黄河中游晚第三纪与第四纪古气候关系初探

通过对黄河中游红粘土所记录的古气候特征的研究,表明诸如古季风等第四纪古气候的许多重要特征在新第三纪晚期已见雏形,形成了上第三系红粘土和第四系黄土在粒度分布,对气候变化敏感的地球化学元素的波动形式及淋溶层一淀积层的多次叠置等方面的相似性。这些特征是古气候发展中共性的表现。从新第三纪末期,动物群组成开始明显变化,向着分异度降低和优势现象明显的方向发展,是古环境趋于极性的表现。

Preliminary Comparison of Paleoclimatic Characteristics in Quaternary and Late Neogene

The occurrence of the aeolian sediments, which reflect the forming of paleomosoon, is one of the important events during the geological history. Neogene red beds and Quaternary loess in the middle reaches of the Yellow River have close inherent connection in many aspects, therefore, the paleoclimatic evolution between them is a worthwhile research field. The remarkable climatic feature during the loess forming was the alternate developing between wet-hot summer monsoon and dry-cold winter monsoon, it caused the alternate appearances of loess and paleosol in the profile. This cyclic change of paleoclimate had already occurred in varying extent in Late Neogene. Red beds have the fellowing features: distributed on the slop, no hydrobios fossil, no bedding, homogeneous compositions and no relationship with the bedrock. These features not only occur in the same profile but also in different localities. In the Loess Plateau, red beds show the similar characters in chemical composition, grand size, clay mineral assemblage and the interbeds of the claying horizon and calcic horizon, these phenomenon at great extent may be related to the transported way. In addition, paleomagnetic data from some profiles indicate a comformable contact between Neogene and Quaternary. For the similarity between loess and red beds mentioned above, the view of Late Neogene earth sediments formed by dust is tally with the sedimental backgroud then. So it is reasonable to regard the Neogene red beds as the aeolian sediments. This conclusion shows that paleomonsoon is not the characteristic of Quaternary paleoclimate, it has arisen from Late Neogene.