GEOL Mid-term #2, Chapters 5-7
The most common end product of the chemical weathering of feldspar is a) clay minerals b) pyroxene c) amphibole d) calcite.
a) clay minerals
what are the factors that affect soil formation?
(residual soil is developed on bedrock, transported soil is developed on flood deposits. soil is thin to nonexistent on steep slopes due to erosion) 1) Parent Material -The character of a soil depends partly on the parent material from which it develops -Source of the weathered mineral matter that makes up most of a soil -Granite: -A soil developing on weathering granite will be sandy, as sand-sized particles of quartz and feldspar are released from the granite -As the feldspar grains weather completely, fine-grained clay minerals are formed -The resulting soil will contain a variety of grain sizes and will have drainage and water-retention properties conducive to plant growth -Basalt: -A soil forming on basalt may never be sandy, even in its early stages of development -If chemical weathering processes are more prevalent than mechanical weathering processes, the fine-grained feldspars in the basalt will weather directly to fine-grained clay minerals -Since the parent rock had no coarse-grained minerals and no quartz to begin with, the resulting soil may lack sand -Such a soil may not drain well, although it can be quite fertile -Residual soils: Develop from weathering of the bedrock beneath them -Transported soils: -Do not develop from locally formed rock -regolith brought in from some other region -Parent material from which it is formed -example: Flood Mud deposits and Loess Wind deposits -Transported soils are generally more fertile than residual soils -parent material is transported from many different locations -more variety in the chemical makeup of the parent material -Greater variety of nutrients 2) Slope -The optimal topography for soil formation is flat or gently sloping uplands, allowing good drainage, minimal erosion, and healthy vegetation cover -Steep Slopes: Soils tend to be thin or nonexistent on steep slopes -gravity keeps water and soil particles moving downhill -Vegetation is sparse on steep slopes -little organic matter to provide nutrients -Bottomlands: Very thick but poorly drained and waterlogged -Vegetation in the bottomlands does not decay completely, and thick, dark layers of peat may form 3) Living Organisms -Primary role: -provide organic material to the soil -Decomposing plants form humus -Supplies nutrients to the soil -aids in water retention -the decaying plant matter releases organic acids that increase chemical weathering of rocks -Growing plants send roots deep into the soil, breaking up the underlying bedrock and opening up pore spaces -Burrowing organisms: ants, worms, and rodents -bring soil particles to the surface -mix the organic and mineral components of the soil -create passageways, which: -circulation of air and water -increasing chemical weathering -accelerating soil formation -Microorganisms such as bacteria, fungi, and protozoa promote the decomposition of organic matter to humus. some bacteria fix nitrogen in the soil, making it available for uptake by plants -The interdependency of plants, animals, and soil is a mutually beneficial and delicately balanced system 4) Climate Perhaps the most influential factor affecting soil thickness and character -Same parent materials / Same topography -significantly different soil types under different climatic conditions -Temperature and precipitation -chemical or mechanical weathering processes will dominate -strongly influence the rate and depth of weathering -the amount and types of vegetation and animal life that contribute to soil formation are also determined by climate -Temperate, moist climates: -Europe and the eastern United States -generally characterized by downward movement of water through Earth materials -soils tend to be fertile -Soils have a high content of aluminum and iron oxides -Soils have well-developed horizons -Effective downward leaching due to high rainfall and to the acids produced by decay of abundant humus -Hardpan: a hard layer of Earth material -clay minerals, silica, and iron compounds have accumulated -Arid climates: Western United States -soils tend to be thin -Soils characterized by Little leaching, scant humus, upward movement of soil water beneath the land surface -subsurface evaporation and capillary action -salts are precipitated within the soil -extreme example of salt buildup can be found in desert alkali soils, in which heavy concentrations of toxic sodium salts may prevent plant growth -Extremely wet climates (e.g., tropical rainforest): -Highly leached and unproductive soils (Laterites) -Most nutrients come from thick O/A horizons -Some Laterites are composed of ore grade aluminum oxides: AL 2O3*NH2O -The intense leeching of the soil takes everything else and leaves just the Aluminum oxide behind. 5) Time -the character of a soil changes with time -Short time frame: Characteristics of the Parent material Dominates -Young soils can retain the structure of the parent rock; bedding layers -As time progresses, climate eventually predominate -Soils forming from many different kinds of igneous, metamorphic, and sedimentary rocks can become quite similar, given the same climate and enough time -In the long term, the only characteristic of the parent rock to have significance is the presence or absence of coarse grains of quartz
What are soil horizons? How do they form?
-A soil horizon is simply a soil layer -As soils mature, distinct layers form in them -These soil layers are called soil horizons and they can be distinguished from one another by appearance and chemical composition -
how does acid dissolution work?
