华北平原古河道发育的环境条件及其沉积特征

全新世以来,气候和新构造运动控制了华北平原古河道的发育,而许多重要河流由于流经黄土地区,搬运和沉积了大量粒径为0.01-0.25毫米的泥沙,因而加速了河道的变迁。此外,地貌、人类活动等因素也在不同程度上影响了古河道的发育。在华北平原环境条件的影响下,古河道在空间分布、地貌形态、地层结构、颗粒特征、物质成分乃至所含化石等方面,都呈现比较明显的沉积特征,这些特征可以作为识别全新世以来华北平原古河道的指标。

THE ENVIRONMENTAL CONDITIONS OF THE DEVELOPMENT OF PALEOGHANNELS IN THE HUA BEI (NORTH CHINA) PLAIN AND THEIR SEDIMENTAL CHARACTERISTICS

Since the Holocene,climatic changes and neotectonic movements have controlled the development of paleochannels on the Huabei Plain,Some major rivers flow over loess regions.The transport a great deal of load,and most of the particles are within the size range 0.01-0.25mm.It has brought changes to the channels at great speed.Besides,the reliefs and artificial action have influenced the development of paleochannels.Distribution of paleochannels on the Huabei Plain is characterized by radial pattern.They are separately distributed in two types of landforms:strip highland and trough-shaped depression.The composition of materials contain two layers,the lower layer of deposits is thick sand body,and the upper layer of deposits consists primarily of thin loam and/or clay strata.The structures of paleochannel deposit show horizontal thin bedding and various cross-bedding in the order of up-and-down.The grain sizes of the composition of materials are smaller.The average psephicity is less than moderate.The sand body of the paleochannel presents long prism in geometry.The mineral assemblages of paleochannels in Hua Bei Plain are different and complex.The paleochannels in Huabei Plain are rich in ground water,which commonly contain less salt,but fossils are less.The electric character-istics of paleochannels show reaction of high resistance.