【摘要】 民和黄土地处黄土高原与青藏高原东北缘的交接部位,对气候反应较敏感。对该黄土1.87～0.70MaBP段进行了CaCO3和有机碳总量(TOC)的采样分析。民和黄土CaCO3含量在5.89%～18.63%之间变化,平均11.41%;有机碳含量较低,在0.007%~0.452%之间,平均0.088%。民和黄土中的CaCO3含量明显高于兰州、洛川和西安等地,而有机碳含量则远低于上述地区。黄土中CaCO3和有机碳含量变化反映了该区1.87MaBP以来气候变干冷的趋向。分别受复杂的CaCO3来源与类型、困难的采样、地区上的差异对比等和有机碳保存条件、沉积速率以及“埋藏效应”的影响,黄土中的CaCO3和有机碳的波动变化作为气候变化的替代性指标存在一定的局限性。文章最后指出,在实际应用中,黄土(特别是黄土高原西北部)中CaCO3和有机碳气候指标应结合其他环境指标共同使用,才能从中提取正确的古气候信息。更多还原

【Abstract】 Situated in the intersection area of the Loess Plateau and the northeastern margin of the Qinghai-Tibet Plateau,the Minhe loess is sensitive to the climate.Analysis of the CaCO 3 and total organic carbon(TOC)contents in the187-0.70Ma interval of the Minhe loess shows that the content of CaCO 3 in the Minhe loess ranges from5.89to18.63%,averaging11.41%and that the content of TOC is lower,ranging from0.007%to0.452%with an average of0.88%.The CaCO 3 content in the Minhe loess is notably higher than those in Lanzhou,Luochuan and Xi ’ an,but the TOC content is much lower than those in the aforesaid areas.The variations of the CaCO 3 and TOC contents in the Minhe loess indicate that the climate in the area had a trend of becoming cold and dry since1.87Ma BP.The variations of CaCO 3 and TOC in loess as substitute proxies of climatic changes have certain limitations due to influences of complex sources and types of CaCO 3 ,difficult sampling and differential comparisons among areas,as well as preservation conditions,sedimentation rates and"burial-effect"of TOC.At last,the paper points out that in actual applications the climatic proxies of CaCO 3 and TOC in loess,especially loess in the northwestern part of the Loess Plateau,must be used together with other climatic proxies,and then correct paleoclimatic information can be extracted.更多还原