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Loriu Plateau
Loriu Plateau is an elevated Precambrian bedrock exposure at the southwest margin of Lake Turkana in Kenya. The plateau is only seasonally habitable due to aridity and was once home to fauna otherwise rare in Turkana. Loriu is west of and adjacent to the Barrier Volcano at the southernmost portion of Lake Turkana. Location Loriu is bounded by Lake Turkana to the east, Kapedo to the south, the Kerio River to the west, and Kerio River delta to the north. The plateau is 64 kilometers running from north to south, approximately 8 kilometers wide, and is capped by Tertiary volcanic lava flows. The western margin of Loriu rises gradually while the eastern margin is defined by a fault scarp more than 366 meters high in some locations. The maximum altitude of the plateau is 1,463 meters. Animal and plant life The Turkana basin was previously home to a great diversity and number of animal species, many of which became the basis for names of both places and people in the region. A number of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Precambrian
The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the Phanerozoic Eon, which is named after Cambria, the Latinised name for Wales, where rocks from this age were first studied. The Precambrian accounts for 88% of the Earth's geologic time. The Precambrian is an informal unit of geologic time, subdivided into three eons ( Hadean, Archean, Proterozoic) of the geologic time scale. It spans from the formation of Earth about 4.6 billion years ago ( Ga) to the beginning of the Cambrian Period, about million years ago ( Ma), when hard-shelled creatures first appeared in abundance. Overview Relatively little is known about the Precambrian, despite it making up roughly seven-eighths of the Earth's history, and what is known has largely been discovered from the 1960s onwards. The Precambrian fos ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Horst (geology)
In physical geography and geology, a horst is a raised fault block bounded by normal faults. Horsts are typically found together with grabens. While a horst lifted or remains stationary, the grabens on either side subside. This is often caused by extensional forces pulling apart the crust. Horsts may represent features such as plateaus, mountains, or ridges on either side of a valley. Horsts can range in size from small fault-blocks, up to large regions of stable continent that have not been not folded or warped by tectonic forces. The word ''Horst'' in German means "mass" or "heap," and was first used in the geological sense in 1883 by Eduard Suess in ''The Face of the Earth.''Originally published in 1883 in German as "Das Antlitz der Erde", translated and published in English in 1904 Geomorphology Horsts may have either symmetrical or asymmetrical cross-sections. If the normal faults to either side have similar geometry and are moving at the same rate, the horst is likely ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Turkana Basin
An '' Acacia'' tree in the Kokiselei river, northern Kenya The greater Turkana Basin in East Africa (mainly northwestern Kenya and southern Ethiopia, smaller parts of eastern Uganda and southeastern South Sudan) determines a large endorheic basin, a drainage basin with no outflow centered around the north-southwards directed Gregory Rift system in Kenya and southern Ethiopia. The deepest point of the basin is the endorheic Lake Turkana, a brackish soda lake with a very high ecological productivity in the Gregory Rift. A narrower definition for the term ''Turkana Basin'' is also in widespread use and means Lake Turkana and its environment within the confines of the Gregory Rift in Kenya and Ethiopia. This includes the lower Omo River valley in Ethiopia. The Basin in the narrower definition is a site of geological subsidence containing one of the most continuous and temporally well controlled fossil records of the Plio-PleistoceneFeibel, C., 2011, "A Geological History of the T ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nephelinite
Nephelinite is a fine-grained or aphanitic igneous rock made up almost entirely of nepheline and clinopyroxene (variety augite). If olivine is present, the rock may be classified as an olivine nephelinite. Nephelinite is dark in color and may resemble basalt in hand specimen. However, basalt consists mostly of clinopyroxene (augite) and calcic plagioclase. Basalt, alkali basalt, basanite, tephritic nephelinite, and nephelinite differ partly in the relative proportions of plagioclase and nepheline. Alkali basalt may contain minor nepheline and does contain nepheline in its CIPW normative mineralogy. A critical ratio in the classification of these rocks is the ratio nepheline/(nepheline plus plagioclase). Basanite has a value of this ratio between 0.1 and 0.6 and also contains more than 10% olivine. Tephritic nephelinite has a value between 0.6 and 0.9. Nephelinite has a value greater than 0.9. Le Maitre (2002) defines and discusses these and other criteria in the classification of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dike (geology)
A dike or dyke, in geological usage, is a sheet of rock that is formed in a fracture of a pre-existing rock body. Dikes can be either magmatic or sedimentary in origin. Magmatic dikes form when magma flows into a crack then solidifies as a sheet intrusion, either cutting across layers of rock or through a contiguous mass of rock. Clastic dikes are formed when sediment fills a pre-existing crack.Essentials of Geology, 3rd Ed, Stephen Marshak Magmatic dikes A magmatic dike is a sheet of igneous rock that cuts across older rock beds. It is formed when magma fills a fracture in the older beds and then cools and solidifies. The dike rock is usually more resistant to weathering than the surrounding rock, so that erosion exposes the dike as a natural wall or ridge. It is from these natural walls that dikes get their name. Dikes preserve a record of the fissures through which most mafic magma (fluid magma low in silica) reaches the surface. They are studied by geologists for the cl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Miocene
