China: Materials for a loess landscape☆
China: Materials for a loess landscape☆
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DOI：
10.1016/j.catena.2013.11.016
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发表时间：
2014-06
期刊：
影响因子：
6.2
通讯作者：
I. Smalley;K. O’Hara-Dhand;J. Kwong
中科院分区：
文献类型：
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作者：
I. Smalley;K. O’Hara-Dhand;J. Kwong
由于种种原因，人们认为中国黄土的物质来源于北方的沙漠，“沙漠”起源的观点被广泛接受。但是，巴特勒，在澳大利亚于1956年，投怀疑的实际存在的沙漠黄土，这导致了相当大的讨论。这一论点的一个方面（由Smalley和Vita-Finzi于1968年提出）认为，没有沙漠特有的机制可以产生大量的黄土物质。由于沉积物的范围和厚度巨大，将这一想法应用于中国黄土特别合适。如此大量的黄土物质是如何产生的？Smalley和Krinsley（1978）提出了一系列可能导致中国黄土形成的事件。这就要求黄土必须是山地黄土（最终由Smalley和Derbyshire在1990年定义）--黄土是在西部山区形成的;黄河在将黄土带到黄土存款区方面发挥了作用;沙漠地区的黄土物质处于运输状态。1978年的模型已经被一系列巧妙而复杂的实验证明是正确的。特别是对锆石的分析产生了数据，使粒子源得以确定。锆石颗粒被证明是黄土景观的关键组成部分，但模式颗粒仍然是粉砂大小的石英颗粒。问题是为什么黄土材料具有如此有限的尺寸范围。黄土物质的形成受什么因素的控制？在石英颗粒中，似乎是两个事件的组合和相互作用产生了尺寸控制。高低石英转换引入拉应力;原始花岗岩中石英颗粒的共晶尺寸也限制了应力发展水平。所产生的应力水平导致颗粒尺寸积约为粗粉粒尺寸。
For various reasons it was thought that material for the great Chinese loess deposits originated in the deserts of the north—and the idea of a ‘desert’ origin was widely accepted. But Butler, in Australia in 1956, cast doubt on the actual existence of desert loess and this led to considerable discussion. One facet of the argument (advocated by Smalley and Vita-Finzi, 1968) proposed that there were no desert specific mechanisms which could produce the large amounts of loess material observed. Applying this idea to the Chinese loess was particularly appropriate because of the huge extent and thickness of the deposits. How was this vast amount of loess material produced?Smalley and Krinsley (1978) proposed a sequence of events that could lead to the formation of the Chinese loess. This required that the loess be a mountain loess (eventually defined by Smalley and Derbyshire, 1990)—the material was made in the mountains to the west; and the Yellow River had a role to play in bringing it to the loess deposit region; and that loess material in desert regions was in a state of transit.The 1978 model has been proved to be true by a whole sequence of ingenious and intricate experiments. In particular the analysis of zircons has produced data allowing particle sources to be identified. The zircon particle proves to be a key component of the loess landscape; but the mode particle remains the silt-sized quartz particle.The problem running in parallel with the ‘how did the material form?’ question is the puzzle of why loess material has such a restricted size range. What controls operate on the formation of loess material? In the quartz particles it appears that a combination and interaction of two events produce a size control. The high–low quartz transformation introduces tensile stresses; the eutectic sizing of the quartz particles in the original granite also constrains the level of stress development. The stress levels produced cause a particle size product of around coarse silt size.