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Silcrete
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. 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. Human use In Au ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Silcrete Mcr1
Silcrete is an friability, 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 hardness, 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, South Australia, Stuart Range of South Australia. Silcrete can be found at a lesser extent throughout the world especially England (e.g. ''Hertfordshire puddingstone and Sarsen, sarsen stone''), and France. In the Great Plains of the United States, polished silcrete cobbles are locally common on the surface and in river gravels east of the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Stuart Range, South Australia
The Stuart Range is a low upland in central South Australia, extending about with a north-west to south-east alignment and passing within to the south-east of Coober Pedy. Name The range is named after John McDouall Stuart, the first European explorer to pass through the area, in 1858. Formation During the Late Cretaceous and Tertiary, central Australia experienced crustal compression resulting in very broad, low-amplitude folding, and the Stuart Range formed on a basement upwarp. Underlying the Stuart Range, the folded sediments include the Early Cretaceous (Aptian-Albian) Bulldog Shale, consisting of grey marine mudstones. Where the Bulldog Shale has been exposed at the surface for long periods it has been subjected to deep chemical weathering, resulting in bleaching and the "multi-hued, picturesque colouration" found in the Arckaringa-Stuart Range landscape. The prolonged chemical weathering also dissolved silica which, transported through the regolith by the movement o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Blombos Point White
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.Tribolo, C., et al. (2006) TL dating of burnt lithics from Blombos Cave (South Africa): further evidence for the antiquity of modern human behaviour. Archaeometry, 48, 341–357.Jacobs, Z., et al. (2006) Extending the chronology of deposits at Blombos Cave, South Africa, back to 140 ka using optical dating of single and multiple grains of quartz. Journal of Human Evolution, 51, 255–73.Henshilwood, Christopher S., et al. (2011) A 100,000-Year-Old Ochre-Processing Workshop at Blombos Cave, South Africa. Science, 334, 219–222, .Jacobs, Zenobia, et al. (2013) An improved OSL chronology for the Still Bay layers at Blombos Cave, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Fishtail Projectile Point
Fishtail points, also known as Fell points are a style of Paleoindian projectile point widespread across much of South America at the end of the Late Pleistocene, around 13-12,000 years ago. They are thought to have been multifunctional, serving as cutting tools, as well as hafted to spears to use as hunting weapons, possibly in combination with spear throwers. Chronology and origin Their chronological timing is disputed. Some authors favour a short chronology spanning 12,800–12,200 years Before Present (BP), while others favour 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. Description, use and association with other tools The name "Fishtail point" derives from the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Sarsen
Sarsen stones are silicification, 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. Geology Sarsen stones are the post-glacial remains of a cap of Cenozoic silcrete that once covered much of southern England. This is thought to have formed during Neogene to Quaternary weathering by the silicification of Upper Paleocene Lambeth Group sediments, resulting from acid leaching. Etymology There are several potential sources for the word "sarsen." The first is that word "sarsen" is a shortening of "Saracen stone" which arose in the Wiltshire dialect. In the Middle Ages, "Saracen" was a common name for Muslims, and came by extension to be used for anything regarded as non-Christian, whether Muslim or pagan in contrast to Christianity. The second is that "sarsen" is vernacular variation of the Indo-European "sasan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Duricrust
Duricrust is a hard layer on or near the surface of soil. Duricrusts can range in thickness from a few millimeters or centimeters to several meters. It is a general term (not to be confused with duripan) for a zone of chemical precipitation and hardening formed at or near the surface of sedimentary bodies through pedogenic or non-pedogenic processes. It is typically formed by the accumulation of soluble minerals deposited by mineral-bearing waters that move upward, downward, or laterally by capillary action. It is commonly assisted in arid settings by evaporation.Dixon, J.C. and McLaren, S.J., 2009. ''Duricrusts''. In A.J. Parsons and A.D. Abrahams, ed., pp. 123-151. ''Geomorphology of desert environments.'' Springer, Dordrecht. Woolnough, W.G., 1930. ''The influence of climate and topography in the formation and distribution of products of weathering.'' ''Geological Magazine'', 67(3), pp.123-132. There are different types of duricrusts, each distinguished by a dominant mineralo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Hertfordshire Puddingstone
