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39-907: The formation was first described by Hubach in 1931 as part of the Usme Formation and redefined and named in 1963 by Julivert after the La Regadera Reservoir . The Regadera Formation consists mainly of quartz arenitic sandstone and conglomerates with some shale beds. The Regadera Formation overlies the Bogotá Formation and is overlain by the Usme and Tilatá Formations . The age has been estimated, based on palynological data of Echitriporites trianguliformis var. orbicularis , Nothofagidites sp. and Multiporopollenites pauciporatus , to be Middle to Late Eocene . The depositional environment has been interpreted as

78-758: A braided river setting. The Regadera Formation is apart from its type locality in the synclinal of Usme , the valley of the Tunjuelo River , found in the synclinal of Sisga . In the Tunjuelo River valley, the Regadera Formations is present in the escarpments on the river banks. Sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains, cemented together by another mineral. Sandstones comprise about 20–25% of all sedimentary rocks . Most sandstone

117-480: A thin section using a method like the Gazzi-Dickinson Method . This yields the relative percentages of quartz, feldspar, and lithic grains and the amount of clay matrix. The composition of a sandstone can provide important information on the genesis of the sediments when used with a triangular Q uartz, F eldspar, L ithic fragment ( QFL diagrams ). However, geologist have not been able to agree on

156-591: A cold, stagnant portion of the mantle wedge. Initial theories proposed that the oceanic trenches and magmatic arcs were the primary suppliers of the accretionary sedimentation wedges in the forearc regions. More recent discovery suggests that some of the accreted material in the forearc region is from a mantle source along with trench turbidites derived from continental material. This theory holds due to evidence of pelagic sediments and continental crust being subducted in processes known as sediment subduction and subduction erosion respectively. Over geological time there

195-448: A forearc basin(s), outer-arc high, accretionary prism and the trench itself. The forearc subduction interface can include a seismogenic zone, where megathrust earthquakes can occur, a decoupled zone, and a viscously coupled zone. The accretionary prism is located at the slope of the trench break where there is significantly decreased slope angle. Between the break and the magmatic arc, a sedimentary basin filled with erosive material from

234-490: A heat flow of ~30–40 mW/m , which indicates cold, strong mantle. One good example is the Mariana forearc, where scientists have done extensive research. In this setting there is an erosive margin and forearc slope which consists of 2 km high and 30 km diameter serpentine- mud volcanoes . The erosive properties of these volcanoes are consistent with the metamorphic grades (blueschists) expected for this region in

273-478: A sandstone goes through as the degree of kinetic processing of the sediments increases. Dott's (1964) sandstone classification scheme is one of many such schemes used by geologists for classifying sandstones. Dott's scheme is a modification of Gilbert's classification of silicate sandstones, and it incorporates R.L. Folk's dual textural and compositional maturity concepts into one classification system. The philosophy behind combining Gilbert's and R. L. Folk's schemes

312-462: A set of boundaries separating regions of the QFL triangle. Visual aids are diagrams that allow geologists to interpret different characteristics of a sandstone. For example, a QFL chart can be marked with a provenance model that shows the likely tectonic origin of sandstones with various compositions of framework grains. Likewise, the stage of textural maturity chart illustrates the different stages that

351-445: A twofold classification: Cement is what binds the siliciclastic framework grains together. Cement is a secondary mineral that forms after deposition and during burial of the sandstone. These cementing materials may be either silicate minerals or non-silicate minerals, such as calcite. Sandstone that becomes depleted of its cement binder through weathering gradually becomes friable and unstable. This process can be somewhat reversed by

390-837: Is a distinction that can be recognized in the field . In turn, the distinction between an orthoquartzite and a metaquartzite is the onset of recrystallization of existing grains. The dividing line may be placed at the point where strained quartz grains begin to be replaced by new, unstrained, small quartz grains, producing a mortar texture that can be identified in thin sections under a polarizing microscope. With increasing grade of metamorphism, further recrystallization produces foam texture , characterized by polygonal grains meeting at triple junctions, and then porphyroblastic texture , characterized by coarse, irregular grains, including some larger grains ( porphyroblasts .) Sandstone has been used since prehistoric times for construction, decorative art works and tools. It has been widely employed around

429-550: Is composed of quartz or feldspar , because they are the most resistant minerals to the weathering processes at the Earth's surface. Like uncemented sand , sandstone may be imparted any color by impurities within the minerals, but the most common colors are tan, brown, yellow, red, grey, pink, white, and black. Because sandstone beds can form highly visible cliffs and other topographic features, certain colors of sandstone have become strongly identified with certain regions, such as

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468-425: Is constant recycling of the forearc deposits due to erosion, deformation and sedimentary subduction. The constant circulation of material in the forearc region (accretionary prism, forearc basin and trench) generates a mixture of igneous, metamorphic and sedimentary sequences. In general, there is an increase in metamorphic grade from trench to arc where highest grade (blueschist to eclogite) is structurally uplifted (in

