The Origin Of Neogene's Red Clay In The Middle Reaches Of Yellow River

In the middle reaches of Yellow River of North China, there are sometimes Neogene's red clay deposits with variable thickness underlying the overlapping integrated sequence of Quaternary loess, which was nominated, also named as "red clay" by Liu Dongsheng, as "Hipparion red clay" by the excavation of the fossils of Hipparion. Based on evidences in respective aspect, different researchers stick to different hypothesis in terms of the genesis of red clay, which serves as basis of the reconstruction of paleo-environment. It is of great scientific importance to understand the characteristics, patterns and mechanism of the environmental evolvement in large scale of time through the appropriate interpretation of series of significant geological and environmental events since Tertiary. With which the paleo-environmental information was endowed, it is crucial to study the exact. formative process of red clay deposit before the discussing of paleo-environmental meanings of the red clay sequence.Through the systematic sampling of sedimentary sequences at some representative Neogene red clay sections located in the climate-sensitive areas of the middle reaches of Yellow River and the employment of modern analytical methods, this paper correlates the sedimentary characters of grain size and magnetic fabric properties of Neogene red clay, Quaternary loess-paleosol, hydraulic loess, riverbed mud deposits, river terrace sediments and country rock of the petrifactions preserved in the Neogene's red clay to decipher and then restore the accumulative process according to the evolution of the geomorphology of basement via the comprehensive analysis of micro-texture of the sediments under SEM, the properties of the fossils excavated from red clay in taphomony and the regional distributive pattern of red clay, the genetic model of red clay can be finally reached.The research indicated:â‘ The deposit of Neogene's red clay in the middle reaches of Yellow River is an evolutional product controlled by multi-factors such as geology, tectonics and climate. The regional distribution of red clay is strongly dominated by the undulation of basement and a sedimentary center located in the relative lower area of basement with thick red clay deposits of hydraulic properties exists.â‘¡Neogene red clay had a genetic model that the incipient material is carried by wind through air and after accumulation of the original material some segments of the deposit were re-cumulated by fluviation under control of geomorphology of the basement and climatic factors, so it was endowed with some characteristics of aquatic sediments.â‘¢The genesis of Neogene red clay can be bracketed into 4 types as gradual-slope-ravine-type, highland-type, mountain-foot-type, slope-bead-string-type genetic models.