1.
Sedimentary
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Sedimentary rocks are types of rock that are formed by the deposition and subsequent cementation of that material at the Earths surface and within bodies of water. Sedimentation is the name for processes that cause mineral and/or organic particles to settle in place. The particles that form a rock by accumulating are called sediment. Sedimentation may also occur as minerals precipitate from solution or shells of aquatic creatures settle out of suspension. The sedimentary rock cover of the continents of the Earths crust is extensive, sedimentary rocks are only a thin veneer over a crust consisting mainly of igneous and metamorphic rocks. Sedimentary rocks are deposited in layers as strata, forming a structure called bedding, sedimentary rocks are also important sources of natural resources like coal, fossil fuels, drinking water or ores. The study of the sequence of rock strata is the main source for an understanding of the Earths history, including palaeogeography, paleoclimatology. The scientific discipline that studies the properties and origin of rocks is called sedimentology. Sedimentology is part of both geology and physical geography and overlaps partly with other disciplines in the Earth sciences, such as pedology, geomorphology, geochemistry, sedimentary rocks have also been found on Mars. Clastic sedimentary rocks are composed of rock fragments that were cemented by silicate minerals. Clastic rocks are composed largely of quartz, feldspar, rock fragments, clay minerals, and mica, any type of mineral may be present, clastic sedimentary rocks, are subdivided according to the dominant particle size. Most geologists use the Udden-Wentworth grain size scale and divide unconsolidated sediment into three fractions, gravel, sand, and mud and this tripartite subdivision is mirrored by the broad categories of rudites, arenites, and lutites, respectively, in older literature. The subdivision of these three categories is based on differences in clast shape, conglomerates and breccias), composition. Conglomerates are dominantly composed of rounded gravel, while breccias are composed of dominantly angular gravel, composition of framework grains The relative abundance of sand-sized framework grains determines the first word in a sandstone name. Naming depends on the dominance of the three most abundant components quartz, feldspar, or the lithic fragments that originated from other rocks, all other minerals are considered accessories and not used in the naming of the rock, regardless of abundance. Clean sandstones with open space are called arenites. Muddy sandstones with abundant muddy matrix are called wackes, six sandstone names are possible using the descriptors for grain composition and the amount of matrix. Mudrocks are sedimentary rocks composed of at least 50% silt- and clay-sized particles and these relatively fine-grained particles are commonly transported by turbulent flow in water or air, and deposited as the flow calms and the particles settle out of suspension
2.
Point Lobos
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Point Lobos is just south of Carmel-by-the-Sea, California, United States, at the north end of the Big Sur coast of the Pacific Ocean. Point Lobos contains a number of hiking trails, many next to the ocean, and it is the site of a historic marine reserve, which was expanded in 2007. It is also the home to a museum on whaling, which includes a building once used by area fishermen. The longstanding wildlife protection and scenic seascape have led to Point Lobos reputation as a local recreational scuba diving destination. The parks origins are owed to engineer Alexander Allan, who purchased a parcel of land in 1933 to prevent it from being developed. It was to be subdivided into 1,000 lots under the name of Carmelito, the iconic Point Lobos area is geologically unique and contains a rich and diverse plant and animal life both on shore and in the water. Called the greatest meeting of land and water in the world by landscape artist Francis McComas, the geological history of Point Lobos describes the rocks that create the headlands and inlets that make Point Lobos famous. Carmel submarine canyon lies just north of Point Lobos, like Monterey Canyon to the north the canyon provides cold, nutrient-rich water to the surface during upwelling events. These nutrient rich waters fuel the high primary productivity seen in Carmel and Monterey Bays, the original Point Lobos Ecological Reserve was created in 1973. As one of Californias oldest and best known no-take reserves, its large, in 2007, the Ecological Reserve was expanded and renamed with the establishment of The Point Lobos SMR and Point Lobos SMCA by the California Department of Fish and Game. Point Lobos SMR covers 5.36 square miles, the SMR protects all marine life within its boundaries. Fishing and take of all living marine resources is prohibited, the marine reserve is bounded by the mean high tide line and straight lines connecting the following points in the order listed, 36°31. 70’ N. lat. 121°55. 55’ W. long. 36°31. 70’ N. lat. 121°58. 25’ W. long, 36°28. 88’ N. lat. 121°58. 25’ W. long. And 36°28. 88’ N. lat. 121°56. 30’ W. long, Point Lobos SMCA covers 8.83 square miles. Harvest of all living marine resources is prohibited in the area except the recreational and commercial take of salmon, albacore. The area is bounded by lines connecting the following points in the order listed except where noted. 36°31. 70’ N. lat. 122°01. 30’ W. long, thence southward along the three nautical mile offshore boundary to 36°28. 88’ N. lat. 122°00. 55’ W. long. 36°28. 88’ N. lat. 121°58. 25’ W. long, and 36°31. 70’ N. lat. 121°58. 25’ W. long
3.
Clastic rock
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Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus, chunks and smaller grains of rock broken off other rocks by physical weathering. Geologists use the term clastic with reference to sedimentary rocks as well as to particles in sediment transport whether in suspension or as bed load, clastic sedimentary rocks are rocks composed predominantly of broken pieces or clasts of older weathered and eroded rocks. Clastic sediments or sedimentary rocks are classified based on size, clast and cementing material composition. The classification factors are often useful in determining a samples environment of deposition, an example clastic environment would be a river system in which the full range of grains being transported by the moving water consist of pieces eroded from solid rock upstream. Grain size varies from clay in shales and claystones, through silt in siltstones, sand in sandstones, the Krumbein phi scale numerically orders these terms in a logarithmic size scale. Siliciclastic rocks are clastic rocks that are composed almost exclusively of silicon. The composition of sedimentary rocks includes the chemical and mineralogical components of the framework as well as the cementing material that make up these rocks. Boggs divides them into four categories, major minerals, accessory minerals, rock fragments, major minerals can be categorized into subdivisions based on their resistance to chemical decomposition. Those that possess a great resistance to decomposition are categorized as stable, while those that do not are considered less stable, the most common stable mineral in siliciclastic sedimentary rocks is quartz. Quartz makes up approximately 65 percent of framework grains present in sandstones, less stable minerals present in this type of rocks are feldspars, including both potassium and plagioclase feldspars. Feldspars comprise a considerably lesser portion of framework grains and minerals and they only make up about 15 percent of framework grains in sandstones and 5% of minerals in shales. Clay mineral groups are present in mudrocks but can be found in other siliciclastic sedimentary rocks at considerably lower levels. Accessory minerals are associated with those whose presence in the rock are not directly important to the classification of the specimen and these generally occur in smaller amounts in comparison to the quartz, and feldspars. Furthermore, those that do occur are generally heavy minerals or coarse grained micas, rock fragments also occur in the composition of siliciclastic sedimentary rocks and are responsible for about 10 -15 percent of the composition of sandstone. They generally make up most of the gravel size particles in conglomerates, though they sometimes are, rock fragments are not always sedimentary in origin. They can also be metamorphic or igneous, chemical cements vary in abundance but are predominantly found in sandstones. The two major types, are based and carbonate based
4.
Sedimentary rock
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Sedimentary rocks are types of rock that are formed by the deposition and subsequent cementation of that material at the Earths surface and within bodies of water. Sedimentation is the name for processes that cause mineral and/or organic particles to settle in place. The particles that form a rock by accumulating are called sediment. Sedimentation may also occur as minerals precipitate from solution or shells of aquatic creatures settle out of suspension. The sedimentary rock cover of the continents of the Earths crust is extensive, sedimentary rocks are only a thin veneer over a crust consisting mainly of igneous and metamorphic rocks. Sedimentary rocks are deposited in layers as strata, forming a structure called bedding, sedimentary rocks are also important sources of natural resources like coal, fossil fuels, drinking water or ores. The study of the sequence of rock strata is the main source for an understanding of the Earths history, including palaeogeography, paleoclimatology. The scientific discipline that studies the properties and origin of rocks is called sedimentology. Sedimentology is part of both geology and physical geography and overlaps partly with other disciplines in the Earth sciences, such as pedology, geomorphology, geochemistry, sedimentary rocks have also been found on Mars. Clastic sedimentary rocks are composed of rock fragments that were cemented by silicate minerals. Clastic rocks are composed largely of quartz, feldspar, rock fragments, clay minerals, and mica, any type of mineral may be present, clastic sedimentary rocks, are subdivided according to the dominant particle size. Most geologists use the Udden-Wentworth grain size scale and divide unconsolidated sediment into three fractions, gravel, sand, and mud and this tripartite subdivision is mirrored by the broad categories of rudites, arenites, and lutites, respectively, in older literature. The subdivision of these three categories is based on differences in clast shape, conglomerates and breccias), composition. Conglomerates are dominantly composed of rounded gravel, while breccias are composed of dominantly angular gravel, composition of framework grains The relative abundance of sand-sized framework grains determines the first word in a sandstone name. Naming depends on the dominance of the three most abundant components quartz, feldspar, or the lithic fragments that originated from other rocks, all other minerals are considered accessories and not used in the naming of the rock, regardless of abundance. Clean sandstones with open space are called arenites. Muddy sandstones with abundant muddy matrix are called wackes, six sandstone names are possible using the descriptors for grain composition and the amount of matrix. Mudrocks are sedimentary rocks composed of at least 50% silt- and clay-sized particles and these relatively fine-grained particles are commonly transported by turbulent flow in water or air, and deposited as the flow calms and the particles settle out of suspension
5.
Gravel
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Gravel /ˈɡrævəl/ is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel is categorized by the Udden-Wentworth scale into granular gravel and pebble gravel, one cubic metre of gravel typically weighs about 1,800 kg. Gravel is an important commercial product, with a number of applications, many roadways are surfaced with gravel, especially in rural areas where there is little traffic. Globally, far more roads are surfaced with gravel than with concrete or tarmac, both sand and small gravel are also important for the manufacture of concrete. Large gravel deposits are a geological feature, being formed as a result of the weathering. The action of rivers and waves tends to pile up gravel in large accumulations and this can sometimes result in gravel becoming compacted and concreted into the sedimentary rock called conglomerate. Where natural gravel deposits are insufficient for human purposes, gravel is often produced by quarrying and crushing hard-wearing rocks, such as sandstone, limestone, quarries where gravel is extracted are known as gravel pits. Southern England possesses particularly large concentrations of them due to the deposition of gravel in the region during the Ice Ages. As of 2006, the United States is the leading producer and consumer of gravel. The word gravel comes from the Breton language, adding the -el suffix in Breton denotes the component parts of something larger. Thus gravel means the stones which make up such a beach on the coast. Many dictionaries ignore the Breton language, citing Old French gravele or gravelle, Gravel often has the meaning a mixture of different size pieces of stone mixed with sand and possibly some clay. American English also allows small stones without sand mixed in also known as crushed stone, types of gravel include, Bank gravel, naturally deposited gravel intermixed with sand or clay found in and next to rivers and streams. Also known as Bank run or River run, bench gravel, a bed of gravel located on the side of a valley above the present stream bottom, indicating the former location of the stream bed when it was at a higher level. Creek rock, this is rounded, semi-polished stones, potentially of a wide range of types. It is also used as concrete aggregate and less often as a paving surface. Crushed stone, rock crushed and graded by screens and then mixed to a blend of stones and fines and it is widely used as a surfacing for roads and driveways, sometimes with tar applied over it. Crushed stone may be made from granite, limestone, dolomite, also known as crusher run, DGA QP, and shoulder stone
6.
