Silcrete Artefacts Research Articles

Early human occupation of Australia’s eastern seaboard

Secure archaeological evidence for human occupation on the eastern seaboard of Australia before ~ 25,000 years ago has proven elusive. This has prompted some researchers to argue that the coastal margins remained uninhabited prior to 25 ka. Here we show evidence for human occupation beginning between 30 ± 6 and 49 ± 8 ka at Wallen Wallen Creek (WWC), and at Middle Canalpin Creek (MCA20) between 38 ± 8 and 41 ± 8 ka. Both sites are located on the western side of Minjerribah (North Stradbroke Island), the second largest sand island in the world, isolated by rising sea levels in the early Holocene. The earliest occupation phase at both sites consists of charcoal and heavily retouched stone artefacts made from exotic raw materials. Heat-treatment of imported silcrete artefacts first appeared in sediment dated to ~ 30,000 years ago, making these amongst Australia’s oldest dated heat-treated artefacts. An early human presence on Minjerribah is further suggested by palaeoenvironmental records of anthropogenic burning beginning by 45,000 years ago. These new chronologies from sites on a remnant portion of the continental margin confirm early human occupation along Sahul’s now-drowned eastern continental shelf.

Mapping Middle Stone Age human mobility in the Makgadikgadi Pans (Botswana) through multi-site geochemical provenancing of silcrete artefacts

Analyses of the distance over which lithic raw materials were transported for use in stone tool production provide important insights into early human mobility through prehistoric landscapes. This study combines the use of geochemical provenancing, chaîne opératoire analysis and geochronology to examine patterns of lithic raw material procurement at five single-use open-air Middle Stone Age (MSA) archaeological sites in Ntwetwe Pan, part of the Makgadikgadi Pans complex in north-central Botswana. Maximum ages of the five sites ranged from 106 ± 3 to 69 ± 7 ka, with site formation thought to have occurred before and after a lake high stand dated to c. 72-57 ka. Tool manufacture at all sites was largely confined to the production of MSA points, with silcrete used exclusively as the raw material. Geochemical provenancing investigations aimed to identify the specific silcrete outcrops used as lithic raw material sources. Analysis of contemporary pan floor deposits show that sediment (and hence silcrete) geochemistry in Ntwetwe is determined by the proportional sediment input into the pan from fluvial systems with different catchment geologies. Immobile trace element signatures for 46 waste manufacturing flakes were compared against equivalent data for 321 silcrete samples collected at outcrops within and beyond Ntwetwe Pan. Waste flakes were chosen to be representative of the main silcrete raw material types present within the artefact assemblage at each site. Fifteen waste flakes were shown to match specific outcrops on the basis of their geochemical signatures and petrographic properties; all matching outcrops were within Ntwetwe Pan, at distances ranging from 7 to 55 km from individual sites. Multi-site analysis of procurement patterns identifies common silcrete source areas, revealing a preference for silcrete from particular locations within Ntwetwe Pan. Given that the five archaeological sites were likely occupied at different times, this resource preference may have been a longer-term behavioural feature of MSA populations in the Ntwetwe region. The distances over which silcrete was transported in Ntwetwe Pan are smaller than identified in investigations at similar-aged MSA sites in northwest Botswana. The reasons for the different silcrete procurement ranges in the two regions are likely related to silcrete availability and/or raw material preference, but this requires further investigation.

The survival of artefacts from different historical phases in shallow open sites and the need for spit excavations: An overview from the Cumberland Plain, Western Sydney, Australia

It has often been thought that shallow open sites (<50 cm of artefact-bearing deposit) in the undulating landscape of the Cumberland Plain would not retain any chronologically meaningful vertical distributions. The prevailing geomorphic model has proposed that artefacts discarded by people at different times would have been buried and mixed together by bioturbation. To address this model, this paper analyses the vertical distributions of artefacts at 21 open sites and finds that 13 of those sites show vertical variation in the proportions of indurated mudstone/silicified tuff (IMST), silcrete and/or quartz artefacts. The trends shown by the distributions are broadly consistent with a known regional change in raw material use and indicate the survival of some chronologically meaningful artefact variation with depth of the deposit. In addition, sites with increased proportions of older IMST artefacts in deeper deposits tend to be associated with larger streams and tend to occur at low elevations. This suggests that the survival of older artefacts could be related in part to long-term geomorphic processes visible at the landscape scale. The results indicate that sites may have differing histories of visitation, artefact discard, geomorphic processes and survival of evidence, and that careful, stratigraphic excavation is warranted.

