Diagenesis in Okavango fan and adjacent dune deposits with implications for the record of palaeo-environmental change in Makgadikgadi–Okavango–Zambezi basin, northern Botswana

Ringrose, Susan; Huntsman-Mapila, P.; Downey, W. S.; Coetzee, S. H.; Fey, Martin; Vanderpost, Cornelis; Vink, B.W.; Kemosidile, Thebe; Kolokose, Dikitso

doi:10.1016/j.geomorph.2008.02.008

Cited by 24 publications

(21 citation statements)

References 44 publications

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“…7b). Thorium abundance is generally low in the 936 m calcretes (b1-7 ppm) Table 1 Profile details for duricrust from PMSB strandlines and inferred repeat periods when same strandlines incorporated more recent groundwater flow (modified after Ringrose et al, 2005Ringrose et al, , 2008 and higher in the intergrade deposits (2-23 ppm). (Table 3) One anomalously high Th value occurs in the calcrete in the 906 m strandline (SOW10 S3, Fig.…”

Section: U Th W Y and Halogensmentioning

confidence: 99%

“…4). The Okavango river catchment for instance includes Taylor and McClennan (1981) and Gromet et al (1984). extensive, open water bodies perennially undergoing evaporation/ evapo-transpiration leading to relative Ca 2+ enrichment (Wolski and Savenije;Ringrose et al, 2008). If a geochemical similarity is assumed over time, then inflow water with a relatively high Ca 2+ concentration (McCarthy and Ellery, 1995;Cronberg, 1996) could flow into the PMSB through surface water sources (such as the Boteti river, Fig.…”

Section: Local and Non-local Bedrock Sources Relative To Different Dumentioning

confidence: 99%

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Origins of strandline duricrusts around the Makgadikgadi Pans (Botswana Kalahari) as deduced from their chemical and isotope composition

Ringrose

Harris

Huntsman-Mapila

et al. 2009

Sedimentary Geology

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Section: U Th W Y and Halogensmentioning

confidence: 99%

Section: Local and Non-local Bedrock Sources Relative To Different Dumentioning

confidence: 99%

Origins of strandline duricrusts around the Makgadikgadi Pans (Botswana Kalahari) as deduced from their chemical and isotope composition

Ringrose

Harris

Huntsman-Mapila

et al. 2009

Sedimentary Geology

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“…Ringrose et al . () suggested that the kind of clay mineral present in Okavango area sediments suggested neoformation under alternating flooding and dry regimes, similar to those described in the Boteti palaeo‐estuary. Clay minerals in the study area (smectite, with illite and halloysite) are found in association with the already formed bSiO 2 /CaO aggregates (Tables and ).…”

Section: Discussionmentioning

confidence: 88%

“…Clay mineral neoformation in Makgadikgadi pan strandlines has been previously reported in Ringrose et al . () while possibly neoformed smectites have also been inferred from island environments in the Okavango region (Ringrose et al ., ). In terms of a possible clay origin, Owen () indicates that colloidal particles in alkaline solutions are negatively charged and so (may) co‐precipitate with hydroxides of Fe, Al, Mn or Mg creating clay‐like substances at high salinities.…”

Section: Discussionmentioning

confidence: 99%

“…Ringrose et al . () describe similar Okavango precipitates in island, floodplain and dune sediments, as silica‐enriched diagenetic products termed clay enhanced amorphous silica (CEAS). CEAS is enriched with both CaCO 3 and silica reflecting the changing water table geochemistry which ranges from smectite‐dominated flood periods (along with silica precipitation) to sepiolite‐dominated drier periods (which promote CaCO 3 precipitation).…”

Section: Introductionmentioning

confidence: 99%

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Diagenetic transformations and silcrete–calcrete intergrade duricrust formation in palaeo‐estuary sediments