Pebble
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A pebble is a clast of rock with a particle size of 2 to 64 millimetres based on the Krumbein phi scale of sedimentology. Pebbles are generally considered larger than granules and smaller than cobbles, a rock made predominantly of pebbles is termed a conglomerate. Pebble tools are among the earliest known man-made artifacts, dating from the Palaeolithic period of human history, a beach composed chiefly of surface pebbles is commonly termed a shingle beach. This type of beach has armoring characteristics with respect to wave erosion, as well as ecological niches that provide habitat for animals and plants. Inshore banks of shingle exist in locations, such as the entrance to the River Ore. Pebbles come in colors and textures and can have streaks, known as veins. Pebbles are mostly smooth but, dependent on how frequently they come in contact with the sea, pebbles left above the high water mark may have growths of organisms such as lichen on them, signifying the lack of contact with seawater. Pebbles are found in two locations – on the beaches of various oceans and seas, and inland where ancient seas used to cover the land, when then the seas retreated, the rocks became landlocked. They can also be found in lakes and ponds, pebbles can also form in rivers, and travel into estuaries where the smoothing continues in the sea. Beach pebbles and river pebbles are distinct in their geological formation, beach pebbles form gradually over time as the ocean water washes over loose rock particles. The result is a smooth, rounded appearance, the typical size range is from 2 mm to 50 mm. The colors range from translucent white to black, and include shades of yellow, brown, red and green. Some of the more plentiful pebble beaches are found along the coast of the Pacific Ocean, beginning in the United States and extending down to the tip of South America in Argentina. Other pebble beaches are found in northern Europe, along the coast of the U. K. and Ireland, on the shores of Australia, inland pebbles are usually found along the shores of large rivers and lakes. These pebbles form as the water washes over rock particles on the bottom. The smoothness and color of river pebbles depends on several factors, such as the composition of the soil of the banks, the chemical characteristics of the water. Because river current is gentler than the waves, river pebbles are usually not as smooth as beach pebbles. The most common colors of rock are black, grey, green, brown
7.
Cobble (geology)
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A cobble is a clast of rock defined on the Udden–Wentworth scale as having a particle size of 64–256 millimeters, larger than a pebble and smaller than a boulder. Other scales define a cobbles size in different terms. A rock made predominantly of cobbles is termed a conglomerate, cobblestone is a building material based on cobbles. Cobbles, also called cobblestones, derive their name from the word cob, the term is further related to the German Kopf, meaning head. Chester Wentworth referred to cobbles as cobble bowlders in his 1922 paper that would become the basis for the Udden–Wentworth scale, within the widely used Krumbein phi scale of grain sizes, cobbles are defined as clasts of rock ranging from −6 to −8 φ. This classification corresponds with the Udden–Wentworth size scale which defines cobbles as clasts with diameters from 64–256 millimeters, on this scale, cobbles are larger than pebbles which measure 4–64 millimeters in diameter and smaller than boulders, whose diameters range from 256–4,096 millimeters. On the Udden–Wentworth scale, a fraction of cobbles is classified as gravel while a lithified sample primarily composed of cobbles is a conglomerate. The Committee on Sedimentation of the US National Research Council has recommended that in situ cobbles be identified by their process of origination, various attempts have been made to refine the Udden–Wentworth scale, including its definition of cobbles. In 1968, D. J. Doeglas proposed subdividing the cobble designation into two fractions, small cobbles and large cobbles and they proposed defining fine cobbles as those with diameters from 64–128 millimeters and coarse cobbles as those with diameters from 128–256 millimeters. When occurring in streams, cobbles are likely to be found in mountain valley streambeds that are moderately steep, cobbles are also transported by glaciers and deposited as with other grades of sediment as till. If the till is water-laid, finer particles like sand and pebbles may be washed away, leaving a deposit of only boulders. Glacially transported cobbles tend to share several identifying features including a tabular shape, cobble conglomerates may be alluvial in origin or the product of stone avalanches, a type of debris flow resulting from unconsolidated cobbles and gravel. In such stone avalanches, well-rounded cobbles may travel the farthest on account of their low rolling friction, when the product of alluvial processes, the cobble conglomerates matrix consists of gravel and coarse sand. In contrast, the matrices of flow-deposited conglomerates are primarily mud, bunte, K. Abt, S. R. Sampling Surface and Subsurface Particle-Size Distributions in Wadable Gravel- and Cobble-Bed Streams for Analyses in Sediment Transport, Hydraulics, and Streambed Monitoring. Fort Collins, CO, United States Forest Service, hsü, K. J. Physics of Sedimentology, Textbook and Reference. New York City, Harper and Row
8.
Boulder
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In geology, a boulder is a rock fragment with size greater than 25.6 centimetres in diameter. Smaller pieces are called cobbles and pebbles, while a boulder may be small enough to move or roll manually, others are extremely massive. In common usage, a boulder is too large for a person to move, smaller boulders are usually just called rocks or stones. The word boulder is short for boulder stone, from Middle English bulderston or Swedish bullersten, in places covered by ice sheets during Ice Ages, such as Scandinavia, northern North America, and Siberia, glacial erratics are common. Erratics are boulders picked up by ice sheets during their advance and they are called erratic because they typically are of a different rock type than the bedrock on which they are deposited. One of them is used as the pedestal of the Bronze Horseman in Saint Petersburg, boulder sized clasts are found in some sedimentary rocks, such as coarse conglomerate and boulder clay. The climbing of large boulders is called bouldering, road debris Monolith Media related to Boulders at Wikimedia Commons
9.
Consolidation (soil)
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Consolidation is a process by which soils decrease in volume. According to Karl von Terzaghi consolidation is any process which involves a decrease in water content of saturated soil without replacement of water by air, in general it is the process in which reduction in volume takes place by expulsion of water under long term static loads. It occurs when stress is applied to a soil causes the soil particles to pack together more tightly. When this occurs in a soil that is saturated with water, water will be squeezed out of the soil, the magnitude of consolidation can be predicted by many different methods. In the Classical Method, developed by Terzaghi, soils are tested with an oedometer test to determine their compression index and this can be used to predict the amount of consolidation. When stress is removed from a soil, the soil will rebound. If the stress is reapplied, the soil will consolidate again along a recompression curve, the soil which had its load removed is considered to be overconsolidated. This is the case for soils which have previously had glaciers on them, the highest stress that it has been subjected to is termed the preconsolidation stress. The over consolidation ratio or OCR is defined as the highest stress experienced divided by the current stress, a soil which is currently experiencing its highest stress is said to be normally consolidated and to have an OCR of one. A soil could be considered underconsolidated immediately after a new load is applied, the process of consolidation is often explained with an idealized system composed of a spring, a container with a hole in its cover, and water. In this system, the spring represents the compressibility or the structure of the soil itself, the container is completely filled with water, and the hole is closed. A load is applied onto the cover, while the hole is still unopened, at this stage, only the water resists the applied load. As soon as the hole is opened, water starts to drain out through the hole, after some time, the drainage of water no longer occurs. Now, the spring alone resists the applied load and this method assumes consolidation occurs in only one-dimension. Laboratory data is used to construct a plot of strain or void ratio versus effective stress where the stress axis is on a logarithmic scale. The plots slope is the index or recompression index. The equation for consolidation settlement of a consolidated soil can then be determined to be. E0 is the void ratio
10.
Sediment
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For sediment in beverages, see dregs. For example, sand and silt can be carried in suspension in water and on reaching the sea be deposited by sedimentation. Sediments are most often transported by water, but also wind, beach sands and river channel deposits are examples of fluvial transport and deposition, though sediment also often settles out of slow-moving or standing water in lakes and oceans. Desert sand dunes and loess are examples of transport and deposition. Glacial moraine deposits and till are ice-transported sediments, sediment can be classified based on its grain size and/or its composition. Sediment size is measured on a log base 2 scale, called the Phi scale, composition of sediment can be measured in terms of, parent rock lithology mineral composition chemical make-up. This leads to an ambiguity in which clay can be used as both a size-range and a composition, sediment is transported based on the strength of the flow that carries it and its own size, volume, density, and shape. Stronger flows will increase the lift and drag on the particle, causing it to rise, rivers and streams carry sediment in their flows. This sediment can be in a variety of locations within the flow and these relationships are shown in the following table for the Rouse number, which is a ratio of sediment fall velocity to upwards velocity. If the upwards velocity is less than the settling velocity, but still high enough for the sediment to move, it will move along the bed as bed load by rolling, sliding. If the upwards velocity is higher than the velocity, the sediment will be transported high in the flow as wash load. As there are generally a range of different particle sizes in the flow, sediment motion can create self-organized structures such as ripples, dunes, antidunes on the river or stream bed. These bedforms are often preserved in rocks and can be used to estimate the direction. Overland flow can erode soil particles and transport them downslope, the erosion associated with overland flow may occur through different methods depending on meteorological and flow conditions. If the initial impact of rain droplets dislodges soil, the phenomenon is called rainsplash erosion, if overland flow is directly responsible for sediment entrainment but does not form gullies, it is called sheet erosion. If the flow and the substrate permit channelization, gullies may form, glaciers carry a wide range of sediment sizes, and deposit it in moraines. The overall balance between sediment in transport and sediment being deposited on the bed is given by the Exner equation and this expression states that the rate of increase in bed elevation due to deposition is proportional to the amount of sediment that falls out of the flow. This can be localized, and simply due to obstacles, examples are scour holes behind boulders, where flow accelerates
11.