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 (lower Eocene, 56-55 million years ago). Geological origin The flints were eroded from the surrounding c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Botswana
Botswana, officially the Republic of Botswana, is a landlocked country in Southern Africa. Botswana is topographically flat, with approximately 70 percent of its territory part of the Kalahari Desert. It is bordered by South Africa to the south and southeast, Namibia to the west and north, Zambia to the north, and Zimbabwe to the northeast. With a population of slightly over 2.4 million people and a comparable land area to France, Botswana is one of the List of countries and dependencies by population density, most sparsely populated countries in the world. It is essentially the nation-state of the Tswana people, who constitute nearly 80 percent of the population. The Tswana ethnic group are descended mainly from Bantu peoples, Bantu-speaking peoples who Bantu expansion, migrated into southern Africa, including modern Botswana, in several waves before AD 600. In 1885, the British Empire, British colonised the area and declared a protectorate named Bechuanaland. As part of the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Okavango Delta
The Okavango Delta or Okavango Grassland is a vast inland delta in Botswana formed where the Okavango River reaches a tectonic trough at an elevation of in the central part of the endorheic basin of the Kalahari Desert. It is a UNESCO World Heritage Site as one of the few interior delta systems that do not flow into a sea or ocean, with a wetland system that is largely intact. All the water reaching the delta is ultimately evaporated and transpired. Each year, about of water spreads over the area. Some flood waters drain into Lake Ngami. The area was once part of Lake Makgadikgadi, an ancient lake that had mostly dried up by the early Holocene. The Moremi Game Reserve is on the eastern side of the delta. The delta was named one of the Seven Natural Wonders of Africa, which were officially declared on 11 February 2013 in Arusha, Tanzania. On 22 June 2014, the Okavango Delta became the 1000th site to be officially inscribed on the UNESCO World Heritage List. Geograp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Stonehenge
Stonehenge is a prehistoric Megalith, megalithic structure on Salisbury Plain in Wiltshire, England, west of Amesbury. It consists of an outer ring of vertical sarsen standing stones, each around high, wide, and weighing around 25 tons, topped by connecting horizontal lintel stones, held in place with mortise and tenon joints, a feature unique among contemporary monuments. Inside is a ring of smaller bluestones. Inside these are free-standing trilithons, two bulkier vertical sarsens joined by one lintel. The whole monument, now ruinous, is aligned towards the sunrise on the summer solstice and sunset on the winter solstice. The stones are set within Earthwork (archaeology), earthworks in the middle of the densest complex of Neolithic British Isles, Neolithic and Bronze Age Britain, Bronze Age monuments in England, including several hundred ''tumuli'' (burial mounds). Stonehenge was constructed in several phases beginning about 3100 BC and continuing until about 1600 B ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Avebury
Avebury () is a Neolithic henge monument containing three stone circles, around the village of Avebury in Wiltshire, in south-west England. One of the best-known prehistoric sites in Britain, it contains the largest megalithic stone circle in the world. It is both a tourist attraction and a place of religious importance to contemporary pagans. Constructed over several hundred years in the third millennium BC, during the Neolithic, or New Stone Age, the monument comprises a large henge (a bank and a ditch) with a large outer stone circle and two separate smaller stone circles situated inside the centre of the monument. Its original purpose is unknown, although archaeologists believe that it was most likely used for some form of ritual or ceremony. The Avebury monument is a part of a larger prehistoric landscape containing several older monuments nearby, including West Kennet Long Barrow, Windmill Hill and Silbury Hill. By the Iron Age, the site had been effectively abandon ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Heel Stone
The Heel Stone is a single large block of sarsen stone standing within the Avenue outside the entrance of the Stonehenge earthwork in Wiltshire, England. In section it is sub-rectangular, with a minimum thickness of , rising to a tapered top about high. Excavation has shown that a further is buried in the ground. It is from the centre of Stonehenge circle. It leans towards the southwest nearly 27 degrees from the vertical. The stone has an overall girth Girth may refer to: Mathematics * Girth (functional analysis), the length of the shortest centrally symmetric simple closed curve on the unit sphere of a Banach space * Girth (geometry), the perimeter of a parallel projection of a shape * Girth ... of and weighs about 35 tons. It is surrounded by the Heelstone Ditch. See also * List of individual rocks References * Atkinson, R J C, ''Stonehenge'' (Penguin Books, 1956) * Cleal, Walker, & Montague, ''Stonehenge in its Landscape'' (London, English Heritage 1995) * C ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
