Silcrete

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Silcrete (siliceous paleosol) in the Waddens Cove Formation (formed during the Pennsylvanian), Sydney Basin, Nova Scotia Silcrete mcr1.JPG
Silcrete (siliceous paleosol) in the Waddens Cove Formation (formed during the Pennsylvanian), Sydney Basin, Nova Scotia

Silcrete is an indurated (resists crumbling or powdering) soil duricrust formed when surface soil, sand, and gravel are cemented by dissolved silica. The formation of silcrete is similar to that of calcrete, formed by calcium carbonate, and ferricrete, formed by iron oxide. It is a hard and resistant material, and though different in origin and nature, appears similar to quartzite. As a duricrust, there is potential for preservation of root structures as trace fossils.

Silcrete is common in the arid regions of Australia and Africa often forming the resistant cap rock on features such as the breakaways of the Stuart Range of South Australia. Silcrete can be found at a lesser extent throughout the world especially England (e.g. Hertfordshire puddingstone and sarsen stone ), and France. [1] In the Great Plains of the United States, polished silcrete cobbles are locally common on the surface and in river gravels east of the outcrops of the Ogallala Formation. [2] [3]

Human use

In Australia, silcrete was widely used by Aboriginal people for stone tool manufacture, and as such, it was a tradeable commodity, and silcrete tools can be found in areas that have no silcrete groundmass at all, similar to the European use of flint.

Tools made out of silcrete which has not been heat treated are difficult to make with flintknapping techniques. It is widely believed by stone tool experts that the technology to treat silcrete by burying under a hot fire was known 25,000 years ago in Europe. Heating changes the stone structure making it more easily flaked. [4] This process may have been the first use of so-called pyrotechnology by early mankind. [5] [6]

Bifacial silcrete point from Blombos Cave, South Africa, Middle Stone Age
(71,000 BCE) (scale bar = 5cm) Blombos point white.JPG
Bifacial silcrete point from Blombos Cave, South Africa, Middle Stone Age
(71,000 BCE) (scale bar = 5cm)

In South Africa at Pinnacle Point researchers have determined that two types of silcrete tools were developed between 60,000 and 80,000 years ago and used the heat treatment technique. There is evidence to suggest the technique may have been known as early as 164,000 years ago. [4] [7]

The peoples of the African Middle Stone Age (MSA) showed a preference for silcrete tools, sourcing the material from up to 200 km to use in place of more accessible quartz and quartzite. MSA quarries have recently been found in Botswana south of the Okavango Delta. Evidence was found that raw silcrete blanks and blocks were transported prior to heat treating during the MSA. The geochemical signatures of the fragments can be used to identify where many of the individual pieces were quarried. [8]

The builders of Stonehenge in southern England used this stone for the Heel Stone and sarsen circle uprights. Avebury and many other megalithic monuments in southern England are also built with sarsen stones.

In the Great Plains of the United States, silcrete cobbles and boulders up to 16 kilograms (35 lb) of Neogene/early-Quaternary age are found on uplands bordering the Ogallala outcrop and were used as chipped tool stone as early as the Early Ceramic (ca. 400–1100 CE) Keith phase of the Woodland culture. [3] [2]

In a survey of Fishtail points from the Late Pleistocene of Uruguay, approximately 54% of the studied points were made of silcrete, far more than any other rock type, with silcrete tools being transferred hundreds of kilometres from their original outcrop. [9]

Related Research Articles

<span class="mw-page-title-main">Flint</span> Cryptocrystalline form of the mineral quartz

Flint, occasionally flintstone, is a sedimentary cryptocrystalline form of the mineral quartz, categorized as the variety of chert that occurs in chalk or marly limestone. Historically, flint was widely used to make stone tools and start fires.