507-523: Is likely formed during eogenesis. Deeper burial is accompanied by mesogenesis , during which most of the compaction and lithification takes place. Compaction takes place as the sand comes under increasing pressure from overlying sediments. Sediment grains move into more compact arrangements, ductile grains (such as mica grains) are deformed, and pore space is reduced. In addition to this physical compaction, chemical compaction may take place via pressure solution . Points of contact between grains are under

546-431: Is redeposited in the unstrained pore spaces. Mechanical compaction takes place primarily at depths less than 1,000 meters (3,300 ft). Chemical compaction continues to depths of 2,000 meters (6,600 ft), and most cementation takes place at depths of 2,000–5,000 meters (6,600–16,400 ft). Unroofing of buried sandstone is accompanied by telogenesis , the third and final stage of diagenesis. As erosion reduces

585-443: Is that it is better able to "portray the continuous nature of textural variation from mudstone to arenite and from stable to unstable grain composition". Dott's classification scheme is based on the mineralogy of framework grains, and on the type of matrix present in between the framework grains. In this specific classification scheme, Dott has set the boundary between arenite and wackes at 15% matrix. In addition, Dott also breaks up

624-518: Is the companion region behind the volcanic arc. Many forearcs have an accretionary wedge which may form a topographic ridge known as an outer arc ridge that parallels the volcanic arc. A forearc basin between the accretionary wedge and the volcanic arc can accumulate thick deposits of sediment, sometimes referred to as an outer arc trough. Due to collisional stresses as one tectonic plate subducts under another, forearc regions are sources for powerful earthquakes. During subduction , an oceanic plate

663-407: Is thrust below another tectonic plate, which can be oceanic or continental . Water and other volatiles in the subducting plate cause flux melting in the upper mantle , creating magma that rises and penetrates the overriding plate, forming a volcanic arc . The weight of the subducting slab flexes the overriding plate and creates an oceanic trench . This area between the trench and the arc is called

702-621: The Global Heritage Stone Resource . In some regions of Argentina, the orthoquartzite-stoned facade is one of the main features of the Mar del Plata style bungalows. Forearc basin A forearc is a region in a subduction zone between an oceanic trench and the associated volcanic arc . Forearc regions are present along convergent margins and eponymously form 'in front of' the volcanic arcs that are characteristic of convergent plate margins. A back-arc region

741-618: The Magnitogorsk forearc region. There are two models which characterize a forearc basin formation and deformation and are dependent on sediment deposition and subsidence (see figure). The first model represents a forearc basin formed with little to no sediment supply. Conversely, the second model represents a basin with a healthy sediment supply. Basin depth depends on the supply of oceanic plate sediments, continentally derived clastic material and orthogonal convergence rates. The accretionary flux (sediment supply in and out) also determines

780-491: The application of tetraethyl orthosilicate (Si(OC 2 H 5 ) 4 ) which will deposit amorphous silicon dioxide between the sand grains. The reaction is as follows. Pore space includes the open spaces within a rock or a soil. The pore space in a rock has a direct relationship to the porosity and permeability of the rock. The porosity and permeability are directly influenced by the way the sand grains are packed together. Sandstones are typically classified by point-counting

819-473: The common minerals most resistant to weathering processes at the Earth's surface, as seen in the Goldich dissolution series . Framework grains can be classified into several different categories based on their mineral composition: Matrix is very fine material, which is present within interstitial pore space between the framework grains. The nature of the matrix within the interstitial pore space results in

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858-456: The depositional environment, older sand is buried by younger sediments, and it undergoes diagenesis . This mostly consists of compaction and lithification of the sand. Early stages of diagenesis, described as eogenesis , take place at shallow depths (a few tens of meters) and are characterized by bioturbation and mineralogical changes in the sands, with only slight compaction. The red hematite that gives red bed sandstones their color

897-407: The depth of burial, renewed exposure to meteoric water produces additional changes to the sandstone, such as dissolution of some of the cement to produce secondary porosity . Framework grains are sand-sized (0.0625-to-2-millimeter (0.00246 to 0.07874 in) diameter) detrital fragments that make up the bulk of a sandstone. Most framework grains are composed of quartz or feldspar , which are

936-446: The different types of framework grains that can be present in a sandstone into three major categories: quartz, feldspar, and lithic grains. When sandstone is subjected to the great heat and pressure associated with regional metamorphism , the individual quartz grains recrystallize, along with the former cementing material, to form the metamorphic rock called quartzite . Most or all of the original texture and sedimentary structures of

975-420: The forearc region, with the area behind the arc and away from the trench known as the back-arc region . The mantle region between the overriding plate and the subducting slab experiences corner flow near the back-arc driven by the down dip motion of the subducting slab. At the same time, the temperature of the mantle wedge closer to the trench is dominated by the denser and colder subducting slab, resulting in

