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58-714: Wonderwerk Cave is an archaeological site, formed originally as an ancient solution cavity in dolomite rocks of the Kuruman Hills , situated between Danielskuil and Kuruman in the Northern Cape Province , South Africa. It is a National Heritage Site, managed as a satellite of the McGregor Museum in Kimberley. Geologically, hillside erosion exposed the northern end of the cavity, which extends horizontally for about 140 m (460 ft) into

116-592: A Grade I site (i.e.: of national significance). Declaration as a National Heritage Site followed, being published in the Government Gazette on 12 March 2010. Coupled in a serial nomination with Border Cave and Klasies River Mouth for South Africa's Tentative List for World Heritage inscription, it was re-nominated in its own right for the Tentative List in April 2009. Wonderwerk Cave was one of

174-422: A different element or a different isotope of the original element. In rock and other materials of similar density, most of the cosmic ray flux is absorbed within the first meter of exposed material in reactions that produce new isotopes called cosmogenic nuclides . At Earth's surface most of these nuclides are produced by neutron spallation . Using certain cosmogenic radionuclides , scientists can date how long

232-434: A drop of dilute hydrochloric acid is dropped on it. This distinguishes dolomite from limestone, which is also soft but reacts vigorously with dilute hydrochloric acid. Dolomite usually weathers to a characteristic dull yellow-brown color due to the presence of ferrous iron. This is released and oxidized as the dolomite weathers. Dolomite is usually granular in appearance, with a texture resembling grains of sugar . Under

290-405: A high percentage of CaMg(CO 3 ) 2 in which natural caves or solution tubes have formed. Both calcium and magnesium go into solution when dolomite rock is dissolved. The speleothem precipitation sequence is: calcite , Mg-calcite, aragonite , huntite and hydromagnesite . Hence, the most common speleothem (secondary deposit) in caves within dolomite rock karst , is calcium carbonate in

348-544: A high-calcium limestone, such as manufacture of sodium carbonate . Dolomite is used for production of magnesium chemicals, such as Epsom salt , and is used as a magnesium supplement. It is also used in the manufacture of refractory materials . As with limestone caves , natural caves and solution tubes typically form in dolomite rock as a result of the dissolution by weak carbonic acid. Caves can also, less commonly, form through dissolution of rock by sulfuric acid . Calcium carbonate speleothems (secondary deposits) in

406-662: A particular nuclide is a function of geomagnetic latitude, the amount of sky that can be seen from the point that is sampled, elevation, sample depth, and density of the material in which the sample is embedded. Decay rates are given by the decay constants of the nuclides. These equations can be combined to give the total concentration of cosmogenic radionuclides in a sample as a function of age. The two most frequently measured cosmogenic nuclides are beryllium-10 and aluminum-26 . These nuclides are particularly useful to geologists because they are produced when cosmic rays strike oxygen-16 and silicon-28 , respectively. The parent isotopes are

464-404: A particular surface has been exposed, how long a certain piece of material has been buried, or how quickly a location or drainage basin is eroding. The basic principle is that these radionuclides are produced at a known rate, and also decay at a known rate. Accordingly, by measuring the concentration of these cosmogenic nuclides in a rock sample, and accounting for the flux of the cosmic rays and

522-566: A result, attempts to precipitate dolomite from seawater precipitate high-magnesium calcite instead. This substance, which has an excess of calcium over magnesium and lacks calcium-magnesium ordering, is sometimes called protodolomite . Raising the temperature makes it easier for magnesium to shed its hydration shell, and dolomite can be precipitated from seawater at temperatures in excess of 60 °C (140 °F). Protodolomite also rapidly converts to dolomite at temperatures of 250 °C (482 °F) or higher. The high temperatures necessary for

580-512: A rock sample. These rates are usually estimated empirically by comparing the concentration of nuclides produced in samples whose ages have been dated by other means, such as radiocarbon dating , thermoluminescence , or optically stimulated luminescence . The excess relative to natural abundance of cosmogenic nuclides in a rock sample is usually measured by means of accelerator mass spectrometry . Cosmogenic nuclides such as these are produced by chains of spallation reactions. The production rate for

638-553: A symposium convened by Chazan and Horwitz at the site. They have since been published in a series of papers, and in a special issue on the site published in 2015. In April 2021, archaeologists from the University of Toronto and the Hebrew University announced the results of magnetostratigraphy and cosmogenic dating of the cave. According to the paper published in the journal Quaternary Science Reviews , making of

