河北柳江盆地柳江村上石盒子组露头研究

Outcrops investigation in the Upper Shihezi Formation in the Liujiang Village, Liujiang Basin, Hebei

关键词:  侧积体  侧积层  废弃河道  高弯度曲流河  宽深比

Key words:  lateral accretionary body  lateral accretionary layer  abandoned channel  high-sinuosity meandering stream  width/depth ratio

摘要:

目前资料对柳江盆地上石盒子组沉积特征的描述比较简略,针对这种情况,本团队详细考察了柳江村小北山露头,以期揭示上石盒子组更多的沉积特征。通过对3条剖面进行分层,并详细描述岩层的岩性特征和沉积构造,认为该露头发育有侧积体和典型的牛轭湖,为曲流河沉积体系。根据河相经验公式算出其弯曲度大于1.7,为高弯度曲流河。在演化过程中,曲流河的规模逐渐变小,同时经历了频繁改道和迁移。此项研究对于实习教学和河流构型研究均有参考价值。

Abstract:

With the emphasis on three cross sections I, Ⅱ and Ⅲ, a detailed investigation has been made for the Upper Shihezi Formation outcrops in the Liujiang Village, Liujiang Basin, Hebei, aiming at the better understanding of sedimentary characteristics of the Upper Shihezi Formation. The typical lateral accretionary bodies and an oxbow lake are recognized in the investigated outcrops, suggesting the development of the meandering stream system in the outcrops area. Moreover, the sinuosity indexes of more than 1.7 based on the fluvial empirical formulas also show that the outcrops area herein may be inferred to be the channels of the high-sinuosity meandering stream system. The steadily variations in size and flow direction may reflect that the high-sinuosity meandering stream has gone through the complicated evolution of the frequent channel diversion and migration during the long geological history. The findings in this investigation may provide helpful reference to the study of meandering stream architectures and mapping of the sedimentary facies and palaeogeographic maps of North China.