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Río Seco De La Quebrada Formation
The Río Seco de la Quebrada Formation is a Triassic geological formation in Mendoza Province, Argentina. Fossils of cynodonts such as '' Cynognathus, Diademodon,'' and ''Pascualgnathus'' have been found in this formation, along with dicynodonts such as ''Vinceria'' and '' Acratophorus''. Based on biostratigraphy, the Río Seco de la Quebrada Formation is considered to have formed during the Anisian stage, as it shares fauna with the upper subzones of the ''Cynognathus'' Assemblage Zone in South Africa. However, radiometric dating controversially argues that it was deposited during the early Carnian stage, 10 million years younger than expected otherwise. Geology The Río Seco de la Quebrada Formation (RSQ) is the younger of the two formations in the Puesto Viejo Group, overlying the older Quebrada de los Fósiles Formation (QF). The Puesto Viejo Group is a geologically isolated succession of Triassic sedimentary and igneous rock exposed in the area of the San Rafael Block. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
San Rafael Block
The San Rafael Block or San Rafael Massif (Spanish: ''Bloque de San Rafael'' or ''Macizo de San Rafael'') is an uplifted area in central Mendoza Province, Argentina. The San Rafael Block is both a geographic and a tectonic unit. From a tectonostratigraphic view, some geologists consider it an exposure of the Cuyania (Precordillera) terrane being its southern extension. The San Rafael Block crops out to the south of the other exposures of Cuyania. The San Rafael Block forms the northeastern boundary of the Neuquén Basin. See also * North Patagonian Massif The North Patagonian Massif or Somún Cura Massif (Spanish language, Spanish: ''Macizo Norpatagónico'', ''Macizo Nordpatagónico'' or ''Macizo de Somún Cura'') is a massif in northern Patagonia located in the Argentine provinces of Río Negro Pro ... * Reserva Provincial La Payunia * San Rafael orogeny References {{reflist Geology of Mendoza Province Geography of Mendoza Province ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pascualgnathus
''Pascualgnathus'' is an extinct genus of traversodontid cynodonts from the Middle Triassic of Argentina. Fossils have been found from the Río Seco de la Quebrada Formation of the Puesto Viejo Group. The type species ''P. polanskii'' was named in 1966. Description ''Pascualgnathus'' is a small traversodontid. It has large upper canine teeth and small postcanine teeth. The postcanine teeth of ''Pascualgnathus'' and other traversodontids are wide, allowing them to eat plant material. The upper postcanines of ''Pascualgnathus'' are rectangular. Each has a central ridge and a cusp on the side facing the mouth. There are also two cusps on the side of the tooth facing the lips, with one being larger than the other. The lower postcanines have less of a rectangular shape and have only two cusps. Unlike the upper postcanines, they are longer than they are wide. Classification When ''Pascualgnathus'' was first named in 1966, it was considered a member of the family Diademodontidae more c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tuff
Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock containing 25% to 75% ash is described as tuffaceous (for example, ''tuffaceous sandstone''). Tuff composed of sandy volcanic material can be referred to as volcanic sandstone. Tuff is a relatively soft rock, so it has been used for construction since ancient times. Because it is common in Italy, the Romans used it often for construction. The Rapa Nui people used it to make most of the ''moai'' statues on Easter Island. Tuff can be classified as either igneous or sedimentary rock. It is usually studied in the context of igneous petrology, although it is sometimes described using sedimentological terms. Tuff is often erroneously called tufa in guidebooks and in television programmes. Volcanic ash The material that is expelled in a volcanic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fissure Vent
A fissure vent, also known as a volcanic fissure, eruption fissure or simply a fissure, is a linear volcanic vent through which lava erupts, usually without any explosive eruption, explosive activity. The vent is often a few metres wide and may be many kilometres long. Fissure vents can cause large flood basalts which run first in lava channels and later in lava tubes. After some time, the eruption tends to become focused at one or more spatter cones. Small fissure vents may not be easily discernible from the air, but the crater rows (see Laki) or the canyons (see Eldgjá) built up by some of them are. The Dike_(geology)#Magmatic_dikes, dikes that feed fissures reach the surface from depths of a few kilometers and connect them to deeper magma chamber, magma reservoirs, often under volcanic centers. Fissures are usually found in or along rifts and rift zones, such as Iceland and the East African Rift. Fissure vents are often part of the structure of shield volcanoes. Icelan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shale
Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especially quartz and calcite.Blatt, Harvey and Robert J. Tracy (1996) ''Petrology: Igneous, Sedimentary and Metamorphic'', 2nd ed., Freeman, pp. 281–292 Shale is characterized by its tendency to split into thin layers ( laminae) less than one centimeter in thickness. This property is called '' fissility''. Shale is the most common sedimentary rock. The term ''shale'' is sometimes applied more broadly, as essentially a synonym for mudrock, rather than in the more narrow sense of clay-rich fissile mudrock. Texture Shale typically exhibits varying degrees of fissility. Because of the parallel orientation of clay mineral flakes in shale, it breaks into thin layers, often splintery and usually parallel to the otherwise indistinguishable beddin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sandstone
Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) because they are the most resistant minerals to weathering processes at the Earth's surface. Like uncemented sand, sandstone may be any color due to impurities within the minerals, but the most common colors are tan, brown, yellow, red, grey, pink, white, and black. Since sandstone beds often form highly visible cliffs and other topographic features, certain colors of sandstone have been strongly identified with certain regions. Rock formations that are primarily composed of sandstone usually allow the percolation of water and other fluids and are porous enough to store large quantities, making them valuable aquifers and petroleum reservoirs. Quartz-bearing sandstone can be changed into quartzite through metamorphism, usually related to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cross-bedding
