岷江上游近两万年前发生了什么事件?

What happened on the upstream of Minjiang River in Sichuan Province 20 000 years ago

在对岷江1933年叠溪古镇地震滑坡调查研究中,对较场大滑坡上覆盖的较古老的土黄色厚土层进行详细研究,发现并确认这是一套静水环境下的河湖相沉积物,定名为叠溪古堰塞湖相沉积。这套湖相沉积物厚度最大可达200余m,根据14C测试,形成于约两万年以前。此后在叠溪下游以及岷江支流杂谷脑河中又发现了几个古堰塞湖沉积物,测年初步判定,也都形成于距今两万年左右。这一事实揭示两万年以前岷江上游曾发生过一次重大的变动,系列堰塞湖几乎在同一时期出现,形成了特殊的生态环境,消亡过程必然对其下游乃至川西平原环境的演化发生重要影响。堰塞湖沉积物中记载了地质环境和古气候环境变化的信息,是深入系统研究青藏高原前缘地质环境近期演化规律的极为可贵的资料。文中对这些古堰塞湖作了简要介绍,并就一些主要问题进行初步讨论。

A huge natural paleo-dammed lake deposit named ＂Diexi paleo-dammed lake＂ in Diexi ancient county was discovered in 1999. It is situated above the basin of the upper Minjiang River in Sichuan Province, China. The thickness of this lacustrine deposit is variable, reaching up to 200 m at some locations. Carbon-14 chronology has shown that this lacustrine deposit was formed about 20 000 years ago. Subsequently, other smaller paleo-dammed lake deposits have been discovered downstream of the Diexi area above the basin of Zagunao River （a tributary of Min）iang River）. According to our geological analysis and chronometry results, they were formed around the same period as the ＂Diexi paleo-dammed lake＂. Based on these discoveries, we believe that there were important geographical changes happening in the region around that time, which resulted in a series of barrier lakes, which must have brought environmental changes to this area. The outburst of these dammed lakes and their eventual dying out, could have played an important role in the subsequent change of the environment in the region of Minkiang River, as well as the western Sichuan basin. In addition, paleo-dammed lake lacustrine sediments left a significant and important record of change in the paleo-environment and paleoclimate of the area, which are also invaluable in studying the evolutionary process of the regional geo-environment at the eastern side of the Qinghai-Tibet altiplano. The discovery of these paleo-dammed lakes and related problems are introduced and discussed in this paper.