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696-453: A very high ratio of calcium to magnesium. Dolomite is used for many of the same purposes as limestone, including as construction aggregate ; in agriculture to neutralize soil acidity and supply calcium and magnesium; as a source of carbon dioxide ; as dimension stone ; as a filler in fertilizers and other products; as a flux in metallurgy ; and in glass manufacturing . It cannot substitute for limestone in chemical processes that require

754-568: Is cosmogenic radionuclide dating . Earth is constantly bombarded with primary cosmic rays , high energy charged particles – mostly protons and alpha particles . These particles interact with atoms in atmospheric gases, producing a cascade of secondary particles that may in turn interact and reduce their energies in many reactions as they pass through the atmosphere. This cascade includes a small fraction of hadrons, including neutrons. When one of these particles strikes an atom it can dislodge one or more protons and/or neutrons from that atom, producing

812-465: Is a collection of geochronological techniques for estimating the length of time that a rock has been exposed at or near Earth's surface. Surface exposure dating is used to date glacial advances and retreats , erosion history, lava flows, meteorite impacts, rock slides, fault scarps , cave development, and other geological events. It is most useful for rocks which have been exposed for between 10 and 10 years. The most common of these dating techniques

870-439: Is bombarded by a spallation product: oxygen of the quartz is transformed into Be and the silicon is transformed into Al. Each of these nuclides is produced at a different rate. Both can be used individually to date how long the material has been exposed at the surface. Because there are two radionuclides decaying, the ratio of concentrations of these two nuclides can be used without any other knowledge to determine an age at which

928-467: Is characterized by its nearly ideal 1:1 stoichiometric ratio of magnesium to calcium. It is distinct from high-magnesium limestone in that the magnesium and calcium form ordered layers within the individual dolomite mineral grains, rather than being arranged at random, as they are in high-magnesium calcite grains. In natural dolomite, magnesium is typically between 44 and 50 percent of total magnesium plus calcium, indicating some substitution of calcium into

986-471: Is known as dolomitization and any intermediate product is known as dolomitic limestone . The "dolomite problem" refers to the vast worldwide depositions of dolomite in the past geologic record in contrast to the limited amounts of dolomite formed in modern times. Recent research has revealed sulfate-reducing bacteria living in anoxic conditions precipitate dolomite which indicates that some past dolomite deposits may be due to microbial activity. Dolomite

1044-681: Is no consistent trend in its abundance with age, but most dolomite appears to have formed at high stands of sea level. Little dolomite is found in Cenozoic beds (beds less than 65 million years old), which has been a time of generally low sea levels. Times of high sea level also tend to be times of a greenhouse Earth , and it is possible that greenhouse conditions are the trigger for dolomite formation. Many dolomites show clear textural indications that they are secondary dolomites, formed by replacement of limestone. However, although much research has gone into understanding this process of dolomitization ,

1102-423: Is not seen to precipitate in the oceans. Likewise, geologists have not been successful at precipitating dolomite from seawater at normal temperatures and pressures in laboratory experiments. This is likely due to a very high activation energy for nucleating crystals of dolomite. The magnesium ion is a relatively small ion, and it acquires a tightly bound hydration shell when dissolved in water. In other words,

1160-419: Is resistant to erosion and can either contain bedded layers or be unbedded. It is less soluble than limestone in weakly acidic groundwater , but it can still develop solution features ( karst ) over time. Dolomite rock can act as an oil and natural gas reservoir. Dolomite takes its name from the 18th-century French mineralogist Déodat Gratet de Dolomieu (1750–1801), who was one of the first to describe

1218-416: Is secondary, formed by replacement of calcium by magnesium in limestone. The preservation of the original limestone texture can range from almost perfectly preserved to completely destroyed. Under a microscope, dolomite rhombs are sometimes seen to replace oolites or skeletal particles of the original limestone. There is sometimes selective replacement of fossils, with the fossil remaining mostly calcite and

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1276-541: Is stained by Alizarin Red S while dolomite grains are not. Dolomite rock consisting of well-formed grains with planar surfaces is described as planar or idiotopic dolomite, while dolomite consisting of poorly-formed grains with irregular surfaces is described as nonplanar or xenotopic dolomite. The latter likely forms by recrystallization of existing dolomite at elevated temperature (over 50 to 100 °C (122 to 212 °F)). The texture of dolomite often shows that it

