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Lecture 3UTP Geoscience QAB2023


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The 50% of coursework marks:-10% - tests (2)

- 5% - quiz (1)

- 10% - laboratory work (2)- 15% - assignments (3)

- 10% - presentations (2)


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Lecture Topic Notes1 Overview I

2 Overview II 1-Feb

3 Weathering and the Sedimentary Cycle I 3-Feb

4 Weathering and the Sedimentary Cycle II 8-Feb

5 Weathering and the Sedimentary Cycle III 10-Feb

6 Sediment transport I 17-Feb

7 Sediment transport II 22-Feb

8 Sediment transport III 24-Feb

9 Sediment transport IV 1-Mar10 Sediment transport V 4-Mar

11 Sedimentation, sedimentary structures and textures I 8-Mar

12 Sedimentation, sedimentary structures and textures II 10-Mar

13 Sedimentation, sedimentary structures and textures III 15-Mar


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The BIGquestion: What is the origin ofsedimentary rock?

Hydrologic cycle

The rock cycle

the sedimentary cycle Weathering biological, chemical and

physical


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Rocks are composed primarily of minerals and can bean amalgam of different minerals or can be composedof one mineral.

Over 3500 minerals have been identified; most ofthese can be found in the earth's crust. Some of theearth's minerals are exceedingly popular - fewer than20 minerals compose more than 95% of the earth'scrust.

There are three different ways rock can be created onearth and thus there are three main classifications ofrock, based on the three processes - igneous,sedimentary, and metamorphic.

UTP Geoscience QAB2023ecture 1

Slide 1


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SEDIMENTARY ROCKS form in layers, or strata,they can be distinguished from igneous andmetamorphic rocks in the fields. A handspecimen usually

breaks along layered surfaces. Another keyfeature that sets them apart is their fossilcontent -fossils are never found in crystallineigneous rocks and only rarely in metamorphic

rocks. The origins of the particles that make upsedimentary rocks determinetheir appearance and give clues to their identi-ty


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Sedimentary rocks form at, or very near, theEarth s surface where rocks particlestransported by wind, water and ice aredeposited on dry land, on the beds of riversand lakes and in marine environments:beaches, deltas and the sea.
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Sedimentary rockis a type of rockthat is formed by sedimentationofmaterial at the Earth's surface and within bodies of water. Sedimentationis the collective name for processes that cause mineraland/or organicparticles (detritus) to settle and accumulate or minerals to precipitatefrom a solution. Particles that form a sedimentary rock by accumulatingare called sediment. Before being deposited, sediment was formed byweatheringand erosionin a source area, and then transported to theplace of deposition by water, wind, mass movementor glaciers.

The sedimentary rock cover of the continents of the Earth's crustisextensive, but the total contribution of sedimentary rocks is estimated tobe only 5% of the total volume of the crust. Sedimentary rocks are only athin veneer over a crust consisting mainly of igneousand metamorphicrocks.

Sedimentary rocks are deposited in stratathat form a structure calledbedding. The study of sedimentary rocks and rock strata provides

