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首页> 外文期刊>Earth Surface Processes and Landforms: The journal of the British Geomorphological Research Group >Evolution and degradation of flat-top mesas in the hyper-arid Negev, Israel revealed from 10Be cosmogenic nuclides
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Evolution and degradation of flat-top mesas in the hyper-arid Negev, Israel revealed from 10Be cosmogenic nuclides

机译：从10Be宇宙成因核素揭示以色列超干旱内盖夫平顶台地的演化和退化

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摘要

Mesas are ubiquitous landforms in arid and semiarid regions and are often characterized by horizontal stratified erodible rocks capped by more resistant strata. The accepted conceptual model for mesa evolution and degradation considers reduction in the width of the mesa flat-top plateau due to cliff retreat but ignores possible denudation of the mesa flat-top and the rates and mechanism of erosion. In this study we examine mesas in the northeastern hyperarid Negev Desert where they appear in various sizes and morphologies and represent different stages of mesa evolution. The variety of mesas within a single climatic zone allows examination of the process of mesa evolution through time. Two of the four sites examined are characterized by a relatively wide (200-230 m) flat-top and a thick caprock whereas the other two are characterized by a much narrower remnant flat-top (several meters) and thinner caprock. We use the concentration of the cosmogenic nuclide (10)~Be for:(a) determining the chronology of the various geomorphic features associated with the mesa; and (b) understanding geomorphic processes forming the mesa. The (10)~Be data, combined with field observations, suggest a correlation between the width of flat-top mesa and the denudation and cliff retreat rates. Our results demonstrate that:(a) cliff retreat rates decrease with decreasing width of the flat-top mesa; (b) vertical denudation rates increase with decreasing width of the flat-top mesa below a critical value (~60 m, for the Negev Desert); (c) the reduction in the width of the flat-top mesa is driven mainly by cliff retreat accompanied by extremely slow vertical denudation rate which can persist for a very long time (>10~6 Ma); and (d) when the width of the mesa decreases below a certain threshold, its rate of denudation increases dramatically and mesa degradation is completed in a short time.
机译：Mesas是干旱和半干旱地区无处不在的地貌，通常以水平分层的易蚀岩石为特征，并被更具抵抗力的地层覆盖。台面演化和退化的公认概念模型考虑了因悬崖退缩而导致台面平顶高原的宽度减小，但忽略了台面平顶的可能剥蚀以及侵蚀的速率和机制。在这项研究中，我们研究了东北超干旱内盖夫沙漠的台面，它们以各种大小和形态出现，并代表台面演化的不同阶段。单个气候区内的台地种类繁多，可以检查台地随着时间的演变过程。所检查的四个站点中的两个站点的特征是相对较宽（200-230 m）的平顶和厚的盖岩，而另两个站点的特征是残留的平坦顶面（几米）和更薄的盖层。我们将宇宙性核素（10）〜Be的浓度用于：（a）确定与台地相关的各种地貌特征的年代顺序; （b）了解形成台地的地貌过程。 （10）〜Be数据结合实地观察表明，平顶台地的宽度与剥蚀率和悬崖退缩率之间存在相关性。我们的结果表明：（a）悬崖的退缩率随着平顶台面宽度的减小而减小; （b）垂直剥蚀率随平顶台面宽度的减小（低于内临界值约60 m）而低于临界值; （c）平顶台面宽度的减小主要是由于悬崖撤退并伴随着非常缓慢的垂直剥蚀速率，该剥蚀速率可以持续很长时间（> 10〜6 Ma）; （d）当台面的宽度减小到某个阈值以下时，其剥蚀速率急剧增加，并且台面在短时间内完成降解。

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