1334-543: Is subject to high rates of evaporation. This results in precipitation of gypsum and aragonite , raising the magnesium to calcium ratio of the remaining brine. The brine is also dense, so it sinks into the pore space of any underlying limestone ( seepage refluxion ), flushing out the existing pore fluid and causing dolomitization. The Permian Basin of North America has been put forward as an example of an environment in which this process took place. A variant of this model has been proposed for sabkha environments in which brine

1392-635: Is sucked up into the dolomitizing limestone by evaporation of capillary fluids, a process called evaporative pumping . Another model is the mixing-zone or Dorag model, in which meteoric water mixes with seawater already present in the pore space, increasing the chemical activity of magnesium relative to calcium and causing dolomitization. The formation of Pleistocene dolomite reefs in Jamaica has been attributed to this process. However, this model has been heavily criticized, with one 2004 review paper describing it bluntly as "a myth". A 2021 paper argued that

1450-476: Is thermodynamically favorable, with a Gibbs free energy of about -2.2 kcal/mol. In theory, ordinary seawater contains sufficient dissolved magnesium to cause dolomitization. However, because of the very slow rate of diffusion of ions in solid mineral grains at ordinary temperatures, the process can occur only by simultaneous dissolution of calcite and crystallization of dolomite. This in turn requires that large volumes of magnesium-bearing fluids are flushed through

1508-473: The Zamani Project . Key team members who have worked on the dating of the lower units are the late Hagai Ron (magnetostratigraphic or palaeomagnetic dating), Ari Matmon ( cosmogenic isotope dating ), Robyn Pickering ( U/Pb dating) and Naomi Porat ( Optically stimulated luminescence dating). Results of these archaeological, dating, sedimentological and palaeoenvironmental studies were first reported at

1566-608: The 100 sites selected for the 2010 World Monuments Watch by the World Monuments Fund . In 2005, the Zamani Project documented the Wonderwerk Cave in 3D. A 3D model, panorama tour, images of the point cloud, sections and plans are available on www.zamaniproject.org . Dolomite (rock) Most dolomite was formed as a magnesium replacement of limestone or of lime mud before lithification . The geological process of conversion of calcite to dolomite

1624-571: The Later Stone Age levels from cultural and archaeozoological perspectives respectively. Work led by Michael Chazan of the University of Toronto , Liora Kolska Horwitz of The Hebrew University and Francesco Berna of Simon Fraser University , in collaboration with the McGregor Museum (where excavated assemblages are housed), was carried out from around 2008. A digital model of the site was created by laser scanning, forming part of

1682-488: The McGregor Museum, was declared a National Monument of South Africa in 1993. It was opened to the public, as a site museum, in 1993. In the same year a major graffiti-removal project was carried out. In 2000 new legislation made the site a Provincial Heritage Site. Between 2003 and 2009 it was assessed in terms of the grading system prescribed by the National Heritage Resources Act and graded as

1740-406: The base of a hill. Accumulated deposits inside the cave, up to 7 m (23 ft) in-depth, reflect natural sedimentation processes such as water and wind deposition as well as the activities of animals, birds, and human ancestors over some 2 million years. The site has been studied and excavated by archaeologists since the 1940s and research here generates important insights into human history in

1798-417: The cave some 2 million years ago. Rock art occurs in the form of parietal paintings within the first 40 m (130 ft) from the entrance, possibly all less than 1000 years old, and small engraved stones found within the deposit, mainly from the Later Stone Age sequence where they date back some 10,500 years. The associations of older engraved or striated pieces have yet to be substantiated. Major damage

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1856-561: The cave's contemporary social or ritual significance relate inter alia to the occasional collecting of water, by local African people, for healing purposes. There are other nearby sites where beliefs concerning the ritual power of water (associations with a mythic watersnake are remarked upon), for example by members of the Zion Christian Church , include the Kuruman Eye and Boesmanspit . The past ritual significance of

1914-424: The cave, currently studied by Louis Scott but initially examined by E.M. van Zinderen Bakker . Lloyd Rossouw is researching phytoliths from the cave, which show changing vegetation profiles, while preserved charcoal is being studied by Marion Bamford to generate data on woody plants. Deposition processes have been the focus of work by Karl Butzer and, currently, Paul Goldberg and Francesco Berna. Indications of

1972-416: The deep interior of the cave which is characterized by "singular acoustic and visual qualities." They argue that the site provides a "unique and extensive diachronic record of milestones in the development of symbolic behavior" and "evidence to support the position that elements of symbolic behaviour emerged long before the dispersal of modern humans out of Africa." Wonderwerk Cave, within a servitude ceded to