-Acids are the most effective agent of Chemical Weathering -The Hydrogen ions given off by acids disrupts the crystalline arrangement of atoms within some minerals -The H+ can replace other ions of similar size and charge in the crystal lattice -Na+, K+, Ca++ -The substitution changes the original mineral into a different mineral -Several natural sources for acids: Sulfuric, hydrofluoric acids emitted by volcanic eruptions, and strong acid -Mine waste as sulfur-containing minerals oxidize and form acids at the surface -The most abundant acid on the Earth is formed when Carbon Dioxide Gas (CO2) dissolves in water -An acid is a chemical compound that gives off Hydrogen ions (H+) when in solution -Water and Carbon Dioxide Gas form Carbonic Acid H2CO3 -Dissociates into H+ and HCO3- in solution (in water) -CO2 (.03%) exists in the Earth's Atmosphere -Rain absorbs some of the CO2 -Rain is slightly acidic -This problem is aggravated in urban areas -The Hydrogen ions given off by acids disrupts the crystalline arrangement of atoms within some minerals -The H+ can replace other ions of similar size and charge in the crystal lattice -Na+, K+, Ca++ -the substitution changes the original mineral into a different mineral -The most important natural source of acid for rock weathering at Earth's surface is dissolved carbon dioxide (CO2) in water -Water and carbon dioxide form carbonic acid (H2CO3), a weak acid that dissociates into the hydrogen ion and the bicarbonate ion -Even though carbonic acid is a weak acid, it is so abundant at Earth's surface that it is the single most effective agent of chemical weathering
What is the most effective agent of chemical weathering?
-Acids are the most effective agent of Chemical Weathering -The most abundant acid on the Earth is formed when Carbon Dioxide Gas (CO2) dissolves in water -Carbonic Acid is the single most effective agent of Chemical weathering
What is an acid? What is pH?
-An acid is chemical compound that gives off Hydrogen ions (H+) when in solution -Water and Carbon Dioxide Gas form Carbonic Acid H2CO3 -Dissociates into H+ and HCO3- in solution -PH, quantitative measure of the acidity or basicity of aqueous or other liquid solutions - the values of the concentration of the hydrogen ion
How do (Granitic) batholiths form?
-Batholiths are large bodies of igneous rock formed beneath the Earth's surface by the intrusion and solidification of magma. -It is commonly composed of coarse-grained rocks (e.g., granite or granodiorite)
Describe the differences between the continuous and the discontinuous branches of Bowen's reaction series (As a melt transitions from Mafic Basaltic composition to a Felsic Granitic Composition)
-Bowen's reaction series has two pathways for minerals to form as magma cools: on the left is the discontinuous series -This refers to the fact that one mineral is transformed into a different mineral through chemical reactions -On the right is the continuous series, where plagioclase feldspar goes from being rich in calcium to being rich in sodium.
what is differential weathering?
-Caused by different types of rock to weather at different rates -Resistant sandstone cap protects weak shale pedestal from weathering and erosion -Differential weathering of more resistant red sandstone layers and softer shale layers form scenic cliffs -Shale: -Composed of soft clay minerals -Tends to weather and erode much faster than sandstone -Sandstone: -Composed of hard quartz
what are detrital sedimentary rocks (Clastic)?
-Cemented sediment grains from pre-existing rocks -Most common sedimentary rock type -Shale, Sandstones, conglomerates, Breccias, Siltstones, Claystones and Mudstones -Rock fragments can be either identifiable pieces, pebbles of granite or shale -individual mineral grains; sand-sized quartz and feldspar crystals -Usually composed of: Clay minerals, Quartz, Feldspars, Micas clastic sedimentary rocks: sandstone -Medium-grained clastic sedimentary rock -Sandstones show a great deal of variation in mineral composition, degree of sorting, and degree of rounding -Medium-grained clastic sedimentary rock -Types determined by composition: -Quartz sandstone - >90% quartz grains -Arkose - mostly feldspar and quartz grains -Graywacke - sand grains surrounded by dark, fine-grained matrix, often clay-rich clastic sedimentary rocks: quartz sandstone - >90% quartz grains -Quartz grains in a quartz sandstone; well-sorted; well-rounded -Suggests transported for great distances: -Environment; beach sand; dune sand clastic sedimentary rocks: arkose -More than 25% Feldspar and quartz grains -Minimal Chemical weathering of the Feldspars -Usually contain coarse, angular grains -Short transportation distances -Mountains of granite in a desert -an alluvial fan
what is chemical weathering?
-Chemical weathering: decomposition of rock from exposure to atmospheric gases (carbon dioxide, oxygen and water vapor) and water -new chemical compounds form
how does the earth manufacture granites in a rock cycle approach?
-Deep mantle rock undergoes partial melting to form a magma -the magma body moves up through the Earth and eventually solidifies deep underground -Assuming the original magma had the composition of a granite, the igneous rock would be a granite
weathering and diamond concentration
-Diamond hardest mineral known -extremely resistant to weathering -very strong covalent bonding of carbon -diamonds are often concentrated by weathering -Diamonds are brought to the surface of Earth in kimberlite pipes -the ultramafic rock in the pipe is preferentially weathered and eroded away
what are the consequences of erosion?
