为混杂堆积物粒度分布特征的度量指标。根据计算,该剖面主要接近于泥石流和石冰川的粒度分数维,而与冰碛物的粒度分数维有较大差别。综上得出,本区沉积物成因主要是间冰期季风气候下的山地泥石流和沟谷流水的洪-冲积及冰期干冷的冰缘环境下的冻融堆积。

THE APPLICATION OF FRACTAL METHOD TO STUDYING QUATERNARY SEDIMENTAL ENVIRONMENT IN LUSHAN AREA

The past study has revealed that there is a close relation between the value of Fe³⁺/Fe²⁺ and the climatic conditions for forming sediments.Viewing the phenomenon at a different angle,the authors found that the sediments with high value of Fe³⁺/Fe²⁺ also have more thermophilous sporopollen. Going a step further.we can find that there is a positive correlation between the value of Fe³⁺/Fe²⁺ and the paleo-temperature for forming the sediments.The positive correlation is similar to a power exponent relation.If the value of Fe³⁺/Fe²⁺ in vertical profile has an autocorrelation,then the value will show a fractal curve.The relation betewwn the Fe³⁺/Fe²⁺ value and paleo-temperature can use a formula to express.that is,T=a+bx^D.where,T is paleo-temperature.x is the value of Fe³⁺/Fe²⁺,a and b are constants,and D is the fractal dimension of the Fe³⁺/Fe²⁺ series.Based on the results of sporopollen identification and the testing data of Fe³⁺/Fe²⁺.this paper establishes a nonlinear formula to infer the paleo-temperature in the area,i.e.T=2.3+0.09x^1.31.Using the above formula to determine the paleo-temperature change in the area since Q₂,we can find that the inferred result has a relative mean deviation of <5%,and this method is more obvious to illustrate the paleo-temperature fluctuation.The inferred result shows that there are 3 times obvious(cold or warm) climate fluctuation in the area since Q₂.During the period.the highest annual mean air-temperature was about 22℃,and the lowest value was 3℃ or so.No minus annual mean air temperature was not found.