Principle of original horizontality
The Principle of Original Horizontality states that layers of sediment are originally deposited horizontally under the action of gravity. It is a dating technique. The principle is important to the analysis of folded and tilted strata and it was first proposed by the Danish geological pioneer Nicholas Steno. As one of Stenos Laws, the Principle of Original Horizontality served well in the nascent days of geological science, however, it is now known that not all sedimentary layers are deposited purely horizontally. This is known as the angle of repose, and an example is the surface of sand dunes. Similarly, sediments may drape over an inclined surface, these sediments are usually deposited conformably to the pre-existing surface. Also sedimentary beds may pinch out along strike, implying that slight angles existed during their deposition, thus the Principle of Original Horizontality is widely, but not universally, applicable in the study of sedimentology and structural geology. Law of superposition Principle of lateral continuity Principle of cross-cutting relationships Principle of faunal succession
Geology is an earth science concerned with the solid Earth, the rocks of which it is composed, and the processes by which they change over time. Geology can refer generally to the study of the features of any terrestrial planet. Geology gives insight into the history of the Earth by providing the evidence for plate tectonics, the evolutionary history of life. Geology plays a role in engineering and is a major academic discipline. The majority of data comes from research on solid Earth materials. These typically fall into one of two categories and unconsolidated material, the majority of research in geology is associated with the study of rock, as rock provides the primary record of the majority of the geologic history of the Earth. There are three types of rock, igneous and metamorphic. The rock cycle is an important concept in geology which illustrates the relationships between three types of rock, and magma. When a rock crystallizes from melt, it is an igneous rock, the sedimentary rock can be subsequently turned into a metamorphic rock due to heat and pressure and is weathered, eroded and lithified, ultimately becoming a sedimentary rock.
Sedimentary rock may be re-eroded and redeposited, and metamorphic rock may undergo additional metamorphism, all three types of rocks may be re-melted, when this happens, a new magma is formed, from which an igneous rock may once again crystallize. Geologists study unlithified material which typically comes from more recent deposits and these materials are superficial deposits which lie above the bedrock. Because of this, the study of material is often known as Quaternary geology. This includes the study of sediment and soils, including studies in geomorphology and this theory is supported by several types of observations, including seafloor spreading, and the global distribution of mountain terrain and seismicity. This coupling between rigid plates moving on the surface of the Earth and the mantle is called plate tectonics. The development of plate tectonics provided a basis for many observations of the solid Earth. Long linear regions of geologic features could be explained as plate boundaries, mid-ocean ridges, high regions on the seafloor where hydrothermal vents and volcanoes exist, were explained as divergent boundaries, where two plates move apart.
Arcs of volcanoes and earthquakes were explained as convergent boundaries, where one plate subducts under another, transform boundaries, such as the San Andreas Fault system, resulted in widespread powerful earthquakes. Plate tectonics provided a mechanism for Alfred Wegeners theory of continental drift and they provided a driving force for crustal deformation, and a new setting for the observations of structural geology
Cross-cutting relationships is a principle of geology that states that the geologic feature which cuts another is the younger of the two features. It is a dating technique in geology. There are several types of cross cutting relationships, Structural relationships may be faults or fractures cutting through an older rock. Intrusional relationships occur when an igneous pluton or dike is intruded into pre-existing rocks, stratigraphic relationships may be an erosional surface cuts across older rock layers, geological structures, or other geological features. Sedimentological relationships occur where currents have eroded or scoured older sediment in an area to produce, for example. Paleontological relationships occur where animal activity or plant growth produces truncation and this happens, for example, where animal burrows penetrate into pre-existing sedimentary deposits. Geomorphological relationships may occur where a feature, such as a river. In a similar example, an impact crater excavates into a layer of rock.
Cross-cutting relationships may be compound in nature, for example, if a fault were truncated by an unconformity, and that unconformity cut by a dike. Based upon such compound cross-cutting relationships it can be seen that the fault is older than the unconformity which in turn is older than the dike, using such rationale, the sequence of geological events can be better understood. Cross-cutting relationships may be seen cartographically and microscopically, in other words, these relationships have various scales. A cartographic crosscutting relationship might look like, for example, a large fault dissecting the landscape on a large map, megascopic cross-cutting relationships are features like igneous dikes, as mentioned above, which would be seen on an outcrop or in a limited geographic area. Microscopic cross-cutting relationships are those that require study by magnification or other close scrutiny, for example, penetration of a fossil shell by the drilling action of a boring organism is an example of such a relationship.