-Eroded soil particles have to go somewhere -Deposited as sediments -Streams -Flood plains -lakes -reservoirs -Erosion and sedimentation: -natural processes -unnatural rate -mechanized farming -Chesapeake Bay watershed -Since colonial times -Forest land -Cleared for farming and timber -Erosion of soils -Deposition in Chesapeake Bay -787 acres of new land -Reduction in average water depth•increased dredging -Reduction in water clarity -Decrease in light penetration -preventing light from reaching the bottom of the bay -aquatic vegetation cannot survive in the reduced light -The Dust Bowl: American Midwest during the 1930s -Advances in farm equipment allowed farmers to practice intensive row crop agriculture -100 million acres of prairie -planted in long rows of crops: corn, soybeans, wheat -Drought in the 1930s: -crops failed -soil was left exposed to the high winds -Huge dust cloud -black rollers -burying vehicles and drifting like snow against houses
what is feldspar weathering?
-Feldspar alters to an entirely different type of mineral -Felspar is a framework silicate that converts to a sheet silicate -When feldspar interacts with a hydrogen it forms clay minerals -Clay mineral is a hydrous aluminum silicate with a sheet-silicate structure like that of mica -Hydrogen ion (H+) replaces the Potassium (K+) In the the feldspar structure -The potassium (K+) is released into the environment -Silica is also Released into the environment
Chemical Weathering (Summation)
-Feldspars: -Most common minerals in crust -Slightly acidic rainwater attacks feldspar -Clay minerals produced -K+, Na+, Ca++ ions released into water -Other minerals: -Ferromagnesian minerals -Clays, iron oxides, Mg++ ions produced, SiO -More complex silicate bonds lead to lower weathering susceptibility -Olivine most susceptible to chemical weathering -Due to Ionic bonds between Silicon-Oxygen Tetrahedron and Iron and Magnesium Ions -Quartz least susceptible to chemical weathering -Exclusively Covalent Bonds throughout the structure -Warm, wet climatic conditions maximize weathering
what is an example of chemical weathering?
-Granite undergoing chemical weathering -Some minerals are chemically changed into different minerals -Feldspar transforms into a clay mineral (with a crystal structure similar to mica).
chemical weathering: c02 and water
-Large amounts of carbon dioxide also dissolve in water that percolates through soil -Soil pores are filled with a gas mixture that differs from air -Soil gas has a much higher content of carbon dioxide: decay of organic matter, respiration of soil organisms -CO2 is concentrated to 10% in the pore spaces of soils -Water percolating through soils becomes more acidic. -Attacks minerals in the unweathered base surface -Some Minerals dissolve directly into solution -The mineral Calcite goes into solution (dissolves) when exposed to carbon dioxide and water
What is lithification?
-Lithification is the process by which sediment is compacted into rock due to pressure -General term for processes converting loose sediment into sedimentary rock -Agents of Lithification: Compaction, Cementation, Another process is crystallization of minerals from solution that doesn't go through the loose sediment stage
what is sediment?
-Loose, solid particles of mineral that originate from: -Weathering and erosion of preexisting rocks (detrital sediments) -Precipitation from solution (chemical sediments), which includes secretion by organisms in the water -These particles usually collect in layers on Earth's surface -Unconsolidated / Separate grains unattached to one another -Detrital sediment particles are classified and defined according to the size of individual fragments -Sediments -Beach sand/lake bottom mud / Dust particles settling out of the air
Why do mafic (Basaltic) magmas tend to reach the surface much more often than felsic (Granitic / Rhyolite) magmas?
-Mafic magmas are less viscous -This is due to the Silica content -Felsic magmas have a greater silica content increasing the viscosity
Describe at least three processes that mechanically weather rock. How does mechanical weathering differ from chemical weathering?
-Mechanical weathering breaks rocks into smaller pieces without changing their composition -Chemical weathering breaks down rocks by forming new minerals that are stable at the Earth's surface -at least three processes that mechanically weather rock are frost action, plant growth and burrowing animals
Describe what happens to each mineral within granite during the complete chemical weathering of granite in a humid climate. List the final products for each mineral.
-Quartz resist weathering, so its least susceptible to chemical attack at Earth's surface -granite is an intrusive felsic igneous rock that contains feldspar, quartz, and mica -when exposed to complete chemical weathering in a humid climate, the feldspar breaks down and forms clay minerals (sheet silicates, stable at earth's surface) -feldspar -> (under influence of CO2 and H2O) main solid product = clay mineral -ferromagnesian minerals (including biotite mica) -> (under influence of CO2 and H2O) main solid product = clay mineral -muscovite mica -> (under influence of CO2 and H2O) main solid product = clay mineral -quartz -> (under influence of CO2 and H2O) main solid product = quartz grains (sand) -calcite -> (under influence of CO2 and H2O) main solid product = ?
what is frost heave?
-Rock cools faster than the surrounding soil -Layer of ice forms under the rock causing the rock to lift out of the soil -Real problem for farms with rocky soils -Every year a new crop of rock
What is spheroidal weathering?
-Rock has been rounded by weathering -Initial blocky shape -Chemical weathering acts more rapidly or intensely on the corners and edges of a rock than on the smooth rock faces
how does weathering changes rocks?
