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地球表面每时每刻都在经历各式各样的侵蚀作用,了解侵蚀过程及其速率大小有助于人们认识许多重要的地质作用和过程。本文介绍的内容是长江流域河流沉积物宇宙成因核素~(10)Be的研究工作,目的是在于定量估算长江流域及其子流域的平均侵蚀速率,更好地理解沉积物的由源到汇过程以及评价人类活动对水土流失的影响提供自然背景,分析样品来自于长江主要干流和支流的表层现代沉积。研究表明,长江干流~(10)Be含量从金沙江流域到长江口呈现出由高到低的趋势,不同的是支流~(10)Be含量值偏低而且比较稳定。这很可能受核素产生率和侵蚀速率两个因素的共同影响。在长江上游干流沉积物中~(10)Be含量最高,随着低含量物质的不断从支流汇入,产生“西高东低”的现象。~(10)Be侵蚀速率估算表明长江干流金沙江上游段平均侵蚀速率较低,在44.7~48.1m/Ma之间;长江中游段(枝江至彭泽)长江干流侵蚀速率数据变化较大,在65.7~175m/Ma的范围内波动;到长江口平均侵蚀速率比较稳定,在50~60m/Ma之间变化。与干流相比,长江支流侵蚀速率显著偏高。侵蚀速率最高的地区在大渡河-岷江流域,平均侵蚀速率在300m/Ma之上;侵蚀速率最低的区域发生在乌江流域,平均的侵蚀速率在10~30m/Ma之间。比较长江流域~(10)Be和水文估算的侵蚀速率可以看出,水文估算总体上反映的侵蚀速率要普遍高于~(10)Be反映的侵蚀速率。大渡河-岷江流域地表侵蚀速率高主要与构造活动、地貌发育、岩石特征以及气候条件等自然因素有关。嘉陵江、汉江等流域水文数据估算侵蚀速率明显超过~(10)Be估算的结果,可能与地形地貌等地质因素对侵蚀作用的影响显著下降,以及人类长期活动导致水土流失加剧有关。
The surface of the earth is experiencing various kinds of erosion all the time, and understanding the erosion process and its rate helps to understand many important geological processes and processes. The content of this paper is the study of cosmic genetic nuclide ~ (10) Be in river sediments in the Yangtze River Basin. The purpose of this paper is to quantitatively estimate the average erosion rate of the Yangtze River and its sub-basins and to better understand the sediment source- Process and to assess the impact of human activities on soil erosion, providing a natural context for the analysis of samples from the modern depositional surface sediments of the main streams and tributaries of the Yangtze River. The results show that the content of ~ (10) Be in the mainstream of the Yangtze River tended to change from high to low from the Jinsha River to the mouth of the Yangtze River. The difference was that the ~ (10) Be content in the tributaries was low and stable. This is likely to be influenced by both nuclide production rate and erosion rate. The content of ~ (10) Be in the sediments of the upper reaches of the Yangtze River reaches the highest, with the continuous introduction of low-level substances from the tributaries, resulting in the phenomenon of “West-East-East-Low”. ~ (10) Be erosion rate shows that the average erosion rate of the upper reaches of the Jinsha River in the Yangtze River is relatively low, ranging from 44.7 to 48.1m / Ma; the erosion rate of the main stream in the middle reaches of the Yangtze River (Zhijiang to Pengze) Fluctuating in the range of 65.7-175 m / Ma. The average erosion rate to the Yangtze Estuary was relatively stable and varied from 50 to 60 m / Ma. Compared with the mainstream, the erosion rate of the tributaries of the Yangtze River is significantly higher. In Daduhe-Minjiang River basin, the highest erosion rate is above 300m / Ma. The lowest erosion rate occurs in Wujiang River basin with an average erosion rate of 10-30m / Ma. Comparing the estimated erosion rates of ~ (10) Be and hydrology in the Yangtze River Basin, we can see that the hydrological estimation generally reflects the erosion rate generally higher than the erosion rate reflected by ~ (10) Be. Dadu River - The high rate of surface erosion in the Minjiang River Basin is mainly related to the natural factors such as tectonic activity, geomorphology, rock characteristics and climatic conditions. The estimated erosion rates of hydrological data of Jialing River and Hanjiang River obviously exceed the results of ~ (10) Be estimation, which may be related to the significant influence of geological factors such as topography and geomorphology on erosion and the long-term human activities leading to the aggravation of soil erosion.