Sand
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Sand is a naturally occurring granular material composed of finely divided rock and mineral particles. It is defined by size, being finer than gravel and coarser than silt, Sand can also refer to a textural class of soil or soil type, i. e. a soil containing more than 85% sand-sized particles by mass. The second most common type of sand is calcium carbonate, for example aragonite, for example, it is the primary form of sand apparent in areas where reefs have dominated the ecosystem for millions of years like the Caribbean. Sand is a non renewable resource over human timescales, and sand suitable for making concrete is in high demand, in terms of particle size as used by geologists, sand particles range in diameter from 0.0625 mm to 2 mm. An individual particle in this size is termed a sand grain. Sand grains are between gravel and silt, a 1953 engineering standard published by the American Association of State Highway and Transportation Officials set the minimum sand size at 0.074 mm. A1938 specification of the United States Department of Agriculture was 0.05 mm. Sand feels gritty when rubbed between the fingers. ISO14688 grades sands as fine, medium and coarse with ranges 0.063 mm to 0.2 mm to 0.63 mm to 2.0 mm. In the United States, sand is commonly divided into five sub-categories based on size, very fine sand, fine sand, medium sand, coarse sand, and very coarse sand. These sizes are based on the Krumbein phi scale, where size in Φ = -log2D, on this scale, for sand the value of Φ varies from −1 to +4, with the divisions between sub-categories at whole numbers. The composition of sand is highly variable, depending on the local rock sources. The gypsum sand dunes of the White Sands National Monument in New Mexico are famous for their bright, arkose is a sand or sandstone with considerable feldspar content, derived from weathering and erosion of a granitic rock outcrop. Some sands contain magnetite, chlorite, glauconite or gypsum, Sands rich in magnetite are dark to black in color, as are sands derived from volcanic basalts and obsidian. Chlorite-glauconite bearing sands are typically green in color, as are sands derived from basaltic with a high olivine content, many sands, especially those found extensively in Southern Europe, have iron impurities within the quartz crystals of the sand, giving a deep yellow color. Sand deposits in some areas contain garnets and other resistant minerals, the study of individual grains can reveal much historical information as to the origin and kind of transport of the grain. Quartz sand that is weathered from granite or gneiss quartz crystals will be angular. It is called grus in geology or sharp sand in the trade where it is preferred for concrete. Sand that is transported long distances by water or wind will be rounded, people who collect sand as a hobby are known as arenophiles
12.
Silt
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Silt is granular material of a size between sand and clay, whose mineral origin is quartz and feldspar. Silt may occur as a soil or as sediment mixed in suspension with water in a body of such as a river. It may also exist as soil deposited at the bottom of a water body, Silt has a moderate specific area with a typically non-sticky, plastic feel. Silt usually has a floury feel when dry, and a slippery feel when wet, Silt can be visually observed with a hand lens. Silt is created by a variety of physical processes capable of splitting the generally sand-sized quartz crystals of primary rocks by exploiting deficiencies in their lattice and these involve chemical weathering of rock and regolith, and a number of physical weathering processes such as frost shattering and haloclasty. The main process is abrasion through transport, including fluvial comminution, aeolian attrition and it is in semi-arid environments that substantial quantities of silt are produced. Silt is sometimes known as rock flour or stone dust, especially produced by glacial action. Mineralogically, silt is composed mainly of quartz and feldspar, sedimentary rock composed mainly of silt is known as siltstone. Liquefaction created by an earthquake is silt suspended in water that is hydrodynamically forced up from below ground level. In the Udden–Wentworth scale, silt particles range between 0.0039 and 0.0625 mm, larger than clay but smaller than sand particles, ISO14688 grades silts between 0.002 mm and 0.063 mm. In actuality, silt is chemically distinct from clay, and unlike clay, grains of silt are approximately the size in all dimensions, furthermore. Clays are formed from thin plate-shaped particles held together by electrostatic forces, according to the U. S. Department of Agriculture Soil Texture Classification system, the sand-silt distinction is made at the 0.05 mm particle size. The USDA system has been adopted by the Food and Agriculture Organization, in the Unified Soil Classification System and the AASHTO Soil Classification system, the sand-silt distinction is made at the 0.075 mm particle size. Silts and clays are distinguished mechanically by their plasticity, Silt is easily transported in water or other liquid and is fine enough to be carried long distances by air in the form of dust. Thick deposits of silty material resulting from deposition by aeolian processes are called loess. Silt and clay contribute to turbidity in water, Silt is transported by streams or by water currents in the ocean. When silt appears as a pollutant in water the phenomenon is known as siltation, Silt, deposited by annual floods along the Nile River, created the rich, fertile soil that sustained the Ancient Egyptian civilization. In south east Bangladesh, in the Noakhali district, cross dams were built in the 1960s whereby silt gradually started forming new land called chars, the district of Noakhali has gained more than 28 square miles of land in the past 50 years
13.
Clay
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Clay is a fine-grained natural rock or soil material that combines one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure. Clays are plastic due to water content and become hard, brittle. Depending on the content in which it is found, clay can appear in various colours from white to dull grey or brown to deep orange-red. Although many naturally occurring deposits include both silts and clay, clays are distinguished from other fine-grained soils by differences in size, silts, which are fine-grained soils that do not include clay minerals, tend to have larger particle sizes than clays. There is, however, some overlap in size and other physical properties. The distinction between silt and clay varies by discipline, geologists and soil scientists usually consider the separation to occur at a particle size of 2 µm, sedimentologists often use 4–5 μm, and colloid chemists use 1 μm. Geotechnical engineers distinguish between silts and clays based on the plasticity properties of the soil, as measured by the soils Atterberg limits, ISO14688 grades clay particles as being smaller than 2 μm and silt particles as being larger. These solvents, usually acidic, migrate through the rock after leaching through upper weathered layers. In addition to the process, some clay minerals are formed through hydrothermal activity. There are two types of deposits, primary and secondary. Primary clays form as residual deposits in soil and remain at the site of formation, secondary clays are clays that have been transported from their original location by water erosion and deposited in a new sedimentary deposit. Clay deposits are associated with very low energy depositional environments such as large lakes. Depending on the source, there are three or four main groups of clays, kaolinite, montmorillonite-smectite, illite, and chlorite. Chlorites are not always considered to be a clay, sometimes being classified as a group within the phyllosilicates. There are approximately 30 different types of clays in these categories. Varve is clay with visible annual layers, which are formed by deposition of those layers and are marked by differences in erosion. This type of deposit is common in glacial lakes
14.
Matrix (geology)
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The matrix or groundmass of rock is the finer-grained mass of material wherein larger grains, crystals or clasts are embedded. The matrix of an igneous rock consists of finer-grained, often microscopic and this porphyritic texture is indicative of multi-stage cooling of magma. For example, porphyritic andesite will have large phenocrysts of plagioclase in a fine-grained matrix, also in South Africa, diamonds are often mined from a matrix of weathered clay-like rock called yellow ground. The matrix of sedimentary rocks is finer-grained sedimentary material, such as clay or silt and it also used to describe the rock material in which a fossil is embedded. All sediments are at first in an incoherent condition, and in this state they may remain for an indefinite period. Millions of years have elapsed since some of the early Tertiary strata gathered on the floor, yet they are quite friable. The pressure of newer sediments on underlying masses is one cause of this change. More efficiency is generally ascribed to the action of percolating water, the redeposited cementing material is most commonly calcareous or siliceous. Limestones, which were originally a loose accumulation of shells, corals, the change of aragonite to calcite and of calcite to dolomite, by forming new crystalline masses in the interior of the rock, usually also accelerates consolidations. Silica is less soluble in ordinary waters, but even this ingredient of rocks is dissolved and redeposited with great frequency. Others contain fine scales of kaolin or of mica, argillaceous materials may be compacted by mere pressure, like graphite and other scaly minerals
15.
Calcium carbonate
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Calcium carbonate is a chemical compound with the formula CaCO3. It is a substance found in rocks as the minerals calcite and aragonite and is the main component of pearls and the shells of marine organisms, snails. Calcium carbonate is the ingredient in agricultural lime and is created when calcium ions in hard water react with carbonate ions to create limescale. It is medicinally used as a supplement or as an antacid. Calcium carbonate shares the properties of other carbonates. CaCO3 + CO2 + H2O → Ca2 This reaction is important in the erosion of rock, forming caverns. An unusual form of calcium carbonate is the hexahydrate, ikaite, ikaite is stable only below 6 °C. The vast majority of calcium used in industry is extracted by mining or quarrying. Pure calcium carbonate, can be produced from a quarried source. Alternatively, calcium carbonate is prepared from calcium oxide, other forms can be prepared, the denser, orthorhombic λ-CaCO3 and μ-CaCO3, occurring as the mineral vaterite. The aragonite form can be prepared by precipitation at temperatures above 85 °C, calcite contains calcium atoms coordinated by 6 oxygen atoms, in aragonite they are coordinated by 9 oxygen atoms. The vaterite structure is not fully understood, magnesium carbonate MgCO3 has the calcite structure, whereas strontium and barium carbonate adopt the aragonite structure, reflecting their larger ionic radii. Calcite, aragonite and vaterite are pure calcium carbonate minerals, industrially important source rocks which are predominantly calcium carbonate include limestone, chalk, marble and travertine. Eggshells, snail shells and most seashells are predominantly calcium carbonate, oyster shells have enjoyed recent recognition as a source of dietary calcium, but are also a practical industrial source. While not practical as a source, dark green vegetables such as broccoli. Beyond Earth, strong evidence suggests the presence of Calcium carbonate on Mars, signs of Calcium Carbonate have been detected at more than one location. This provides some evidence for the past presence of liquid water, Carbonate is found frequently in geologic settings and constitute an enormous carbon reservoir. Calcium carbonate occurs as aragonite, calcite and dolomite, the carbonate minerals form the rock types, limestone, chalk, marble, travertine, tufa, and others
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Iron oxide
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Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxides and oxyhydroxides, common rust is a form of iron oxide. Iron oxides are used as inexpensive, durable pigments in paints, coatings. Colors commonly available are in the end of the yellow/orange/red/brown/black range. When used as a coloring, it has E number E172. Limonite Iron oxide nanoparticles List of inorganic pigments Information from Nano-Oxides, http, //chemed. chem. purdue. edu/demos/demosheets/12.3. html http, //minerals. usgs. gov/minerals/pubs/commodity/iron_oxide/ CDC - NIOSH Pocket Guide to Chemical Hazards de
17.
Sedimentary structures
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Sedimentary structures are those structures formed during sediment deposition. There are two kinds of structures, bidirectional and unidirectional. Flow regimes in single-direction flow, which at varying speeds and velocities produce different structures, are called bedforms, in the lower flow regime, the natural progression is from a flat bed, to some sediment movement, to ripples, to slightly larger dunes. Dunes have a vortex in the lee side of the dune, as the upper flow regime forms, the dunes become flattened out, and then produce antidunes. At higher still velocity, the antidunes are flattened and most sedimentation stops, ripple marks usually form in conditions with flowing water, in the lower part of the Lower Flow Regime. There are two types of marks, Symmetrical ripple marks - Often found on beaches, they are created by a two way current, for example the waves on a beach. This creates ripple marks with pointed crests and rounded troughs, which arent inclined more to a certain direction, three common sedimentary structures that are created by these processes are herringbone cross-stratification, flaser bedding, and interference ripples. Asymmetrical ripple marks - These are created by a one way current, for example in a river and this creates ripple marks with still pointed crests and rounded troughs, but which are inclined more strongly in the direction of the current. For this reason, they can be used as palaeocurrent indicators, antidunes are the sediment bedforms created by fast, shallow flows of water with a Froude number greater than 1. Antidunes form beneath standing waves of water that periodically steepen, migrate, the antidune bedform is characterized by shallow foresets, which dip upstream at an angle of about ten degrees that can be up to five meters in length. They can be identified by their low angle foresets, for the most part, antidunes bedforms are destroyed during decreased flow, and therefore cross bedding formed by antidunes will not be preserved. A number of biologically-created sedimentary structures exist, called trace fossils, examples include burrows and various expressions of bioturbation. Ichnofacies are groups of fossils that together help give information on the depositional environment. In general, as deeper burrows become more common, the shallower the water, as surface traces become more common, the water becomes deeper. Microbes may also interact with sediment to form Microbially Induced Sedimentary Structures, soft-sediment deformation structures or SSD, is a consequence of the loading of wet sediment as burial continues after deposition. The heavier sediment squeezes the water out of the sediment due to its own weight. There are three variants of SSD, load structures or load casts are blobs that form when a denser, wet sediment slumps down on. Pseudonodules or ball-and-pillow structures, are pinched-off load structures, these may also be formed by earthquake energy, flame structures, fingers of mud that protrude into overlying sediments
18.