The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recent" because it has 18% fewer modern marine invertebrates than the Pliocene has. The Miocene is preceded by the Oligocene and is followed by the Pliocene. As Earth went from the Oligocene through the Miocene and into the Pliocene, the climate slowly cooled towards a series of ice ages. The Miocene boundaries are not marked by a single distinct global event but consist rather of regionally defined boundaries between the warmer Oligocene and the cooler Pliocene Epoch. During the Early Miocene, the Arabian Peninsula collided with Eurasia, severing the connection between the Mediterranean and Indian Ocean, and allowing a faunal interchange to occur between Eurasia and Africa, including the dispersal of proboscideans into Eurasia. During the la ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mafic
A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include basalt, diabase and gabbro. Mafic rocks often also contain calcium-rich varieties of plagioclase feldspar. Mafic materials can also be described as ferromagnesian. History The term ''mafic'' is a portmanteau of "magnesium" and "ferric" and was coined by Charles Whitman Cross, Joseph P. Iddings, Louis Valentine Pirsson, and Henry Stephens Washington in 1912. Cross' group had previously divided the major rock-forming minerals found in igneous rocks into ''salic'' minerals, such as quartz, feldspars, or feldspathoids, and ''femic'' minerals, such as olivine and pyroxene. However, micas and aluminium-rich amphiboles were excluded, while some calcium minerals containing little iron or magnesium, such as wollastonite or apatite, were incl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phenocryst
300px, Swiss side of the Mont Blanc massif, has large white plagioclase phenocrysts, triclinic minerals that give trapezoid shapes when cut through). 1 euro coins, 1 euro coin (diameter 2.3 cm) for scale. A phenocryst is an early forming, relatively large and usually conspicuous crystal distinctly larger than the grains of the rock groundmass of an igneous rock. Such rocks that have a distinct difference in the size of the crystals are called porphyries, and the adjective porphyritic is used to describe them. Phenocrysts often have euhedral forms, either due to early growth within a magma, or by post-emplacement recrystallization. Normally the term ''phenocryst'' is not used unless the crystals are directly observable, which is sometimes stated as greater than .5 millimeter in diameter. Phenocrysts below this level, but still larger than the groundmass crystals, are termed ''microphenocrysts''. Very large phenocrysts are termed '' megaphenocrysts''. Some rocks contain both ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pyroxene
The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe II) or magnesium (Mg) and more rarely zinc, manganese or lithium, and Y represents ions of smaller size, such as chromium (Cr), aluminium (Al), magnesium (Mg), cobalt (Co), manganese (Mn), scandium (Sc), titanium (Ti), vanadium (V) or even iron (Fe II) or (Fe III). Although aluminium substitutes extensively for silicon in silicates such as feldspars and amphiboles, the substitution occurs only to a limited extent in most pyroxenes. They share a common structure consisting of single chains of silica tetrahedra. Pyroxenes that crystallize in the monoclinic system are known as clinopyroxenes and those that crystallize in the orthorhombic system are known as orthopyroxenes. The name ''pyroxene'' is derived from the Ancient Greek words for 'fire' ( ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Olivine
The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickly on the surface. For this reason, olivine has been proposed as a good candidate for accelerated weathering to sequester carbon dioxide from the Earth's oceans and atmosphere, as part of climate change mitigation. Olivine also has many other historical uses, such as the gemstone peridot (or chrysolite), as well as industrial applications like metalworking processes. The ratio of magnesium to iron varies between the two endmembers of the solid solution series: forsterite (Mg-endmember: ) and fayalite (Fe-endmember: ). Compositions of olivine are commonly expressed as molar percentages of forsterite (Fo) and fayalite (Fa) (''e.g.'', Fo70Fa30). Forsterite's melting temperature is unusually high at atmospheric pressure, almost , whi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Basalt
Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% of all volcanic rock on Earth is basalt. Rapid-cooling, fine-grained basalt is chemically equivalent to slow-cooling, coarse-grained gabbro. The eruption of basalt lava is observed by geologists at about 20 volcanoes per year. Basalt is also an important rock type on other planetary bodies in the Solar System. For example, the bulk of the plains of Venus, which cover ~80% of the surface, are basaltic; the lunar maria are plains of flood-basaltic lava flows; and basalt is a common rock on the surface of Mars. Molten basalt lava has a low viscosity due to its relatively low silica content (between 45% and 52%), resulting in rapidly moving lava flows that can spread over great areas before cooling and solidifying. Flood basalts are thick sequence ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pliocene
The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58See the 2014 version of the ICS geologic time scale million years ago. It is the second and most recent epoch of the Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch. Prior to the 2009 revision of the geologic time scale, which placed the fou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
