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- Title
Dual mechanisms for the formation of fluvial silcretes in the distalreaches of the Okavango Delta fan, Botswana
- Authors
Nash, David J.; Shaw, Paul A.
- Abstract
Silcretes exposed within river-marginal or valley settings have beendescribed in a number of studies, but few models have been suggestedfor the development of these fluvial silcretes. An exception is thatproposed by McCarthy and Ellery (Journal of Sedimentary Research, 1995, Vol. A65, pp. 77-90) to describe mechanisms of early stage near-surface silica diagenesis in the Okavango Delta, Botswana. This paper describes the characteristics and possible origins of massive surfaceand sub-surface silcretes at Samedupe and Boro Junction, beyond the distal margin of the Okavango Delta and further downstream than the sites described by McCarthy and Ellery. Morphological and petrologicalevidence from surface exposures and three sedimentary cores suggeststhat other modes of formation may also be applicable. A dual model of formation is proposed: surface silcretes are suggested to have developed by silica accumulation in seasonal pools remaining after the annual Okavango flood, whilst sub-surface horizons appear to have formed under conditions of varying pH associated with fluctuating groundwater levels beneath the channel floor. This model is reviewed in the context of the fluvial silcrete debate.
- Subjects
PETROLOGY; SOIL science; MORPHOLOGY
- Publication
Earth Surface Processes & Landforms, 1998, Vol 23, Issue 8, p705
- ISSN
0197-9337
- Publication type
Article