Cross-bedding
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In geology, the sedimentary structures known as cross-bedding are the horizontal units that are internally composed of inclined layers. This is a case in geology in which the original depositional layering is tilted, cross-beds or sets are the groups of inclined layers, and the inclined layers are known as cross strata. Cross bedding forms during deposition on the surfaces of bedforms such as ripples and dunes. Examples of these bedforms are ripples, dunes, anti-dunes, sand waves, hummocks, bars, Cross-bedding is widespread in many environments. Environments in which movement is fast enough and deep enough to develop large-scale bed forms fall into three natural groupings, rivers, tide-dominated coastal and marine settings. Cross beds can tell much about what an area was like in ancient times. The direction the beds are dipping indicates paleocurrent, the direction of sediment transport. The type and condition of sediments can tell geologists the type of environment, studying modern analogs allows geologists to draw conclusions about ancient environments. Paleocurrent can be determined by seeing a cross-section of a set of cross-beds, however, to get a true reading, the axis of the beds must be visible. It is also difficult to distinguish between the beds of a dune and the cross beds of an antidune. This could lead to misinterpretation since dunes dip downstream while antidunes dip upstream, the direction of motion of the cross-beds can show ancient flow or wind directions. The foresets are deposited at the angle of repose, so geologists are able to measure dip direction of the cross-bedded sediments, however, most cross-beds are not tabular, they are troughs. Since troughs can give a 180 degree variation of the dip of foresets, in this case, true paleocurrent direction is determined by the axis of the trough. Paleocurrent direction is important in reconstructing past climate and drainage patterns, sand dunes preserve the prevalent wind directions, Cross-bedding is formed by the downstream migration of bedforms such as ripples or dunes in a flowing fluid. The fluid flow causes sand grains to saltate up the side of the bedform. At this point, the crest of granular material has grown too large and will be overcome by the force of the depositing fluid, repeated avalanches will eventually form the sedimentary structure known as cross-bedding, with the structure dipping in the direction of the paleocurrent. The angle and direction of cross-beds are generally fairly consistent, individual cross-beds can range in thickness from just a few tens of centimeters, up to hundreds of feet or more depending upon the depositional environment and the size of the bedform. Cross-bedding can form in any environment in which a fluid flows over a bed with mobile material and it is most common in stream deposits, tidal areas, and in aeolian dunes
19.
Graded bedding
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In geology, a graded bed is one characterized by a systematic change in grain or clast size from the base of the bed to the top. Most commonly this takes the form of grading, with coarser sediments at the base. Normally graded beds generally represent depositional environments which decrease in energy as time passes. They are perhaps best represented in turbidite strata, where they indicate a strong current that deposits heavy, coarse sediments first. They can also form in terrestrial stream deposits, in reverse or inverse grading the bed coarsens upwards. This type of grading is relatively uncommon but is characteristic of sediments deposited by grain flow and it is also observed in eolian ripples. These deposition processes are examples of granular convection, graded bedding is a sorting of particles according to clast size and shape on a lithified horizontal plane. The term is an explanation as to how a geologic profile was formed, stratification on a lateral plane is the physical result of active depositing of different size materials. Density and gravity forces in the movement of these materials in a confined system will result in a separating of the detritus settling with respect to size. This will result in dense, higher porosity clasts at the top and denser, less porous clasts consolidated on the bottom. Inversely graded beds are composed of large clasts on the top, grades of the bedding material are determined by precipitation of solid components compared to the viscosity of the medium in which the particles will precipitate from. Steno’s Principle of Original Horizontality explains that rock layers form in layers over an underdetermined time scale. Nicholas Steno first published his hypothesis in 1669 after recognizing that fossils were preserved in layers of rock, for materials to settle in stratified layers the defining quality is periodicity. There must be repeated depositional events with changes in precipitation of materials over time, the thickness of graded beds ranges from 1 millimeter to multiple meters. There is no set time limit in which the layers will be formed, uniformity of size and shape of materials within the bed form must be present on a present or previously horizontal plane. Weathering, the chemical or physical forces breaking apart the solid materials that will be potentially transported, erosion, The movement of material due to weathering forces that have freed materials for movement. Deposition, The material settles on a horizontal plane either through chemical or physical precipitation, note, The secondary processes of compaction, cementation, and lithification, help to hold a stratified bed in place. In aeolian or fluid environments, where there is a decrease in transport energy over time
20.
Breccia
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Breccia is a rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix that can be similar to or different from the composition of the fragments. The word has its origins in the Italian language, in which it means either loose gravel or stone made by cemented gravel. A breccia may have a variety of different origins, as indicated by the named types including sedimentary breccia, tectonic breccia, igneous breccia, impact breccia, and hydrothermal breccia. Sedimentary breccia is a type of sedimentary rock which is made of angular to subangular. A conglomerate, by contrast, is a rock composed of rounded fragments or clasts of pre-existing rocks. Both breccia and conglomerate are composed of fragments averaging greater than 2 millimetres in size, the angular shape of the fragments indicates that the material has not been transported far from its source. Sedimentary breccia consists of angular, poorly sorted, immature fragments of rocks in a finer grained groundmass which are produced by mass wasting and it is lithified colluvium or scree. Thick sequences of sedimentary breccia are generally formed next to fault scarps in grabens, Breccia may occur along a buried stream channel where it indicates accumulation along a juvenile or rapidly flowing stream. Sedimentary breccia may be formed by debris flows. Turbidites occur as fine-grained peripheral deposits to sedimentary breccia flows, in a karst terrain, a collapse breccia may form due to collapse of rock into a sinkhole or in cave development. Fault breccia results from the action of two fault blocks as they slide past each other. Subsequent cementation of these fragments may occur by means of the introduction of mineral matter in groundwater. Volcanic pyroclastic rocks are formed by explosive eruption of lava and any rocks which are entrained within the eruptive column and this may include rocks plucked off the wall of the magma conduit, or physically picked up by the ensuing pyroclastic surge. Lavas, especially rhyolite and dacite flows, tend to form volcanic rocks by a process known as autobrecciation. This occurs when the thick, nearly solid lava breaks up into blocks, the resulting breccia is uniform in rock type and chemical composition. Lavas may also pick up rock fragments, especially if flowing over unconsolidated rubble on the flanks of a volcano, within the volcanic conduits of explosive volcanoes the volcanic breccia environment merges into the intrusive breccia environment. There the upwelling lava tends to solidify during quiescent intervals only to be shattered by ensuing eruptions, clastic rocks are also commonly found in shallow subvolcanic intrusions such as porphyry stocks, granites and kimberlite pipes, where they are transitional with volcanic breccias. Intrusive rocks can become brecciated in appearance by multiple stages of intrusion and this may be seen in many granite intrusions where later aplite veins form a late-stage stockwork through earlier phases of the granite mass
21.
Calcite
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Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate. The Mohs scale of hardness, based on scratch hardness comparison. Other polymorphs of calcium carbonate are the minerals aragonite and vaterite, aragonite will change to calcite at 380–470 °C, and vaterite is even less stable. Calcite is derived from the German Calcit, a term coined in the 19th century from the Latin word for lime and it is thus etymologically related to chalk. Calcite crystals are trigonal-rhombohedral, though actual calcite rhombohedra are rare as natural crystals, however, they show a remarkable variety of habits including acute to obtuse rhombohedra, tabular forms, prisms, or various scalenohedra. Calcite exhibits several twinning types adding to the variety of observed forms and it may occur as fibrous, granular, lamellar, or compact. Cleavage is usually in three directions parallel to the rhombohedron form and its fracture is conchoidal, but difficult to obtain. It has a defining Mohs hardness of 3, a gravity of 2.71. Color is white or none, though shades of gray, red, orange, yellow, green, blue, violet, brown, calcite is transparent to opaque and may occasionally show phosphorescence or fluorescence. A transparent variety called Iceland spar is used for optical purposes, acute scalenohedral crystals are sometimes referred to as dogtooth spar while the rhombohedral form is sometimes referred to as nailhead spar. Single calcite crystals display an optical property called birefringence and this strong birefringence causes objects viewed through a clear piece of calcite to appear doubled. The birefringent effect was first described by the Danish scientist Rasmus Bartholin in 1669, at a wavelength of ~590 nm calcite has ordinary and extraordinary refractive indices of 1.658 and 1.486, respectively. Between 190 and 1700 nm, the refractive index varies roughly between 1.9 and 1.5, while the extraordinary refractive index varies between 1.6 and 1.4. Calcite, like most carbonates, will dissolve with most forms of acid, calcite can be either dissolved by groundwater or precipitated by groundwater, depending on several factors including the water temperature, pH, and dissolved ion concentrations. Although calcite is fairly insoluble in water, acidity can cause dissolution of calcite. Ambient carbon dioxide, due to its acidity, has a slight solubilizing effect on calcite, calcite exhibits an unusual characteristic called retrograde solubility in which it becomes less soluble in water as the temperature increases. When conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together or it can fill fractures. On a landscape scale, continued dissolution of calcium carbonate-rich rocks can lead to the expansion and eventual collapse of cave systems, high-grade optical calcite was used in World War II for gun sights, specifically in bomb sights and anti-aircraft weaponry
22.
Hematite
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Hematite, also spelled as haematite, is the mineral form of iron oxide, one of several iron oxides. Hematite crystallizes in the lattice system, and it has the same crystal structure as ilmenite. Hematite and ilmenite form a solid solution at temperatures above 950 °C. Hematite is colored black to steel or silver-gray, brown to reddish brown and it is mined as the main ore of iron. Varieties include kidney ore, martite, iron rose and specularite, while the forms of hematite vary, they all have a rust-red streak. Hematite is harder than iron, but much more brittle. Maghemite is a hematite- and magnetite-related oxide mineral, huge deposits of hematite are found in banded iron formations. Gray hematite is typically found in places that can have still standing water or mineral hot springs, the mineral can precipitate out of water and collect in layers at the bottom of a lake, spring, or other standing water. Hematite can also occur without water, however, usually as the result of volcanic activity, the name hematite is derived from the Greek word for blood αἷμα haima, due to the red coloration found in some varities of hematite. The color of hematite lends itself to use as a pigment, ochre is a clay that is colored by varying amounts of hematite, varying between 20% and 70%. Red ochre contains unhydrated hematite, whereas yellow ochre contains hydrated hematite, the principal use of ochre is for tinting with a permanent color. The red chalk writing of this mineral was one of the earliest in the history of humans, the powdery mineral was first used 164,000 years ago by the Pinnacle-Point man possibly for social purposes. Hematite residues are found in graves from 80,000 years ago. Near Rydno in Poland and Lovas in Hungary red chalk mines have been found that are from 5000 BC, rich deposits of hematite have been found on the island of Elba that have been mined since the time of the Etruscans. Adding to the surprise was a transition with a decrease in temperature at around 260 K to a phase with no net magnetic moment. The disappearance of the moment with a decrease in temperature at 260 K is caused by a change in the anisotropy which causes the moments to align along the c axis, in this configuration, spin canting does not reduce the energy. The magnetic properties of bulk hematite differ from their nanoscale counterparts, for example, the Morin transition temperature of hematite decreases with a decrease in the particle size. Two other end-members are referred to as protohematite and hydrohematite, enhanced magnetic coercivities for hematite have been achieved by dry-heating a 2-line ferrihydrite precursor prepared from solution
23.
