Study On The Basic Characteristics And Genetic Mechanism Of The Thick Overburben Layer In China Southwest

In recent years, China's hydropower resources in the process of developing and found that the modern riverbed following general accumulation on the decameter and even hundreds meters thick loose deposits. A large number of bed drilling information revealed that almost all the major rivers in the riverbed there are thick overburben layer. Thick overburben layer refers to the accumulation in the river, more than 30 m thickness of the Quaternary loose deposits. Valley thick overburben layer the existence of not only seriously affected and restricted the work of the dam site selection, the impact of the relevant basin hydropower resources development and utilization and planning, but also to the dam design such as dam-choice, anti-seepage measures brought great design difficulties.This paper in the collection of existing hydropower stations on the basis of survey data, the focus of the hydropower station on the river bed drilling and related information in the measured data collection, analysis of the basic characteristics and the development and distnbution rule of all the major rivers in western China's thick overburben layer, and analysis of its deep valley and the deep accumulation of reasons. Through the Minjiang River and Jinsha, Yalong and Dadu rivers focus on the deep alluvium in the valleys the basic characteristics and distribution of the research, that the deep alluvium in the valleys in western China, most of the river's cover can be divided into three tiers in the longitudinal direction: In the lower part for the late Pleistocene alluvial and glacial fluvial boulders and pebbles gravel layer; in the middle part for the late Pleistocene Ice-Water, Colluvium, Slope wash, natural damming lake accumulation and accretion mixed mainly with the increase accumulation layer; in the upper part for the Holocene normal fluvial facies sediment; At the same time in the distribution of development, thick overburben layer with the characteristics of regional distribution. Through the formation of the Qinghai-Tibet Plateau research, since the formation of the Qinghai-Tibet Plateau has been uplifting upward movement in the state, the southwestern region of crustal uplift of the impact of the Qinghai-Tibet Plateau, has been uplifting or intermittent uplift the state. Therefore, the crustal movements with the views of movement can not be fully explained the deep alluvium in the valleys of the regional issues. In this paper, under the guidance of instructors, due to global climate change, sea level caused substantial changes in the movements, the valley is deep-cover the root causes of regional distribution.According to collect the southwestern region of the hydropower station bored age of information revealed, in addition to local rivers, the above-mentioned several major rivers and river bed cover the bottom are formed in the now 20 ka before about the central cause of more than a cover for the age of 15～19 ka; upper part of the normal river sediments, now about 6～7 ka. This shows that the current river bed at the bottom of the 20 ka ago and began to take shape, both said at least 20 ka before the West Valley area strongly eroded the incident occurred. The Yumu-Ice Age (about 20,000 years ago) stage, the global sea level has dropped significantly. According to sequence stratigraphy point of view, the sharp decline in glacial sea-level, the river will greatly reduce the erosion of base-level, with the result that under the surface at the base level, making the river more than the drop, which could accommodate space disappeared, the driving force of the river Enhanced, thus triggered a strong erosion of the river valley cut back and eventually form deep ancient river valley. As the ice late (late Ice Age) sea level is rising gradually, the erosion of base-level uplift result, sea water from the river mouth started gradually retreat, rivers to reduce vertical slope, carrying capacity weakened, back to strengthen the role accumulation, large accumulation of sediments, to form the valley's deep cover.At the same time, in local rivers, tectonic origin, climate causes or collapse-slide accumulation causes play a strengthening or weakening role in the formation of the deep alluvium in the valleys.