-Rocks undergo both mechanical weathering and chemical weathering -mechanical weathering: physical disintegration of rock without changes of the chemical composition -mechanical weathering: Making small rocks out of big rocks -mechanical weathering: water freezing and expanding in cracks can cause rocks to disintegrate physically -Granite may be broken into smaller pieces by frost action -Original crystals of quartz, feldspar, and ferromagnesian minerals are unchanged
erosion and soils
-Same kind of processes that create soils can destroy them -Splash Erosion: Raindrops strike soil and dislodge particles -Sheet erosion: Entrains the dislodged soil particles and move them away from the soil -Wind erosion: Generally less significant than water -Problem in arid and semiarid regions -The fertility components are lost -clays, silts, and organic matter -Requires increased use of fertilizers to maintain their productivity
what is sediment size?
-Sediment size decreases with increased transport distance -Rule of thumb: The big stuff settles out faster than the small stuff
what is compaction?
-Sediments aggregate as loose piles of materials -Loose piles have empty pore spaces -40-50 % of a sand deposit may be empty pore spaces -The addition of new material (Overburden) compresses the material: Decreases the overall volume, Decreases the pore space, Drives out water from the pore spaces
weathering processes create sediments
-Sediments are particles of organic or inorganic matter that accumulate in a loose, unconsolidated form -mud and sand and soil
what is deposition?
-Settling and coming to rest of transported material -Deposition of detrital sediments -Accumulation of chemical or organic sediments, typically in water -Clam shells on the sea floor -Plant material on the floor of a swamp -Deposition of salt crystals can take place as seawater evaporates -Precipitation/ hot springs may deposit calcite or silica as the warm water cools -the process by which sediment settles out of the water or wind carrying it -Environment of deposition is the location in which deposition occurs -Each environment is marked by characteristic physical, chemical, and biological conditions: -Mud on the seafloor VS mud on a lake bottom -Sand on a beach VS sand desert dune -Some differences: -Varying sediment sources -Varying transporting agents -Most are conditions in the environments of deposition
what is ferromagnesian weathering?
-Similar to the feldspars -Ferromagnesian convert to sheet silicates (Clay mineral) -Iron and Magnesium are freed from the structure -magnesium ions -iron oxides (hematite, limonite, and goethite)
Why do stone buildings tend to weather more rapidly in cities than in rural areas?
-Urban areas have a higher concentration of pollutants in the air, usually from cars and manufacturing -This increase in pollutants usually means that rain and standing water are more acidic than waters found in rural areas -These more acidic waters weather materials faster -because there tends to be more air pollution is urban cities that can weather stone buildings -Acid rain exist in cities rather than rural areas because of higher sulfuric acid from burning fossilsƒ
Name and sketch the soil horizons that form in a humid climate. Explain how the layers (horizons) form.
-Soil layer are called soil horizons and can be distinguished from one another by appearance and chemical composition -The O Horizon is the upper most layer that consist entirely of organic material like ground vegetation, fallen leaves and highly composed plant material called humus -The humus form the O Horizon mixes with weathered mineral matter to form A Horizon which is a dark color soil layer rich in organic matter and high in biological activity -Both O and A Horizon forms the top soil -Organic acids and carbon dioxide produced by decaying plants in the topsoil percolate down into the E Horizon or zone of leaching and help dissolve minerals such as iron and calcium -the material leached downward from the E Horizon accumulates in the B Horizon or zone of accumulation which consists of clay and stained red or brown by hematite and limonite -The C Horizon is incompletely weathered parent material that lies below the B Horizon and this horizon is the transitional between the unweathered rock or sediment below the developing soil above -Bedrock contains parent material which largely comprises continuous masses of hard rocks
what is soil?
-Soil: a layer of weathered, unconsolidated material on top of bedrock -Capable of supporting plant growth -Common soil constituents: 1) Clay minerals 2) Quartz 3) Water 4) Organic matter -Soil horizons: -A soil horizon is simply a soil layer -Soil Horizons can be distinguished from one another by appearance and chemical composition -Boundaries between soil horizons are usually transitional rather than sharp -Transitional means that they blend on in the another -they are classified by letters -Soil horizon lettering scheme: 1) O horizon - uppermost layer; organic material 2) A horizon - dark layer rich in humus, organic acids 3) E horizon - zone of leaching; fine-grained components removed by percolating water 4) B horizon - zone of accumulation; clays and iron oxides leached down from above 5) C horizon - partially weathered bedrock -An average soil: 45% rock and mineral fragments, including clay -5% decomposed organic matter -Humus -50% pore space -the rock and mineral fragments in a soil provide an anchoring place for the roots of plants -The clay minerals: attract water molecules and plant-nutrient ions which loosely held and available for uptake by plant roots -The humus: releases weak acids, contributes to the chemical weathering of soil, produces plant nutrients, and increases the water retention ability of the soil -the pore spaces: essential component of a fertile soil, water and air circulate through the pore spaces which carry dissolved nutrients and carbon dioxide, it is necessary for the growth of plantsw
soils and climate
-Soils are classified into 12 Orders -These orders are distinguished by the characteristics of the horizons present -Soil thickness and composition are greatly affected by climate -Wet climates: -More chemical weathering and thicker soils -Soils in moderately wet climates tend to have significant clay -rich layers -Concentrations of clay minerals, silica, and iron compounds in the B horizon -May be solid enough to form a hardpan -Hardpan: General term for hard layer of earth material; think rock layer in soil -Arid climates: -Less chemical weathering and thinner soils -Subsurface evaporation leads to the build-up of salts -Calcite-rich accumulation zones may form, cementing soil together into a hardpan -Extremely wet climates (e.g., tropical rainforest): -Highly leached and unproductive soils (Laterites) -Most nutrients come from thick O/A horizons -Some Laterites are composed of ore-grade aluminum oxides -AL 2O3 * NH2O -The intense leeching of the soil takes everything else and leaves just the Aluminum oxide behind
How does an acid disrupt a mineral?