1014-433: The greatest strain, and the strained mineral is more soluble than the rest of the grain. As a result, the contact points are dissolved away, allowing the grains to come into closer contact. Lithification follows closely on compaction, as increased temperatures at depth hasten deposition of cement that binds the grains together. Pressure solution contributes to cementing, as the mineral dissolved from strained contact points

1053-442: The hardness of individual grains, uniformity of grain size and friability of their structure, some types of sandstone are excellent materials from which to make grindstones , for sharpening blades and other implements. Non-friable sandstone can be used to make grindstones for grinding grain, e.g., gritstone . A type of pure quartz sandstone, orthoquartzite, with more of 90–95 percent of quartz, has been proposed for nomination to

1092-493: The much lower temperatures and pressures associated with diagenesis of sedimentary rock, but diagenesis has cemented the rock so thoroughly that microscopic examination is necessary to distinguish it from metamorphic quartzite. The term orthoquartzite is used to distinguish such sedimentary rock from metaquartzite produced by metamorphism. By extension, the term orthoquartzite has occasionally been more generally applied to any quartz-cemented quartz arenite . Orthoquartzite (in

1131-464: The narrow sense) is often 99% SiO 2 with only very minor amounts of iron oxide and trace resistant minerals such as zircon , rutile and magnetite . Although few fossils are normally present, the original texture and sedimentary structures are preserved. The typical distinction between a true orthoquartzite and an ordinary quartz sandstone is that an orthoquartzite is so highly cemented that it will fracture across grains, not around them. This

1170-518: The overriding and underthrusting plates in the forearc regions have shown to evolve strong coupling mechanisms which result in megathrust earthquakes such as the Tohoku-oki earthquake which occurred off the Pacific coast of Northeast Japan (Tian and Liu. 2013). These mega thrust earthquakes may be correlated with low values of heat flow generally associated with forearc regions. Geothermal data shows

1209-411: The prisms) compared to the younger deposits (basins). Forearc regions are also where ophiolites are emplaced should obduction occur, but such deposits are not continuous and can often be removed by erosion. As tectonic plates converge, the closing of an ocean will result in the convergence of two landmasses, each of which is either an island arc or continental margin. When these two bodies collide,

Regadera Formation - Misplaced Pages Continue

1248-638: The product of physical and chemical weathering of bedrock. Weathering and erosion are most rapid in areas of high relief, such as volcanic arcs , areas of continental rifting , and orogenic belts . Eroded sand is transported by rivers or by the wind from its source areas to depositional environments where tectonics has created accommodation space for sediments to accumulate. Forearc basins tend to accumulate sand rich in lithic grains and plagioclase . Intracontinental basins and grabens along continental margins are also common environments for deposition of sand. As sediments continue to accumulate in

1287-404: The rate at which the sedimentation wedges grow within the forearc. The age of the oceanic crust along with the convergent velocity controls the coupling across the converging interface of the continental and oceanic crust. The strength of this coupling controls the deformation associated with the event and can be seen in the forearc region deformation signatures. The intense interaction between

1326-712: The red rock deserts of Arches National Park and other areas of the American Southwest . Rock formations 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 tectonic compression within orogenic belts . Sandstones are clastic in origin (as opposed to either organic , like chalk and coal , or chemical , like gypsum and jasper ). The silicate sand grains from which they form are

1365-402: The result is orogenesis , at which time the underthrusting oceanic crust slows down. In early stages of arc-continent collision, there is uplift and erosion of the accretionary prism and forearc basin. In the later stages of collision, the forearc region may be sutured, rotated and shortened which can form syn-collisional folds and thrust belts. At the surface, the forearc region can include

1404-417: The sandstone are erased by the metamorphism. The grains are so tightly interlocked that when the rock is broken, it fractures through the grains to form an irregular or conchoidal fracture. Geologists had recognized by 1941 that some rocks show the macroscopic characteristics of quartzite, even though they have not undergone metamorphism at high pressure and temperature. These rocks have been subject only to

1443-481: The tectonic forcing which causes the oceanic lithosphere to descend. The relationship between surface slope and subduction thrust also plays a huge role in the variation of forearc structure and deformation. A subduction wedge can be classified as either stable with little deformation or unstable with pervasive internal deformation (see section on Models). Some common deformation in forearc sediments are synsedimentary deformation and olistostromes , such as that seen in

1482-413: The volcanic arc and substrate can accumulate into a forearc basin which overlays the oldest thrust slices in the wedge of the forearc region. In general, the forearc topography (specifically in the trench region) is trying to achieve an equilibrium between buoyancy and tectonic forces caused by subduction. Upward motion of the forearc is related to buoyancy forces and the downward motion is associated with

1521-626: The world in constructing temples, churches, homes and other buildings, and in civil engineering . Although its resistance to weathering varies, sandstone is easy to work. That makes it a common building and paving material, including in asphalt concrete . However, some types that have been used in the past, such as the Collyhurst sandstone used in North West England , have had poor long-term weather resistance, necessitating repair and replacement in older buildings. Because of

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