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An experimental examination of the theory of shoreline autoretreat

海岸线自动后退理论的实验检验

基本信息

批准号：
10640442
负责人：
MUTO Tetsuji
金额：
$ 2.62万
依托单位：
Nagasaki University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 1999
项目状态：
已结题

项目摘要

The theory of shoreline autoretreat predicts that even if the rate of change of relative sea level [A] is constant (>0) and if any other basin dynamic conditions including the rate of sediment supply [S] (>0) and remain constant, the shoreline inevitably begins to retreat landward at a relatively early stage of delta growth and finally reaches the break point where the clear angular configuration of the delta front is lost suddenly. This autoretreat theory was examined with flume experiments in which a miniature of delta is built under a controlled steady state (A=const>0, S=const>0). The experimental results and related notions are summarized as below.l. The autoretreat of shoreline has been substantiated. Just as predicted from the theory, the deltas experienced the landward turnaround of a shoreline and subsequently the occurrence of a geometrical break event, without any change of basin conditions.2. A semiquantitative method to detect temporal changes in ancient basin dynamic conditions has been found from the discussion based on the theory of shoreline autoretreat. The applicability of this method was illustrated with the Paleogene regressive succession in the Central Tertiary Trough, west Spitsbergen.3. A series of the three-dimensional experiments has given negative evaluation to the conventional notion that any significant change in the entire sediment-stacking pattern of a sedimentary system is principally due to a significant temporal change of an external or allocyclic factor rather than to inbuilt or autocyclic mechanisms within the depositional system itself. In the transgressive phase, the delta plain retreats in a step-like manner, and the abandoned deltaplains, being submerged with water-level rise, are preserved as multiple stepped terraces. This particular behavior of a delta is related to the autoretreat effect combined with the autocyclic lateral-shifting processes of sediment-feeding streams.

海岸线自退理论预测，即使相对海平面变动率[A]恒定（>0），如果包括供沙率[S]（>0）在内的任何其他盆地动力条件保持不变，在三角洲生长的相对早期阶段，海岸线不可避免地开始向陆地退缩，并最终达到断裂点，三角洲前缘的清晰角度构型突然丧失。这种自退理论通过水槽实验进行了检验，在水槽实验中，在受控的稳定状态（a =const>， S=const>）下建立了一个微型三角洲。实验结果及相关概念总结如下：海岸线的自退已得到证实。正如理论所预测的那样，三角洲经历了海岸线向陆地的翻转，随后发生了几何断裂事件，而盆地条件没有任何变化。在岸线自退理论的基础上，提出了一种探测古盆地动力条件时间变化的半定量方法。以斯匹次卑尔根西部中部第三系海槽古近系退退演替为例，说明了该方法的适用性。一系列三维实验否定了传统观念，即沉积体系的整个沉积堆积格局的任何重大变化主要是由于外部或异旋回因素的重大时间变化，而不是沉积体系本身的内置或自旋回机制。在海侵期，三角洲平原呈阶梯状后退，被遗弃的三角洲平原因水位上升而被淹没，形成多级阶梯阶地。三角洲的这种特殊行为与自退效应和输沙河流的自旋回侧向移动过程有关。