摘要
通过对甘肃灵台风成黄土－古土壤－红粘土序列中钙质结核的野外分布及形态特征观察，并对主元素和微量元素进行化学分析，发现结核中氧化物活动组分和惰性组分含量的比值在剖面中自下而上逐渐变大，反映了结核形成时其上覆土层所经历的淋溶程度逐渐增强；而ＭｇＯ含量和用ＣａＣＯ_３含量校正后的ＭｇＯ／ＣａＯ比值则逐渐减小，指示结核形成时环境温度逐渐降低。灵台剖面自下而上不同层位结核中Ｓｒ／Ｂａ比值及ＣａＣＯ_３含量的变化同氧化物含量及比值变化具有类似的特征，暗示了黄土高原自晚第三纪到第四纪间冰期的气候总体有向冷湿方向演化的趋势。其中红粘土堆积中钙质结核Ｓｒ／Ｂａ比值的大幅变化，说明结核的形成既有强烈淋溶成因，又有地下水强烈蒸发作用的参与，暗示了在晚第三纪，黄土高原可能有以强降水和强蒸发为组合的湿热气候波动特征。
Main chemical components and trace elements analysis on the calcareous nodules in Lingtai eolian de- posits show that there is a general increasing tendency of the ratios of (CaO + MgO) / (SiO_2+ Al_2O_3) upwards, in dicating that leaching intensity of the overlying soil is increasing when the nodules forming. However, the MgO content and MgO/CaO ratio corrected by CaCO_3 content are decreasing upwards, which reflects the environment temperature is decreasing generally since the late Tertiary. Variations of the Sr/Ba ratio and CaCO_3 content prove that the forming of calcareous nodules in different periods is closely related to the climate conditions. The large scale variation of the Sr/Ba ratio of calcareous nodules in Lingtai red clay deposits, illustrates that both the leaching and evaporating processes have contribution to the forming of carbonate nodules, which indicates that the late Tertiary climate may be dominated by the combination of strong rainfall and evaporating characteristics. Contents of oxides and CaCO_3 and the ratios of movable to stable oxides and Sr/Ba in carbonate nodules show the similar variations upwards, which indicates that the climate on Chinese Loess Plateau is generally becoming more colder and wetter from late Tertiary to Quaternary interglacial periods.
出处
《地球化学》
CAS
CSCD
北大核心
2000年第3期277-282,共6页
Geochimica
基金
国家重点基础研究发展规划项目!(G1999043401)
中国科学院"九五"重大项目!(KZ-951-A1-402)
国家自然
关键词
风尘沉积
钙质结核
化学组分
甘肃
地球化学
eolian deposits
calcareous nodules
chemical components
Sr/Ba ratio
Gansu Province
