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DOI	10.1002/esp.4976
	Reassessing southern African silcrete geochemistry: implications for silcrete origin and sourcing of silcrete artefacts
	Webb, John A.; Nash, David J.
通讯作者	Webb, JA
来源期刊	EARTH SURFACE PROCESSES AND LANDFORMS
ISSN	0197-9337
EISSN	1096-9837
出版年	2020
卷号	45 期号:13 页码:3396-3413
英文摘要	A synthesis of the geochemistry of silcretes and their host sediments in the Kalahari Desert and Cape coastal zone, using isocon comparisons, shows that silcretes in the two regions are very different. Kalahari Desert silcretes outcrop along drainage-lines and within pans, and formed by groundwater silicification of near-surface Kalahari Group sands. Silicification was approximately isovolumetric. Few elements were lost; silicon (Si) and potassium (K) were gained as microquartz precipitated in the sediment porosity and glauconite formed in the sub-oxic groundwater conditions. The low titanium (Ti) content reflects the composition of the host sands. Additional elements in the Kalahari Desert silcretes were supplied in river water and derived from weathering of silicates in basement rocks. Evaporation under an arid climate produced high-pH groundwater that mobilized and precipitated Si; this process is still occurring. In the Cape coastal zone, pedogenic silcretes cap hills and plateaus, overlying deeply weathered argillaceous bedrock. Silicification resulted from intensive weathering that destroyed the bedrock silicates, almost completely removing most elements and causing a substantial volume decrease. Some of the silica released formed a microcrystalline quartz matrix, and most Ti precipitated as anatase, so the Cape silcretes contain relatively high Ti levels. The intense weathering that formed the Cape silcretes could have occurred in the Eocene, during and after the Palaeocene-Eocene Thermal Maximum, when more acidic rainfall and high temperatures resulted in intensified silicate weathering worldwide. This could have been responsible for widespread formation of pedogenic silcretes elsewhere in Africa and around the globe. Trace element sourcing of silcrete artefacts to particular outcrops has most potential in the Cape, where differences between separate bedrock areas are reflected in the silcrete composition. In the Kalahari Desert, gains of some elements can override compositional differences of the parent material, and sourcing should be based on elements that show the least change during silicification. (C) 2020 John Wiley & Sons, Ltd.
英文关键词	silcrete South Africa Kalahari Desert isocon artefact sourcing
类型	Article
语种	英语
开放获取类型	Green Submitted
收录类别	SCI-E ; SSCI
WOS记录号	WOS:000568618200001
WOS关键词	CALCRETE INTERGRADE DURICRUSTS ; OLIGOMIOCENE TORQUAY GROUP ; CAPE COASTAL ZONE ; MIDDLE STONE-AGE ; OKAVANGO DELTA ; KALAHARI DESERT ; CHEMICAL SEDIMENTATION ; HEAVY MINERALS ; DISTAL REACHES ; BOTSWANA
WOS类目	Geography, Physical ; Geosciences, Multidisciplinary
WOS研究方向	Physical Geography ; Geology
资源类型	期刊论文
条目标识符	http://119.78.100.177/qdio/handle/2XILL650/328231
作者单位	[Webb, John A.] La Trobe Univ, Dept Ecol Environm & Evolut, Bundoora, Vic 3086, Australia; [Nash, David J.] Univ Brighton, Sch Environm & Technol, Brighton, E Sussex, England; [Nash, David J.] Univ Witwatersrand, Sch Geog Archaeol & Environm Studies, Johannesburg, South Africa
推荐引用方式 GB/T 7714	Webb, John A.,Nash, David J.. Reassessing southern African silcrete geochemistry: implications for silcrete origin and sourcing of silcrete artefacts[J],2020,45(13):3396-3413.
APA	Webb, John A.,&Nash, David J..(2020).Reassessing southern African silcrete geochemistry: implications for silcrete origin and sourcing of silcrete artefacts.EARTH SURFACE PROCESSES AND LANDFORMS,45(13),3396-3413.
MLA	Webb, John A.,et al."Reassessing southern African silcrete geochemistry: implications for silcrete origin and sourcing of silcrete artefacts".EARTH SURFACE PROCESSES AND LANDFORMS 45.13(2020):3396-3413.