Quartz
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Quartz is the second most abundant mineral in Earths continental crust, behind feldspar. There are many different varieties of quartz, several of which are semi-precious gemstones, since antiquity, varieties of quartz have been the most commonly used minerals in the making of jewelry and hardstone carvings, especially in Eurasia. The word quartz is derived from the German word Quarz and its Middle High German ancestor twarc, the Ancient Greeks referred to quartz as κρύσταλλος derived from the Ancient Greek κρύος meaning icy cold, because some philosophers apparently believed the mineral to be a form of supercooled ice. Today, the rock crystal is sometimes used as an alternative name for the purest form of quartz. Quartz belongs to the crystal system. The ideal crystal shape is a six-sided prism terminating with six-sided pyramids at each end, well-formed crystals typically form in a bed that has unconstrained growth into a void, usually the crystals are attached at the other end to a matrix and only one termination pyramid is present. However, doubly terminated crystals do occur where they develop freely without attachment, a quartz geode is such a situation where the void is approximately spherical in shape, lined with a bed of crystals pointing inward. α-quartz crystallizes in the crystal system, space group P3121 and P3221 respectively. β-quartz belongs to the system, space group P6222 and P6422. These space groups are truly chiral, both α-quartz and β-quartz are examples of chiral crystal structures composed of achiral building blocks. The transformation between α- and β-quartz only involves a comparatively minor rotation of the tetrahedra with respect to one another, although many of the varietal names historically arose from the color of the mineral, current scientific naming schemes refer primarily to the microstructure of the mineral. Color is an identifier for the cryptocrystalline minerals, although it is a primary identifier for the macrocrystalline varieties. Pure quartz, traditionally called rock crystal or clear quartz, is colorless and transparent or translucent, common colored varieties include citrine, rose quartz, amethyst, smoky quartz, milky quartz, and others. The most important distinction between types of quartz is that of macrocrystalline and the microcrystalline or cryptocrystalline varieties, the cryptocrystalline varieties are either translucent or mostly opaque, while the transparent varieties tend to be macrocrystalline. Chalcedony is a form of silica consisting of fine intergrowths of both quartz, and its monoclinic polymorph moganite. Other opaque gemstone varieties of quartz, or mixed rocks including quartz, often including contrasting bands or patterns of color, are agate, carnelian or sard, onyx, heliotrope, amethyst is a form of quartz that ranges from a bright to dark or dull purple color. The worlds largest deposits of amethysts can be found in Brazil, Mexico, Uruguay, Russia, France, Namibia, sometimes amethyst and citrine are found growing in the same crystal. It is then referred to as ametrine, an amethyst is formed when there is iron in the area where it was formed
24.
Till
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Till or glacial till is unsorted glacial sediment. Till is derived from the erosion and entrainment of material by the ice of a glacier. It is deposited some distance down-ice to form terminal, lateral, medial, till is classified into primary deposits, laid down directly by glaciers, and secondary deposits, reworked by fluvial transport and other processes. Glacial drift is the graded and extremely heterogeneous sediment of a glacier. Its content may vary from clays to mixtures of clay, sand, gravel and this material is mostly derived from the subglacial erosion and entrainment by the moving ice of the glaciers of previously available unconsolidated sediments. Bedrock can also be eroded through the action of glacial plucking and abrasion, eventually, the sedimentary assemblage forming this bed will be abandoned some distance down-ice from its various sources. This is the process of glacial till deposition, when this deposition occurs at the base of the moving ice of a glacier, the sediment is called lodgement till. Rarely, eroded unconsolidated sediments can be preserved in the till along with their original sedimentary structures, till is deposited at the terminal moraine, along the lateral and medial moraines and in the ground moraine of a glacier. Prospectors use trace minerals in tills as clues to follow the glacier upstream to find kimberlite diamond deposits, in cases where till has been indurated or lithified by subsequent burial into solid rock, it is known as the sedimentary rock tillite. Matching beds of ancient tillites on opposite sides of the south Atlantic Ocean provided early evidence for continental drift, the same tillites also provide some support to the Precambrian Snowball Earth glaciation event hypothesis. There are various types of classifying tills, primary deposits – laid down directly by glacier action secondary deposits – reworked by fluvial transport, erosion, traditionally a further set of divisions has been made to primary deposits, based upon the method of deposition. Lodgement tills – sediment which has been deposited by plastering of glacial debris from a sliding glacier bed, deformation tills – Sediment which has been disaggregated and homogenised by shearing in the sub glacial deformed layer. Melt out tills – Released by melting of stagnant or slowly moving debris-rich glacier ice, split up into sub glacial melt out till and supraglacial melt-out till. Sublimation till – similar to melt out till, except the ice is lost through sublimation rather than melt, often occurs only in extremely cold and arid conditions, mainly in Antarctica. Van der Meer et al.2003 have suggested that these classifications are outdated and should instead be replaced with only one classification
25.
Debris flow
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Debris flows descending steep channels commonly attain speeds that surpass 10 meters per second, although some large flows can reach speeds that are much greater. Debris flows with volumes ranging up to about 100,000 cubic meters occur frequently in mountainous regions worldwide, the largest prehistoric flows have had volumes exceeding 1 billion cubic meters. As a result of their high sediment concentrations and mobility, debris flows can be very destructive, notable debris-flow disasters of the twentieth century involved more than 20,000 fatalities in Armero, Colombia in 1985 and tens of thousands in Vargas State, Venezuela in 1999. Debris flows have volumetric sediment concentrations exceeding about 40 to 50%, by definition, “debris” includes sediment grains with diverse shapes and sizes, commonly ranging from microscopic clay particles to great boulders. Media reports often use the term mudflow to describe debris flows, on Earths land surface, mudflows are far less common than debris flows. However, underwater mudflows are prevalent on submarine continental margins, where they may spawn turbidity currents, Debris flows in forested regions can contain large quantities of woody debris such as logs and tree stumps. Sediment-rich water floods with solid concentrations ranging from about 10 to 40% behave somewhat differently from debris flows and are known as hyperconcentrated floods, normal stream flows contain even lower concentrations of sediment. Debris flows can be triggered by rainfall or snowmelt, by dam-break or glacial outburst floods. Debris flows can be more frequent following forest and brush fires, in Japan a large debris flow or landslide is called yamatsunami, literally mountain tsunami. Debris flows are accelerated downhill by gravity and tend to follow steep mountain channels that debouche onto alluvial fans or floodplains, the front, or head of a debris-flow surge often contains an abundance of coarse material such as boulders and logs that impart a great deal of friction. Trailing behind the high-friction flow head is a lower-friction, mostly liquefied flow body that contains a percentage of sand, silt. These fine sediments help retain high pore-fluid pressures that enhance debris-flow mobility, in some cases the flow body is followed by a more watery tail that transitions into a hyperconcentrated stream flow. Debris flows tend to move in a series of pulses, or discrete surges, wherein each pulse or surge has a head, body. Debris-flow deposits are readily recognizable in the field and they make up significant percentages of many alluvial fans and debris cones along steep mountain fronts. Lateral levees can confine the paths of ensuing debris flows, through dating of trees growing on such deposits, the approximate frequency of destructive debris flows can be estimated. This is important information for development in areas where debris flows are common. Ancient debris-flow deposits that are exposed only in outcrops are more difficult to recognize and this poor sorting of sediment grains distinguishes debris-flow deposits from most water-laid sediments. Other geological flows that can be described as debris flows are typically given more specific names, the word lahar is of Indonesian origin, but is now routinely used by geologists worldwide to describe volcanogenic debris flows
26.
Cambrian
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The Cambrian Period was the first geological period of the Paleozoic Era, of the Phanerozoic Eon. The Cambrian lasted 55.6 million years from the end of the preceding Ediacaran Period 541 million years ago to the beginning of the Ordovician Period 485.4 mya and its subdivisions, and its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latinised form of Cymru, the Welsh name for Wales, as a result, our understanding of the Cambrian biology surpasses that of some later periods. The rapid diversification of lifeforms in the Cambrian, known as the Cambrian explosion, most of the continents were probably dry and rocky due to a lack of vegetation. Shallow seas flanked the margins of several continents created during the breakup of the supercontinent Pannotia, the seas were relatively warm, and polar ice was absent for much of the period. The United States Federal Geographic Data Committee uses a barred capital C ⟨Є⟩ character similar to the capital letter Ukrainian Ye ⟨Є⟩ to represent the Cambrian Period, the proper Unicode character is U+A792 Ꞓ LATIN CAPITAL LETTER C WITH BAR. Despite the long recognition of its distinction from younger Ordovician Period rocks and older Supereon Precambrian rocks, the base of the Cambrian lies atop a complex assemblage of trace fossils known as the Treptichnus pedum assemblage. Pedum in Namibia, Spain and Newfoundland, and possibly, in the western USA, the stratigraphic range of T. pedum overlaps the range of the Ediacaran fossils in Namibia, and probably in Spain. The Cambrian Period followed the Ediacaran Period and was followed by the Ordovician Period, the Cambrian is divided into four epochs and ten ages. Currently only two series and five stages are named and have a GSSP, because the international stratigraphic subdivision is not yet complete, many local subdivisions are still widely used. In some of these subdivisions the Cambrian is divided into three epochs with locally differing names – the Early Cambrian, Middle Cambrian and Furongian, rocks of these epochs are referred to as belonging to the Lower, Middle, or Upper Cambrian. Trilobite zones allow biostratigraphic correlation in the Cambrian, each of the local epochs is divided into several stages. The International Commission on Stratigraphy list the Cambrian period as beginning at 541 million years ago, the lower boundary of the Cambrian was originally held to represent the first appearance of complex life, represented by trilobites. The recognition of small shelly fossils before the first trilobites, and Ediacara biota substantially earlier and this formal designation allowed radiometric dates to be obtained from samples across the globe that corresponded to the base of the Cambrian. Early dates of 570 million years ago quickly gained favour, though the used to obtain this number are now considered to be unsuitable. A more precise date using modern radiometric dating yield a date of 541 ±0.3 million years ago, most continental land was clustered in the Southern Hemisphere at this time, but was drifting north. Large, high-velocity rotational movement of Gondwana appears to have occurred in the Early Cambrian, the sea levels fluctuated somewhat, suggesting there were ice ages, associated with pulses of expansion and contraction of a south polar ice cap. In Baltoscandia a Lower Cambrian transgression transformed large swathes of the Sub-Cambrian peneplain into a epicontinental sea, the Earth was generally cold during the early Cambrian, probably due to the ancient continent of Gondwana covering the South Pole and cutting off polar ocean currents
27.
