The palynological assemblage of the Longjiang Formation in Zhalantun area, Inner Mongolia, and its geological implications

Located in the southeastern Chenjisihan Town of Zhalantun area, the Longjiang Formation in the ChenjisihanYizhan contains abundant palynological fossils but rare macrofossils. The lithological assemblages of the lower Longjiang Formation are composed mainly of sedimentary tuff, tuff, sandstone and conglomerate, while those of the upper Longjiang Formation comprise predominantly andesite and dacite. By analyzing the palynological fossils from the Longjiang Formation in the ChengjisihanYizhan area, the Cyclogranisporites-Erlianpollis pollen assemblage zone was recognized. Several palynological fossils, such as Erlianpollis, Cicatricosisporites and Pilosisporites, indicate that the palynological fossils of the Longjiang Formation of Chengjisihan area formed in Early Cretaceous. In combination with geological characteristics and quantitative analysis of plant fossils and palynological fossils, vegetation species of the Longjiang Formation point to a subtropical climate and a warm and humid environment.