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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 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. In Australia, silcrete was widely ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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] |
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 surroundin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 and (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, 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 mineralog ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Great Plains
The Great Plains (french: Grandes Plaines), sometimes simply "the Plains", is a broad expanse of flatland in North America. It is located west of the Mississippi River and east of the Rocky Mountains, much of it covered in prairie, steppe, and grassland. It is the southern and main part of the Interior Plains, which also include the tallgrass prairie between the Great Lakes and Appalachian Plateau, and the Taiga Plains and Boreal Plains ecozones in Northern Canada. The term Western Plains is used to describe the ecoregion of the Great Plains, or alternatively the western portion of the Great Plains. The Great Plains lies across both Central United States and Western Canada, encompassing: * The entirety of the U.S. states of Kansas, Nebraska, North Dakota and South Dakota; * Parts of the U.S. states of Colorado, Iowa, Minnesota, Missouri, Montana, New Mexico, Oklahoma, Texas and Wyoming; * The southern portions of the Canadian provinces of Alberta, Saska ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kansas River
The Kansas River, also known as the Kaw, is a river in northeastern Kansas in the United States. It is the southwesternmost part of the Missouri River drainage, which is in turn the northwesternmost portion of the extensive Mississippi River drainage. Its two names both come from the Kanza (Kaw) people who once inhabited the area; ''Kansas'' was one of the anglicizations of the French transcription ''Cansez'' () of the original '' kką:ze''. The city of Kansas City, Missouri, was named for the river, as was later the state of Kansas. The river valley averages in width, with the widest points being between Wamego and Rossville, where it is up to wide, then narrowing to or less in places below Eudora and De Soto. Much of the river's watershed is dammed for flood control, but the Kansas River is generally free-flowing and has only minor obstructions, including diversion weirs and one low-impact hydroelectric dam. Course Beginning at the confluence of the Republican a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nova Scotia
Nova Scotia ( ; ; ) is one of the thirteen provinces and territories of Canada. It is one of the three Maritime provinces and one of the four Atlantic provinces. Nova Scotia is Latin for "New Scotland". Most of the population are native English-speakers, and the province's population is 969,383 according to the 2021 Census. It is the most populous of Canada's Atlantic provinces. It is the country's second-most densely populated province and second-smallest province by area, both after Prince Edward Island. Its area of includes Cape Breton Island and 3,800 other coastal islands. The Nova Scotia peninsula is connected to the rest of North America by the Isthmus of Chignecto, on which the province's land border with New Brunswick is located. The province borders the Bay of Fundy and Gulf of Maine to the west and the Atlantic Ocean to the south and east, and is separated from Prince Edward Island and the island of Newfoundland (island), Newfoundland by the Northumberland Stra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Woodland Period
In the classification of archaeological cultures of North America, the Woodland period of North American pre-Columbian cultures spanned a period from roughly 1000 BCE to European contact in the eastern part of North America, with some archaeologists distinguishing the Mississippian period, from 1000 CE to European contact as a separate period. The term "Woodland Period" was introduced in the 1930s as a generic term for prehistoric sites falling between the Archaic hunter-gatherers and the agriculturalist Mississippian cultures. The Eastern Woodlands cultural region covers what is now eastern Canada south of the Subarctic region, the Eastern United States, along to the Gulf of Mexico. This period is variously considered a developmental stage, a time period, a suite of technological adaptations or "traits", and a "family tree" of cultures related to earlier Archaic cultures. It can be characterized as a chronological and cultural manifestation without any massive changes in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quaternary
The Quaternary ( ) is the current and most recent of the three period (geology), periods of the Cenozoic era (geology), Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ago to the present. The Quaternary Period is divided into two epochs: the Pleistocene (2.58 million years ago to 11.7 thousand years ago) and the Holocene (11.7 thousand years ago to today, although a third epoch, the Anthropocene, has been proposed but is not yet officially recognised by the ICS). The Quaternary Period is typically defined by the cyclic growth and decay of continental ice sheets related to the Milankovitch cycles and the associated climate and environmental changes that they caused. Research history In 1759 Giovanni Arduino (geologist), Giovanni Arduino proposed that the geological strata of northern Italy could be divided into four successive formations or "orders" ( it, quattro ord ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Neogene
The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago (Mya) to the beginning of the present Quaternary Period Mya. The Neogene is sub-divided into two epochs, the earlier Miocene and the later Pliocene. Some geologists assert that the Neogene cannot be clearly delineated from the modern geological period, the Quaternary. The term "Neogene" was coined in 1853 by the Austrian palaeontologist Moritz Hörnes (1815–1868). During this period, mammals and birds continued to evolve into modern forms, while other groups of life remained relatively unchanged. The first humans ('' Homo habilis'') appeared in Africa near the end of the period. Some continental movements took place, the most significant event being the connection of North and South America at the Isthmus of Panama, late in the Pliocene. This cut off the warm ocean currents from the Pacific t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Okavango Delta
The Okavango Delta (or Okavango Grassland; formerly spelled "Okovango" or "Okovanggo") in Botswana is a swampy inland delta formed where the Okavango River reaches a tectonic trough at an altitude of 930–1,000 m in the central part of the endorheic basin of the Kalahari. All the water reaching the delta is ultimately evaporated and transpired and does not flow into any sea or ocean. 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, a national park, is on the eastern side of the delta. The delta was named as 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. Geography Floods The Okavango is produced by season ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Botswana
Botswana (, ), officially the Republic of Botswana ( tn, Lefatshe la Botswana, label= Setswana, ), is a landlocked country in Southern Africa. Botswana is topographically flat, with approximately 70 percent of its territory being the Kalahari Desert. It is bordered by South Africa to the south and southeast, Namibia to the west and north, and Zimbabwe to the northeast. It is connected to Zambia across the short Zambezi River border by the Kazungula Bridge. A country of slightly over 2.3 million people, Botswana is one of the most sparsely populated countries in the world. About 11.6 percent of the population lives in the capital and largest city, Gaborone. Formerly one of the world's poorest countries—with a GDP per capita of about US$70 per year in the late 1960s—it has since transformed itself into an upper-middle-income country, with one of the world's fastest-growing economies. Modern-day humans first inhabited the country over 200,000 years ago. The Tswa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pinnacle Point
Pinnacle Point a small promontory immediately south of Mossel Bay, a town on the southern coast of South Africa. Excavations since the year 2000 of a series of caves at Pinnacle Point have revealed occupation by Middle Stone Age people between 170,000 and 40,000 years ago. The focus of excavations has been at Cave 13B (PP13B), where the earliest evidence for the systematic exploitation of marine resources (shellfish) and symbolic behaviour has been documented, and at Pinnacle Point Cave 5–6 (PP5–6), where the oldest evidence for the heat treatment of rock to make stone tools has been documented. The only human remains have been recovered from younger deposits at PP13B which are years old. History of the research The discoveries at Pinnacle Point have been made by an international team, headed by palaeoanthropologist Curtis Marean from the Institute of Human Origins of the Arizona State University as well as researchers from South Africa ( UCT), Australia (Archaeology Prog ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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