Core sample
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A core sample is a cylindrical section of a naturally occurring substance. Most core samples are obtained by drilling with special drills into the substance, for example sediment or rock, the hole made for the core sample is called the core bowling. A variety of core samplers exist to sample different media under different conditions, more continue to be invented on a regular basis. In the coring process, the sample is pushed more or less intact into the tube, removed from the tube in the laboratory, it is inspected and analyzed by different techniques and equipment depending on the type of data desired. Core samples can be taken to test the properties of materials, such as concrete, ceramics, some metals and alloys. Core samples can also be taken of living things, including human beings, the range of equipment and techniques applied to the task is correspondingly great. Core samples are most often taken with their axis oriented roughly parallel to the axis of a borehole. However it is possible to take core samples from the wall of an existing borehole. Taking samples from an exposure, albeit an overhanging rock face or on a different planet, is almost trivial. The penetration forces, if recorded, give information about the strength of different depths in the material and this technique is common in both civil engineering site investigations and geological studies of recent aquatic deposits. The low strength of the materials penetrated means that cores have to be relatively small, vibracoring, in which the sampler is vibrated to allow penetration into thixotropic media. Again, the strength of the subject material limits the size of core that can be retrieved. A mechanism is normally needed to retain the cylindrical sample in the coring tool, the mechanical forces imposed on the core sample by the tool frequently lead to fracture of the core and loss of less-competent intervals, which can greatly complicate interpretation of the core. Cores can routinely be cut as small as a few millimeters in diameter up to over 150 millimeters in diameter, percussion sidewall coring uses robust cylindrical bullets explosively propelled into the wall of a borehole to retrieve a small, short core sample. These tend to be shattered, rendering porosity/ permeability measurements dubious. Many samples can be attempted in a run of the tools. Several tools can often be ganged together for a single run and this is an important consideration in planning sample programmes. Rotary sidewall coring where a miniaturised automated rotary drilling tool is applied to the side of the borehole to cut a sample similar in size to a percussion sidewall core and these tend to suffer less deformation than percussion cores
28.
Alaska
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Alaska is a U. S. state located in the northwest extremity of North America. To the north are the Chukchi and Beaufort seas–the southern parts of the Arctic Ocean, the Pacific Ocean lies to the south and southwest. Alaska is the largest state in the United States by area, the 3rd least populous, approximately half of Alaskas residents live within the Anchorage metropolitan area. Alaskas economy is dominated by the fishing, natural gas, military bases and tourism are also a significant part of the economy. The United States purchased Alaska from the Russian Empire on March 30,1867, the area went through several administrative changes before becoming organized as a territory on May 11,1912. It was admitted as the 49th state of the U. S. on January 3,1959, the name Alaska was introduced in the Russian colonial period when it was used to refer to the peninsula. It was derived from an Aleut, or Unangam idiom, which refers to the mainland of Alaska. Literally, it means object to which the action of the sea is directed, Alaska is the northernmost and westernmost state in the United States and has the most easterly longitude in the United States because the Aleutian Islands extend into the Eastern Hemisphere. Alaska is the only non-contiguous U. S. state on continental North America and it is technically part of the continental U. S. but is sometimes not included in colloquial use, Alaska is not part of the contiguous U. S. often called the Lower 48. The capital city, Juneau, is situated on the mainland of the North American continent but is not connected by road to the rest of the North American highway system. Alaskas territorial waters touch Russias territorial waters in the Bering Strait, as the Russian Big Diomede Island, Alaska has a longer coastline than all the other U. S. states combined. Alaska is the largest state in the United States by total area at 663,268 square miles, over twice the size of Texas, Alaska is larger than all but 18 sovereign countries. Counting territorial waters, Alaska is larger than the area of the next three largest states, Texas, California, and Montana. It is also larger than the area of the 22 smallest U. S. states. Also referred to as the Panhandle or Inside Passage, this is the region of Alaska closest to the rest of the United States, as such, this was where most of the initial non-indigenous settlement occurred in the years following the Alaska Purchase. The region is dominated by the Alexander Archipelago as well as the Tongass National Forest and it contains the state capital Juneau, the former capital Sitka, and Ketchikan, at one time Alaskas largest city. The Alaska Marine Highway provides a vital transportation link throughout the area. The Interior is the largest region of Alaska, much of it is uninhabited wilderness, Fairbanks is the only large city in the region
29.
Nerriga, New South Wales
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Nerriga is a small village in the Southern Tablelands of New South Wales, Australia in Queanbeyan-Palerang Regional Council. It is situated at the edge of Morton National Park, on the Braidwood - Nowra road, the population of Nerriga and the surrounding localities at the 2011 census was 367. In 1828, grazier George Galbraith was listed as the owner of some 2,000 acres of land on the Endrick River and this property was then known as Narriga. The name Nerriga was first recorded by surveyor Robert Hoddle on an 1828 expedition of the Shoalhaven River, following Galbraiths death in 1837, his land holdings were subsequently auctioned. In 1840, James Larmer surveyed a site and a route over the mountains from Nerriga to Vincentia. It was intended that this pass, known as the Wool Road would allow movement of produce to a port on Jervis Bay from the Braidwood. The road was completed in 1841, a distance of approximately 37 miles at an estimated cost of £997, in 1842, the existing road linking Nerriga to Braidwood was substantially upgraded. Both projects utilised convict labour under the command of Nerriga landowner Colonel John Mackenzie, the building still stands today, but is now known as the Bark Tree Hotel. Records show that between 1878–1901, the peak of production in the area, some 14,177 ounces of gold were produced from the Nerriga Mining Division, some quartz reefs were also worked in the area, however the yields from these activities were not significant. Prospecting on a large scale continued through to the 1960s, a community celebration was held to mark the completion of the upgrade
30.
Australia
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Australia, officially the Commonwealth of Australia, is a country comprising the mainland of the Australian continent, the island of Tasmania and numerous smaller islands. It is the worlds sixth-largest country by total area, the neighbouring countries are Papua New Guinea, Indonesia and East Timor to the north, the Solomon Islands and Vanuatu to the north-east, and New Zealand to the south-east. Australias capital is Canberra, and its largest urban area is Sydney, for about 50,000 years before the first British settlement in the late 18th century, Australia was inhabited by indigenous Australians, who spoke languages classifiable into roughly 250 groups. The population grew steadily in subsequent decades, and by the 1850s most of the continent had been explored, on 1 January 1901, the six colonies federated, forming the Commonwealth of Australia. Australia has since maintained a liberal democratic political system that functions as a federal parliamentary constitutional monarchy comprising six states. The population of 24 million is highly urbanised and heavily concentrated on the eastern seaboard, Australia has the worlds 13th-largest economy and ninth-highest per capita income. With the second-highest human development index globally, the country highly in quality of life, health, education, economic freedom. The name Australia is derived from the Latin Terra Australis a name used for putative lands in the southern hemisphere since ancient times, the Dutch adjectival form Australische was used in a Dutch book in Batavia in 1638, to refer to the newly discovered lands to the south. On 12 December 1817, Macquarie recommended to the Colonial Office that it be formally adopted, in 1824, the Admiralty agreed that the continent should be known officially as Australia. The first official published use of the term Australia came with the 1830 publication of The Australia Directory and these first inhabitants may have been ancestors of modern Indigenous Australians. The Torres Strait Islanders, ethnically Melanesian, were originally horticulturists, the northern coasts and waters of Australia were visited sporadically by fishermen from Maritime Southeast Asia. The first recorded European sighting of the Australian mainland, and the first recorded European landfall on the Australian continent, are attributed to the Dutch. The first ship and crew to chart the Australian coast and meet with Aboriginal people was the Duyfken captained by Dutch navigator, Willem Janszoon. He sighted the coast of Cape York Peninsula in early 1606, the Dutch charted the whole of the western and northern coastlines and named the island continent New Holland during the 17th century, but made no attempt at settlement. William Dampier, an English explorer and privateer, landed on the north-west coast of New Holland in 1688, in 1770, James Cook sailed along and mapped the east coast, which he named New South Wales and claimed for Great Britain. The first settlement led to the foundation of Sydney, and the exploration, a British settlement was established in Van Diemens Land, now known as Tasmania, in 1803, and it became a separate colony in 1825. The United Kingdom formally claimed the part of Western Australia in 1828. Separate colonies were carved from parts of New South Wales, South Australia in 1836, Victoria in 1851, the Northern Territory was founded in 1911 when it was excised from South Australia
31.
Grain size
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Particle size, also called grain size, refers to the diameter of individual grains of sediment, or the lithified particles in clastic rocks. The term may also be applied to other granular materials and this is different from the crystallite size, which refers to the size of a single crystal inside a particle or grain. A single grain can be composed of several crystals, granular material can range from very small colloidal particles, through clay, silt, sand, gravel, and cobbles, to boulders. Size ranges define limits of classes that are given names in the Wentworth scale used in the United States, the Krumbein phi scale, a modification of the Wentworth scale created by W. C. This equation can be rearranged to find diameter using φ, D = D0 ×2 − ϕ In some schemes, ISO 14688-1 is applicable to natural soils in situ, similar man-made materials in situ and soils redeposited by people. An accumulation of sediment can also be characterized by the size distribution. A sediment deposit can undergo sorting when a particle size range is removed by an agency such as a river or the wind, a Scale of Grade and Class Terms for Clastic Sediments
32.
Depositional environment
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In most cases the environments associated with particular rock types or associations of rock types can be matched to existing analogues. However, the back in geological time sediments were deposited. Sedimentary Environments, Processes, Facies and Stratigraphy, sedimentary Environments Classification Charts Depositional environments on e-notes
33.
