摘要
揭示河流系统响应气候变化和地表抬升的机制是理解流域地貌演化以及水系发育过程的基础,其核心难题是如何充分认识它们在阶地发育中扮演的角色。以往的研究倾向于分开讨论气候变化和地表抬升在河流阶地发育中的作用,认为河流堆积/侧蚀和下切行为分别与冰期和间冰期气候对应,或者将阶地作为地表抬升的直接证据。首先,从上下游河段对比的视角初步解释了黄河中游响应气候变化和地表相对汾渭盆地抬升发育阶地的过程。1.2 Ma以来黄河下蚀鄂尔多斯地块和峨眉台地分别形成了7级阶梯状阶地和6级堆积阶地序列。黄土地层分析结合年代学研究揭示这些阶地面都直接上覆一层古土壤,指示它们形成于气候由冰期向间冰期的过渡阶段,即使在沉降的盆地依然如此。然而,黄河中游并没有在1.2 Ma以来的每一次冰期向间冰期转换都发育阶地,说明气候虽能通过控制河流堆积-侧蚀与下切行为的转换决定阶地的形成时代,但其本身并不是阶地形成的唯一控制因素。在峨眉台地沉降的背景下,黄河无法形成正常的阶梯状阶地序列,取而代之的是堆叠的阶地序列(阶地越年轻拔河高度越大);而当鄂尔多斯地块相对汾渭盆地抬升缓慢时,黄河仅能在极为干旱的冰期向间冰期过渡阶段形成阶地;相比之下,它们相对汾渭盆地抬升速率都足够快速时,驱动黄河近乎对每一次的冰期向间冰期转换都能做出响应而发育阶地。以上黄河中游阶地与气候和地表抬升的对比模式揭示出,快速地表抬升也是阶梯状阶地序列发育不可或缺的因素,能驱使河流在冰期向间冰期过渡阶段显著下切,拉大相邻阶地面垂直距离从而利于后期保存。因此,研究认为黄河中游发育的系列阶地是响应气候变化和地表相对汾渭盆地抬升的结果。
The challenge to understanding fluvial response to climate change and surface uplift is a thorough dis⁃tinguishing between their roles within terrace formation,which can provide an excellent insight to the landform and drainage evolution in catchment scale.Previous studies tend to correlate terrace development with climate change or surface uplift separately,attributing deposition-lateral erosion and incision to glacial-interglacial cli⁃mate,or regarding fluvial terrace even as a direct evidence of surface uplift.A preliminary explanation for the terrace development of the middle reaches of Yellow River is proposed by linking its upper and lower reaches.In comparison with the past work,river terrace here is considered as a combination result of fluvial response to cli⁃mate change and relative surface uplift.Intermittent downcutting by the middle reaches of Yellow River on the uplifted Ordos Block and Emei Platform relative to the subsiding Fenwei Basin has created 7 terrace staircases and a sequence of 6 aggradational terraces,respectively,during the past 1.2 Ma.The analysis of loess stratigra⁃phy combined with geochronology revealed that these terraces were overlaid directly by a basal paleosol layer on the fluvial sediments,indicating that the abandonment of these treads due to incision by the Yellow River oc⁃curred at the transition from glacial to interglacial climates.This suggests that the glacial-interglacial climate cy⁃cle probably has a temporal control on the terrace generation by determining the fluvial behavior alternation be⁃tween deposition-lateral erosion and incision,even though the Yellow River develops in the subsiding Fenwei Basin.Remarkably,terrace records however are absent at some transitions from glacial to interglacial climate,indicating that climate cycle may not be the only decisive factor for terrace occurrence.The terrace generation may be sporadic and in the form of unusual stacked pattern before the Emei Platform was uplifted within the east⁃ern Fenwei Basin.And when
作者
潘保田
胡振波
PAN Baotian;HU Zhenbo(Key Laboratory of Western China’s Environmental Systems,Ministry of Education,College of Earth and Environmental Sciences,Lanzhou University,Lanzhou 730000,China)
出处
《冰川冻土》
CSCD
北大核心
2021年第3期853-863,共11页
Journal of Glaciology and Geocryology
基金
国家自然科学基金项目“积石峡至龙羊峡段黄河的形成与地貌演化研究”(41871001)
国家自然科学基金专项项目“黄河流域地质地表过程与重大灾害效应”(42041006)资助。
关键词
黄河中游
阶地发育
鄂尔多斯地块
汾渭盆地
峨眉台地
the middle reaches of Yellow River
terrace
Ordos block
Fenwei Basin
Emei Platform