information about the subsurfacethatis useful for civil engineering, forexample in the construction of roads, houses, tunnelscanalsorotherconstructions.Sedimentary rocks are also important sources of naturalresourceslike coal, fossil fuels, drinking wateror ores.
http://en.wikipedia.org/wiki/Rock_(geology)http://en.wikipedia.org/wiki/Sedimentationhttp://en.wikipedia.org/wiki/Mineralhttp://en.wikipedia.org/wiki/Organic_matterhttp://en.wikipedia.org/wiki/Detritushttp://en.wikipedia.org/wiki/Mineralhttp://en.wikipedia.org/wiki/Precipitation_(chemistry)http://en.wikipedia.org/wiki/Precipitation_(chemistry)http://en.wikipedia.org/wiki/Organic_matterhttp://en.wikipedia.org/wiki/Solutionhttp://en.wikipedia.org/wiki/Solutionhttp://en.wikipedia.org/wiki/Detritushttp://en.wikipedia.org/wiki/Precipitation_(chemistry)http://en.wikipedia.org/wiki/Solutionhttp://en.wikipedia.org/wiki/Sedimenthttp://en.wikipedia.org/wiki/Sedimenthttp://en.wikipedia.org/wiki/Weatheringhttp://en.wikipedia.org/wiki/Weatheringhttp://en.wikipedia.org/wiki/Sedimenthttp://en.wikipedia.org/wiki/Erosionhttp://en.wikipedia.org/wiki/Erosionhttp://en.wikipedia.org/wiki/Weatheringhttp://en.wikipedia.org/wiki/Erosionhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Windhttp://en.wikipedia.org/wiki/Mass_wastinghttp://en.wikipedia.org/wiki/Glacierhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Windhttp://en.wikipedia.org/wiki/Mass_wastinghttp://en.wikipedia.org/wiki/Glacierhttp://en.wikipedia.org/wiki/Crust_(geology)http://en.wikipedia.org/wiki/Igneous_rockhttp://en.wikipedia.org/wiki/Metamorphic_rockhttp://en.wikipedia.org/wiki/Metamorphic_rockhttp://en.wikipedia.org/wiki/Igneous_rockhttp://en.wikipedia.org/wiki/Metamorphic_rockhttp://en.wikipedia.org/wiki/Metamorphic_rockhttp://en.wikipedia.org/wiki/Bed_(geology)http://en.wikipedia.org/wiki/Stratumhttp://en.wikipedia.org/wiki/Bed_(geology)http://en.wikipedia.org/wiki/Subsurfacehttp://en.wikipedia.org/wiki/Civil_engineeringhttp://en.wikipedia.org/wiki/Subsurfacehttp://en.wikipedia.org/wiki/Roadhttp://en.wikipedia.org/wiki/Roadhttp://en.wikipedia.org/wiki/Househttp://en.wikipedia.org/wiki/Tunnelhttp://en.wikipedia.org/wiki/Tunnelhttp://en.wikipedia.org/wiki/Civil_engineeringhttp://en.wikipedia.org/wiki/Canalhttp://en.wikipedia.org/wiki/Civil_engineeringhttp://en.wikipedia.org/wiki/Roadhttp://en.wikipedia.org/wiki/Househttp://en.wikipedia.org/wiki/Tunnelhttp://en.wikipedia.org/wiki/Canalhttp://en.wikipedia.org/wiki/Natural_resourcehttp://en.wikipedia.org/wiki/Natural_resourcehttp://en.wikipedia.org/wiki/Coalhttp://en.wikipedia.org/wiki/Fossil_fuelhttp://en.wikipedia.org/wiki/Drinking_waterhttp://en.wikipedia.org/wiki/Orehttp://en.wikipedia.org/wiki/Natural_resourcehttp://en.wikipedia.org/wiki/Natural_resourcehttp://en.wikipedia.org/wiki/Coalhttp://en.wikipedia.org/wiki/Fossil_fuelhttp://en.wikipedia.org/wiki/Drinking_waterhttp://en.wikipedia.org/wiki/Orehttp://en.wikipedia.org/wiki/Orehttp://en.wikipedia.org/wiki/Drinking_waterhttp://en.wikipedia.org/wiki/Fossil_fuelhttp://en.wikipedia.org/wiki/Coalhttp://en.wikipedia.org/wiki/Natural_resourcehttp://en.wikipedia.org/wiki/Natural_resourcehttp://en.wikipedia.org/wiki/Canalhttp://en.wikipedia.org/wiki/Tunnelhttp://en.wikipedia.org/wiki/Househttp://en.wikipedia.org/wiki/Roadhttp://en.wikipedia.org/wiki/Civil_engineeringhttp://en.wikipedia.org/wiki/Subsurfacehttp://en.wikipedia.org/wiki/Bed_(geology)http://en.wikipedia.org/wiki/Stratumhttp://en.wikipedia.org/wiki/Metamorphic_rockhttp://en.wikipedia.org/wiki/Metamorphic_rockhttp://en.wikipedia.org/wiki/Igneous_rockhttp://en.wikipedia.org/wiki/Crust_(geology)http://en.wikipedia.org/wiki/Glacierhttp://en.wikipedia.org/wiki/Mass_wastinghttp://en.wikipedia.org/wiki/Windhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Erosionhttp://en.wikipedia.org/wiki/Weatheringhttp://en.wikipedia.org/wiki/Sedimenthttp://en.wikipedia.org/wiki/Solutionhttp://en.wikipedia.org/wiki/Precipitation_(chemistry)http://en.wikipedia.org/wiki/Detritushttp://en.wikipedia.org/wiki/Organic_matterhttp://en.wikipedia.org/wiki/Mineralhttp://en.wikipedia.org/wiki/Sedimentationhttp://en.wikipedia.org/wiki/Rock_(geology)


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Water is the source of all life on earth. Thedistribution of water, however, is quite varied; manylocations have plenty of it while others have verylittle.

