黄土高原古土壤成土过程的特异性及发生学意义

中国西北地区 ,从中新世以来就有持续不断的风尘沉积。这种风尘沉积作用即使在气候较为湿热的古土壤发育时期也未中断。黄土上土壤发生的独特性在于成土过程与风尘沉积的同步性。这种独特的成土过程使得土壤剖面深厚而均匀 ,常呈复合性状。古土壤与下伏黄土 ,不再是土壤与母质的关系 ;古土壤的真正母质应是成土过程中不断添加的风尘物质。古土壤中并不存在埋藏A层 ,对古土壤进行A、B、C等发生学层次的划分值得商榷。由于富含碳酸钙风尘物质的不断添入 ,成土作用强度受到不断削弱 ,绝大多数古土壤的成土作用强度未达到棕壤的发育强度。

PECULIARITIES IN SOIL-FORMING PROCESSES OF PALEOSOLS IN THE LOESS PLATEAU AND THEIR PEDOGENIC IMPLICATION

Ever since the Miocene time,aeolian dust has been falling down over Northwestern China,forming the Loess Plateau.The dust sedimentations have never been intermitted even in the soilforming periods when the climates were warmer and wetter.The peculiarity of the pedogenic processes of the loess lies in the synchronization of the soil forming processes and sedimentation of aeolian dust,thus making the profile thick and uniform,with complex properties.The parent materials of the paleosols are not the underlying loess,but the aeolian materials,which were accumulated constantly during the soilforming processes.There is not typical buried A horizon in the paleosols.It is not reasonable to classify paleosol profiles into A,B and C horizons.Owing to the continuous input of dust with plenty of carbonate,the pedogenic strength of the paleosols is steadily weakened,and thus has even not yet reached the level of the Brown Soil in most cases in Loess Plateau.