近代河流沉积与地震地层学解释

Recent river sediments and seismic stratigraphic interpretation

对近代沉积的研究工作帮助了地震地层学解释人员在地震剖面上理解和追索地下地层的岩性、岩相变化。但是，特别是对于陆相地层，解释人员往往忽略了河流沉积的历史性侧向侵蚀作用、搬运作用及再沉积作用。本文作者以黄河及长江的沉积历史变迁作为两个典型实例，说明了下列事实：在一条辫状河或曲流河流域中的河道、天然堤、心滩、曲流沙坝、牛轭湖及泛滥平原等等，它们的平面位置在地史中每几百年就会显著地改变。然而盆地的沉积速率却很慢，每一千年只能沉积0．03m至2．0m。每条河流都只能用频繁的决口及改道来铺平整个盆地。这就造成了河流沉积不断受到改造，最后在地下变成一个复杂的岩性混合体。因此，一个好的解释人员应当注意思考一个问题，即河流相地层中，要追踪单独的一个河道或者一个曲流砂坝简直是太难了。一条古河道只有在很稀罕的情况下，即它的最后一幕被后来沉积物快速掩埋，才能保留下来。在某种情况下，湖泊相沉积也会由于湖泊的变迁而造成相类似的问题。

Geophysicists working on seismic stratigraphy make research on recent sediments to investigate the lithology and lithofacies variations in subsurface, usually ignoring the historical effects from lateral erosion,transportation and resedimentation especially for land facies strata.Based on the historical sediment's evolution of Yellow and Yangtse Rivers, the author is intended to make certain of the fact as: The planar locations of river courses,natural dikes,channel bars,meander bars,oxbow lakes,nood plains and so on in the drainage area of a braided or meander river were seen to significantly alter every hundreds of years in geological history, while the basin's sedimentation velocity is so slow,say, 0. 03- 2. 0 m every thousand of years.Each river strives to flatten the whole basin by frequently breaching dikes or changing its course, which lead the rivcr's scdimentation to be constantly reformed and finally to become a complex lithological hybrid. It's known to an experienced geophysicist that it is very difficult to trace a single river course of a meander bar in river facies strata. In fact a paleo current can retain only for thc Iast scene in its cvolution on condition that the scene is rapidly buried by the subsequent sediments. Similarly,the same case may happen to lacustrine facies sediments due to lake's evolution under specific circumstances.