Kalahari valley calcretes: their nature, origins, and environmental significance

Nash, David J.; McLaren, Sue

doi:10.1016/s1040-6182(03)00011-9

Cited by 88 publications

(59 citation statements)

References 49 publications

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“…9d), with the characteristics of the silcrete fabric suggesting that outcrops had formed by the gradual silicification of a valley calcrete Nash and McLaren, 2003;Nash et al, 2004;Nash and Ullyott, 2007). Pending controlled experiments, it appears unlikely that the knapping properties of the silcretes from the four sampling areas would be affected by these slight differences in micromorphology.…”

Section: Petrological Analysesmentioning

confidence: 98%

Going the distance: Mapping mobility in the Kalahari Desert during the Middle Stone Age through multi-site geochemical provenancing of silcrete artefacts

Nash

Coulson

Staurset

et al. 2016

Journal of Human Evolution

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This study utilises geochemical provenancing of silcrete raw materials, in combination with chaîne opératoire analyses, to explore lithic procurement and behavioural patterns in the northern Kalahari Desert during the Middle Stone Age (MSA). New data from the sites of Rhino Cave, Corner Cave, and ≠Gi in northwest Botswana, combined with earlier results from White Paintings Shelter, reveal that the long distance transport of silcrete for stone tool manufacture was a repeated and extensively used behaviour in this region. Silcrete was imported over distances of up to 295 km to all four sites, from locations along the Boteti River and around Lake Ngami. Significantly, closer known sources of silcrete of equivalent quality were largely bypassed. Silcrete artefacts were transported at various stages of production (as partially and fully prepared cores, blanks, and finished tools) and, with the exception of ≠Gi, in large volumes. The import occurred despite the abundance of locally available raw materials, which were also used to manufacture the same tool types. On the basis of regional palaeoenvironmental data, the timing of the majority of silcrete import from the Boteti River and Lake Ngami is constrained to regionally drier periods of the MSA. The results of our investigation challenge key assumptions underlying predictive models of human mobility that use distance-decay curves and drop-off rates. MSA peoples in the Kalahari appear to have been more mobile than anticipated, and repeatedly made costly choices with regard to both raw material selection and items to be transported. We conclude that (i) base transport cost has been overemphasised as a restrictive factor in predictive models, and (ii) factors such as source availability and preference, raw material quality, and potential sociocultural influences significantly shaped prehistoric landscape use choices.3

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Section: Petrological Analysesmentioning

confidence: 98%

Going the distance: Mapping mobility in the Kalahari Desert during the Middle Stone Age through multi-site geochemical provenancing of silcrete artefacts

Nash

Coulson

Staurset

et al. 2016

Journal of Human Evolution

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“…These are often grouped together as "groundwater calcretes." However, as Nash and McLaren (2003) argue, this term is not particularly helpful, frequently being applied to any calcrete that has developed just above, at, or below the water table. These authors instead suggest that distinct types of non-pedogenic calcrete should be recognized on the basis of the geomorphological setting in which carbonate accumulation took place.…”

Section: Valley and Channel Calcretesmentioning

confidence: 99%

“…Channel calcretes can be defined as calcium carbonate accumulations that cement sediments immediately above, at or below the water table in confined impermeable bedrock channels (Nash and McLaren, 2003). They are variable in size and shape, reaching up to several meters thickness, but, critically, cement the full channel cross-section (see Maizels, 1990a,b;Rakshit and Sundaram, 1998;Smith, 1998, 2003;Mack et al, 2000;McLaren, 2004 for examples).…”

Section: Valley and Channel Calcretesmentioning

confidence: 99%

“…In contrast to channel calcretes, they rarely occupy the entire valley width or full thickness of alluvial fill, often exhibiting undulating surfaces, and 'pinching out' laterally at distance from the valley axis (cf. Miller, 1937;Netterberg, 1969;Carlisle et al, 1978;Mann and Horwitz, 1979;Carlisle, 1983;Reeves, 1983;Kaemmerer and Revel, 1991;Butt, 1992;Nash et al, 1994;Nash and McLaren, 2003). The bestdeveloped valley calcretes within Australian and Kalahari paleodrainage systems reach up to 10 km width, 100 km length, and several tens of meters in thickness (Arakel and McConchie, 1982;Arakel, 1986Arakel, , 1991Jacobson et al, 1988;Arakel et al, 1989;Nash et al, 1994).…”

