Variations of the CaCO3 and total organic carbon contents in the Minhe loess and their limitations as climatic proxies

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 CaCO3 and total organic carbon (TOC) contents in the 187-0.70 Ma interval of the Minhe loess shows that the content of CaCO3 in the Minhe loess ranges from 5.89 to 18.63%, averaging 11.41% and that the content of TOC is lower, ranging from 0.007% to 0.452% with an average of 0.88%. The CaCO3 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 CaCO3 and TOC contents in the Minhe loess indicate that the climate in the area had a trend of becoming cold and dry since 1.87 Ma BP. The variations of CaCO3 and TOC in loess as substitute proxies of climatic changes have certain limitations due to influences of complex sources and types of CaCO3, 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 CaCO3 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.