A stone tool is, in the most general sense, any tool made either partially or entirely out of stone. Although stone tool-dependent societies and cultures still exist today, most stone tools are associated with prehistoric cultures that have become extinct. Archaeologists often study such prehistoric societies, and refer to the study of stone tools as lithic analysis. Ethnoarchaeology has been a valuable research field in order to further the understanding and cultural implications of stone tool use and manufacture.

<span class="mw-page-title-main">Rock (geology)</span> Naturally occurring mineral aggregate

In geology, rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its chemical composition, and the way in which it is formed. Rocks form the Earth's outer solid layer, the crust, and most of its interior, except for the liquid outer core and pockets of magma in the asthenosphere. The study of rocks involves multiple subdisciplines of geology, including petrology and mineralogy. It may be limited to rocks found on Earth, or it may include planetary geology that studies the rocks of other celestial objects.

<span class="mw-page-title-main">Quartzite</span> Hard, non-foliated metamorphic rock

Quartzite is a hard, non-foliated metamorphic rock which was originally pure quartz sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to grey, though quartzites often occur in various shades of pink and red due to varying amounts of hematite. Other colors, such as yellow, green, blue and orange, are due to other minerals.

<span class="mw-page-title-main">Sarsen</span> Type of sandstone block found in southern England

Sarsen stones are silicified sandstone blocks found extensively across southern England on the Salisbury Plain and the Marlborough Downs in Wiltshire; in Kent; and in smaller quantities in Berkshire, Essex, Oxfordshire, Dorset, and Hampshire.

<span class="mw-page-title-main">Hertfordshire puddingstone</span> Conglomerate sedimentary rock

Hertfordshire puddingstone is a conglomerate sedimentary rock composed of rounded flint pebbles cemented together by a younger matrix of silica quartz. The distinctive rock is largely confined to the English counties of Buckinghamshire and Hertfordshire but small amounts occur throughout the London Basin. It is quite commonly found in fields in and around Chesham, where pieces can be seen as boundary stones and in rockeries. Despite a superficial similarity to concrete, it is an entirely natural silcrete. A fracture runs across both the pebbles and the sandy matrix as both have equal strength unlike concrete where the pebbles remain whole and a fracture occurs only in the matrix. Like other puddingstones, it derives its name from the manner in which the embedded flints resemble the plums in a pudding. It forms the local base of the Upnor Formation of the Lambeth Group.

<span class="mw-page-title-main">Blombos Cave</span> Archaeological site in Western Cape, South Africa

Blombos Cave is an archaeological site located in Blombos Private Nature Reserve, about 300 km east of Cape Town on the Southern Cape coastline, South Africa. The cave contains Middle Stone Age (MSA) deposits currently dated at between c. 100,000 and 70,000 years Before Present (BP), and a Late Stone Age sequence dated at between 2000 and 300 years BP. The cave site was first excavated in 1991 and field work has been conducted there on a regular basis since 1997, and is ongoing.

<span class="mw-page-title-main">Middle Stone Age</span> Period in African prehistory

The Middle Stone Age was a period of African prehistory between the Early Stone Age and the Late Stone Age. It is generally considered to have begun around 280,000 years ago and ended around 50–25,000 years ago. The beginnings of particular MSA stone tools have their origins as far back as 550–500,000 years ago and as such some researchers consider this to be the beginnings of the MSA. The MSA is often mistakenly understood to be synonymous with the Middle Paleolithic of Europe, especially due to their roughly contemporaneous time span; however, the Middle Paleolithic of Europe represents an entirely different hominin population, Homo neanderthalensis, than the MSA of Africa, which did not have Neanderthal populations. Additionally, current archaeological research in Africa has yielded much evidence to suggest that modern human behavior and cognition was beginning to develop much earlier in Africa during the MSA than it was in Europe during the Middle Paleolithic. The MSA is associated with both anatomically modern humans as well as archaic Homo sapiens, sometimes referred to as Homo helmei. Early physical evidence comes from the Gademotta Formation in Ethiopia, the Kapthurin Formation in Kenya and Kathu Pan in South Africa.