Section: Valley and Channel Calcretesmentioning

confidence: 99%

“…In both types, a minor proportion of the carbonate may be supplied via atmospheric input, but the main carbonate source is shallow groundwater moving laterally into and along the channel/valley. As with pedogenic calcrete, evaporation or evapotranspiration may be important mechanisms triggering carbonate precipitation in near-surface sediments, but CO2 degassing associated with a fluctuating water table is likely to be more significant at depth (Nash and McLaren, 2003;Nash and Smith, 2003). Studies of valley calcretes within Australian paleodrainage systems suggest that the thickest calcretes form within the zone of groundwater fluctuation, with their thickness attributed to progressive carbonate accumulation associated with a fluctuating but gradually falling water table (Arakel and McConchie, 1982;Arakel, 1986Arakel, , 1991Jacobson et al, 1988).…”

Section: Valley and Channel Calcretesmentioning

confidence: 99%

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The West Water Formation (Hualapai Plateau, Arizona, USA) as a calcrete-paleosol sequence, and its implications for the Paleogene-Neogene evolution of the southwestern Colorado Plateau

Hill

Polyak

Nash

et al. 2017

Palaeogeography, Palaeoclimatology, Palaeoecology

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ABSTRACT. Analyses of stratigraphic sequences within the paleocanyons of the HualapaiPlateau, Arizona, are important because these deposits offer the only evidence for the Paleogene-Neogene geological history of the Grand Canyon area. In this paper, we focus on the origins and paleoenvironmental significance of the West Water Formation, located within the Milkweed and West Water paleocanyons on the Hualapai Plateau. We propose that the supposed "limestone unit" of the West Water Formation at and near its type section is not a limestone; rather, it is a 21 m-thick valley calcrete, overprinted by a ~1-2 m-thick pedogenic calcrete, and subsequently dolomitized in its upper-to-middle sections, with a superimposed 4 m-thick red paleosol. We also propose that this unit is not coeval in age or origin with the Long Point limestone on the Coconino Plateau, and that the presence of a complex calcretedolocrete-paleosol alters previous interpretations associated with this unit. Evidence for a calcrete-paleosol origin, beyond the West Water Formation's lack of fossils, includes: its predominantly micritic calcite-palygorskite composition; its textures characteristic of valley and pedogenic calcrete deposits (as exhibited by thin section, SEM, and TEM analyses); and its association with a relatively thick overlying red paleosol that also contains abundant palygorskite. Stable carbon and oxygen isotope values from carbonate cements are also within the range expected of a near-surface calcrete. Carbonate minerals within the calcrete-dolocrete were precipitated at or near the water table in a valley setting due to evaporation and/or CO2 degassing in a semi-arid to arid environment of deposition. High

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Introducing a terrestrial carbon pool in warm desert bedrock mountains, southwestern USA

Harrison

Dorn

2014

Global Biogeochemical Cycles

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Growth of the Phoenix metropolitan area led to road cut or house platform exposures of the internal bedrock material of surrounding semiarid mountain ranges. Similar exposures in the surrounding Sonoran and Mojave Deserts reveal the presence of sedimentary calcium carbonate infilling the preexisting fracture matrix of the bedrock. Field surveys at 31 sites with bedrock fractures filled with carbonate, referred to as BFFC in the following text, reveal an average of 0.079 ± 0.036 mTC/m 2 stored in the upper 2 m of analyzed bedrock exposures. Backscattered electron microscopy images indicate the presence of carbonate at the micron scale, not included in this estimate of carbon storage. Pilot radiocarbon and Sr isotope analyses suggest that one of the surveyed BFFC veins was flushed into the bedrock from a nonbedrock source during the wetter last glacial period in the late Pleistocene.

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Kalahari valley calcretes: their nature, origins, and environmental significance

Cited by 88 publications

References 49 publications

Going the distance: Mapping mobility in the Kalahari Desert during the Middle Stone Age through multi-site geochemical provenancing of silcrete artefacts

Going the distance: Mapping mobility in the Kalahari Desert during the Middle Stone Age through multi-site geochemical provenancing of silcrete artefacts

The West Water Formation (Hualapai Plateau, Arizona, USA) as a calcrete-paleosol sequence, and its implications for the Paleogene-Neogene evolution of the southwestern Colorado Plateau

Introducing a terrestrial carbon pool in warm desert bedrock mountains, southwestern USA

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