Reassessing southern African silcrete geochemistry: implications for silcrete origin and sourcing of silcrete artefacts

AbstractA synthesis of the geochemistry of silcretes and their host sediments in the Kalahari Desert and Cape coastal zone, using isocon comparisons, shows that silcretes in the two regions are very different. Kalahari Desert silcretes outcrop along drainage‐lines and within pans, and formed by groundwater silicification of near‐surface Kalahari Group sands. Silicification was approximately isovolumetric. Few elements were lost; silicon (Si) and potassium (K) were gained as microquartz precipitated in the sediment porosity and glauconite formed in the sub‐oxic groundwater conditions. The low titanium (Ti) content reflects the composition of the host sands. Additional elements in the Kalahari Desert silcretes were supplied in river water and derived from weathering of silicates in basement rocks. Evaporation under an arid climate produced high‐pH groundwater that mobilized and precipitated Si; this process is still occurring.In the Cape coastal zone, pedogenic silcretes cap hills and plateaus, overlying deeply weathered argillaceous bedrock. Silicification resulted from intensive weathering that destroyed the bedrock silicates, almost completely removing most elements and causing a substantial volume decrease. Some of the silica released formed a microcrystalline quartz matrix, and most Ti precipitated as anatase, so the Cape silcretes contain relatively high Ti levels. The intense weathering that formed the Cape silcretes could have occurred in the Eocene, during and after the Palaeocene‐Eocene Thermal Maximum, when more acidic rainfall and high temperatures resulted in intensified silicate weathering worldwide. This could have been responsible for widespread formation of pedogenic silcretes elsewhere in Africa and around the globe.Trace element sourcing of silcrete artefacts to particular outcrops has most potential in the Cape, where differences between separate bedrock areas are reflected in the silcrete composition. In the Kalahari Desert, gains of some elements can override compositional differences of the parent material, and sourcing should be based on elements that show the least change during silicification. © 2020 John Wiley &amp; Sons, Ltd.

The antiquity of Australian silcrete heat treatment: Lake Mungo and the Willandra Lakes

The evolution of heat treatment for stone artefact production is a subject of major interest for our understanding of early modern humans. In this study, we examine the evidence from one region in Australia to provide a new record of the antiquity of heat treatment, explore chronological shifts in the frequency of heat treatment, and discuss the implications of these findings for early population dynamics and the technical knowledge early settlers might have brought with them. Until now, Australian heat treatment has only dated back 25000 years. This study of the Willandra Lakes, including Lake Mungo, has identified the oldest systematic evidence of heat treatment yet reported in Australia, dating to ∼42000 years. We also document time-dependent directional change in the frequency of the practice. At those early times, with over 60% of all silcrete artefacts heat-treated, we hypothesize that the practice was mastered and integrated as a recurrent technical solution to the complexities of knapping silcrete. Over time, the use of heat treatment decreased progressively until less than 10% of the artefacts were heat-treated in the terminal Holocene. This trajectory has implications for understanding the antiquity of heat treatment on the Australian continent and for investigating the factors that governed its use.

Heat treatment of Kalahari and Cape silcretes: impacts upon silcrete chemistry and implications for geochemical provenancing

Recent studies in southern Africa and eastern Australia have demonstrated the feasibility of using a geochemical fingerprinting approach to determine the source locations from which silcrete raw materials were procured prior to their use in stone tool manufacture. The impact of intentional heat treatment of silcrete upon its chemistry, however, is unknown, meaning that heat-treated silcrete artefacts have to date been excluded from provenancing studies. This investigation presents the first high-resolution experimental analysis of the impacts of heat treatment upon the chemical composition of silcrete. The study compares the composition of unheated control samples against samples heat-treated to target temperatures of up to 600 °C taken from four silcrete blocks from South Africa and Botswana. Chemical compositions of samples are determined using ICP-MS and ICP-AES. Experimental results indicate that heat treatment has a limited impact upon silcrete chemistry. Only 7 out of 65 minor, trace and rare earth elements analysed (Al2O3, Fe2O3, K2O, As, Cr, Cs and Cu) were depleted beyond expected error limits following controlled heating. There was no consistent pattern of elemental depletion across the four silcrete samples, although a greater number of elements were depleted from chalcedony-cemented Kalahari silcretes compared with microquartz-cemented Cape silcretes. We conclude that it is safe to use chemical data from heat-treated artefacts from the Cape as part of geochemical fingerprinting studies; however, we recommend that Cu and Cs concentrations be omitted from any statistical analyses until the effects of heat treatment upon these elements are fully understood. We echo the conclusions of previous studies by recommending that chalcedony-cemented silcrete artefacts that show signs of burning or intentional heat treatment be excluded from provenancing studies in the Kalahari and potentially elsewhere.