Cross-cutting relationships can be used in conjunction with radiometric age dating to effect an age bracket for geological materials that cannot be dated by radiometric techniques. A radiometric age date from crystals in dike A will give the age date for the layer in question and likewise. This provides an age bracket, or range of possible ages, Principle of original horizontality Principle of lateral continuity Principle of faunal succession Cross Cutting. Ed. K. Lee Lerner and Brenda Wilmoth Lerner, nicolai Stenonis solido intra solidum naturaliter contento dissertationis prodromus. Florentiae, ex typographia sub signo Stellae Hutton, theory of the Earth,1795 Lyell, Charles
Siltation or siltification is the pollution of water by particulate terrestrial clastic material, with a particle size dominated by silt or clay. It refers both to the concentration of suspended sediments, and to the increased accumulation of fine sediments on bottoms where they are undesirable. Siltation is most often caused by erosion or sediment spill. Siltation is the term for being unambigiuous, even if not entirely stringent since it includes other particle sizes than silt. The origin of the sediment transport into an area may be erosion on land. In rural areas the erosion source is typically soil degradation due to intensive or inadequate agricultural practices, leading to soil erosion, the result will be an increased amount of silt and clay in the water bodies that drain the area. In water the main source is sediment spill from dredging, from the transportation of dredged material on barges. Such deposition may be made to get rid of unwanted material, such as the dumping of material dredged from harbours.
The deposition may have as purpose to build up the coastline, artificial islands, climate change affect siltation rates. While the sediment in transport is in suspension, it acts as a pollutant for those who require clean water and this includes uses such as for cooling or in industrial processes, and it includes aquatic life that are sensitive to suspended material in the water. While nekton have been found to avoid spill plumes in the water, among the most sensitive organisms are coral polyps. Generally speaking, hard bottom communities and mussel banks are more sensitive to siltation than sand, unlike in the sea, in a stream the plume will cover the entire channel, except possibly for backwaters, which is why fish will be directly affected in most cases. Siltation can affect navigation channels, or irrigation channels and it refers to the undesired accumulation of sediments in channels intended for vessels, or for distributing water. One may distinguish between measurements at the source, during transport, and within the affected area, source measurements of erosion may be very difficult, since the lost material may be a fraction of a millimeter per year.5 kg/s.
Also sediment spill is better measured in transport than at the source, to distinguish the spill contribution, the background turbidity is subtracted from the spill plume turbidity. Since the spill plume in open water varies in space and time, an integration over the plume is required. These measurements are close to the source, in the order of a few hundred meters. Anything beyond a work area buffer zone for sediment spill is considered the impact area
In science, buoyancy or upthrust, is an upward force exerted by a fluid that opposes the weight of an immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid, thus the pressure at the bottom of a column of fluid is greater than at the top of the column. Similarly, the pressure at the bottom of an object submerged in a fluid is greater than at the top of the object and this pressure difference results in a net upwards force on the object. For this reason, an object whose density is greater than that of the fluid in which it is submerged tends to sink, If the object is either less dense than the liquid or is shaped appropriately, the force can keep the object afloat. This can occur only in a reference frame, which either has a gravitational field or is accelerating due to a force other than gravity defining a downward direction. In a situation of fluid statics, the net upward force is equal to the magnitude of the weight of fluid displaced by the body.
The center of buoyancy of an object is the centroid of the volume of fluid. Archimedes principle is named after Archimedes of Syracuse, who first discovered this law in 212 B. C, more tersely, Buoyancy = weight of displaced fluid. The weight of the fluid is directly proportional to the volume of the displaced fluid. Thus, among completely submerged objects with equal masses, objects with greater volume have greater buoyancy and this is known as upthrust. Suppose a rocks weight is measured as 10 newtons when suspended by a string in a vacuum with gravity acting upon it, suppose that when the rock is lowered into water, it displaces water of weight 3 newtons. The force it exerts on the string from which it hangs would be 10 newtons minus the 3 newtons of buoyancy force,10 −3 =7 newtons. Buoyancy reduces the apparent weight of objects that have sunk completely to the sea floor and it is generally easier to lift an object up through the water than it is to pull it out of the water. The density of the object relative to the density of the fluid can easily be calculated without measuring any volumes.
