[技术讨论]冲积扇的问题 [复制链接]

看到有人讨论三角洲和扇三角洲的区别，想请教下个问题------冲积扇的问题：
有人分泥石流冲积扇、辫状河冲积扇
还有国外有人在这两种类型上加了个“低弯度曲流河冲积扇”这一类型，这类型就不说了
泥石流冲积扇还比较好理解，辫状河冲积扇是怎么形成的？以及辫状河冲积扇沉积特征如何 ，是不是就是以河道沉积和漫流沉积为主，粒度如何？沉积构造有哪些？
辫状河冲积扇的扇根有没有砾岩、砂砾岩一类的泥石流沉积物，而且扇中沉积物粒度是不是就比较细了，毕竟是辫状河道沉积啊，那就以正序沉积为主了？
下图的这个干旱型和润湿型是不是就可以说是泥石流型和辫状河型了？

辫状河冲积扇一般是只季节性河流流出山口形成的冲积扇，一般来说分选相对比洪水形成的泥石流冲积扇好；并且两种类型的冲积扇扇根部位都会有砾石沉积；从平面展布上看由于辫状河冲积扇是稳定的水流形成的，所以展布面积大，而泥石流冲积扇应该算是一种事件性沉积，所以分布面积相对小；
再从流体机制上看，泥石流冲积扇的形成与重力流有关，所以偶尔会观察到一些反序结构，而辫状河冲积扇以牵引流为主，所以说应该是一种正常的正粒序。
希望大家批评指正！~~~~

好像我没有在文献里看到过辫状河冲积扇这样一个名词，国外的文献里，有alluvial fan专指冲积扇，意指一种河流出山口沉积，而有fan delta意指比邻物源高地的入水沉积，叫做“扇三角洲”，还有braided delta“辫状河三角洲”主要为辫状河体系入海或入湖的沉积，两者在空间上一般相距很远，这是近年来大家有所公认的。  推荐薛良清、Galloway的《扇三角洲、辫状河三角洲与三角洲体系的分类》

陆上环境：冲积扇－辫状河－洪水沉积体系

对2楼回答：
在 The okavango fan and the classification of subaerial fan systems一文中的“braided fluvial fan”能翻译成辫状河冲积扇么？
作者为I.G.Stanistreet，T.S.McCarthy.  Sedimentary Geology,1993,85(1)

冲积扇应该是相对近源的陆上沉积，扇三角洲可以分陆上和水下两部分

我们说冲积扇一般说是路上的，没有进湖或海，而冲积扇直接进湖，我们就说是扇三角洲；至于说辫状河冲积扇好象一般没这么说的，因为冲积扇本身就是近源的，从山口出来到开阔地带形成的饿。

Controversy exists over the classification of fluvially formed subaerial fans. Authors either restrict alluvial fans to debris flow dominated types or extend the spectrum to fans dominated by braided rivers. The Okavango Fan provides an end member which extends this spectrum to fans dominated by meandering and low sinuosity rivers. The fan is a large (150 km radial axis) shallowly sloping (0.00036), highly vegetated subaerial fan, which can be subdivided into four subenvironments. These are: (1) the entry corridor or Panhandle characterized by single and anastomosing meander belts; (2) the upper fan characterized by meander belts diverging from the fan apex, comprising peat-confined meandering channels, with interchannel swamps forming thick peats; (3) the middle fan with highly confined single and anastomosing low sinuosity rivers and less common prograding meander belts whose channels are confined by thick peats with, however, little chance of peat preservation; and (4) the lower fan in which annual floods from relatively unconfined channels spread over the fan surface and interact with pre-existing aeolian and lacustrine deposits. With the recognition of this new fan type, the spectrum of subaerial fan types can be expressed in terms of: (1) debris flow dominated fans of which the Death Valley fans are a member; (2) braided river dominated fans of which the Kosi Fan is a member; and (3) low sinuosity/meandering (losimean) river dominated fans of which the Okavango Fan is a member. This spectrum can be expressed in terms of variation in slope, maximum size and percentage of surface vegetation, but crucial to the evolution of the various fan types is variation in the flashy to continuous nature of the discharge and the degree of channel confinement evident on the fan surface. Comparable ancient examples of the three fan types are recognizable, many of which provide intermediates between the ideal end members. Debris flow dominated and braid dominated fan types are known from throughout earth history. However, the losimean fan type, because of its reliance on confining vegetation, may only have developed after the Devonian Period. The spectrum of subaerial fan types can be expressed on a triangular field of variation with the vertices defined by the relative importance of the processes which shaped a particular fan system be they debris flows, processes associated with braided rivers or processes associated with meandering and low sinuosity rivers.

在河流成因的陆上扇体分类上仍然存在争议。学者们有将之限定为碎屑流主控冲积扇类型的，也有将之延伸为辫状河成因扇体类型的。奥卡万戈扇提供了一种新端元类型，使河流成因的扇的概念得到扩展，这是一种为底弯度曲流河主控的扇。这种扇是一个范围极大（半径150公里）的缓斜坡（0.00036，这应该是坡度正切函数，译者注），植被极为丰富，可以分为四个亚环境。分别是：（1）入口走廊；以单独的曲流河道以及河道汇聚口沉积带为特征；（2）上扇；以曲流河河道沉积为主，和冲积扇的扇顶不同，它沉积了泥炭为主的曲流河倒沉积，在河道巨厚泥炭沉积间充斥着沼泽；（3）扇中；……
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你这个问题我好几天前就想回答了，可惜太忙，现在想做完这一段，一看，楼主已经看过了，那就没必要继续献丑。另外推荐一篇FLUVIAL FANS: MYTHS, MISCONCEPTIONS, AND THE END OF THE TERMINAL-FAN MODEL
COLIN P. NORTH AND GAIL L. WARWICK写的
另外，A.D.Mail有关于扇三角洲的专著Fan Deltas另外还有一本The geology of fluvial deposits coarse-grained deltas忘了是谁写的了，这些内容应该有所裨益的，总体来说，冲积扇可以认为是出山麓堆积，这个序列在平面上看起来，接着是辫状河三角洲（少数也有Chen称辫状河扇的），然后是低弯度扇，最后是扇三角洲，这是目前关于完整的扇的沉积大家一个总的序列吧，这是从它们所处的地理位置上一个大致的分类。具体的沉积特征，那就要查书了，我没有专门搞这个东西，没有总结哈，抱歉

辫状河三角洲的亚相怎么划分~~

辫状河三角洲的亚相和普通三角洲的亚相划分一样，也分为三角洲平原，三角洲前缘和前三角洲。
辫状河三角洲都是粗碎屑沉积，所以也叫粗碎屑三角洲。