摘要:有重要的地学意义。本文通过野外观察，结合常量元素、碳酸盐和磁化率，对祁连山东段甘肃白银地区晚泥盆世古土壤地球化学特征及古气候进行研究。结果表明：大红沟（DHG）剖面和磁窑（CY）剖面古土壤碳酸盐含量从剖面顶部向下是逐渐呈升高趋势，由于碳酸盐溶解度小，导致碳酸盐在土壤中聚集，形成钙质土壤表明气候环境是干旱或半干旱。通过对DHG和CY剖面样品常量元素分析，发现其化学成分相对均一，Na、Ca值较低，古土壤化学风化指数（CIA）平均值为46.59，显示出较弱的化学风化强度，气候环境为干旱。磁化率范围为3.14×10-8 m3/kg～11.2×10-8 m3/kg，磁化率的变化反映了古土壤的风化成壤强度的变化情况，DHG剖面的磁化率明显高于CY剖面，表明DHG剖面的风化成壤作用强，CY剖面的风化成壤作用弱。同时结合泥裂和肺鱼洞穴遗迹所反映的干旱—半干旱气候特征，推断研究区晚泥盆世时期气候以干旱—半干旱为主。
关键词: 晚泥盆世/
古土壤/
古气候/
元素地球化学/
磁化率/
祁连山东段
Abstract:Loess is one of the most widely distributed sediments in northwestern China. The paleosols with a large amount of geological information can well reflect the paleoenvironment. It has important geologic significance for restoring the paleoenvironment and paleoclimate of the research area. In this paper, the geochemical characteristics and paleoclimate of the Late Devonian paleosol in the Baiyin area in Gansu Province were studied by the methods of field observation, combined with carbonate, constant element and magnetic susceptibility. The results showed that the content of carbonate in paleosols in Dahonggou（DHG）and Ciyao（CY）profiles gradually increased from the top to the bottom. Due to the low solubility of carbonate, it accumulated in the soil, indicating that the climate environment was arid or semi-arid. By analyzing the constant element of DHG and CY profile samples, it was found that the chemical composition was relatively uniform, the Na and Ca values were low with an average value of the paleo-soil chemical weathering index（CIA）of 46.59, which implied a weak chemical weathering intensity and the climate is arid. The change of magnetic susceptibility reflects the change of weathering strength of paleosol. The magnetic susceptibility of DHG profile is significantly higher than that of CY profile, suggesting that the weathering（to form the soil by the wind）of DHG profile is strong, and the CY profile being weak instead. Comprehensive analysis shows that the palaeoclimatic environment in Baiyin area of Gansu Province during a certain period of Late Devonian was mainly arid.
Key words:The Late Devonian/
Paleosols/
Paleoclimate/
Geochemistry/
Magnetism/
Eastem section of Qilian Mountain
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