|
Magaliesberg00edit
The Magaliesberg (historically also known as ''Macalisberg'' or ''Cashan Mountains'') of northern South Africa, is a modest but well-defined mountain range composed mainly of quartzites. It rises at a point south of the Pilanesberg (and the Pilanesberg National Park) to form a curved prominence that intersects suburban Pretoria before it peters out some to the east, just south of Bronkhorstspruit. The highest point of the Magaliesberg is reached at Nooitgedacht, about above sea level. A cableway reaching to the top of the mountain range is located at Hartbeespoort Dam, providing sweeping views of the Magaliesberg and surrounding area. Geology The Magaliesberg has ancient origins. Its composition is ascribed to successive geological processes over a very protracted history. Its quartzites, shales, chert and dolomite were deposited as sediments in an inland basin on top of a 3 billion year old Archaean Basement Complex, known as the Kaapvaal craton. This process of s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hartebeespoort Dam
Hartbeespoort Dam (also known as ''Harties'') is an arch type dam situated in the North West (South African province), North West Province of South Africa. It lies in a valley to the south of the Magaliesberg mountain range and north of the Witwatersberg mountain range, about 35 kilometres north west of Johannesburg and 20 kilometres west of Pretoria. The name of the dam means "dam at the gorge of the hartebeest" (a species of antelope) in Afrikaans language, Afrikaans. This "poort" in the Magaliesberg was a popular spot for hunters, where they cornered and shot the hartebeest. The dam was originally designed for irrigation, which is currently its primary use, as well as for domestic and industrial use. The dam is considered to be in a Trophic state index, hypereutrophic state since the early 1970s. Mismanagement of waste water treatment from urban zones within the Hartbeespoort Dam catchment area is largely to blame, having distorted the food web with over 280 tons of phosphate an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hartbeespoort Dam
Hartbeespoort Dam (also known as ''Harties'') is an arch type dam situated in the North West Province of South Africa. It lies in a valley to the south of the Magaliesberg mountain range and north of the Witwatersberg mountain range, about 35 kilometres north west of Johannesburg and 20 kilometres west of Pretoria. The name of the dam means "dam at the gorge of the hartebeest" (a species of antelope) in Afrikaans. This "poort" in the Magaliesberg was a popular spot for hunters, where they cornered and shot the hartebeest. The dam was originally designed for irrigation, which is currently its primary use, as well as for domestic and industrial use. The dam is considered to be in a hypereutrophic state since the early 1970s. Mismanagement of waste water treatment from urban zones within the Hartbeespoort Dam catchment area is largely to blame, having distorted the food web with over 280 tons of phosphate and nitrate deposits. The town of Hartbeespoort is situated close to the dam ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ravine
A ravine is a landform that is narrower than a canyon and is often the product of streambank erosion. Ravines are typically classified as larger in scale than gullies, although smaller than valleys. Ravines may also be called a cleuch, dell, ghout (Nevis), gill or ghyll, glen, gorge, kloof (South Africa), and chine (Isle of Wight) A ravine is generally a fluvial slope landform of relatively steep (cross-sectional) sides, on the order of twenty to seventy percent in gradient. Ravines may or may not have active streams flowing along the downslope channel which originally formed them; moreover, often they are characterized by intermittent streams, since their geographic scale may not be sufficiently large to support a perennial stream. Definition According to Merriam-Webster, a ravine is "a small, narrow, steep-sided valley that is larger than a gully and smaller than a canyon and that is usually worn by running water". Some societies and languages do not differentiate b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dolerite
Diabase (), also called dolerite () or microgabbro, is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-grained to aphanitic chilled margins which may contain tachylite (dark mafic glass). ''Diabase'' is the preferred name in North America, while ''dolerite'' is the preferred name in the rest of the English-speaking world, where sometimes the name ''diabase'' refers to altered dolerites and basalts. Some geologists prefer to avoid confusion by using the name ''microgabbro''. The name ''diabase'' comes from the French , and ultimately from the Greek 'act of crossing over, transition', whereas the name ''dolerite'' comes from the French , from the Greek 'deceitful, deceptive', because it was easily confused with diorite. Petrography Diabase normally has a fine but visible texture of euhedral lath-shaped plagioclase crystals (62%) set in a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Intrusive Rock
Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form ''Igneous intrusion, intrusions'', such as batholiths, dike (geology), dikes, Sill (geology), sills, laccoliths, and volcanic necks.Intrusive RocksIntrusive rocks accessdate: March 27, 2017.Igneous intrusive rocks, accessdate: March 27, 2017.Britannica.comintrusive rock , geology , Britannica.com accessdate: March 27, 2017. Intrusion is one of the two ways igneous rock can form. The other is extrusive rock, extrusion, such as a Types of volcanic eruptions, volcanic eruption or similar event. An intrusion is any body of intrusive igneous rock, formed from magma that cools and solidifies within the crust of the planet. In contrast, an ''extrusion'' consists of extrusive rock, formed above the surface of the crust. Some geologists use the term plutonic rock synonymously with intrusive rock, but other geologists subdivide intrusive rock, by crystal size, into coarse-grai ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dip Slope
