虎头梁砾石钙膜的研究与意义

THE DISCOVERY OF GRAVEL CALICHE AT HUTOULIANG AND ITS SIGNIFICANCE

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40~21 ka 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21~7.6 ka BP、7.6~3.1 ka BP和3.1~0 ka BP 3个阶段的河流下切速率分别为1.8、4.2、2.9 mm·a^-1.这种下切速率的差异应主要是由气候变化造成的.

Caliche lamination contains abundant paleo-climate and age information,shades of caliche micro-lamination 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 40-21 ka BP by comparison of characteristic curve of caliche lamination and characteristic curves of deep-sea oxygen isotope,and by 14 C 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 lake’s extinction.It was calculated that the downcutting rate were 1.8,4.2 and 2.9 mm·a^-1 in 21~76 ka BP,7.6~3.1 ka BP and 3.1~0 ka BP stages according to elevation differences and age data of river terraces.The difference in downcutting rate should be mainly caused by climate change.