Sedimentological and geochemical evidence for palaeo-environmental change in the Makgadikgadi subbasin, in relation to the MOZ rift depression, Botswana

Silcrete is a type of duricrust formed by the near-surface accumulation of secondary silica within a soil, sediment, rock or weathered material. A variety of models of formation have been put forward, involving silicification in both pedogenic and non-pedogenic settings.The resulting silcrete types differ in terms of their macroscale characteristics, micromorphology, areal extent and behavioural properties. Such differences have significant implications in a range of geological, geomorphological, archaeological and engineering contexts, making the correct identification of silcrete type of considerable importance. This paper reviews the properties of pedogenic, groundwater, drainage-line and pan/lacustrine silcretes, and identifies many characteristics that may be diagnostic. It also discusses a number of more problematic macro-and micro-scale features common to both pedogenic and non-pedogenic silcretes. It concludes with a short checklist to aid the future identification of different silcrete types in the landscape and geological record.

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“…3d) may be irregularly shaped, lenticular or nodular (e.g. Armenteros et al, 1995;Ringrose et al, 2005).…”

Section: Characteristics Of Non-pedogenic Silcretesmentioning

confidence: 99%

Distinguishing pedogenic and non-pedogenic silcretes in the landscape and geological record

Ullyott

Nash

2016

Proceedings of the Geologists' Association

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“…3). The contemporary pans of Ntwetwe, Sua, and the numerous smaller pans that surround them are relics of paleolakes that once covered much of northern Botswana (Burrough et al, 2009;Ringrose et al, 2005). Average annual rainfall ranges from 359 mm in Rakops to 545 mm in Maitengwe, along a southwest-northeast rainfall gradient.…”

Section: Study Sitementioning

confidence: 99%

“…Pan soils are solonchaks, with shallow leptosols, regosols and arenosols in fringing areas (De Wit and Nachtergaele, 1990;Wang et al, 2007) which can become calcified in areas immediately surrounding the pans (Mees and Van Ranst, 2011;Ringrose et al, 2005;White and Eckardt, 2006). Pan sediment is clay-rich and mixed with salts derived from shallow near-surface water, as well as deeper brines dominated by NaCl and Na 2 CO 3 (Department of Environmental Affairs and Centre for Applied Research, 2010;Gould, 1986).…”

Section: Study Sitementioning

confidence: 99%

Seasonal differences in soil CO2 efflux and carbon storage in Ntwetwe Pan, Makgadikgadi Basin, Botswana

et al. 2014

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The carbon cycle in salt pans is complex and poorly understood. Field-based data are needed to improve regional estimates of C storage and land-atmosphere CO 2 fluxes from dryland environments where pans are prevalent. This paper provides a first estimate of C stores and CO 2 efflux within the salt pan, grassland and woodland of Ntwetwe Pan in the Makgadikgadi Basin, Botswana. C fluxes and stores associated with cyanobacteria-salt crusts are also determined. Total C stores are approximately an order of magnitude greater than on neighbouring Kalahari Sands at 675 ± 41, 760 ± 94 and 274 ± 15 tons ha −1 to 1 m depth in the woodland, grassland and salt pan respectively. Most of the C is found as carbonate, with organic C comprising 4.6-10% of total C. CO 2 efflux increased with temperature and also increased for a few hours after flooding of the pan surface. Crusts were a small net contributor to CO 2 efflux in the dry season but could be a net CO 2 sink in the wet season. The biogeochemistry of the sediment is likely to facilitate rapid conversion of organic C from aquatic organisms, biological crusts and algal mats into inorganic carbonates. Although further work is required to improve estimates of the spatial and temporal distribution of C, our data have demonstrated the substantial C store with the Makgadikgadi environment and the important role of biological crusts in the C cycle.

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“…the Makgadikgadi and Chilwa basins of southern Africa), breaks in sediment accumulation are indistinct, difficult to access and, when exposed, often dominated by post-depositional processes (e.g. Ringrose et al, 2005). In these instances, characteristic of environments dominated by unconsolidated sediment (where depositional beach ridge formation is common), process-based interpretations can be problematic.…”

Section: Stage Process Involved In Beach Ridge Development (Oval A)mentioning

confidence: 99%

Geomorphological contributions to palaeolimnology on the African continent

Burrough

Thomas

2009

Geomorphology

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Sedimentological and geochemical evidence for palaeo-environmental change in the Makgadikgadi subbasin, in relation to the MOZ rift depression, Botswana

Cited by 73 publications

References 39 publications

Distinguishing pedogenic and non-pedogenic silcretes in the landscape and geological record

Distinguishing pedogenic and non-pedogenic silcretes in the landscape and geological record

Seasonal differences in soil CO2 efflux and carbon storage in Ntwetwe Pan, Makgadikgadi Basin, Botswana

Geomorphological contributions to palaeolimnology on the African continent

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