-The Hydrogen ions given off by acids disrupts the crystalline arrangement of atoms within some minerals -The H+ can replace other ions of similar size and charge in the crystal lattice -For instance Na+, K+, Ca++ -The substitution changes the original mineral into a different mineral
how does oxidation work?
-The iron in ferromagnesian minerals must be freed from the silicate structure: Olivine, Pyroxenes, Amphiboles, and Biotite -Once the iron is freed from the crystal it can combine with Oxygen to create an Iron Oxide -4Fe+3 + 3O2 -> 2Fe2O3 -Iron + Oxygen -> Iron oxide -This is the mineral Hematite -If water is present the oxide forms the mineral limonite, a hydrated iron oxide -Fe2O3 * NH2O -The N in the equation means that the structure can have a variable amount of water -Soil and sedimentary rocks are often stained red, brown or yellow with iron oxides
Using the rock cycle, explain how sediment is formed and may become a sedimentary rock.
-The key processes of the rock cycle are crystallization, erosion and sedimentation, and metamorphism -Weathering wears rocks at the Earth's surface down into smaller pieces. The small fragments are called sediments. Running water, ice, and gravity all transport these sediments from one place to another by erosion. During sedimentation, the sediments are laid down or deposited. In order to form a sedimentary rock, the accumulated sediment must become compacted and cemented together.
What is preservation?
-The maintenance of resources in their present condition -Sediment must be preserved -Typically burial under additional sediments -Not all sediments are preserved as sedimentary layers -Land sediments are easily eroded; Not commonly preserved. -Sediments on the sea floor easier to preserve -In general, sediments are most likely to be preserved by: Deposited in a subsiding (sinking) basin or covered or buried by later sediments
What is cementation?
-The process in which dissolved minerals crystallize and glue particles of sediment together -Water moves through remaining pore space -Precipitation of minerals as a cement -Calcite: Dissolved calcium and bicarbonate ions are common in surface and underground waters -Silica, Iron oxides, Clays -Ca2+ + 2HCO3- -> CaCo3 + H2O + CO2 -Ca2+ + 2HCO3- = dissolved ions -CaCo3 = calcite
chemical weathering continued
-The processes that transform rocks and minerals exposed to water and air into new chemical products (minerals) -Minerals change gradually at the surface until they come into equilibrium, or balance, with the surrounding conditions -There are two types: 1) oxidation -Irons Rusts -Fires Burn 2) Acid Dissolution
mechanical weathering
-The type of weathering in which rock is physically broken into smaller pieces -Pressure release: Removal of overlying rock allowing expansion and fracturing of the rock -Pressure release: Over time the overlaying rock can be removed by weathering processes -Pressure release: When the pluton reaches the surface and the overburden is gone, the rock is no longer compressed and is free to expand -Pressure release: The expansion causes fractures in the rock -Granites: large plutonic bodies that form deep underground -The overlaying weight of rock is called the overburden -The overburden compresses the granite -Plant growth: Growing roots widen fractures -Burrowing animals: Open up channels for water and air
what is frost wedging and how does it work?
-Water percolates into a crack in the rock -Water expands when it freezes causing the rock to split along the crack -Most effective in areas with frequent Freeze / Thaw cycles (Daily): Mountain Ranges -Frost wedging is the process by which water seeps into cracks in a rock, expands on freezing, and thus enlarges the cracks -The effectiveness of frost wedging is related to the frequency of freezing and thawing
Compare and contrast the weathering rate and weathering products for Ca-rich plagioclase in the following localities: -Central Pennsylvania with 40 inches of rain per year -Death Valley with 2 inches of rain per year -An Alaskan mountaintop where water is frozen year-round.