Evolution of Silcrete Heat Treatment in Australia—a Regional Pattern on the South-East Coast and Its Evolution over the Last 25 ka

We document long-term evolution in the rate of heat treatment in Eastern Australia and explore them as a technological response to dynamic industrial and social contexts that developed in the last 25 millennia. We employed methods previously used in Africa but novel in Australia to infer long-term directional changes in the relative frequency of silcrete artefacts that were heat-treated. Our methods involved independent and cross-verifying tests of the presence or absence of heat treatment, employing visual classifications and surface roughness measures. These methods revealed a coherent series of increases over time in the landscapes around Sydney, so that Late Holocene assemblages displayed higher rates of heat treatment than terminal Pleistocene or Early Holocene ones. We hypothesise that the directional trend towards greater frequencies of heat-treated artefacts on Australia’s eastern seaboard is explicable in terms of the context of technological shifts towards microlith production superimposed onto an even longer term process of lithic resource depletion, perhaps compounded with the development of political barriers to the redistribution of knappable stone.

Lead (Pb) isotope signatures for silcrete sources from the Willandra Lakes region, Australia: A pilot study of a new method for provenancing silcrete artefacts

Silcrete was often used to make stone tools and the ubiquity of this material in the archaeological record has sparked considerable interest in developing techniques that can be used to trace its geographic origin. However, the highly variable physical and chemical properties of silcrete means that artefacts made from this raw material have proved difficult to provenance. This paper describes the use of Pb isotope analysis to characterize and differentiate silcrete sources in the Willandra Lakes region, a UNESCO World Heritage listed site in southeastern Australia. The sample collection strategy employed in the field has allowed Pb isotope variation both within and between the silcrete sources to be described. Pb isotope variation within each silcrete source does not exhibit spatial patterning, but Pb isotope signatures differ between silcrete sources in the Willandra Lakes region, and clear separation between more distant sources, is demonstrated. This represents a first step in being able to use isotope analysis to investigate how silcrete from different sources was used and how it was moved around the landscape.

The Cranebrook Terrace revisited: recent excavations of an early Holocene alluvial deposit on the banks of the Nepean River, NSW, and their implications for future work in the region

We present the results of a compliance-based excavation on the banks of Peach Tree Creek within the alluvial margin of the Nepean River, Penrith, NSW. The excavations consisted of (i) two mechanically excavated trenches (3 × 1 m) in controlled 20 cm spits to depths of 4 m below surface, and (ii) a subsequent stage of manual salvage excavation (6 m2) focussing on the artefact-bearing levels indicated by the testing phase. The excavations identified two sedimentary deposits, with the lowest being part of the Cranebrook Formation, a deep alluvial deposit within which artefacts dating to >40 ka have been previously reported. We recovered four indurated mudstone/tuff and two coarse silcrete artefacts, all having characteristics of the late Pleistocene/early Holocene, and which we have OSL dated to >9.5 ka from the upper portion of the Richmond Unit of the Cranebrook Formation (3.5–3.9 m below the surface). Along with a greater understanding of the formation (only a part of which was deposited during the last 50 ka) and recent archaeological discoveries, our results lend increasing support for visitation of the Nepean river corridor by Aboriginal people as a part of the initial colonisation of Australia. It remained a key locale for occupation and visitation throughout the late Pleistocene. Finally, we discuss the current NSW State government guidelines for investigating archaeological deposits and identify concerns about their effectiveness and applicability when investigating areas of potentially deep stratigraphy along the banks of the Nepean River.

Elemental differences: Geochemical identification of aboriginal silcrete sources in the Arcadia Valley, eastern Australia

Portable X-ray Fluorescence (PXRF) analysis was applied to silcrete artefacts from surface concentrations in the southern Arcadia Valley, eastern Australia. These artefacts were manufactured from river cobbles, as shown by the waterworn cortex, and could have been obtained from three sources: Dawson River, Carnarvon Creek and/or Clematis Creek. PXRF analyses of cobbles from these sites, evaluated using nonparametric statistics (because the data are skewed) and confidence ellipses, showed that the three sources can be distinguished by their Fe and Zr concentrations. Comparison with artefact analyses showed that many artefacts were probably sourced from Clematis Creek, with a substantial number from Dawson River but few, if any, from Carnarvon Creek. The sourcing pattern indicates that Aboriginal people in the Arcadia Valley were influenced not only by proximity when procuring silcrete, but also quality, cobble size and traditional mobility strategies. Carnarvon Creek was ignored because of its distance from the artefact sites and lower quality silcrete. Clematis Creek was the most favoured source because although distant from the artefact sites, it contained large silcrete cobbles (sufficient for the manufacture of large scrapers and knives), and was probably visited frequently due to its central location in the traditional country of the Karingbal People.

