摘要
以青藏高原东北缘的拉脊山南坡一黄土剖面(P-22)为研究对象,分析了古土壤层和现代土壤层的发育特征,讨论了其环境指示意义以及作为土壤母质的黄土的可能来源。初步结果显示:(1)与黄土高原、青海湖周边以及附近盆地的黄土相比,拉脊山南坡的黄土具有粘粒含量偏高、CaCO3含量偏低的特点。(2)P-22剖面古土壤层的母质为粘黄土,现代土壤层的母质为黄土,说明拉脊山(南坡)在古壤层形成时期位于黄土堆积消减带上,而现代土壤层形成时期位于黄土堆积带上。(3)P-22剖面的粘土矿物组合为伊利石+高岭石+蛭石,不同于黄土高原黄土的伊利石+蒙脱石+高岭石组合,说明形成拉脊山(南坡)黄土的气候条件比黄土高原更加冷干。(4)综合分析风化淋溶指数(ba值)、Rb/Sr比、CaCO3含量、伊利石/高岭石比值和伊利石结晶度等环境指标,结果表明P-22剖面从下至上(由老到新)化学风化强度呈现逐渐增强的趋势,即拉脊山地区的气候条件有逐渐向温暖和湿润方向演化的倾向。(5)土壤发育指数(SI)显示,尽管拉脊山地区的气候特点以冷干为主,但在黄土母质基础上仍然可以发育土壤。研究结果将有助于了解高原地区不同气候背景下土壤的发生过程及其形成速率,促进该地区的农业的可持续发展。
The northeastern margin of the Tibetan Plateau(TP) holds an important location where the Westerly,the East Asian and Indian Monsoon current join,thus it is sensitive to regional and global climates.As a major carbon reservoir,the organic matter of soil in the Tibetan Plateau is of great significance to global carbon fixation with ca.23.44% of China carbon storage and ca.2.4% of global.This paper presents a multi-proxy study of a loess-paleosol profile,located on the south slope of the Laji Mountain,northeastern margin of the Tibetan Plateau.Soil development indices of both modern soil and paleosol layers of the profile were obtained through physical and geochemical analyses(e.g.grain-size,organic matter,carbonate contents,element concentrations and clay minerals),in order to distinguish their origin of parent material of loess in the study area and to discuss their environmental implications.The results indicate(1) that the loess on the south slope of the Laji Mountain is characterized by relatively high clays,low silt and CaCO3 contents with relative to its counterparts in the loess profile and adjacent basins around Lake Qinghai and(2) that clayish loess is its parent material of the paleosol layer.In contrary,loess as the partent material for modern soil layer is much coarser.These differences reflect the divergences in origins of parent material of soil layers,namely the paleosol has been developed by loess deposited on subduction zone,while loess for modern soil was deposited on accumulation zone.(3) The clay mineral assemblage of the studied profile is basically kaolinite + illite + vermiculite,which is different from the illite + montmorillonite + kaolinite pattern on the Loess Plateau,implying a cooler and drier climate condition.(4) The chemical weathering intensity as presented by ba value,Rb/Sr ratios,CaCO3 contents,illite/kaolinite ratio and crystallinity index of illite shows an increasing tendency upwardly,indicating a gradual transition from cold-dry to relatively warm-humid climate dominance at the Laji Mountain area.(5) For both the palesol and the modern soil layers,the soil development index(SI) also exhibits an increasing tendency upwardly,indicating that although the cold-dry climate prevailed at the Laji Mountain area,relatively stronger pedogenesis still occurred on the loess.The physical and geochemical indices of the studied soil profile on the south slope of the Laji Mountain,northeastern margin of the TP would helpful for better understanding the mechanism of soil formation and the accumulation rate under different climatic conditions,and also helpful for the sustainable development of agriculture in the study area.
出处
《干旱区地理》
CSCD
北大核心
2011年第5期733-738,共6页
Arid Land Geography
基金
国家科技支撑计划项目(编号:2007BAC30B05)