-Weathering is a process of alteration of chemical and physical properties of rock at the surface or near it -Rocks undergo mechanical weathering in the form of physical disintegration as well as chemical weathering through decomposition -Weathering is carried out by the action of air, water, and microorganisms -The process of weathering generates sand, mud, and soil -It is a relatively slow and time consuming process -The rate of weathering is the pace at which the rock is converted into sediments -It depends on various factors such as duration of atmospheric exposure, rock composition, and the effect of climate -The products formed as a result mainly depend on the constituents that comprise the rock -Plagioclase is a feldspar type of rock, weathering of calcium rich plagioclase results in the conversion of original mineral to an entirely different type of mineral. It generally forms clay minerals by the action of hydrogen ion present in carbonic acid -A. Central Pennsylvania with 40 inches of rain per year: -Area experiences moderate amount of rainfall -The rainwater percolates and travels through the soil, gathering upper part of the soil and carbon dioxide from the atmosphere -The rate of weathering is usually normal -The product formed is usually clay mineral, and oxide of aluminum and silica -The action of hydrogen ions releases the potassium ions, which along with bicarbonate ions are carried by ground water -The calcium and carbonate ions may combine to form calcium carbonate -Some amount of silica that cannot fit into the clay mineral is also carried as run off -B. Death Valley with two inches of rain per year: -Rainfall in the area is extremely less -The rare of weathering is thus less as compared to Pennsylvania -the main product formed as a result of weathering is clay mineral and free ions along with silica C. An Alaskan Mountain top where water is frozen year-round: -Weathering in these parts is greatly influenced by frost action -The process of weathering thus proceeds at a very low rate -The most common action of frost observed is frost wedging, where action of freezing water causes the rock to pry apart -The main product formed is clay mineral as well as ions of hydrogen, bicarbonate, and silica
what is weathering?
-Weathering is the group of destructive processes that change physical and chemical character of rocks at or near Earth's surface -weathering makes the planet habitable -weathering affects the composition of the atmosphere -weathering produces soils that are crucial for agriculture
what is pressure release?
-When pressure on the surface rock is released causing the rock to expand -The process by which the release of an over pressure allows a rock to expand and crack. Sometimes called unloading.
why is weathering important to life on Earth?
-Without weathering, geologic features would build up but would be less likely to break down -Weathering is the process that changes solid rock into sediments -With weathering, rock is disintegrated -Forces like wind and water move the rock pieces -They mix with matter like sand to become sediment -Weathering and erosion help shape Earth's surface
what is thermal cycling?
-a cycle consisting of three steps carried out at different temperatures -Large temperature changes fracture rocks by repeated expansion and contraction
how does rock weather?
-igneous minerals crystallize at high temperature and sometimes high pressure -in general these materials are not in equilibrium with surface conditions -The minerals will change to be more stable in the new environment: Notion of lowest energy state
What are sedimentary rocks?
-formed by the deposition of material at the Earth's surface and within bodies of water -Formed from: -eroded mineral grains = detrital Sedimentary rocks -minerals precipitated from low-temperature solution = chemical Sedimentary rocks -consolidation of the organic remains of plants = organic Sedimentary rocks
What is the chemical equation of the solution of Carbon Dioxide in water to form Acid?
-forms carbonic acid, -Water and Carbon Dioxide Gas form Carbonic Acid H2CO3
what is transportation?
-from sediment to rock -Movement of sediment away from its source, typically by water, wind, or ice (includes Gravity) -During transportation, sediment continues to weather and change in character in proportion to the distance the sediment is moved -Measures of transportation distances: -Rounding, Sorting, Sediment Size -Intuitions on transportation distances are sometimes more of an art than a science
What is hematite?
-iron ore -Iron Oxide, FE2O
what are the two different uses of the word clay?
1) Clay-sized particle -Can be composed of any mineral less than 1/256 mm -Quartz 2) A clay mineral -silicate minerals with a sheet-silicate structure
Name at least three natural sources of acid in solution. Which one is most important for chemical weathering?
1) sulfuric, hydrofluoric acids emitted by volcanic eruptions 2) Mine waste as sulfur containing minerals oxidize 3) The most abundant acid on the Earth is formed when Carbon Dioxide Gas (CO2) dissolves in water
Explain what happens chemically when calcite dissolves. Show the reaction in a chemical equation
-the carbon dioxide & water combine to form carbonic acid, which dissociated into the hydrogen ion and the bicarbonate ion -CaCO3 + H+ + HCO3 - ->/-< Ca++ + 2HCO3-
what are some effects of weathering?
1) Destruction of building materials -Building blocks of limestone or marble show solution effects of chemical weathering in a surprisingly short time 2) Discoloration of surface outcrops 3) Production of soil 4) Impacts the atmosphere -Removes carbon dioxide 5) Creates interesting and unusual rock shapes -Spheroidal weathering -Differential weathering
chemical weathering: actual weather and climate
-the inorganic carbon cycle helps regulate Earth's ClimateCO2 is a green house gas that impacts temperature of the Atmosphere -Warm Earth's climate: -chemical weathering increases -Formation of limestone increases Increase in CO2 pulled from the atmosphere -cools the climate -Cool Earth's climate: -chemical weathering decreases -limestone formation decreases -CO2 accumulates in the atmosphere -volcanism -The Earth Warms up
what is exfoliation?
-the peeling off of curved layers of rock -The process of shedding layers (spalling) is called exfoliation -Exfoliation Domes are large landforms with this property like Half Dome in Yosemite
what is rounding?
