冀西北张北康保一带新生代红层的地质特征

Geological Characters of the Cenozoic Red Beds in Zhangbei-Kangbao Region, Northwestern Hebei Province

冀西北坝上高原的张北、康保等地发育着两套新生代红层,分别为上新世石匣组和中更新世赤城组。石匣组为一套深红、绛红色的粘土、砂砾层,岩性、岩相变化大,其中含有丰富的具铁锰质薄膜的钙质结核和黑色锰质斑点,并有丰富的三趾马动物群化石和孢粉。孢粉中喜暖喜湿分子约占 19 %,形成于炎热湿润气候条件下,与现代北亚热带气候条件相似。赤城组为一套冲洪积红黄色亚粘土夹棕红色粘土、砂组成,分布较为局限,含个体小、形状不规则的钙质结核,并有周口店动物群的化石分子和孢粉。孢粉中以中性喜温的松属占绝对优势,喜暖喜湿的分子约占7.6 %,形成于温和较湿润气候条件下。

Two different red beds are located in the Bashang Plateau, Zhangbei-Kangbao Region, Northwestern Hebei Province. They are named Pliocene Shixia Formation and Mid-Pleistocene Chicheng Formation respectively. Shixia Formation is composed of dark red, brown red clay and sandy gravels. The lithology and lithofacies changes frequently. It is rich in calcareous concretions with femic membrane on it and black manganous spots. And it also contents abundant Hipparion fauna fossils and sporopollen. The thermophilous and hygrophilous sporopollen is about 19% of all. It formed in torrid and wet climate, which resembles the climate of the northern subtropical zone in the modern time. Chicheng Formation is made of light red, red yellow alluvial-pluvial sub-clay,brown clay and sand. It distributes locally and contents calcareous concretions with small and abnormal shape. And it contents Zhoukoudian fauna fossils and sporopollen. The neutral thermophilous pine-genus sporopollen predominates over all, and hygrophilous sporopollen is about 7.6%. It formed in the mild and wet climate.