黄河、永定河发育历史与流域新生代古湖演变间的相互关系

THE RELATIONSHIP BETWEEN DEVELOPMENTS OF THE YELLOW RIVER AND THE YONGDIN RIVER, AND THE EVOLUTION OF FOSSIL LAKE OF DRAINAGE BASIN IN THE CENOZOIC ERA.

据两河谷地两侧都有山麓侵蚀面存在,且侵蚀面上局部残存上新世古冲积物质,推断两河带形成时代不晚于上新世中早期。上新世末,随着流域出现内陆断陷湖盆,两河均由外流河变为内流河,即由外流期转为内流期。据最近在三门峡发现的哺乳动物化石,和泥河湾地区地层与年代学资料,内流期延续到早更新世末,或中更新世中期。此后,两河重新转入外流期,延续至今仍保持外流状态。

According to the existance of mountain erosional surfaces on each side of the two river valleys and also the remaining paleo-alluvial deposit of Pli- ocene epoch on some parts of erosional surfaces, it is inferred that the for- mation of the two rivers didn't occur after the early and middle period of Pliocene epoch.At the end of Pliocene epoch,the two rivers all changed from the exterion to interion ones because the interion lake basin took place, showing that the exterion epoch was replaced by the interion epoch. The mammals fossil discovered recently in San menxia and the bate of stratigra- phy and chronology indicate that the interion epoch continued until the end of early Pleiseocene or the middle of Middle Pleiseocene and then the two rivers shifted to the exterion epoch again, keeping exterion till today.