Turbidite
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A turbidite is the geologic deposit of a turbidity current, which is a type of sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Turbidites were first properly described by Arnold H and this vertical succession of sedimentary structures, bedding, and changing lithology is representative of strong to waning flow regime currents and their corresponding sedimentation. It is unusual to see all of a complete Bouma cycle and it is now recognized that the vertical progression of sedimentary structures described by Bouma applies to turbidites deposited by low-density turbidity currents. As the sand concentration of a flow increases, grain-to-grain collisions within the turbid suspension create dispersive pressures that become important in hindering further settling of grains, as a consequence, a slightly different set of sedimentary structures develops in turbidites deposited by high-density turbidity currents. This different set of structures is known as the Lowe sequence, which is a classification that complements, but does not replace. Turbidites are sediments which are transported and deposited by density flow, the distinction is that, in a normal river or stream bed, particles of rock are carried along by frictional drag of water on the particle. The water must be travelling at a velocity in order to suspend the particle in the water. The greater the size or density of the relative to the fluid in which it is travelling. Density based flow, however, occurs when liquefaction of sediment during transport causes a change to the density of the fluid and this is usually achieved by highly turbulent liquids which have a suspended load of fine grained particles forming a slurry. In this case, larger fragments of rock can be transported at water velocities too low to otherwise do so because of the density contrast. This condition occurs in many environments aside from simply the deep ocean, turbidites in sediments can occur in carbonate as well as siliciclastic sequences. A different vertical progression of sedimentary structures characterize high-density turbidites, massive accumulations of turbidites and other deep water deposits may result in the formation of submarine fans. Density currents may be triggered in areas of sediment supply by gravitational failure alone. Turbidites can represent a high record of seismicity, and terrestrial storm/flood events depending on the connectivity of canyon/channel systems to terrestrial sediment sources. Proterozoic gold deposits are known from turbidite basin deposits. Turbidite deposits typically occur in foreland basins, the Encyclopedia of Oceanography, Encyclopedia of earth sciences series 1, Van Nostrand Reinhold Company, New York, p. 945–946. Morey, A. Johnson, J. E. Gutierrez-Pastor, J. Eriksson, mutti, E. & Ricci Lucci, F. Turbidite facies and facies associations. In, Examples of turbidite facies and associations from selected formations of the northern Apennines, congress of Sedimentology, Field Trip A-11, p. 21–36
34.
Imbrication (sedimentology)
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Imbrication is observed in conglomerates and some volcaniclastic deposits. In conglomerates the shape of many clasts can be approximated to an ellipsoid, with an axis, an intermediate axis. A-axis imbrication where the axes of the clasts are oriented parallel to the flow direction. This fabric is characteristic of clasts carried in suspension and this is preserved in the case of a fast-waning flow in which the clasts are deposited without any significant rolling. This fabric is characteristic of clasts carried as bedload and this imbrication forms as the clasts are rolled along the base of a channel. The flat clasts roll onto those downstream and come to rest with their downstream end propped up by the downstream pebbles, the type of imbrication is generally related to paleoflow direction. Wadell found the long axis aligned with paleocurrent, and dipping basinward in glacial sediments, http, //meguma. earthsciences. dal. ca/classes/2203/2203-Conglomerates. ppt Imbricated gravels along the Truckee River
35.
Marine transgression
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A marine transgression is a geologic event during which sea level rises relative to the land and the shoreline moves toward higher ground, resulting in flooding. Transgressions can be caused either by the sinking or the ocean basins filling with water. Transgressions and regressions may be caused by events such as orogenies. During the Cretaceous, seafloor spreading created a relatively shallow Atlantic basin at the expense of deeper Pacific basin and this reduced the worlds ocean basin capacity and caused a rise in sea level worldwide. As a result of sea level rise, the oceans transgressed completely across the central portion of North America. The opposite of transgression is regression, in which the sea level relative to the land. Sedimentary facies changes may indicate transgressions and regressions and are easily identified. Thus, a transgression reveals itself in the column when there is a change from nearshore facies to offshore ones. A regression will feature the opposite pattern, with offshore facies changing to nearshore ones, the strata represent regressions less clearly, as their upper layers are often marked by an erosional unconformity. These are both idealized scenarios, in practice identifying transgression or regressions can be more complicated, for instance, a regression may be indicated by a change from carbonates to shale only, or a transgression from sandstone to shale, and so on. Lateral changes in facies are also important, a well-marked transgression sequence in an area where a sea was deep may be only partial farther away. One should consider such factors when interpreting a specific sedimentary column, current sea level rise Dunkirk transgression Ingression coast Marine terrace Sequence stratigraphy Submerged forest
36.
Unconformity
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An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the layer was exposed to erosion for an interval of time before deposition of the younger. The significance of angular unconformity was shown by James Hutton, who found examples of Huttons Unconformity at Jedburgh in 1787, the rocks above an unconformity are younger than the rocks beneath. An unconformity represents time during which no sediments were preserved in a region, the local record for that time interval is missing and geologists must use other clues to discover that part of the geologic history of that area. The interval of time not represented is called a hiatus. A disconformity is an unconformity between parallel layers of rocks which represents a period of erosion or non-deposition. Disconformities are marked by features of subaerial erosion and this type of erosion can leave channels and paleosols in the rock record. A paraconformity is a type of disconformity in which the separation is a simple bedding plane with no obvious buried erosional surface. A nonconformity exists between sedimentary rocks and metamorphic or igneous rocks when the rock lies above and was deposited on the pre-existing. Namely, if the rock below the break is igneous or has lost its bedding due to metamorphism, the whole sequence may later be deformed and tilted by further orogenic activity. A typical case history is presented by the evolution of the Briançonnais realm during the Jurassic. A paraconformity is a type of unconformity in which strata are parallel, there is no apparent erosion and it is also called nondepositional unconformity or pseudoconformity. A buttress unconformity occurs when younger bedding is deposited against older strata thus influencing its bedding structure. S, bureau of Mines Dictionary of Mining, Mineral, and Related Terms published on CD-ROM in 1996
37.
Shore
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A shore or a shoreline is the fringe of land at the edge of a large body of water, such as an ocean, sea, or lake. Shores are influenced by the topography of the landscape, as well as by water induced erosion. The geological composition of rock and soil dictates the type of shore which is created, Riviera is an Italian word for shoreline, ultimately derived from Latin ripa. It came to be applied as a name to the coast of the Ligurian Sea, in the form riviera ligure. Historically, the Ligurian Riviera extended from Capo Corvo south of Genoa, north and west into what is now French territory past Monoco, now it is divided into the Italian Riviera and the French Riviera. Although the French use the term Riviera to refer to the Italian Riviera, as a result of the fame of the Ligurian rivieras, the term came into English to refer to any shoreline, especially one that is sunny, topographically diverse and popular with tourists. Such places using the term include the Australian Riviera in Queensland, offshore or Intertidal zone Ballantine Scale Coastal path Shorezone Anders, F. J. and Byrnes, M. R. Accuracy of shoreline change rates as determined from maps and aerial photographs Shore and Beach, v.59, processes influencing the transport and fate of contaminated sediments in the coastal ocean—Boston Harbor and Massachusetts Bay, U. S. Geological Survey Circular 1302, pp. 1–89. Equilibrium beach profiles—characteristics and applications Journal of Coastal Research, v.7, the Budget of Littoral Sediments—Concepts and Applications Shore and Beach, v.64, pp. 18–26. Meade, R. H. Sources, sinks and storage of river sediments in the Atlantic drainage of the United States Journal of Geology, v.90, an Assessment of the Nations Shorelines, USA Shore and Beach v.71, no. Stockdon, H. F. Sallenger, A. H. List, J. H. and Holman, estimation of shoreline position and change using airborne topographic lidar data Journal of Coastal Research, v.18, no. The use of models to predict beach behavior for U. S. coastal engineering—A critical review Journal of Coastal Research, v.16. Media related to Shores at Wikimedia Commons shore, the American Heritage Dictionary of the English Language
38.
Bedload
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The term bed load or bedload describes particles in a flowing fluid that are transported along the bed. Bed load is complementary to suspended load and wash load, bed load moves by rolling, sliding, and/or saltating. Generally, bed load downstream will be smaller and more rounded than bed load upstream. This quantity reads as, τ ∗ = u ∗2 g d, where u ∗ is the velocity, s is the relative particle density, d is an effective particle diameter which is entrained by the flow. Specifically, q s is a monotonically increasing nonlinear function of the excess Shields stress ϕ, typically expressed in the form of a power law
39.
Death Valley National Park
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Death Valley National Park is a national park in the United States. Straddling the border of California and Nevada, located east of the Sierra Nevada, the park protects the northwest corner of the Mojave Desert and contains a diverse desert environment of salt-flats, sand dunes, badlands, valleys, canyons, and mountains. It is the largest national park in the lower 48 states and has declared an International Biosphere Reserve. Approximately 91% of the park is a wilderness area. It is the hottest, driest and lowest of the parks in the United States. The second-lowest point in the Western Hemisphere is in Badwater Basin, the park is home to many species of plants and animals that have adapted to this harsh desert environment. Some examples include creosote bush, bighorn sheep, coyote, and the Death Valley pupfish, several short-lived boom towns sprang up during the late 19th and early 20th centuries to mine gold and silver. The only long-term profitable ore to be mined was borax, which was transported out of the valley with twenty-mule teams, the valley later became the subject of books, radio programs, television series, and movies. Tourism blossomed in the 1920s, when resorts were built around Stovepipe Wells, Death Valley National Monument was declared in 1933 and the park was substantially expanded and became a national park in 1994. The natural environment of the area has been shaped largely by its geology, the valley itself is actually a graben. The oldest rocks are metamorphosed and at least 1.7 billion years old. Ancient, warm, shallow seas deposited marine sediments until rifting opened the Pacific Ocean, additional sedimentation occurred until a subduction zone formed off the coast. This uplifted the region out of the sea and created a line of volcanoes, later the crust started to pull apart, creating the current Basin and Range landform. Valleys filled with sediment and, during the wet times of glacial periods, with lakes, in 2013, Death Valley National Park was designated as a dark sky park by the International Dark-Sky Association. There are two valleys in the park, Death Valley and Panamint Valley. Both of these valleys were formed within the last few million years, the result of this shearing action is additional extension in the central part of Death Valley which causes a slight widening and more subsidence there. Uplift of surrounding mountain ranges and subsidence of the floor are both occurring. The uplift on the Black Mountains is so fast that the fans there are small
40.
Alluvial fan
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An alluvial fan is a fan- or cone-shaped deposit of sediment crossed and built up by streams. If a fan is built up by debris flows it is called a debris cone or colluvial fan. These flows come from a point source at the apex of the fan. Fans are typically found where a canyon draining from mountainous terrain emerges out onto a flatter plain, a convergence of neighboring alluvial fans into a single apron of deposits against a slope is called a bajada, or compound alluvial fan. As a streams gradient decreases, it drops coarse-grained material and this reduces the capacity of the channel and forces it to change direction and gradually build up a slightly mounded or shallow conical fan shape. The deposits are poorly sorted. There will be iso-transport energy lines forming concentric arcs about the point at the apex of the fan. Thus the material will tend to be deposited equally about these lines, Alluvial fans are often found in desert areas subject to periodic flash floods from nearby thunderstorms in local hills. The typical watercourse in an arid climate has a large, funnel-shaped basin at the top, leading to a narrow defile, multiple braided streams are usually present and active during water flows. Phreatophytes are plants that are concentrated at the base of alluvial fans. They have long tap roots 30 to 50 feet to water that has seeped through the fan and hit an impermeable layer, sometimes collecting in springs. These stands of shrubs cling to the soil at their bases, Alluvial fans also develop in wetter climates. Along the upper Koshi tributaries, tectonic forces elevate the Himalayas several millimeters annually, uplift is approximately in equilibrium with erosion, so the river annually carries some 100 million cubic meters of sediment as it exits the mountains. Deposition of this magnitude over millions of years is more than sufficient to account for the megafan, despite overpopulation on the plains, this bhabar zone is highly malarial and has remained largely uninhabited. In North America, streams flowing into Californias Central Valley have deposited smaller, such as that of the Kings River flowing out of the Sierra Nevada creates a low divide, turning the south end of the San Joaquin Valley into an endorheic basin without a connection to the ocean. Alluvial fans are subject to flooding and can be more dangerous than the upstream canyons that feed them. Their slightly convex perpendicular surfaces cause water to spread widely until there is no zone of refuge, if the gradient is steep, active transport of materials down the fan creates a moving substrate that is inhospitable to travel on foot or wheels. But as the gradient diminishes downslope, water comes down from above faster than it can flow away downstream, in the case of the Koshi River, the huge sediment load and megafans slightly convex transverse surface conspire against engineering efforts to contain peak flows inside manmade embankments
41.
