共和盆地黄河阶地砾石组构特征与环境意义

Analysis on Gravel Fabric Characteristics of the Yellow River's Terraces in Gonghe Basin and the Environmental Signification

对共和盆地12级阶地砾石层组构进行数理统计,计算各砾石层砾度、砾态、砾向等参数,分析砾石组构特征并探讨其环境意义。结果表明:(1)各阶地砾石成分复杂,以砂岩和石英岩为主;(2)砾石形态以扁球体为主,磨圆度中等,风化程度较低;(3)砾石层形成时流水作用强弱为T8>T7>T5>T4>T10>T2>T9>T1>T3>T6>T11>T12,其中T1、T3、T4、T7、T8和T11为稳定河流成因,T2、T5、T6、T9、T10和T12为流水冲积成因;(4)各砾石层主要来向和古水流流向与野外观察一致,T1、T2、T5、T6和T10砾石来向与古水流流向复杂,而T3、T4、T7、T8、T9、T11和T12砾石来向与古水流流向简单。研究结果反映的环境意义虽简单,但可与阶地年代数据相结合进一步揭示各阶地形成时的气候环境特征与地面抬升状况。

Based on the mathematical statistics of gravel fabric characteristics of the 12 terraces along Yellow River in the Gonghe Basin,the particle size,shape and orientation of each gravel layer were calculated,and the characteristics of gravel fabrics were analyzed to explore the environmental significance. The studies showed the following aspects:( 1) the components of gravels were complex,mainly including sandstone and quartzite;( 2) the flat sphere was the main shape of gravels,and the roundness of gravel layers was medium and the degree of weathering was low;( 3) the intensities of the flowing water were listed in descending order as T8 > T7 > T5 >T4 > T10 > T2 > T9 > T1 > T3 > T6 > T11 > T12 when the gravel layers were formed,and the gravel layers of T1,T3,T4,T7,T8 and T11 were caused by the stable river,and T2,T5,T6,T9,T10 and T12 were formed in alluvial water environments;( 4) the direction of each gravel layer was consistent with that of field observation,and the directions of gravel sources and ancient water flows in T1,T2,T5,T6 and T10 were complex,while those of T3,T4,T7,T8,T9,T11 and T12 were simple. The environmental significance of this study is relatively simple,but it can be further used to reveal the characteristics of climatic environment and the condition of ground uplifted combined with chronological data of the terrace.