2030-433: The end of the last ice age circa 10 000 years ago – studied by Francis Thackeray. Margaret Avery and Yolanda Fernandez-Jalvo are studying the small mammal remains introduced to the cave sediments as part of the contents of owl droppings and which provide indications as to the palaeenvironmental conditions outside the cave. Also preserved are pollen, another key source of information on changing environmental conditions outside

2088-481: The first archaeological and zooarchaeological investigations. The initial archaeological studies of the 1940s, by Malan, Cooke and Wells, were followed up briefly by K.W. Butzer in the 1970s. Peter Beaumont of the McGregor Museum in Kimberley then carried out major excavations at the site between 1978 and 1993, with Anne Thackeray and Francis Thackeray working at the site in 1979, excavating and researching

2146-531: The formation of dolomite helps explain the rarity of Cenozoic dolomites, since Cenozoic seawater temperatures seldom exceeded 40 °C. It is possible that microorganisms are capable of precipitating primary dolomite. This was first demonstrated in samples collected at Lagoa Vermelha , Brazil in association with sulfate-reducing bacteria ( Desulfovibrio ), leading to the hypothesis that sulfate ion inhibits dolomite nucleation. Later laboratory experiments suggest bacteria can precipitate dolomite independently of

2204-484: The forms of stalactites , stalagmites , flowstone etc., can also form in caves within dolomite rock. “Dolomite is a common rock type, but a relatively uncommon mineral in speleothems”. Both the 'Union Internationale de Spéléologie' (UIS) and the American 'National Speleological Society' (NSS), extensively use in their publications, the terms "dolomite" or "dolomite rock" when referring to the natural bedrock containing

2262-404: The greater temperatures characterizing deeper burial, if a mechanism exists to flush magnesium-bearing fluids through the beds. Mineral dolomite has a 12% to 13% smaller volume than calcite per alkali cation. Thus dolomitization likely increases porosity and contributes to the sugary texture of dolomite. Dolomite is supersaturated in normal seawater by a factor of greater than ten, but dolomite

2320-492: The half-life of the nuclide, it is possible to estimate how long the sample has been exposed to the cosmic rays. The cumulative flux of cosmic rays at a particular location can be affected by several factors, including elevation, geomagnetic latitude, the varying intensity of the Earth's magnetic field , solar winds, and atmospheric shielding due to air pressure variations. Rates of nuclide production must be estimated in order to date

2378-437: The magnesium ion is surrounded by a clump of water molecules that are strongly attracted to its positive charge. Calcium is a larger ion and this reduces the strength of binding of its hydration shell, so it is much easier for a calcium ion than a magnesium ion to shed its hydration shell and bind to a growing crystal. It is also more difficult to nucleate a seed crystal of ordered dolomite than disordered high-magnesium calcite. As

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2436-461: The magnesium layers. A small amount of ferrous iron typically substitutes for magnesium, particularly in more ancient dolomites. Carbonate rock tends to be either almost all calcite or almost all dolomite, with intermediate compositions being quite uncommon. Dolomite outcrops are recognized in the field by their softness (mineral dolomite has a Mohs hardness of 4 or less, well below common silicate minerals) and because dolomite bubbles feebly when

2494-451: The mechanism of dolomitization, the tendency of carbonate rock to be either almost all calcite or almost all dolomite suggests that, once the process is started, it completes rapidly. The process likely occurs at shallow depths of burial, under 100 meters (330 ft), where there is an inexhaustible supply of magnesium-rich seawater and the original limestone is more likely to be porous. On the other hand, dolomitization can proceed rapidly at

2552-571: The microscope, thin sections of dolomite usually show individual grains that are well-shaped rhombs , with considerable pore space. As a result, subsurface dolomite is generally more porous than subsurface limestone and makes up 80% of carbonate rock petroleum reservoirs . This texture contrasts with limestone, which is usually a mixture of grains, micrite (very fine-grained carbonate mud) and sparry cement. The optical properties of calcite and mineral dolomite are difficult to distinguish, but calcite almost never crystallizes as regular rhombs, and calcite

2610-427: The mineral. The term dolomite refers to both the calcium-magnesium carbonate mineral and to sedimentary rock formed predominantly of this mineral. The term dolostone was introduced in 1948 to avoid confusion between the two. However, the usage of the term dolostone is controversial, because the name dolomite was first applied to the rock during the late 18th century and thus has technical precedence. The use of

