Arid
DOI10.1016/j.geomorph.2018.04.008
The near steady state landscape of western Namibia
Matmon, A.1; Enzel, Y.1; Vainer, S.1; Grodek, T.1; Mushkin, A.2
通讯作者Matmon, A.
来源期刊GEOMORPHOLOGY
ISSN0169-555X
EISSN1872-695X
出版年2018
卷号313页码:72-87
英文摘要

Quantitative geomorphic field studies and modeling efforts have focused on the margins of southwestern Africa as an example for landscape evolution in prolonged aridity conditions and tectonic quiescence of passive margins. These efforts concluded that this region is a prime example of a steady state landscape, in which relief changes extremely slowly. Using cosmogenic isotopes, these studies suggested overall landscape exhumation rates of 5-10 m Ma(-1) over the past 105-106 yrs. Slightly slower rates on flat-lying exposed bedrock surfaces and faster exhumation rates along the Namibian Great Escarpment as well as on steep slopes of granitic inselbergs, such as the Gross Spitzkoppe are also documented. Here we explore the state of "steady state" in central Namibia. Concentrations of Be-10 were measured in bedrock and sediment samples collected throughout the watershed of the Ugab River (similar to 29,000 km(2)), which drains the highlands of central Namibia and flows to the Atlantic Ocean. Samples were collected from the main stem of the ephemeral Ugab River, from the slopes and streams draining the Brandberg, which is the largest inselberg in the Namib, and from smaller inselbergs around it. We also sampled several other formerly large, but currently subdued, inselbergs such as the Messum Crater. ’Be concentrations in sediment transported along the axial Ugab River indicate that its drainage basin erodes uniformly at 5-6 m Ma(-1) and sediment transport from its headwaters source to the ocean is rapid. Be-10 concentrations measured in sediment transported in ephemeral streams draining the Brandberg indicate its erosion at similar to 4 m Ma(-1). However, slower rates of 1-3 m Ma(-1) were measured for bedrock samples collected from (a) flat lying bedrock surfaces within the Brandberg, (b) top of small tors that rise only a few meters above their surroundings, and (c) exhumed and denuded large magmatic complexes such as the Messum Crater. Furthermore, we found that bedrock buried under grus in the hyperarid zone of Namib (<100 mm yr(-1)) erodes at similar rates as the exposed bedrock. This difference between the rate of bedrock erosion and the overall average erosion rate of drainage basins has been previously attributed to the contribution of sediment weathered from underneath transported sediment and soil on the pediments. Our results do not fully support this explanation. Results from this and earlier studies point to two possible sources of relatively low dosed (i.e. more rapidly eroding) sediment: (a) the steep slopes and cliffs of the large inselbergs and the Great Escarpment, and (b) rock buried under soil in the upper, semi-arid, parts of the drainage systems, where soil and vegetation can promote weathering of plagioclase and biotite and the disintegration of granitic bedrock.


英文关键词Erosion rates Namibia Passive margins Cosmogenic isotopes
类型Article
语种英语
国家Israel
收录类别SCI-E
WOS记录号WOS:000436202900006
WOS关键词FISSION-TRACK ANALYSIS ; COSMOGENIC NUCLIDES ; BASIN EVOLUTION ; SOUTHERN AFRICA ; EROSION ; RATES ; SEDIMENT ; DENUDATION ; TOPOGRAPHY ; DESERT
WOS类目Geography, Physical ; Geosciences, Multidisciplinary
WOS研究方向Physical Geography ; Geology
来源机构Hebrew University of Jerusalem
资源类型期刊论文
条目标识符http://119.78.100.177/qdio/handle/2XILL650/209663
作者单位1.Hebrew Univ Jerusalem, Fredy & Nadine Herrmann Inst Earth Sci, Edmond J Safra Campus Givat Ram, IL-91904 Jerusalem, Israel;
2.Geol Survey Israel, 30 Malkhe Israel St, IL-95501 Jerusalem, Israel
推荐引用方式
GB/T 7714
Matmon, A.,Enzel, Y.,Vainer, S.,et al. The near steady state landscape of western Namibia[J]. Hebrew University of Jerusalem,2018,313:72-87.
APA Matmon, A.,Enzel, Y.,Vainer, S.,Grodek, T.,&Mushkin, A..(2018).The near steady state landscape of western Namibia.GEOMORPHOLOGY,313,72-87.
MLA Matmon, A.,et al."The near steady state landscape of western Namibia".GEOMORPHOLOGY 313(2018):72-87.
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