<span class="mw-page-title-main">Puddingstone (rock)</span> Colorful conglomerate rock

Puddingstone, also known as either pudding stone or plum-pudding stone, is a popular name applied to a conglomerate that consists of distinctly rounded pebbles whose colours contrast sharply with the colour of the finer-grained, often sandy, matrix or cement surrounding them. The rounded pebbles and the sharp contrast in colour gives this type of conglomerate the appearance of a raisin or Christmas pudding. There are different types of puddingstone, with different composition, origin, and geographical distribution. Examples of different types of puddingstones include the Hertfordshire, Schunemunk, Roxbury, and St. Joseph Island puddingstones.

The Klasies River Caves are a series of caves located east of the Klasies River Mouth on the Tsitsikamma coast in the Humansdorp district of Eastern Cape Province, South Africa. The Klasies River Main (KRM) site consists of 3 main caves and 2 shelters located within a cliff on the southern coast of the Eastern Cape. The site provides evidence for developments in stone tool technology, evolution of modern human anatomy and behavior, and changes in paleoecology and climate in Southern Africa based on evidence from plant remains.

The control of fire by early humans was a critical technology enabling the evolution of humans. Fire provided a source of warmth and lighting, protection from predators, a way to create more advanced hunting tools, and a method for cooking food. These cultural advances allowed human geographic dispersal, cultural innovations, and changes to diet and behavior. Additionally, creating fire allowed human activity to continue into the dark and colder hours of the evening.

The Soanian culture is a prehistoric technological culture from the Siwalik Hills Pakistan. It is named after the Soan Valley in Pakistan. Soanian sites are found along the Siwalik region in present-day India, Nepal and Pakistan. The Soanian culture has been approximated to have taken place during the Middle Pleistocene period or the mid-Holocene epoch (Northgrippian). Debates still goes on today regarding the exact period occupied by the culture due to artefacts often being found in non-datable surface context. This culture was first discovered and named by the anthropology and archaeology team led by Helmut De Terra and Thomas Thomson Paterson. Soanian artifacts were manufactured on quartzite pebbles, cobbles, and occasionally on boulders, all derived from various fluvial sources on the Siwalik landscape. Soanian assemblages generally comprise varieties of choppers, discoids, scrapers, cores, and numerous flake type tools, all occurring in varying typo-technological frequencies at different sites.

<span class="mw-page-title-main">Mumbwa Caves</span> Archaeological site in Zambia

The Mumbwa Caves are an archeological site in Zambia. The site has yielded artifacts that date from the Mesolithic, Neolithic and the Iron Age. The caves are a source of stratified, in situ deposits with faunal and human remains. Mumbwa, with its interior structures, demonstrates the complexity of the behavioral abilities of the people from the Mesolithic. Selection of raw materials along with features such as hearths suggests a population which was modern in its behaviors used to inhabit the Mumbwa Caves. Study and excavation of the Mumbwa Caves is helping to fill in the gaps in the late Pleistocene prehistory of south central Africa.

Howiesons Poort is a technological and cultural period characterized by material evidence with shared design features found in South Africa, Lesotho, and Namibia. It was named after the Howieson's Poort Shelter archaeological site near Grahamstown in South Africa, where the first assemblage of these tools was discovered. Howiesons Poort is believed, based on chronological comparisons between many sites, to have started around 64.8 thousand years ago and ended around 59.5 thousand years ago. It is considered to be a technocomplex, or a cultural period in archaeology classified by distinct and specific technological materials. Howiesons Poort is notable for its relatively complex tools, technological innovations, and cultural objects evidencing symbolic expression. One site in particular, Sibudu Cave, provides one of the key reference sequences for Howiesons Poort. Howiesons Poort assemblages are primarily found at sites south of the Limpopo River.