2668-492: The mixing zone serves as domain of intense microbial activity which promotes dolomitization. A third model postulates that normal seawater is the dolomitizing fluid, and the necessary large volumes are flushed through the dolomitizing limestone through tidal pumping. Dolomite formation at Sugarloaf Key , Florida, may be an example of this process. A similar process might occur during rises in sea level, as large volumes of water move through limestone platform rock. Regardless of

2726-414: The most abundant of these elements, and are common in crustal material, whereas the radioactive daughter nuclei are not commonly produced by other processes. As oxygen-16 is also common in the atmosphere, the contribution to the beryllium-10 concentration from material deposited rather than created in situ must be taken into account. Be and Al are produced when a portion of a quartz crystal (SiO 2 )

2784-442: The most stable polymorph form of calcite. Speleothem types known to have a dolomite constituent include: coatings, crusts, moonmilk , flowstone , coralloids, powder, spar and rafts. Although there are reports of dolomite speleothems known to exist in a number of caves around the world, they are usually in relatively small quantities and form in very fine-grained deposits. Surface exposure dating Surface exposure dating

2842-427: The pore space in the dolomitizing limestone. Several processes have been proposed for dolomitization. The hypersaline model (also known as the evaporative reflux model ) is based on the observation that dolomite is very commonly found in association with limestone and evaporites , with the limestone often interbedded with the dolomite. According to this model, dolomitization takes place in a closed basin where seawater

2900-401: The process remains poorly understood. There are also fine-grained dolomites showing no textural indications that they formed by replacement, and it is uncertain whether they formed by replacement of limestone that left no textural traces or are true primary dolomites. This dolomite problem was first recognized over two centuries ago but is still not fully resolved. The dolomitization reaction

2958-456: The question of whether this can lead to precipitation of dolomite. Dolomitization can sometimes be reversed, and a dolomite bed converted back to limestone. This is indicated by a texture of pseudomorphs of mineral dolomite that have been replaced with calcite. Dedolomitized limestone is typically associated with gypsum or oxidized pyrite , and dedolomitization is thought to occur at very shallow depths through infiltration of surface water with

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3016-434: The simple Oldowan tools and finding of animal bones from the 2.5-metre (8 ft 2 in) thick sedimentary layer inside prove that this cave was occupied by Early Stone Age humans about 2 million years ago. The sediments within the cave exhibit exceptional preservation of organic remains including macro-botanical remains, phytoliths and micro and macro-fauna which shed light inter alia on species extinctions relative to

3074-544: The site is subject to on-going archaeological investigation. The rock art on the walls of the cave near its entrance, being researched by David Morris and engraved stones found in the deposit may implicate changing ritual significance. Aspects of the use of the cave's deep interior reaches are also being considered in these terms. Chazan and Horwitz refer, as Beaumont had done, to the introduction of manuports (unmodified natural stones) "with special sensory properties" by terminal Acheulean hominins, more than 180,000 years ago, to

3132-584: The subcontinent of Southern Africa. Evidence within Wonderwerk cave has been called the oldest controlled fire . Wonderwerk means "miracle" in the Afrikaans language. The cave contains up to 6 m (20 ft) depth of archaeological deposits reflecting human and environmental history through the Earlier, Middle and Later Stone Ages to the present. Cosmogenic dating suggests that basal sediment entered

3190-400: The sulfate concentration. With time other pathways of interaction between microbial activity and dolomite formation have been added to the discord regarding their role in modulation and generation of polysaccharides , manganese and zinc within the porewater. Meanwhile, a contrary view held by other researchers is that microorganisms precipitate only high-magnesium calcite but leave open

3248-422: The surrounding matrix composed of dolomite grains. Sometimes dolomite rhombs are seen cut across the fossil outline. However, some dolomite shows no textural indications that it was formed by replacement of limestone. Dolomite is widespread in its occurrences, though not as common as limestone. It is typically found in association with limestone or evaporite beds and is often interbedded with limestone. There

3306-543: The term dolostone was not recommended by the Glossary of Geology published by the American Geological Institute . In old USGS publications, dolomite was referred to as magnesian limestone , a term now reserved for magnesium -deficient dolomites or magnesium-rich limestones. Dolomite rock is defined as sedimentary carbonate rock composed of more than 50% mineral dolomite . Dolomite

3364-402: Was caused in the 1940s when local farmers dug up large parts of the cave interior to bag and sell organic-rich material as fertiliser – which in fact comprised stratified archaeological deposits containing artifacts, bone and other material that would have been crucial to an understanding of the cultural and palaeoenvironmental history of the site. The presence of bone was reported upon, leading to

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