浸油法测量黄土样品的容重及其意义

Dry Bulk Density of Loess Samples Measured by the Oil-soaked Method

笔者通过对比实验,论证了一种新的测量黄土样品容重的方法——浸油法的精确度和稳定性,并以甘肃灵台剖面为研究对象,测量了L9以上厚约70m的风尘黄土-古土壤堆积序列的容重值。结果表明,古土壤地层单元的容重值要明显高于其上下的黄土层,其变化范围为2.05～2.18g/cm^3,而黄土层的容重值变化范围为1.85～1.98g/cm^3;L9以上不同层位的黄土和古土壤单元容重值随深度变化不大,说明受天然压实作用的影响很弱。通过对比容重和磁化率序列,发现受粉尘源区干燥度、冬季风环流强度和沉降区气候条件综合控制的容重指标,不仅记录了轨道时间尺度的东亚冬、夏季风的相互交替演化,而且典型冰期的容重变化可能揭示了更短时间尺度的季风气候变化信息。

First, writers proves the accuracy and stability of dry bulk density values measured by the oil-socked method based on comparative experiments; then the dry bulk density of loess-paleosol sequences about 70 m thick from L9 to S0 in Lingtai section, Gansu Province, is measured by the oil-socked method. The dry bulk density variations show that the dry bulk density of paleosol layers is higher than that of their overlying and underlying loess layers. The former values change from 2. 05 to 2. 18 g/cm3, the latter from 1. 85 to 1. 98 g/cm3. The average values of dry bulk density from L9 to SO change very little as the burying depth increases, which indicates that natural compaction contributes very little to the dry bulk density. Through a comparison between the magnetic susceptibility and dry bulk density variations, writers find that the dry bulk density variations, which are controlled by the aridity of the eolian source region, the strength of atmospheric circulation and the climatic conditions of the deposition area, not only record the alternation of East Asia winter and summer monsoons on the orbital time scale, but also reveal information of more frequent variations of the East Asia monsoons during the typical glacial periods.