Tempering-residue on heat-treated silcrete: an experimental perspective and a potential analytical protocol

Silcrete heat treatment in the South African Middle Stone Age has been understood as a proxy for several key concepts in the evolution of early anatomically modern humans, although relatively little is yet known about the techniques and procedures used for it. Tempering-residue on heat-treated artefacts is one of the few known proxies for such a heating technique. It was reported to indicate heat treatment in open-air fires rather than in a sand-bath. There are however, several questions that need to be answered before tempering-residue can be used as an unambiguous proxy for heat treatment in open-air fires. These questions included: does it exclusively form in contact with embers? Is it only produced by green wood? We investigate the conditions under which tempering-residue forms using an experimental approach and wood from the zone of natural silcrete occurrence in South Africa. Our results confirm earlier publications by highlighting that tempering-residue only forms during heat treatment in direct contact with embers. Moreover, it indicates the use of green (not dried) wood in these fires. We also propose a potentially non-destructive analysis protocol for identifying tempering-residue on silcrete artefacts using infrared and Raman spectroscopy. The implications of these results for our understanding of early stone heat treatment and Middle Stone Age archaeology in general are highlighted by the ongoing debate about technical complexity, required investment and modern behaviours of early Homo sapiens.

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

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. Middle Stone Age 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.

The geoarchaeology of a Holocene site on the Woolshed Embankment, Lake George, New South Wales

An extensive scatter of stone artefacts recorded as Site WE-1 on the Woolshed Embankment at the northern end of Lake George in southern NSW has been examined in the light of recent information on the lake’s history. Optical dates show that the core of the embankment formed between ~22,000 and 15,000 ya. Archaeological materials have survived in the overlying deposits, though they have been affected to a degree by repeated cultivation. These archaeological assemblages are now able to be interpreted in the light of a reconstruction (by Fitzsimmons and Barrows [2010]) of the Holocene lake history. The site was used during the mid- to late Holocene, initially during the penultimate high lake stand between 6000 and 2400 ya. The artefact assemblage has been inundated periodically by high lake levels, and potentially mixed by wave action. A silcrete- and backed artefact-rich and bipolar artefact-poor assemblage on part of the site was replaced across the whole site by one that had lower proportions of silcrete and backed artefacts and higher proportions of bipolar artefacts, a pattern similar to that observed in other sites in southeast Australia.

Desert Lake: art, science and stories from Paruku

Desert lake: art, science and stories from Paruku Steve Morton, Mandy Martin, Kim Mahood and John Carty (eds) 2013 CSIRO Publishing, Canberra, 312pp, ISBN 9780643106284 (hbk) This volume represents a brilliant fusion of Traditional Knowledge, origin narratives, Western science and contemporary art. It is based on 'deep-time' complex human-landscape relationships from a highly significant lake system known as Paruku in the south-east Kimberley region. Known on cartographic charts as Lake Gregory, it is the only co-ordinated drainage system that flows from the east Kimberley into the expansive linear dune fields of the Great Sandy Desert. The lake was once a mega-lake, many times its current size, reflecting massive monsoonal rains more akin to central Indonesia than the present Kimberley desert edge. It hosted an enhanced aquatic and avian fauna and was likely a highly attractive lake for early settlers--being surrounded by savannah woodlands and grasses with grazing terrestrial fauna. Indeed, it was at such major water bodies that peoples transitioned into the desert hunter-gatherer adaptations we think of today as the ethnographic norm. They persisted in an increasingly arid landscape--with lakes as a chain of connection to previous pluvial states. I first came to Paruku 34 years ago and recall the nascent wiltjas (bough shelters) with small groups of largely elderly people who were re-settling their desert homelands from townships like Halls Creek, having been edged off pastoral regimes due to the new awards. They were re-connecting to old camping places, Dreaming sites and a range of totemic 'runs', rather than being wrapped around the rhythms of mustering and the earlier cattle drives of the nearby Canning Stock Route. They now had green-fields for (re)connection and establishment of community (such as Mulan). Jump ahead almost 30 years and as the last part of the ARC Canning Stock Route 'Rock Art and Jukurrpa Project' we are collaborating with Professor Jim Bowler, a new generation of senior Traditional Owners, and other colleagues in tracking the Two Dogs Dreaming, human occupation patterns and acrylic iconography from Tjurabalan native title holders--all in the sands and exposures of Parnkupirti Creek. With Mike Smith, Jo McDonald, Alan Williams and some 20 traditional custodians and (it felt like) hundreds of visiting school children, we worked back through the unyielding lake muds to locate early artefacts which have been dated to between 45,000 to 50,000 years ago. This was a time period when the energy from floodwaters was very high; large cobbles were pushed across the landscape during flood events and it appears early assemblages of flaked silcrete artefacts were polished and sub-rounded to then lie exposed for millennia in brachiating creeklines fringing the lake. This lavish CSIRO publication profiles community voices, art productions and intersections with science over some 300 pages. The four editors comprise a leading arid zone ecologist, two artists of natural-cultural systems and the deserts, and an anthropologist of Indigenous art. The book is divided into three chronological parts; (a) Deep Time, (b) Recent Times and (c) The Future. There are ten chapters embedded within these parts and they deal with the stratigraphy of archaeology and geomorphology, the historical connections and layered memories of custodians and the lake, its fluctuating freshwater ecology, and the painting of new landscapes of encounter and enterprise --not the least of which is the Indigenous Protected Area regime. …