Density of object density of fluid = weight weight − apparent immersed weight Example, If you drop wood into water, Example, A helium balloon in a moving car. During a period of increasing speed, the air mass inside the car moves in the direction opposite to the cars acceleration, the balloon is pulled this way. However, because the balloon is buoyant relative to the air, it ends up being pushed out of the way, If the car slows down, the same balloon will begin to drift backward. For the same reason, as the car goes round a curve and this is the equation to calculate the pressure inside a fluid in equilibrium
In chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is a substance dissolved in another substance, the mixing process of a solution happens at a scale where the effects of chemical polarity are involved, resulting in interactions that are specific to solvation. The solution assumes the characteristics of the solvent when the solvent is the fraction of the mixture. The concentration of a solute in a solution is the mass of that solute expressed as a percentage of the mass of the whole solution, a solution is a homogeneous mixture of two or more substances. The particles of solute in a solution cannot be seen by the naked eye, a solution does not allow beams of light to scatter. The solute from a solution cannot be separated by filtration and it is composed of only one phase. Homogeneous means that the components of the form a single phase. Heterogeneous means that the components of the mixture are of different phase, the properties of the mixture can be uniformly distributed through the volume but only in absence of diffusion phenomena or after their completion.
Usually, the present in the greatest amount is considered the solvent. Solvents can be gases, liquids or solids, one or more components present in the solution other than the solvent are called solutes. The solution has the physical state as the solvent. If the solvent is a gas, only gases are dissolved under a set of conditions. An example of a solution is air. Since interactions between molecules play almost no role, dilute gases form rather trivial solutions, in part of the literature, they are not even classified as solutions, but addressed as mixtures. If the solvent is a liquid, almost all gases, here are some examples, Gas in liquid, Oxygen in water Carbon dioxide in water – a less simple example, because the solution is accompanied by a chemical reaction. Liquid in liquid, The mixing of two or more substances of the same chemistry but different concentrations to form a constant, alcoholic beverages are basically solutions of ethanol in water. Solid in liquid, Sucrose in water Sodium chloride or any other salt in water, solutions in water are especially common.
Counterexamples are provided by liquid mixtures that are not homogeneous, body fluids are examples for complex liquid solutions, containing many solutes
The ultracentrifuge is a centrifuge optimized for spinning a rotor at very high speeds, capable of generating acceleration as high as 1 000 000 g. There are two kinds of ultracentrifuges, the preparative and the analytical ultracentrifuge, both classes of instruments find important uses in molecular biology and polymer science. Theodor Svedberg invented the analytical ultracentrifuge in 1925, and won the Nobel Prize in Chemistry in 1926 for his research on colloids, the vacuum ultracentrifuge was invented by Edward Greydon Pickels in the Physics Department at the University of Virginia. It was his contribution of the vacuum which allowed a reduction in friction generated at high speeds, vacuum systems enabled the maintenance of constant temperature across the sample, eliminating convection currents that interfered with the interpretation of sedimentation results. In 1946, Pickels cofounded Spinco to market analytical and preparative ultracentrifuges based on his design, Pickels considered his design to be too complicated for commercial use and developed a more easily operated, “foolproof” version.
But even with the design, sales of analytical centrifuges remained low. The company survived by concentrating on sales of preparative ultracentrifuge models, in 1949, Spinco introduced the Model L, the first preparative ultracentrifuge to reach a maximum speed of 40,000 rpm. In 1954, Beckman Instruments, now Beckman Coulter, purchased the company and this allows the operator to observe the evolution of the sample concentration versus the axis of rotation profile as a result of the applied centrifugal field. With modern instrumentation, these observations are electronically digitized and stored for further mathematical analysis, two kinds of experiments are commonly performed on these instruments, sedimentation velocity experiments and sedimentation equilibrium experiments. The size resolution of this method scales approximately with the square of the particle radii, sedimentation equilibrium distributions in the centrifugal field are characterized by Boltzmann distributions. Preparative ultracentrifuges are available with a variety of rotors suitable for a great range of experiments.
