摘要
沉积物中Ｆｅ^（３＋）／Ｆｅ^（２＋）的值与形成时的古温度有益指数关系。假定Ｆｅ^（３＋）／Ｆｅ^（２＋）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Ｆｅ^（３＋）／Ｆｅ^（２＋）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 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=α+bxD.where,T is paleo-temperature.x is the value of Fe3+/Fe2+,αand 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+0.09x1.31.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.In order to identify genesis of sediment formation, the authors suggest a concept about grain size fractal dimension of sediments. On the assumption that the grain diameter(r) and number (N)of the sediments accord with a power exponent relation,that is,N(r)=C/rD,here C is a constant,D is a fractal dimension, thus,the granule of the sediments can be considered as spherical,and they have homogeneous density,consequently,we can get a formula to calculate the grain-size fractal dimension:D=3-(log2(M/m)-log2(M2- m)/(φ2,-φ1,).In the formula,M1/m and M2/m are the granule percentage contents for grain diameter r1 and r2 respectively,φ=-log2r1 and φ2=-log2r2are the logarithms of the grain diameter r1 and r2,D is a measured index of the grain-size diamension distribution.According to the above formula,the authors calculate the different grain-size fractal dimensions of Dajiaochang sediments,moraine,debris flow,rock glacier and alluvium.By contrast,we can find that the Dajiaochang sediments are similar to debris flow and rock glacier according to their grain-size fractal dimensions,but they are different from moraine.Combining paleo-temperature to deduce,the authors think that the Dajiaochang sediments was mainly formed by mountain debris flow and alluvium under monsoon conditions during interglaciation period.Of course.it is impossible to form glacier in the Lushan area under the above climatic conditions.
出处
《地理研究》
CSSCI
CSCD
北大核心
1996年第3期64-69,共6页
Geographical Research
基金
国家博士后科学基金
南京大学现代分析中心测试基金
关键词
分形
庐山地区
沉积环境
第四纪
Fractal dimension
Lushan area
Paleo-sedimentary environment