Desert
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A desert is a barren area of land where little precipitation occurs and consequently living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to the processes of denudation, about one third of the land surface of the world is arid or semi-arid. This includes much of the regions where little precipitation occurs. Deserts can be classified by the amount of precipitation falls, by the temperature that prevails. Deserts are formed by weathering processes as large variations in temperature between day and night put strains on the rocks which consequently break in pieces, although rain seldom occurs in deserts, there are occasional downpours that can result in flash floods. Rain falling on hot rocks can cause them to shatter and the resulting fragments and this picks up particles of sand and dust and wafts them aloft in sand or dust storms. Wind-blown sand grains striking any solid object in their path can abrade the surface, rocks are smoothed down, and the wind sorts sand into uniform deposits. The grains end up as level sheets of sand or are piled high in billowing sand dunes, other deserts are flat, stony plains where all the fine material has been blown away and the surface consists of a mosaic of smooth stones. These areas are known as desert pavements and little further erosion takes place, other desert features include rock outcrops, exposed bedrock and clays once deposited by flowing water. Temporary lakes may form and salt pans may be left when waters evaporate, there may be underground sources of water in the form of springs and seepages from aquifers. Where these are found, oases can occur, plants and animals living in the desert need special adaptations to survive in the harsh environment. Plants tend to be tough and wiry with small or no leaves, water-resistant cuticles, some annual plants germinate, bloom and die in the course of a few weeks after rainfall while other long-lived plants survive for years and have deep root systems able to tap underground moisture. Animals need to cool and find enough food and water to survive. Many are nocturnal and stay in the shade or underground during the heat of the day and they tend to be efficient at conserving water, extracting most of their needs from their food and concentrating their urine. Some animals remain in a state of dormancy for long periods and they then reproduce rapidly while conditions are favorable before returning to dormancy. People have struggled to live in deserts and the surrounding lands for millennia. Nomads have moved their flocks and herds to wherever grazing is available, the cultivation of semi-arid regions encourages erosion of soil and is one of the causes of increased desertification. Many trade routes have been forged across deserts, especially across the Sahara Desert, large numbers of slaves were also taken northwards across the Sahara
42.
Glacier
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A glacier is a persistent body of dense ice that is constantly moving under its own weight, it forms where the accumulation of snow exceeds its ablation over many years, often centuries. Glaciers slowly deform and flow due to stresses induced by their weight, creating crevasses, seracs and they also abrade rock and debris from their substrate to create landforms such as cirques and moraines. Glaciers form only on land and are distinct from the much thinner sea ice, between 35°N and 35°S, glaciers occur only in the Himalayas, Andes, Rocky Mountains, a few high mountains in East Africa, Mexico, New Guinea and on Zard Kuh in Iran. Glaciers cover about 10 percent of Earths land surface, continental glaciers cover nearly 13,000,000 km2 or about 98 percent of Antarcticas 13,200,000 km2, with an average thickness of 2,100 m. Greenland and Patagonia also have huge expanses of continental glaciers, Glacial ice is the largest reservoir of fresh water on Earth. Within high altitude and Antarctic environments, the temperature difference is often not sufficient to release meltwater. A large piece of compressed ice, or a glacier, appears blue as large quantities of water appear blue and this is because water molecules absorb other colors more efficiently than blue. The other reason for the color of glaciers is the lack of air bubbles. Air bubbles, which give a color to ice, are squeezed out by pressure increasing the density of the created ice. The word Glaceon is a loanword from French and goes back, via Franco-Provençal, to the Vulgar Latin glaciārium, derived from the Late Latin glacia, the processes and features caused by or related to glaciers are referred to as glacial. The process of establishment, growth and flow is called glaciation. The corresponding area of study is called glaciology, Glaciers are important components of the global cryosphere. Glaciers are categorized by their morphology, thermal characteristics, and behavior, cirque glaciers form on the crests and slopes of mountains. A glacier that fills a valley is called a valley glacier, a large body of glacial ice astride a mountain, mountain range, or volcano is termed an ice cap or ice field. Ice caps have a less than 50,000 km2 by definition. Glacial bodies larger than 50,000 km2 are called ice sheets or continental glaciers, several kilometers deep, they obscure the underlying topography. Only nunataks protrude from their surfaces, the only extant ice sheets are the two that cover most of Antarctica and Greenland. They contain vast quantities of water, enough that if both melted, global sea levels would rise by over 70 m
43.
Esker
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Eskers are frequently several kilometres long and, because of their peculiar uniform shape, are somewhat like railway embankments. The term esker is derived from the Irish word eiscir, which means ridge or elevation, the Irish word was and is used particularly to describe long sinuous ridges, which are now known to be deposits of fluvio-glacial material. Most eskers are argued to have formed within ice-walled tunnels by streams which flowed within and they tended to form around the time of the glacial maximum when the glacier was slow and sluggish. After the retaining ice walls melted away, stream deposits remained as long winding ridges, water can flow uphill if it is under pressure in an enclosed pipe, such as a natural tunnel in ice. Eskers may also form above glaciers by accumulation of sediment in supraglacial channels, in crevasses, Eskers form near the terminal zone of glaciers, where the ice is not moving as fast and is relatively thin. Plastic flow and melting of the basal ice determines the size and this in turn determines the shape, composition and structure of an esker. Eskers may exist as a channel, or may be part of a branching system with tributary eskers. They are not often found as continuous ridges, but have gaps that separate the winding segments, the ridge crests of eskers are not usually level for very long, and are generally knobby. Eskers may be broad-crested or sharp-crested with steep sides and they can reach hundreds of kilometers in length and are generally 20–30 metres in height. The path of an esker is governed by its pressure in relation to the overlying ice. This process is what produces the wide eskers upon which roads, less pressure, occurring in areas closer to the glacial maximum, can cause ice to melt over the stream flow and create steep-walled, sharply-arched tunnels. The concentration of debris in the ice and the rate at which sediment is delivered to the tunnel by melting. The sediment generally consists of coarse-grained, water-laid sand and gravel and this sediment is stratified and sorted, and usually consists of pebble/cobble-sized material with occasional boulders. Bedding may be irregular but is almost always present, and cross-bedding is common, Eskers are critical to the ecology of Northern Canada. In Sweden Uppsalaåsen stretches for 250 km and passes through Uppsala city, great Esker Park runs along the Back River in Weymouth, Massachusetts and is home to the highest esker in North America. Pispala in Tampere, Finland is on an esker between two lakes carved by glaciers, a similar site is Punkaharju in Finnish Lakeland. The village of Kemnay in Aberdeenshire, Scotland has a 5 km esker locally called the Kemb Hills, there are over 1,000 eskers in the state of Michigan, primarily in the south-central Lower Peninsula. The longest esker in Michigan is the 22 mile long Mason Esker, Esker systems in the U. S. state of Maine can be traced for up to 100 miles
44.
Montserrat (mountain)
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Montserrat is a multi-peaked rocky range located near the city of Barcelona, in Catalonia, Spain. It is part of the Catalan Pre-Coastal Range, the main peaks are Sant Jeroni, Montgrós and Miranda de les Agulles. Montserrat literally means saw mountain in Catalan and it describes its peculiar aspect with multitude of rock formations which are visible from a great distance. The mountain is composed of strikingly pink conglomerate, a form of sedimentary rock, Montserrat is Spains first National Park. In 1493, Christopher Columbus named the Caribbean island of Montserrat Santa Maria de Montserrate, the Benedictine Abbey can be reached by road, by the Aeri de Montserrat cable car, or by the Montserrat Rack Railway. The lower stations of both the railway and the cable car can be reached by Ferrocarrils de la Generalitat de Catalunya train from Barcelonas Plaça dEspanya station. The highest summit of Montserrat is called Sant Jeroni and stands at 1,236 meters above sea-level and it is accessible by hiking trails which connect from the top entrance to the Sant Joan funicular, the monastery, or the base of the mountain. The Cavall Bernat 1,111 meters is an important rock feature popular with climbers, LARSA Montserrat Montserrat General Information Gallery of oblique aerial photos of Montserrat, by Doc Searls Getting to Montserrat from Barcelona city
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Barcelona
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Founded as a Roman city, in the Middle Ages Barcelona became the capital of the County of Barcelona. Barcelona has a cultural heritage and is today an important cultural centre. Particularly renowned are the works of Antoni Gaudí and Lluís Domènech i Montaner. The headquarters of the Union for the Mediterranean is located in Barcelona, the city is known for hosting the 1992 Summer Olympics as well as world-class conferences and expositions and also many international sport tournaments. It is a cultural and economic centre in southwestern Europe, 24th in the world. In 2008 it was the fourth most economically powerful city by GDP in the European Union, in 2012 Barcelona had a GDP of $170 billion, it is leading Spain in both employment rate and GDP per capita change. In 2009 the city was ranked Europes third and one of the worlds most successful as a city brand, since 2011 Barcelona has been a leading smart city in Europe. During the Middle Ages, the city was known as Barchinona, Barçalona, Barchelonaa. Internationally, Barcelonas name is abbreviated to Barça. However, this refers only to FC Barcelona, the football club. The common abbreviated form used by locals is Barna, another common abbreviation is BCN, which is also the IATA airport code of the Barcelona-El Prat Airport. The city is referred to as the Ciutat Comtal in Catalan. The origin of the earliest settlement at the site of present-day Barcelona is unclear, the ruins of an early settlement have been excavated in the El Raval neighbourhood, including different tombs and dwellings dating to earlier than 5000 BC. The founding of Barcelona is the subject of two different legends, the first attributes the founding of the city to the mythological Hercules. In about 15 BC, the Romans redrew the town as a castrum centred on the Mons Taber, under the Romans, it was a colony with the surname of Faventia, or, in full, Colonia Faventia Julia Augusta Pia Barcino or Colonia Julia Augusta Faventia Paterna Barcino. It enjoyed immunity from imperial burdens, the city minted its own coins, some from the era of Galba survive. Some remaining fragments of the Roman walls have incorporated into the cathedral. The cathedral, also known as the Basilica La Seu, is said to have founded in 343