Most rotors are designed to hold tubes that contain the samples, swinging bucket rotors allow the tubes to hang on hinges so the tubes reorient to the horizontal as the rotor initially accelerates. Fixed angle rotors are made of a block of material. Zonal rotors are designed to contain a volume of sample in a single central cavity rather than in tubes. Some zonal rotors are capable of loading and unloading of samples while the rotor is spinning at high speed. Preparative rotors are used in biology for pelleting of fine particulate fractions and they can be used for gradient separations, in which the tubes are filled from top to bottom with an increasing concentration of a dense substance in solution. Sucrose gradients are used for separation of cellular organelles. Gradients of caesium salts are used for separation of nucleic acids, the tremendous rotational kinetic energy of the rotor in an operating ultracentrifuge makes the catastrophic failure of a spinning rotor a serious concern
Exfoliation joints or sheet joints are surface-parallel fracture systems in rock often leading to erosion of concentric slabs. Divide the rock into sub-planar slabs, joint spacing increases with depth from a few centimeters near the surface to a few meters Maximum depth of observed occurrence is around 100 meters. Host rock is generally sparsely jointed, fairly isotropic, and has high compressive strength, can have concave and convex upwards curvatures. Many different theories have suggested, below is a short overview of the most common. This theory was proposed by the pioneering geomorphologist Grove Karl Gilbert in 1904 and is widely found in introductory geology texts. The description of this mechanism has led to terms for exfoliation joints. Laboratory studies show that simple compression and relaxation of rock samples under realistic conditions does not cause fracturing, Exfoliation joints are most commonly found in regions of surface-parallel compressive stress, whereas this theory calls for them to occur in zones of extension.
Horizontal stresses become aligned with the current ground surface as the stress drops to zero at this boundary. Thus large surface-parallel compressive stresses can be generated through exhumation that may lead to tensile rock fracture as described below, rock expands upon heating and contracts upon cooling and different rock-forming minerals have variable rates of thermal expansion / contraction. Daily rock surface temperature variations can be large, and many have suggested that stresses created during heating cause the near-surface zone of rock to expand. Large diurnal or fire-induced temperature fluctuations have been observed to create thin lamination and flaking at the surface of rocks, sometimes labeled exfoliation. However, since diurnal temperature fluctuations only reach a few centimeters depth in rock, mineral weathering by penetrating water can cause flaking of thin shells of rock since the volume of some minerals increases upon hydration. This type of fracturing has been observed in the laboratory since at least 1900, fractures formed in this way are sometimes called axial cleavage, longitudinal splitting, or extensional fractures, and are commonly observed in the laboratory during uniaxial compression tests.
High horizontal or surface-parallel compressive stress can result from regional tectonic or topographic stresses, recognizing the presence of exfoliation joints can have important implications in geological engineering. Most notable may be their influence on slope stability, Exfoliation joints following the topography of inclined valley walls, bedrock hill slopes, and cliffs can create rock blocks that are particularly prone to sliding. Especially when the toe of the slope is undercut, sliding along exfoliation joint planes is likely if the joint dip exceeds the joint’s frictional angle, foundation work may be affected by the presence of exfoliation joints, for example in the case of dams. Exfoliation joints underlying a dam foundation can create a significant leakage hazard, exfoliation joints can exert strong directional control on groundwater flow and contaminant transport. Exfoliating granite Media related to Exfoliation joints at Wikimedia Commons
For sediment in beverages, see dregs. For example 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 wind, beach sands and river channel deposits are examples of fluvial transport and deposition, though sediment 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 and shape. Stronger flows will increase the lift and drag on the particle, causing it to rise 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, 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
Stratigraphy is a branch of geology which studies rock layers and layering. It is primarily used in the study of sedimentary and layered volcanic rocks, stratigraphy has two related subfields, lithologic stratigraphy or lithostratigraphy, and biologic stratigraphy or biostratigraphy. The first practical application of stratigraphy was by William Smith in the 1790s. Another influential application of stratigraphy in the early 19th century was a study by Georges Cuvier, variation in rock units, most obviously displayed as visible layering, is due to physical contrasts in rock type. This variation can occur vertically as layering, or laterally, and these variations provide a lithostratigraphy or lithologic stratigraphy of the rock unit. Key concepts in stratigraphy involve understanding how certain geometric relationships between rock layers arise and what these geometries imply about their original depositional environment. The basic concept in stratigraphy, called the law of superposition, states, in a stratigraphic sequence.
