Silcrete

Nash, David J.; Ullyott, J. Stewart

doi:10.1002/9780470712917.ch4

Cited by 47 publications

(70 citation statements)

References 120 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…A very high silica content, exceeding 97%, is a characteristic feature of these structures (Ullyott et al, 2004). Genetically, two types of silcrete are distinguished; pedogenic and groundwater silcretes (Nash, Ullyott, 2007). The fi rst pedogenic ones form during weathering, with subsurface layers undergoing soil processes.…”

Section: Upper Jurassic Limestone In the Zalew Balaton Area -Genesismentioning

confidence: 99%

The Zalew Balaton Quarry geosite in Trzebinia, southern Poland: an update of geological data

Kamieniarz

2014

geotour

View full text Add to dashboard Cite

show abstract

Section: Upper Jurassic Limestone In the Zalew Balaton Area -Genesismentioning

confidence: 99%

The Zalew Balaton Quarry geosite in Trzebinia, southern Poland: an update of geological data

Kamieniarz

2014

geotour

View full text Add to dashboard Cite

show abstract

“…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: 99%

“…However, in the case of the Kalahari, silcrete outcrops occur most commonly in low-lying landscape positions (e.g., adjacent to rivers, within valleys, or at lake margins; see Nash and Ullyott, 2007) and, therefore, have the potential to become inaccessible as a result of changing hydroclimatic conditions. This can be seen today, where, for example, above average discharges through the Okavango Delta in recent years have led to flooding in the Boteti River and the inundation of the majority of silcrete outcrops along the river bed.…”

Section: Raw Materials Source Accessibility Over Timementioning

confidence: 99%

“…Silcrete has not been documented in these areas, and is unlikely, on the basis of our current understanding of non-pedogenic silcrete formation (cf. Nash and Ullyott, 2007), to have developed there. Further, as Nash et al (2013a) note, if any silcrete is present within the dunefield, it is likely to have remained buried beneath tens of metres of dune sediments for the duration of the MSA.…”

Section: Details Of Silcrete Geochemical Databasementioning

confidence: 99%

See 1 more Smart Citation

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

Self Cite

View full text Add to dashboard Cite

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

show abstract

“…It has been described on every continent except Antarctica 43 (Summerfield, 1983), and is recognised as a major terrestrial silicon sink (Basile-Doelsch 44 et al, 2005). To date, four models have been put forward to explain silcrete formation 45 (Nash and Ullyott, 2007). Pedogenic silcretes are those which form as a result of cycles of 46 downward percolation and precipitation of silica within soil profiles (e.g.…”

Section: Introduction 40mentioning

confidence: 99%

Cap structures as diagnostic indicators of silcrete origin

Ullyott

Nash

Huggett³

2015

Sedimentary Geology

Self Cite

View full text Add to dashboard Cite

pedogenic silcretes indicate that this may no longer be appropriate. This paper presents 17 the first systematic investigation of the micro-fabric, geochemistry and mineralogy of cap 18 structures in groundwater silcretes, through an analysis of conglomeratic varieties 19 (puddingstones) from the southern UK. Our results suggest that cap structures in 20 groundwater silcretes fall within a spectrum of types, related to the degree of sorting in the 21 inter-gravel host sediment. At one end of this spectrum are well-defined caps within 22 otherwise well-sorted, overgrowth-dominated silcretes. These caps exhibit a grain-23 supported fabric, are cemented by micro-and/or cryptocrystalline silica, and contain 24 floating silt-sized quartz and Ti-oxide grains. We propose that these structures developed 25 mainly as a result of in-washing of fine sediments that were subsequently silicified. At the 26 other end of the spectrum are silcretes with caps defined by concentrations of Ti-oxide 27 grains, as opposed to cement type and grain size. These formed mainly as a result of the 28 remobilisation and precipitation of Ti during the silicification of gravels containing interstitial 29 clay-rich sandy sediment. Between these end-members are silcretes with cap structures 30 formed by a combination of in-washing and redistribution of fines plus some local 31 remobilisation of Ti. Overall, the cap structures in this study exhibit a simple 32 micromorphology, lacking the alternating Ti-and silica-rich lamellae typical of pedogenic 33 silcrete. We conclude that the presence of cap structures alone should not be considered 34 diagnostic of pedogenic silicification unless accompanied by other indicators such as a 35 differentiated profile and abundant, complex, way-up structures within the micro-fabric. 36 37

show abstract

Silcrete

Cited by 47 publications

References 120 publications

The Zalew Balaton Quarry geosite in Trzebinia, southern Poland: an update of geological data

The Zalew Balaton Quarry geosite in Trzebinia, southern Poland: an update of geological data

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

Cap structures as diagnostic indicators of silcrete origin

Contact Info

Product

Resources

About