Water exists on earth as a solid (ice), liquid or gas

(water vapor). Oceans, rivers, clouds, and rain, all ofwhich contain water, are in a frequent state of change(surface water evaporates, cloud water precipitates,rainfall infiltrates the ground, etc.).

However, the total amount of the earth's water doesnot change. The circulation and conservation of

earth's water is called the "hydrologic cycle". TheHydrologic Cycle module has been organized into thefollowing sections:


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EvaporationThe transformation of water from a liquidinto a gas, a process which humidifies theatmosphere.

CondensationThe transformation of water from a gas into aliquid, and the processes that lead tocondensation

TransportThe movement of water through theatmosphere
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/evap.rxmlhttp://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/cond/home.rxmlhttp://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/wind/wind.rxmlhttp://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/wind/wind.rxmlhttp://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/cond/home.rxmlhttp://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/evap.rxml


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PrecipitationThe transfer of water from the atmosphere toland. Rain, snow, hail, sleet, and freezing rain arediscussed.

GroundwaterWater located below ground and how it returns tothe surface

TranspirationTransfer of water to the atmosphere by plantsand vegetation.

RunoffRivers, lakes, and streams transport water fromland to the oceans. Too much rainfall can causeexcess runoff, or flooding.
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/prcp.rxmlhttp://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/grnd.rxmlhttp://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/grnd.rxmlhttp://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/trsp.rxmlhttp://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/trsp.rxmlhttp://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/run.rxmlhttp://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/run.rxmlhttp://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/run.rxmlhttp://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/trsp.rxmlhttp://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/grnd.rxmlhttp://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/prcp.rxml


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The rock cycleis a fundamental concept ingeologythatdescribes the dynamic transitions through geologic timeamong the three main rocktypes: sedimentary,metamorphic, and igneous.

As the that follows illustrates, each type of rock is alteredor destroyed when it is forced out of its equilibrium

conditions. An igneous rock such as basaltmay breakdown and

dissolve when exposed to the atmosphere, or melt as it issubductedunder a continent.Due to the driving forces ofthe rock cycle, plate tectonicsand the water cycle, rocksdo not remain in equilibrium and are forced to change as

they encounter new environments. The rock cycle is an illustration that explains how the 3

rock types are related to each other and how processeschange from one type to another over time.
http://en.wikipedia.org/wiki/Geologic_timehttp://en.wikipedia.org/wiki/Geologic_timehttp://en.wikipedia.org/wiki/Geologic_timehttp://en.wikipedia.org/wiki/Rock_(geology)http://en.wikipedia.org/wiki/Sedimentaryhttp://en.wikipedia.org/wiki/Sedimentaryhttp://en.wikipedia.org/wiki/Geologic_timehttp://en.wikipedia.org/wiki/Metamorphic_rockhttp://en.wikipedia.org/wiki/Igneoushttp://en.wikipedia.org/wiki/Igneoushttp://en.wikipedia.org/wiki/Sedimentaryhttp://en.wikipedia.org/wiki/Metamorphic_rockhttp://en.wikipedia.org/wiki/Igneoushttp://en.wikipedia.org/wiki/Basalthttp://en.wikipedia.org/wiki/Earth's_atmospherehttp://en.wikipedia.org/wiki/Earth's_atmospherehttp://en.wikipedia.org/wiki/Subductionhttp://en.wikipedia.org/wiki/Continenthttp://en.wikipedia.org/wiki/Earth's_atmospherehttp://en.wikipedia.org/wiki/Subductionhttp://en.wikipedia.org/wiki/Plate_tectonicshttp://en.wikipedia.org/wiki/Plate_tectonicshttp://en.wikipedia.org/wiki/Plate_tectonicshttp://en.wikipedia.org/wiki/Water_cyclehttp://en.wikipedia.org/wiki/Plate_tectonicshttp://en.wikipedia.org/wiki/Water_cyclehttp://en.wikipedia.org/wiki/Water_cyclehttp://en.wikipedia.org/wiki/Plate_tectonicshttp://en.wikipedia.org/wiki/Continenthttp://en.wikipedia.org/wiki/Subductionhttp://en.wikipedia.org/wiki/Earth's_atmospherehttp://en.wikipedia.org/wiki/Basalthttp://en.wikipedia.org/wiki/Igneoushttp://en.wikipedia.org/wiki/Metamorphic_rockhttp://en.wikipedia.org/wiki/Sedimentaryhttp://en.wikipedia.org/wiki/Rock_(geology)http://en.wikipedia.org/wiki/Geologic_timehttp://en.wikipedia.org/wiki/Geology