-the process involving abrasion of sedimentary particles during transport so that their sharp edges and corners are smoothed off -the Grinding away of sharp edges and corners of rock fragments during transportation -Rules of thumb: -The more angular the grain the shorter the distance of transportation -the more rounded the grain the longer the distance of transportation -Big fragments abrade faster than small ones -Quartz is very tough and resists abrasion -They round according to distance of travel and resistance of material -three types: angular, sub-rounded, and well rounded
what is erosion?
-the process of eroding or being eroded by wind, water, or other natural agents -erosion is physical picking up of rock particles by water, ice, or wind
what are the three types of environment?
1) Environment of Deposition - location where sediment came to rest
Chapter 5: Weathering and Soils
Chapter 5: Weathering and Soils
what is sorting?
-the process whereby sedimentary particles are selected by size during transport -deposits are poorly sorted to well sorted, depending on the range of particle sizes present -Well-sorted sediments: particles are about the same size -Poorly-sorted sediments: particle sizes vary -The larger the grain the easier it is for it to stop moving -Large grains can be near where they formed -The better the sort in terms of size, the longer the transport time or the more specific the transport mechanism -The better the sort in terms of composition the longer the transport time or the more specific the transport mechanism
types of weathering
-the two types of weathering are mechanical weathering and chemical weathering: -Mechanical weathering is physical disintegration: which is processes that break rock into smaller pieces -Six types of Mechanical Weathering: 1) Frost action -Mechanical effect of freezing water on rocks. 2) Pressure-release fracturing 3) Plant growth 4) Burrowing animals 5) Salt wedging 6) Thermal cycling
what is transportation?
-transportation is the movement of eroded particles by water, ice, or wind
what is the inorganic carbon cycle?
1) Carbon dioxide dissolves in water to form carbonic acid in the atmosphere;Carbonic Acid H2CO32 2) Carbonic acid reacts with sediment and rocks during chemical weathering, releasing calcium ions and bicarbonate ions (HCO3−), which are carried by rivers into the sea 3) The precipitation of CaCO3 mineral in the oceans forms layers of limestone rock 4) Deep burial of limestone leads to metamorphism, which causes silica and calcite to form calcium silicate minerals and carbon dioxide -The CO2 remains trapped in Earth's interior until it is released during volcanic eruptions
Chapter 6: Sediment and Sedimentary Rocks
Chapter 6: Sediment and Sedimentary Rocks
what is weathering?
All of the processes that work to change rock at the surface of the earth
what is soil?
Any kind of unconsolidated earth material, a layer of weathered unconsolidated material on top of bedrock
What leeched materials can be found in the B Horizon?
B horizon - zone of accumulation; clays and iron oxides leached down from above
What is the difference between the concentration of CO2 in the air and the soil and why?
CO2 exists in the Earth's Atmosphere at a concentration of .03%, while CO2 is concentrated to 10% in the pore spaces of soils -Water percolating through soils becomes more acidic -The extra CO2 comes from the decomposition of plants and animals and from respiration in soil
what are laterites?
Highly leeched tropical soils
Sketch and describe the lithification of sand to sandstone.
Lithification, complex process whereby freshly deposited loose grains of sediment are converted into rock. Lithification may occur at the time a sediment is deposited or later. Cementation is one of the main processes involved, particularly for sandstones and conglomerates. -the sand becomes sandstone when it is compacted by pressure of overlying deposits and cemented by the precipitation of minerals within the pore spaces between sand grains.
What are the two main gaseous components of the Earth's Atmosphere?
Nitrogen and Oxygen
what is erosion?
Picking up or removal of rock particles by an agent such as running water or glaciers
Why are most beds of sedimentary rock formed horizontally?
Principle of Original Horizontality, states that sediments are deposited in flat, horizontal layers. Sedimentary particles settling under the influence of gravity in a body of water will deposit horizontal layer of sediment.
How does the Earth manufacture granites in a conceptual approach?
Realization that some technical terms are equivalents -Mafic (Maps to) Basalt -Felsic (Maps to) Granite
Rocks exposed at Earth's surface are constantly by what factors?
Rocks exposed at Earth's surface are constantly changed by water, air, temperature variations, and other factors
Describe what clues a geologist uses to interpret where and how a sedimentary rock formed and why this is important.
Sedimentary rocks tell us about past environments at Earth's surface. Because of this, they are the primary story-tellers of past climate, life, and major events at Earth's surface. Each type of environment has particular processes that occur in it that cause a particular type of sediment to be deposited there
Which would weather faster in a humid climate, a quartz sandstone or an arkose? Explain your answer.
Since quartz is resistant to chemical weathering, it tends to concentrate in sand deposits as the less resistant minerals such as feldspar are weathered away. ... So arkose would weather faster in a humid climate than the quartz sandstone.
How does an acid disrupt a mineral?
The Hydrogen ions given off by acids disrupts the crystalline arrangement of atoms within some minerals
How does mechanical weathering speed up Chemical weathering?