Chemostratigraphy studies the changes in the proportions of trace elements and isotopes within. Carbon and oxygen isotope ratios vary with time, and researchers can use those to map subtle changes that occurred in the paleoenvironment and this has led to the specialized field of isotopic stratigraphy. Biostratigraphy or paleontologic stratigraphy is based on evidence in the rock layers. Strata from widespread locations containing the fossil fauna and flora are said to be correlatable in time. Biologic stratigraphy was based on William Smiths principle of succession, which predated. It provides strong evidence for the formation and extinction of species, the geologic time scale was developed during the 19th century, based on the evidence of biologic stratigraphy and faunal succession. One important development is the Vail curve, which attempts to define a global historical sea-level curve according to inferences from worldwide stratigraphic patterns, stratigraphy is commonly used to delineate the nature and extent of hydrocarbon-bearing reservoir rocks and traps of petroleum geology.
Chronostratigraphy is the branch of stratigraphy that places an absolute age, a gap or missing strata in the geological record of an area is called a stratigraphic hiatus. This may be the result of a halt in the deposition of sediment, the gap may be due to removal by erosion, in which case it may be called a stratigraphic vacuity. It is called a hiatus because deposition was on hold for a period of time, a physical gap may represent both a period of non-deposition and a period of erosion. A geologic fault may cause the appearance of a hiatus, magnetostratigraphy is a chronostratigraphic technique used to date sedimentary and volcanic sequences
Law of superposition
The law of superposition is an axiom that forms one of the bases of the sciences of geology and other fields dealing with geological stratigraphy. In its plainest form, it states that in undeformed stratigraphic sequences and this is important to stratigraphic dating, which assumes that the law of superposition holds true and that an object cannot be older than the materials of which it is composed. The law was first proposed in the 17th century by the Danish scientist Nicolas Steno, man made intrusions and activity in the archaeological record need not form chronologically from top to bottom or be deformed from the horizontal as natural strata are by equivalent processes. Some archaeological strata are created by undercutting previous strata, an example would be that the silt back-fill of an underground drain would form some time after the ground immediately above it. Other examples of non vertical superposition would be modifications to standing structures such as the creation of new doors, Superposition in archaeology requires a degree of interpretation to correctly identify chronological sequences and in this sense superposition in archaeology is more dynamic and multi-dimensional. K.
The Earths Dynamic Systems, A Textbook in Physical Geology, by W. Kenneth Hamblin, BYU, Provo, UT, william L. Chesser, Dennis Tasa, c 1978, pg. 115, The Principle of Superposition and Original Horizontality, pg,116, The Principle of Faunal Succession, The Principle of Crosscutting Relations, pg 116-17, The Principle of Inclusion. 40 figs.1 pl.136 pp. London & New York, Academic Press ISBN 0-12-326650-5
A landform is a natural feature of the solid surface of the Earth or other planetary body. Landforms together make up a given terrain, and their arrangement in the landscape is known as topography, landforms are categorized by characteristic physical attributes such as elevation, orientation, rock exposure, and soil type. Oceans and continents exemplify the highest-order landforms, landform elements are parts of a high-order landforms that can be further identified and systematically given a cohesive definition such as hill-tops, saddles and backslopes. Some generic landform elements including, peaks, ridges, pools, Terrain is the third or vertical dimension of land surface. Topography is the study of terrain, although the word is used as a synonym for relief itself. When relief is described underwater, the term bathymetry is used, in cartography, many different techniques are used to describe relief, including contour lines and TIN. Elementary landforms are the smallest homogeneous divisions of the land surface and these are areas with relatively homogeneous morphometric properties, bounded by lines of discontinuity. A plateau or a hill can be observed at various scales ranging from few hundred meters to hundreds of kilometers, the spatial distribution of landforms is often scale-dependent as is the case for soils and geological strata. A number of factors, ranging from plate tectonics to erosion and deposition, can generate, landforms do not include man-made features, such as canals and many harbors, and geographic features, such as deserts and grasslands.
Many of the terms are not restricted to refer to features of the planet Earth, examples are mountains, polar caps, and valleys, which are found on all of the terrestrial planets. The scientific study of landforms is known as geomorphology, landforms may be extracted from a digital elevation model using some automated techniques where the data has been gathered by modern satellites and stereoscopic aerial surveillance cameras. Until recently, compiling the data found in data sets required time consuming. The most detailed DEMs available are measured directly using LIDAR techniques, geomorphology Land List of landforms Open-geomorphometry project Terrain Open-Geomorphometry Project