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A diagram of the rock cyc le. Legend: 1 = magma; 2 = crystallization

(freezing of rock); 3 = igneous rocks; 4 = erosion; 5 = sedimentation; 6 =

sediments & sedimentary rocks; 7 = tectonic burial& metamorphism; 8 =

metamorphic rocks; 9 = melting.

UTP Geoscience QAB2023
http://en.wikipedia.org/wiki/Magmahttp://en.wikipedia.org/wiki/Crystallizationhttp://en.wikipedia.org/wiki/Igneous_rockshttp://en.wikipedia.org/wiki/Erosionhttp://en.wikipedia.org/wiki/Sedimentationhttp://en.wikipedia.org/wiki/Sedimentary_rockshttp://en.wikipedia.org/w/index.php?title=Tectonic_burial&action=edit&redlink=1http://en.wikipedia.org/wiki/Metamorphic_rockshttp://en.wikipedia.org/wiki/Meltinghttp://upload.wikimedia.org/wikipedia/commons/1/16/Rockcycle.jpghttp://en.wikipedia.org/wiki/Meltinghttp://en.wikipedia.org/wiki/Metamorphic_rockshttp://en.wikipedia.org/w/index.php?title=Tectonic_burial&action=edit&redlink=1http://en.wikipedia.org/wiki/Sedimentary_rockshttp://en.wikipedia.org/wiki/Sedimentationhttp://en.wikipedia.org/wiki/Erosionhttp://en.wikipedia.org/wiki/Igneous_rockshttp://en.wikipedia.org/wiki/Crystallizationhttp://en.wikipedia.org/wiki/Magma


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Slide 2


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UTP Geoscience QAB2023


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Slide10


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Weatheringis the breakdown and alteration of rocks

and minerals at or near the Earth's surface intoproducts that are more in equilibrium with theconditions found in this environment.

Most rocksand minerals are formed deep within theEarth's crust where temperatures and pressures differgreatly from the surface.

Because the physical and chemical nature of materialsformed in the Earth's interior are characteristically indisequilibrium with conditions occurring on thesurface.

Because of this disequilbrium, these materials areeasily attacked, decomposed, and eroded by variouschemical and physical surface processes.


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Weathering is the first step for a number of othergeomorphic and biogeochemical processes.

The products of weathering are a major source ofsediments for erosionand deposition.

Many types of sedimentary rocksare composedof particles that have been weathered, eroded,transported, and terminally deposited in basins.

Weathering also contributes to the formation of

soilby providing mineral particles like sand,silt,andclay .


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Elementsand compoundsextracted from therocks and minerals by weathering processessupply nutrients for plant uptake.

The fact that the oceans are saline is the result ofthe release of ion salts from rock and minerals

on the continents. Leachingand runoff transportthese ions from land to the ocean basins wherethey accumulate in seawater.

In conclusion, weathering is a process that isfundamentalto many other aspects of the

hydrosphere, lithosphere, and biosphere. There are three broad categories of mechanisms

for weathering: chemical, physicaland biological.
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The process of weathering can result in the followingthree outcomes on rocksand minerals: (1). The complete loss of particular atomsorcompoundsfrom the weathered surface. (2). The addition of specific atoms or compounds to

the weathered surface. (3). A breakdown of one mass into two or moremasses, with no chemical change in the mineral orrock.