Ringrose

Cassidy²,

Diskin

et al. 2014

Earth Surf Processes Landf

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The Boteti palaeo‐estuary in northern Botswana is located where the endoreic Boteti river, an overflow from the regional Okavango river system, enters the Makgadikgadi pans. The present work considers diagenetic silica and calcium carbonate dominated transformations. The aims are to help identify precursor conditions for the origin of microcrystalline silcrete–calcrete intergrade deposits while developing insight into pene‐contemporaneous silica and calcite matrix formation. General precursor conditions require the presence of cyclical endoreic freshwater inflow into a saline pan. The pan should be deep enough to sustain a permanent watertable under climatic conditions sufficient to cause carbonate fractionation within the groundwater. Freshwater inflow into a saline pan drives the geochemistry of the system (from freshwater to saline, from neutral to high pH). The geochemistry is controlled by the periodicity of inflow relative to salinity levels of phreatic groundwater in the receptor saline pan. The source of most silica and localized CaCO3 is derived from the dissolution and precipitation of micro‐fossils, while more general CaCO3 enrichment stems from saline pan based carbonate fractionation. Diagenetic change leads to colloidal then more consolidated bSiO2/CaO aggregate formation (amorphous silica) followed by transformations into opaline silica over time. Irregular zones of siliceous sediment forming in otherwise calcareous deposits may relate to the irregular occurrence of biogenic silica in the source sediments, inferring a source for local silica mobilization in intergrade deposits. The distribution of calcareous micro‐fossils may have a similar converse effect. Diagenetic evidence from an intergrade deposit with a low SiO2/CaO ratio suggests that transformation occurred more into the pan, while an intergrade deposit with a high SiO2/CaO ratio more likely formed closer to a land margin and was frequently inundated by freshwater. Pene‐contemporaneous silcrete–calcrete intergrade formation under the above conditions may take place where dissolved silica crystallizes out in the vicinity of calcite crystals due to local decreases in pH. The continuing consolidation of bSiO2/CaO aggregates may be facilitated by the presence of increasing amounts of calcite. It appears that CaCO3 may act as a catalyst leading to pene‐contemporaneous bSiO2/CaO aggregate formation. However the processes involved require further work. Copyright © 2013 John Wiley & Sons, Ltd.

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Significantly enhanced mid Holocene fluvial activity in a globally important, arid‐zone wetland: The Okavango Delta, Botswana

Tooth

McCarthy

Duller

et al. 2022

Earth Surf Processes Landf

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Information on past dryland environments is commonly derived from geomorphological landforms and sediments ('geoproxies'). The Okavango Delta in the middle Kalahari, Botswana, has been subject to a long history of arid-humid transitions but its potentially rich archive of fluvial geoproxies is largely untapped. Previous palaeoenvironmental studies in the Delta region have focused mainly on aeolian dunes, lacustrine beach ridges, and rare pollen sequences in surrounding locations, and the Delta's channel dynamics have remained poorly constrained, both chronologically and in quantitative palaeohydrological terms. Focusing on the Delta's Xugana region, we present the first optically stimulated luminescence ages for palaeochannel fills and scroll bars, revealing significantly enhanced fluvial activity in the $7-4 ka interval. Along 120-150 m-wide, sand-bed, sinuous palaeochannels, lateral migration and bend cutoffs were driven by palaeodischarges up to $350-450 m 3 s À1 , at least nine

show abstract

Diagenesis in Okavango fan and adjacent dune deposits with implications for the record of palaeo-environmental change in Makgadikgadi–Okavango–Zambezi basin, northern Botswana

Cited by 24 publications

References 44 publications

Origins of strandline duricrusts around the Makgadikgadi Pans (Botswana Kalahari) as deduced from their chemical and isotope composition

Origins of strandline duricrusts around the Makgadikgadi Pans (Botswana Kalahari) as deduced from their chemical and isotope composition

Diagenetic transformations and silcrete–calcrete intergrade duricrust formation in palaeo‐estuary sediments

Significantly enhanced mid Holocene fluvial activity in a globally important, arid‐zone wetland: The Okavango Delta, Botswana

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