The mechanical weathering of a rock increases the available rock surface for chemical weathering by bringing more of the rock surface into contact with water and air
what is salt wedging?
The pressure of growing salt crystals fractures the rock
what is frost wedging?
The process by which freezing water pries a rock apart
The rate of soil erosion is influenced by several factors:
The rate of soil erosion is influenced by several factors: 1) soil characteristics -Coarse-grained soils with organic content -Most resistant to erosion -Larger pore spaces -Can absorb more water -Less runoff leads to less soil erosion -Rainfall: gentle rain over a long period of time -less splash erosion than a short, heavy rainstorm -More water can infiltrate the soil -less likelihood of sheet erosion occurring 2) Climate 3) Slope -Gentle Slope: Water moves more slowly -Water more likely to percolate down into the soil -Steeper Slope: Faster-moving water -Water does not infiltrate -Water has a greater ability to dislodge and transport soil particles down from the slope 4) vegetation -Plant roots form networks O and A horizons that bind soil particles -The leaf canopy protects the soil from the impact of raindrops, lowering the risk of splash erosion -Thick vegetation can reduce the wind velocity near the ground surface, preventing the loss of soil due to wind erosion -Human activity in the last two centuries has done much to remove the natural vegetation cover on the world's land surface -Large-scale farming operations, grazing, logging, mining, and construction have disrupted prairies, forests, and other natural environments, such as rain forests, leaving the underlying soils vulnerable to the effects of wind and water
How do clay minerals contribute nutrients to a plant?
The root releases an organic acid (H+). The H+ can replace one of the ions on the clay mineral, releasing the ion to be absorbed by the plant
what is exfoliation?
The spalling of concentric layers off of a granite
how does the earth manufacture granites in a chemical approach?
bucket of ions -> chemical bonds (ionic and covalent) -> silicon oxygen tedtrahedron -> silicate structures -> granite -granite starts off as a bunch of ions that then convert and bond together to create chemical bonds, then form into silicon-oxygen tetrahedrons which are silicon atoms bonded with oxygen -these tetrahedrons are then converted into silicate structures, which are basic structural units of every single silicate mineral -we start off with multiple ions which then go through Bowen's Reaction Series in addition to geologic time, which creates granite -Bowen's Reaction Series, theorized by petrologist Norman L. Bowen, describes the process of the crystallization of silicate minerals from magma -It explains the temperature at which minerals crystallize when introduced to a new environment, whether that be cooling, heating, or melting -in the case of forming granite, mantle rock undergoes the process of melting to form magma, which then moves its way up through our Earth, and with the process of geologic time, solidifies deep in the Earth's surface, creating granite -There are many processes that allow granite to be created, one being the movement of plate tectonics -The Earth's surface is constantly shifting and changing due to the Earth's plates, which allows this magma to move its way up through our Earth
how does the earth manufacture granites in a physical approach?
bucket of ions/molten rock -> Plate Tectonic Regime Oceanic Continental Subduction zone -> silicate structures -> bowens reaction series -> magmatic underplating + geologic time = granite
Which of the following are not weathering processes a) Plant growth can break up rocks b) Burrowing animals speed up chemical weathering by enlarging passages for water and air c) cementation d) Forest fires can crack rock
c) cementation
Which of the following processes does not mechanically weather rock? a) Pressure release b) Spalling c) subduction d) Frost wedging
c) subduction
Which is a characteristic of soil horizons? A) They can be distinguished from one another by appearance and chemical composition b) Boundaries between soil horizons are usually transitional rather than sharp c) They are classified by letters d) all of the preceding
d) all of the preceding
Physical disintegration of rock into smaller pieces is called: a) chemical weathering b) transportation c) deposition d) mechanical weathering
d) mechanical weathering
Which is not a type of mechanical weathering? A) Frost wedging b) frost heaving c) pressure release d) oxidation
d) oxidation
What happens to many of the rock-forming minerals due to weathering? a) Feldspar converts to Clay minerals b) The ferromagnesian minerals convert to clay minerals c) Muscovite Mica converts to clay minerals d) Quartz is resistive and doesn't change e) All of the above
e) all of the above
Which of these factors contribute to the rate of soil formation? a) Rainfall b) temperature c) slope d) type of bedrock e) all of the preceding
e) all of the preceding
how does the Earth convert sediment into sandstone?
granite -> feldspar and quartz, (weathered granite) -> transportation rounding sorting -> quartz sand -> depositional environments (river, beach, sand dune, alluvial fan) -> preservation -> lithification/compaction = sandstone OR granite -> feldspar and quartz (weathered granite) -> arkose sandstone, feldspar and quartz -> local trnasportation only gravity -> depositional environments (river, beach, sand dune, alluvial fan) -> preservation -> lithification/compaction = sandstone
How does the Earth convert Granite into the raw materials for Soils?
granite -> weather it (chemical weathering changes the mineralogy, with carbonic acid H2CO3. mechanical weathering is physical disintegration. frost heave is pressure release) -> erode it/transport it (agents of ice, water or wind) -> soil
