我们在河北阳原虎头梁的冻融褶皱砾石层顶部发现一层钙膜砾石.通过对钙膜明暗度曲线分析及其与氧同位素曲线的对比研究,结合~(14)C测年结果,得出虎头梁钙膜的发育时间介于40~21ka BP之间.砾石钙膜的发育代表着曾经地下水位停留在此,说明在泥河湾古湖消亡后,桑干河下切初始阶段有过一段较长时间的停顿.根据河流阶地的高差及年龄数据,计算桑干河虎头梁段在21~7.6ka BP、7.6~3.1ka BP和3.1~0ka BP 3个阶段的河流下切速率分别为1.8、4.2、2.9mm·a~(-1).这种下切速率的差异应主要是由气候变化造成的.
英文摘要:
Caliche lamination contains abundant paleo-climate and age information,shades of caliche microlamination record climate change.A layer of caliche gravel was found in the upper freeze thaw folds gravel layer at Hutouliang,Hebei province.The caliche was dated from 40-21ka BP by comparison of characteristic curve of caliche lamination and characteristic curves of deep-sea oxygen isotope,and by 14C dating.The development of gravel caliche expressed that groundwater level had stay at here at one time,and this indicated downcutting of Sanggan river had a longer pause in the initial stage after the ancient lakes extinction.It was calculated that the downcutting rate were 1.8,4.2and 2.9mm·a~(-1)in 21~76ka BP,7.6~3.1ka BP and 3.1~0ka BP stages according to elevation differences and age data of river terraces.The difference in downcutting rate should be mainly caused by climate change.