In geology, cross-bedding, also known as cross-stratification, is layering within a stratum and at an angle to the main bedding plane. The sedimentary structures which result are roughly horizontal units composed of inclined layers. The original depositional layering is tilted, such tilting not being the result of post-depositional deformation. Cross-beds or "sets" are the groups of inclined layers, which are known as cross-strata. Cross-bedding forms during deposition on the inclined surfaces of bedforms such as ripples and dunes; it indicates that the depositional environment contained a flowing medium (typically water or wind). Examples of these bedforms are ripples, dunes, anti-dunes, sand waves, hummocks, bars, and delta slopes.Collinson, J.D., Thompson, D.B., 1989, Sedimentary Structures (2nd ed): Academic Division of Unwin Hyman Ltd, Winchester, MA, XXX p. Environments in which water movement is fast enough and deep enough to develop large-scale bed forms fall into thre ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sorting (sediment)
Sorting describes the distribution of grain size of sediments, either in unconsolidated deposits or in sedimentary rocks. This should not be confused with crystallite size, which refers to the individual size of a crystal in a solid. Crystallite is the building block of a grain. ''Very poorly sorted'' indicates that the sediment sizes are mixed (large variance); whereas ''well sorted'' indicates that the sediment sizes are similar (low variance). The terms describing sorting in sediments – very poorly sorted, poorly sorted, moderately sorted, well sorted, very well sorted – have technical definitions and semi-quantitatively describe the amount of variance seen in particle sizes. See for details. In the field, sedimentologists use graphical charts to accurately describe the sorting of a sediment using one of these terms. The degree of sorting may also indicate the energy, rate, and/or duration of deposition, as well as the transport process (river, debris flow, wind, glacier ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radiometric Dating
Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares the abundance of a naturally occurring radioactive isotope within the material to the abundance of its decay products, which form at a known constant rate of decay. The use of radiometric dating was first published in 1907 by Bertram Boltwood and is now the principal source of information about the absolute age of rocks and other geological features, including the age of fossilized life forms or the age of Earth itself, and can also be used to date a wide range of natural and man-made materials. Together with stratigraphic principles, radiometric dating methods are used in geochronology to establish the geologic time scale. Among the best-known techniques are radiocarbon dating, potassium–argon dating and uranium–lead dating. By al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
South Africa
South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countries of Namibia, Botswana, and Zimbabwe; and to the east and northeast by Mozambique and Eswatini. It also completely enclaves the country Lesotho. It is the southernmost country on the mainland of the Old World, and the second-most populous country located entirely south of the equator, after Tanzania. South Africa is a biodiversity hotspot, with unique biomes, plant and animal life. With over 60 million people, the country is the world's 24th-most populous nation and covers an area of . South Africa has three capital cities, with the executive, judicial and legislative branches of government based in Pretoria, Bloemfontein, and Cape Town respectively. The largest city is Johannesburg. About 80% of the population are Black South Afri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cynognathus Assemblage Zone
The ''Cynognathus'' Assemblage Zone is a tetrapod biozone utilized in the Karoo Basin of South Africa. It is equivalent to the Burgersdorp Formation, the youngest lithostratigraphic formation in the Beaufort Group, which is part of the fossiliferous and geologically important Karoo Supergroup. The '' Cynognathus'' Assemblage Zone is the youngest of the eight biozones found in the Beaufort Group, and is considered to be late Early Triassic (Olenekian) to early Middle Triassic (Anisian) in age (around 247 Ma). The name of the biozone refers to '' Cynognathus crateronotus'', a large and carnivorous cynodont therapsid which occurs throughout the entire biozone. History The first fossils to be found in the Beaufort Group rocks that encompass the current eight biozones were discovered by Andrew Geddes Bain in 1856. However, it was not until 1892 that it was observed that the geological strata of the Beaufort Group could be differentiated based on their fossil taxa. The initial undert ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Biostratigraphy
Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock Stratum, strata by using the fossil assemblages contained within them.Hine, Robert. “Biostratigraphy.” ''Oxford Reference: Dictionary of Biology'', 8th ed., Oxford University Press, 2019. The primary objective of biostratigraphy is ''correlation'', demonstrating that a particular Horizon (geology), horizon in one geological section represents the same period of time as another horizon at a different section. Fossils within these strata are useful because sediments of the same age can look completely different, due to local variations in the Sedimentary depositional environment, sedimentary environment. For example, one section might have been made up of clays and marls, while another has more chalky limestones. However, if the fossil species recorded are similar, the two sediments are likely to have been laid down around the same time. Ideally these fossils are used to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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