The residue of weathering consists of chemicallyaltered and unaltered materials. The most common

unaltered residue is quartz. Many of the chemicallyaltered products of weathering become very simplesmall compounds or nutrient ions.
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These residues can then be dissolved ortransported by water, released to theatmosphere as a gas, or taken up by plantsfor nutrition. Some of the products of

weathering, less resistant alumino-silicateminerals, become clay particles. Other alteredmaterials are reconstituted by sedimentary ormetamorphicprocesses to become new rocksand minerals.
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Chemical weatheringinvolves the alteration of thechemical and mineralogical composition of the weatheredmaterial. A number of different processes can result inchemical weathering. The most common chemicalweatheringprocesses are hydrolysis,oxidation, reduction,hydration, carbonation, and solution.

Hydrolysisis the weathering reaction that occurs when thetwo surfaces of water andcompound meet.It involves thereaction between mineralions and the ionsof water (OH-and H+), and results in the decomposition of the rocksurface by forming new compounds, and by increasing thepHof the solution involved through the release of thehydroxide ions. Hydrolysis is especially effective in theweathering of common silicate and alumino-silicateminerals because of their electrically charged crystalsurfaces.
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Oxidationisthe reaction that occurs betweencompoundsand oxygen. The net result of thisreaction is the removal of one or moreelectrons from a compound, which causes thestructure to be less rigid and increasingly

unstable. The most common oxides are thoseof iron and aluminum, and their respective redand yellow staining of soils is quite common intropical regions which have high temperaturesand precipitation. Reductionis simply thereverse of oxidation, and is thus caused by theaddition of one or more electrons producing amore stable compound.
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Hydrationinvolves the rigid attachment of H+ and OH-ionsto a reacted compound. In many situations the H andOH ions become a structural part of the crystal lattice ofthe mineral. Hydration also allows for the acceleration ofother decompositional reactions by expanding the crystallattice offering more surface area for reaction.

Carbonationis the reaction of carbonate and bicarbonateionswith minerals. The formation of carbonates usuallytakes place as a result of other chemical processes.Carbonation is especially active when the reactionenvironment is abundant with carbon dioxide. Theformation of carbonic acid, a product of carbon dioxide

and water, is important in the solution of carbonates andthe decomposition of mineral surfaces because of itsacidic nature.
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Water and the ions it carries as it moves through and aroundrocks and minerals can further the weathering process.Geomorphologists call this phenomena solution. The effects ofdissolved carbon dioxide and hydrogen ions in water havealready been mentioned, but solution also entails the effects of anumber of other dissolved compounds on a mineral or rocksurface. Molecules can mix in solution to form a great variety of

basic and acidic decompositional compounds. The extent,however, of rock being subjected to solution is determinedprimarily by climatic conditions. Solution tends to be mosteffective in areas that have humid and hot climates.

The most important factor affecting all of the above mentionedchemical weathering processes is climate. Climatic conditions

control the rate of weathering that takes place by regulating thecatalysts of moisture and temperature. Experimentation hasdiscovered that tropical weathering rates, where temperature andmoisture are at their maximum, are three and a half times higherthan rates in temperate environments.
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Physical weatheringis the breakdown of mineral or rockmaterial by entirely mechanical methods brought about bya variety of causes. Some of the forces originate within therock or mineral, while others are applied externally. Bothof these stresses lead to strain and the rupture of the rock.The processes that may cause mechanical rupture are

abrasion, crystallization, thermal insolation, wetting anddrying, and pressure release. Abrasionoccurs when some force causes two rock

surfaces to come together causing mechanical wearing orgrinding of their surfaces. Collision between rock surfacesnormally occurs through the erosionaltransport ofmaterial by wind, water, or ice.
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rystallizationcan cause the necessary stresses needed forthe mechanical rupturing of rocks and minerals. Crystalgrowth causes stress as a result of a compound's or anelement's change of physical state with change intemperature. The transformation from liquid to solidcrystalline form produces a volumetric change which in turn

causes the necessary mechanical action for rupture. There areprimarily two types of crystal growth that occur; they are iceand salt. Upon freezing the volumetric change of water fromliquid to solid is 9%. This relatively large volumetric changeupon freezing has potentially a great rupturing effect.


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Several researchers have discovered in thelaboratory and the field that frost actionplays a major role in weathering intemperate and polar regions of the Earth.

The threshold temperature for frost actionis at least - 5 Celsius, and it is at thistemperature that the most effectiverupturing occurs.