A dip slope is a topographic or geomorphic surface which slopes in the same direction, and often by the same angle, as the true dip or apparent dip of the underlying strata.Jackson, JA, J Mehl and K Neuendorf (2005) ''Glossary of Geology.'' American Geological Institute, Alexandria, Virginia. 800 pp. Allaby, M (2008) ''A Dictionary of Earth Science.'' Oxford University Press, New York, New York. 654 pp. A dip slope consists of the upper surface of a resistant layer of rock, often called ''caprock'', that is commonly only slightly lowered and reduced in steepness by erosion. Dip slopes form the backslopes of cuestas, homoclinal ridges, hogbacks, and flatirons. The frontslopes of such ridges consist of either an escarpment, a steep slope, or perhaps even a line of cliffs. Generally, cuestas and homoclinal ridges are asymmetrical in that their dip slopes are less steep than their escarpments. In the case of hogbacks and flatirons, the dip of the rocks is so steep that their dip s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Escarpment
An escarpment is a steep slope or long cliff that forms as a result of faulting or erosion and separates two relatively level areas having different elevations. Due to the similarity, the term '' scarp'' may mistakenly be incorrectly used interchangeably with ''escarpment.'' ''Escarpment'' referring to the margin between two landforms, and ''scarp'' referring to a cliff or a steep slope. In this usage an escarpment is a ridge which has a gentle slope on one side and a steep scarp on the other side. More loosely, the term ''scarp'' also describes a zone between a coastal lowland and a continental plateau which shows a marked, abrupt change in elevation caused by coastal erosion at the base of the plateau. Formation and description Scarps are generally formed by one of two processes: either by differential erosion of sedimentary rocks, or by movement of the Earth's crust at a geologic fault. The first process is the more common type: the escarpment is a transition from one seri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bushveld Igneous Complex
The Bushveld Igneous Complex (BIC) is the largest Layered intrusion, layered igneous intrusion within the Earth's Crust (geology), crust. It has been tilted and Erosion, eroded forming the outcrops around what appears to be the edge of a great Basin (geology), geological basin: the Transvaal Basin. It is approximately two billion years old and is divided into four limbs or lobes: northern, eastern, southern and western. It comprises the Rustenburg Layered suite, the Lebowa Granites and the Rooiberg Felsics, that are overlain by the Karoo sediments. The site was first publicised around 1897 by Gustaaf Molengraaff who found the native South African tribes residing in and around the area. Located in South Africa, the BIC contains some of the richest ore deposits on Earth. It contains the world's largest reserves of platinum-group metals (PGMs) and Platinum group, platinum group elements (PGEs) — platinum, palladium, osmium, iridium, rhodium and ruthenium — along with vast quantit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Basement (geology)
In geology, basement and crystalline basement are crystalline rocks lying above the mantle and beneath all other rocks and sediments. They are sometimes exposed at the surface, but often they are buried under miles of rock and sediment. The basement rocks lie below a sedimentary platform or cover, or more generally any rock below sedimentary rocks or sedimentary basins that are metamorphic or igneous in origin. In the same way, the sediments or sedimentary rocks on top of the basement can be called a "cover" or "sedimentary cover". Basement rock consists of continental crustal rock which has been modified several times through tectonic events including deformation, metamorphism, deposition, partial melting and magmatism. Continental crust Basement rock is the thick foundation of ancient, and oldest, metamorphic and igneous rock that forms the crust of continents, often in the form of granite. Basement rock is contrasted to overlying sedimentary rocks which are laid down ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dolomite (rock)
Dolomite (also known as dolomite rock, dolostone or dolomitic rock) is a sedimentary rock, sedimentary carbonate rock that contains a high percentage of the mineral Dolomite (mineral), dolomite, CaMg(CO3)2. It occurs widely, often in association with limestone and evaporites, though it is less abundant than limestone and rare in Cenozoic rock beds (beds less than about 66 million years in age). One of the first geologists to distinguish dolomite from limestone was Déodat Gratet de Dolomieu, a French mineralogist and geologist after whom it is named. He recognized and described the distinct characteristics of dolomite in the late 18th century, differentiating it from limestone. Most dolomite was formed as a magnesium replacement of limestone or of Lime (mineral), lime mud before lithification. The geological process of conversion of calcite to dolomite is known as dolomitization and any intermediate product is known as dolomitic limestone. The "dolomite problem" refers to the v ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chert
Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a precipitation (chemistry), chemical precipitate or a diagenesis, diagenetic replacement, as in petrified wood. Chert is typically composed of the petrified remains of siliceous ooze, the biogenic sediment that covers large areas of the deep ocean floor, and which contains the silicon skeletal remains of diatoms, Dictyochales, silicoflagellates, and radiolarians. Precambrian cherts are notable for the presence of fossil cyanobacteria. In addition to Micropaleontology, microfossils, chert occasionally contains macrofossils. However, some chert is devoid of any fossils. Chert varies greatly in color, from white to black, but is most often found as gray, brown, grayish brown and light green to rusty redW.L. Roberts, T.J. Campbell, G.R. Rapp Jr., ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