Silcrete quarries and artefact distribution in the Central Queensland Highlands, Eastern Australia

AbstractA geoarchaeological study of silcrete in the Central Queensland Highlands highlights the importance of geological context in understanding the procurement, use and transport of artefacts. This study shows, by focusing on a newly discovered silcrete quarry, that silcrete formed beneath basalt by silicification of stream sediments and underlying sandstone. Silcrete outcrops are largely restricted to cliffs where the base of the basalt is exposed, narrowing the location of potential quarries. Silcrete artefacts are abundant throughout the region, and there are clear patterns in the use and distribution of different qualities of silcrete. Fine‐grained grain‐supported silcrete is the dominant artefact lithology because of its excellent flaking quality; it is sufficiently versatile to make flake scrapers and retouched microlithic tools. At one occupation site, the mid‐Holocene appearance of backed artefacts and points was accompanied by an increase in the use of fine‐grained grain‐supported silcrete and a decrease in the exploitation of coarse‐grained matrix‐supported silcrete; the latter was less suited to the manufacture of more curated tools. With increasing distance from silcrete outcrops, there is a decrease in the percentage of silcrete artefacts and an increase in the expedient use of local lithologies. However, silcrete's flaking quality justified its dispersal over distances of &gt;80 kilometres from the nearest outcrop.

Dynamics Of Dispersion Revisited? Archaeological Context and the Study of Aboriginal Knapped Glass Artefacts in Australia

The archaeological study of Aboriginal knapped glass artefacts in Australia has focused almost entirely on glass tool production, and more particularly, on the technology of glass tool production (as opposed, for example, to the social context of glass tool production). In this paper, we suggest the value of an approach which foregrounds context in an attempt to point towards new directions for knapped glass artefact studies in Australia. We make reference to qualitative field observations of Aboriginal knapped glass artefacts located on early copper and lead mining settlements from mid-Western Australia, and return to pioneering work done by Denis Byrne in the same region on silcrete artefacts to illustrate our argument. In doing so, we note the ways in which these studies demonstrate historically changing approaches to the archaeological record by archaeologists from the University of Western Australia, and our own work as Sandra Bowdler’s students in the late 1980s and late 1990s respectively.

Middle Stone Age artefacts from the 1993 and 1995 excavations of Die Kelders Cave 1, South Africa

Renewed excavations at Die Kelders Cave 1 on the southern South African coast have uncovered large collections of Middle Stone Age (MSA) stone artefacts and coloring materials, but not bone or shell artefacts. High percentages of silcrete artefacts in one of the lower layers are confirmed, but there is no evidence for the Howieson's Poort stage of the MSA as previously mooted. The artefacts probably date to the middle–late MSA. The consistency and conservation which characterize the Die Kelders and other non-Howieson's Poort MSA artefact sequences contrast with the faster changes and innovative patterning seen in Later Stone Age sequences. It is not known whether this picture is a consequence of the traditional typological approach to MSA stone artefact analysis, or whether it reflects differences between Middle and Later Stone Age toolmakers in biological cognition capabilities or merely in social relations and worldviews.