<span class="mw-page-title-main">Ogallala Formation</span> Geologic formation in the western United States

The Ogallala Formation is a Miocene to early Pliocene geologic formation in the central High Plains of the western United States and the location of the Ogallala Aquifer. In Nebraska and South Dakota it is also classified as the Ogallala Group. Notably, it records the North American Land Mammal Ages (NALMAs) Hemphillian, Clarendonian, and Barstovian. It also includes an excellent record of grass seeds and other plant seeds, which can be used for biostratigraphic dating within the formation. The Ogallala Formation outcrops of Lake Meredith National Recreation Area preserve fish fossils. Similar specimens from the same unit are found at Alibates Flint Quarries National Monument in Texas.

<span class="mw-page-title-main">Riesenstein (Wolfershausen)</span> Megalith in Hesse, Germany

The Riesenstein is a megalith or menhir, which is situated close to the village of Wolfershausen. It is the largest megalith in the district of Schwalm-Eder-Kreis, Hesse, Germany.

<span class="mw-page-title-main">Valentine Formation</span> Geological formation in midwestern US

The Valentine Formation is a geologic unit formation or member within the Ogallala unit in northcentral Nebraska near the South Dakota border. It preserves fossils dating to the Miocene epoch of the Neogene period and is particularly noted for Canid fossils. This unit consists of loosely-consolidated sandstone that crumbles easily. These sands carry the water of the Ogallala Aquifer and is the source of much of the water in the Niobrara River. A particular feature of the Valentine is lenticular beds of green-gray opaline sandstone that can be identified in other states, including South Dakota, Nebraska, Kansas, and Colorado. Although three mammalian fauna stages can be mapped throughout the range of the Ogallala, no beddings of the Ogallala are mappable and all attempts of formally applying the Valentine name to any mappable lithology beyond the type location have been abandoned. Even so, opaline sandstone has been used to refer to this green-gray opalized conglomerate sandstone that is widely found in the lower Ogallala Formation.

<span class="mw-page-title-main">Fincha Habera, Ethiopia</span> Middle Stone Age archeological site in southern Ethiopia

Fincha Habera is a Middle Stone Age archaeological site located within the Bale Mountains in southern Ethiopia. The rock shelter is located within the largest alpine ecosystem in Africa and is especially notable for the high altitude of the shelter and archaeological site, lying about 4,000 meters above sea level, between the Harcha and Wasama Valleys. During the Late Pleistocene, the Fincha Habera rock shelter was occupied by hunter-gatherers and the site now provides evidence for one of the oldest human occupancies at high-altitudes. The surrounding glacial climate provided conditions of fresh water, vegetation, and sustenance that created a unique environment that allowed these hunter-gatherers to find longer term residence at this shelter.

<span class="mw-page-title-main">Mlambalasi Rock Shelter</span> National Historic Site of Tanzania

The Mlambalasi Rock Shelter is a historic site located in Iringa District of Iringa Region in southern Tanzania, 50 km away from Iringa City. Excavations in 2006 and 2010 by the Iringa Region Archaeological Project uncovered artifactual deposits from the Later Stone Age (LSA), the Iron Age, and the historic periods, as well as external artifacts from the Middle Stone Age (MSA). Direct dating on Achatina shell and ostrich eggshell beads indicates that the oldest human burials at Mlambalasi are from the terminal Pleistocene. Mlambalasi is characterized by interment in the LSA and Iron Age periods, as well as by cycles of use and abandonment.

<span class="mw-page-title-main">Fishtail projectile point</span> Type of projectile point used in South America during the Late Pleistocene

Fishtail points, also known as Fell points are a style of Paleoindian projectile point widespread in South America at the end of the Late Pleistocene. Their chronological timing is disputed, with some authors favouring a short chronology spanning 12,800–12,200 years Before Present (BP), while others favouring a long chronology spanning 13,500–10,200 years BP. It is the earliest widespread lithic style in South America, being contemporaneous in its earlier stages to the use of Clovis points in North America. Fishtail points may be derived from Clovis points, or possibly from Fishtail-like points found on the Gulf Coast of North America and in Central America.

References

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