湖北郧县黄坪村黄土-古土壤序列体积分形维数特征及其环境意义

摘要

本研究运用体积分形维数模型计算了湖北郧县黄坪村(HPC)剖面土壤体积分形维数,剖面分形维值介于2.52～2.78,古土壤S0的分形维数值最大,马兰黄土L1最小,剖面整体分形维数值的大小关系为DS0>DLt>DL0>DL1.研究发现,分形维数值与粘粒含量呈正相关,与粗粉砂含量呈负相关,与磁化率和CIA值成正比,说明分形维数也可以指示成壤环境的演变,即分形维数值的高值,指示气候较为暖湿,反之指示的是气候较为干冷.HPC剖面的分形特征揭示了汉江地区的气候变化历史:晚更新世时期,L1的分形维数仅为2.61,说明气候较为冷干,成壤作用微弱;全新世早期,Lt的分形维数相对L1增至2.71,说明气候条件改善,气温回暖;全新世中期,S0的分形维数相对于Lt增至2.75,表明气候暖湿,成壤作用强烈;全新世晚期,L0的分形维数相对于S0降至2.70,说明汉江地区气候转凉.%The volumetric fractal dimensions of particle-size(D) in soil profile of Huangping Village (HPC), Yunxian County, Hubei Province were calculated by the volumetric fractal dimension mode. The fractal dimension values were between 2. 52 and 2. 78, and the highest one was in the paleosol layer(S0) and the lowest one was in the Malan loess layer(L1). The fractal dimension values in the whole profiles was ranked as DS0 > DLt > DL0 > DL1. This study discovered that the fractal dimension values were positively correlated to the clay content, negatively correlated to the coarse silt content, and was in direct proportion to magnetic susceptibility and CIA value. The fractal dimension could be used to reflect the evolution of pedogenic environment. The higher value reflected warm and humid, whereas lower value reflected arid and cold. The fractal characteristics of HPC soil profile indicted the history of climate change in Hanjiang area. During the late pleistocene, the fractal dimension value of L1 was only 2. 61, indicated cold climate and weak pedogenesis. During the early holocene, the value in Lt increased to 2. 71 compared with L1, which indicated the climate was improved and warmer. During the middle holocene, the value in S0 increased to 2. 75, indicated warm and humid climate and strong pedogenesis. During the late holocene, the value in L0 reduced to 2. 70, indicated that the climate in Hanjiang area became cool.