Late Cenozoic and present-day hillslope erosion dynamics in a passive margin context: stability or instability? Case studies in Northeast Brazil

IF 0.5 4区 地球科学 Q4 GEOGRAPHY, PHYSICAL
J. Peulvast, François Bétard
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引用次数: 16

Abstract

Steep slopes form the marginal scarp of the semi-arid northern Brazilian “Nordeste”, above depressions or corridors connected to a low erosion plain merging seaward with a coastal erosional-gradational piedmont. Dissected pediments and sparse debris fans visible at the base of some escarpments suggest recent erosive activity and possible slope retreat, although most of these forms are decoupled from major valleys. We describe the morphostructural patterns of chosen escarpments, in the basement as well as in the sedimentary cover, and the morphodynamic conditions of their evolution since the Miocene. Only a few scarps show strong structural control. Many of them are mainly inherited landforms, initiated during the Early Cretaceous rifting or the later margin uplift, a situation which suggests long-term stability. Later on, except in one case (the Araripe scarp), only slight or local backwearing took place, associated with downwearing on low surfaces and pediments, probably in diachronic ways. The Neogene clastic sedimentation on piedmonts and coastal areas mainly reflects the occurrence of dry periods inducing widespread stripping of deep soil horizons and erosion of bare rock slopes and surfaces. Dissection stages occurred in periods of more humid climate and/or low sea level. Marks of strong recent of present activity are mainly registered in the rims of the Chapada do Araripe, owing to favourable structural, hydrogeological and climatic conditions. The moderate volumes of Neogene clastic sediments imply overall low uplift and erosion rates until the Present, favourable to morphological and lithological resistance effects in the landscapes. However, slope instabilities are not uncommon, locally leading to well characterized processes, landforms and deposits of gullying and mass wasting. Therefore, hazards related with slope processes never may be neglected, although only small scale events were recorded in recent times, and times of recurrence of larger events are probably much longer than the historic times.
被动边缘环境下的晚新生代和现代山坡侵蚀动力学:稳定还是不稳定?巴西东北部的案例研究
陡峭的斜坡形成了半干旱的巴西北部“Nordeste”的边缘悬崖,在洼地或走廊上,连接着一个低侵蚀平原,向海与海岸侵蚀-梯度山前山前合并。在一些悬崖的底部可以看到解剖的山墙和稀疏的碎屑扇,这表明最近的侵蚀活动和可能的斜坡退缩,尽管这些形式中的大多数与主要山谷分离。我们描述了在基底和沉积盖层中选择的峭壁的形态结构模式,以及中新世以来它们演化的形态动力学条件。只有少数陡坡表现出强烈的构造控制。其中多为继承地貌,形成于早白垩世裂陷或后期边缘隆升时期,具有长期稳定性。后来,除了一个例子(Araripe悬崖),只有轻微或局部的磨损发生,与低表面和山形的下降有关,可能是历时性的。前山地区和沿海地区新近纪碎屑沉积主要反映了干旱期的发生,导致深层土壤层的广泛剥蚀和裸露的岩石斜坡和表面的侵蚀。解剖阶段发生在气候较潮湿和/或海平面较低的时期。由于有利的构造、水文地质和气候条件,最近和现在的强烈活动的标志主要出现在阿拉里佩火山的边缘。新近纪碎屑沉积物的中等体积意味着直到现在整体上较低的隆升和侵蚀速率,有利于景观的形态和岩性抵抗作用。然而,边坡的不稳定性并不罕见,在局部导致了特征明显的过程、地貌和沟壑和块状浪费的沉积。因此,与斜坡过程有关的危险永远不能被忽视,尽管在最近的时间里只记录了小规模的事件,而大事件的复发时间可能比历史时间长得多。
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来源期刊
CiteScore
1.40
自引率
0.00%
发文量
0
审稿时长
>12 weeks
期刊介绍: It publishes original papers, short communications, news and book reviews of Physical Geography, Glaciology, Geomorphology and Quaternary Geology. The journal furthermore publishes the annual reports on italian glaciers, the official transactions of the Comitato Glaciologico Italiano and the Newsletters of the International Association of Geomorphologist.
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