摘要
通过野外调查和实验分析,在西安蓝田安村黄土剖面S_4古土壤剖面中发现了具有指示当时土壤水分含量、地下水富集和水分循环的铁锰结核、针铁矿[α-FeO(OH)],在西安地区确定了风化淋滤黄土层和显著迁出了土壤黏化层的CaCO_3结核淀积层。针铁矿呈褐黄色薄膜分布于土体表面,含量可达3.3%。铁锰结核呈黑褐色球形,电镜下多呈结晶粒状,铁锰成分含量很高。针铁矿和铁锰结核富集层厚0.6m,形成于紧靠地下水的位置。通过研究提出了铁锰结核和风化淋滤黄土层及CaCO_3结核淀积层可作为恢复土壤古水分含量的重要指标。针铁矿、铁锰结核和风化淋滤黄土层的形成以及CaCO_3结核与红色铁质胶膜的迁移深度指示,在S_4古土壤发育时期,西安地区为亚热带气候,当时年平均气温为15~16℃,年平均降水量在900~1000mm之间。那时秦岭失去了亚热带与温带气候分界线的作用。在S_4古土壤发育时期,西安地区土壤重力水分布深度达到了3.3m,当时土壤水在经过蒸发与蒸腾消耗之后,3.3m深度范围内剩余的土壤平均含水量一般为25%左右,在针铁矿和与铁锰结核发育层位含水量接近饱和(50%左右)。当时土壤水分非常充足,水分循环正常,水分平衡为正,有较多水分补给地下水,适于茂盛森林植被发育。本文所确定的古含水量指标为国内外第四纪土壤含水量、水分存在形式与水循环研究提供了标准和方法。
Based on the field investigation and experimental analysis, it was found that iron-manganese concretions, goethite [a-FeO （OH）], which could indicate the soil moisture content, groundwater enrichment and water cycle in the profile of S4 paleosol in An village of Lantian in Xi＇an. It was also determined the weathered and leached loess layer and CaCO3 illuvial layer that significantly migrated out of the argillic layer in Xi＇an area. Goethite was distributed on the earth surface as yellow-brown filas and its content can be up to 3.3~. Iron-manganese concretions was brown-black spherical and crystal granular in the electron microscopy, and the content of iron and manganese was very high. The goethite and iron- manganese concretion layer was about 0.6 m, and formed in the position of the underground water level. According to the research, we could propose that the iron-manganese concretions, the weathered and leached loess layer and CaCO3 illuvial layer can be used as an important index of restoring paleo-moisture content. Goethite, iron-manganese concretions, the formation of weathered and leached loess layer, the migration depth of CaCO3 concretions and red ferrunious films shows that the climate in Xi＇ an is subtropical, of which the mean annual temperature was 15 - 16℃ and the mean annual rainfall was between 900~1000mm during the development period of S4 paleosol. At that time Qinling Mountains lost the function of the boundary between subtropics and temperate zone. In the development period of S4 paleosol, the depth of gravity water in soil in Xi＇an area was 3.3 m, then after the soil water evaporation and transpiration consumption, the rest of the soil water content in 3.3 m depth was about 25%, and it closed to the saturated moisture content （50%） in goethite and iron-manganese concretions development layer. Soil moisture was very sufficient, and normal water cycle and positive water balance occurred, there were more water to recharge the groundwater of groundwater, as it was suitable for the development of lush forest vegetation at that time. The study in this paper has broaden the Quaternary new content and indexes proposed by us can be as standards and methods in studying soil water content, soil water form and water cycle at home and abroad.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2017年第3期678-689,共12页
Acta Geologica Sinica
基金
陕西省自然科学基础研究计划项目(2015JM4153)
中国地质调查局西安地质调查中心项目(水[2016]4)
中国科学院黄土与第四纪地质国家重点实验室项目(SKLLQG1626)资助的成果
关键词
S4古土壤
铁锰结核与针铁矿
古水循环
含水量指标
水分平衡
西安地区
the S4 paleosol
iron-manganese concretions and goethite
paleowater cycle
water balance
water content index
water balance
Xi＇an area