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The crystallization of salt exhibits volumetricchanges from 1 to 5 percent depending on thetemperature of the rock or mineral surface.Most salt weathering occurs in hot arid regions,but it may also occur in cold climates. Forexample, cavernous salt weathering of graniteis widespread in the dry valley regions of SouthVictoria Land, Antarctica. At this locationoutcrops and large boulders are pitted by holes

up to 2 meters in diameter. Researchers havealso found that frost weathering is greatlyenhanced by the presence of salt.


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The physical breakdown of rock by their expansion andcontraction due to diurnal temperature changes is one ofthe most keenly debated topics in rock weatheringresearch. Known as insolation weathering, it is the resultof the physical inability of rocks to conduct heat well. Thisinability to conduct heat results in differential rates ofexpansion and contraction. Thus, the surface of the rockexpands more than its interior, and this stress willeventually cause the rock to rupture. Differentialexpansion and contraction may also be due to the variancein the colors of mineral grains in rock. Dark coloredgrains, because of their absorptive properties, will expandmuch more than light colored grains. Therefore, in a rock

peppered with many different colored grains, rupturingcan occur at different rates at the various mineralboundaries.
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Alternate wetting and dryingof rocks, sometimes known as slaking, canbe a very important factor in weathering. Slaking occurs by themechanism of "ordered water", which is the accumulation of successivelayers of water molecules in between the mineral grains of a rock. Theincreasing thickness of the water pulls the rock grains apart with greattensional stress. Recent research has shown that slaking in combinationwith dissolved sodium sulfate can disintegrate samples of rock in onlytwenty cycles of wetting and drying.

Pressure releaseof rock can cause physical weathering due to unloading.The majority of igneous rocks were created deep under the Earth'ssurface at much higher pressures and temperatures. As erosionbringsthese rock formations to the surface, they become subjected to less andless pressure. This unloading of pressure causes the rocks to fracturehorizontally with an increasing number of fractures as the rockapproaches the Earth's surface. Spalling, the vertical development offractures, occurs because of the bending stresses of unloaded sheetsacross a three dimensional plane.
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Soil formation, or pedogenesis, is the combinedeffect of physical, chemical, biological, andanthropogenicprocesses on soil parent material. Soilgenesis involves processes that develop layers orhorizons in the soil profile. These processes involveadditions, losses, transformations and translocations

of material that compose the soil. Minerals derived from weathered rocks undergo

changes that cause the formation of secondaryminerals and other compounds that are variablysoluble in water, these constituents are moved(translocated) from one area of the soil to other areasby water and animal activity. The alteration andmovement of materials within soil causes theformation of distinctive soil horizons.
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http://upload.wikimedia.org/wikipedia/commons/9/95/Soil_profile.png


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3. Simple chemical processes like solutioncan be enhanced by the carbon dioxideproduced by respiration. Carbon dioxidemixing with water forms carbonic acid.

4. The complex chemical effects that occur asa result of chelation. Chelation is a biologicalprocess where organisms produce organicsubstances, known as chelates, that have theability to decompose minerals and rocks bythe removal of metallic cations.
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5. Organisms can influence the moisture regime in soilsand therefore enhance weathering. Shade from aerialleaves and stems, the presence of roots masses, andhumusall act to increase the availability of water in thesoil profile. Water is a necessary component in severalphysical and chemical weathering processes.

6. Organisms can influence the pHof the soil solution.Respirationfrom plant roots releases carbon dioxide. If thecarbon dioxide mixeswith water carbonic acid is formedwhich lowers soil pH. Cation exchangereactions by whichplants absorb nutrients from the soil can also cause pHchanges. Theabsorption processes often involves theexchange of basiccations for hydrogen ions. Generally,the higher the concentration of hydrogen ions the moreacidica soil becomes.
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Laterite originally proposed to describe thered soils of parts of India

The product of intensely weathered material

rich in hydrated iron and aluminium oxides,low in humus, silica, lime, silicate clays andmost other minerals

Eg: Ugandan laterites 40-50% iron oxide,

20% alumina and 25% silica Evidence of prolonged intensive chemical

weathering


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Kaolinrock agregate of the mineral

kaolinite

Hydrated aluminosilicate clay mineral(Al2O3.2SiO2.2H2O)

Occurs in three geological situations: A residual weathering product

Hydrothermal alteration of feldspars in granite

Formed by intensive weathering of diverse rock

types


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2d weathering 1

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