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What is chemical weathering?

What is chemical weathering?

Description

School: University of Louisiana at Lafayette
Department: Geology
Course: Geology and Man
Professor: Jennifer hargrave
Term: Fall 2016
Tags: Geology, exam, rocks, and metamorphic
Cost: 50
Name: Exam 3 Study Guide Chap. 6-8
Description: Study Guide for the Exam on Thursday! Good Luck! Email me at lvl9835@louisiana.edu with any questions.
Uploaded: 11/01/2016
7 Pages 8 Views 16 Unlocks
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Chapter 6:


What is chemical weathering?



chemical weathering –weathering through an alteration of chemical  composition  

differential weathering – takes place at different rates. Different  properties give different weathering rates.  

erosion – removal of weathered materials (by running water, wind,  glaciers, and waves)

exfoliation dome –large round masses exposed by pressure release expansive soil –soil that contains clay that considerably expands  when wet and contracts when dry. Destroys the foundation of  buildings, roadways, and other structures.  

frost action –water freezing and thawing in cracks. The water will  expand when freezing and create bigger cracks in rock. It would likely  occur in an area where temperatures cool/warm repeatedly.  mechanical weathering- mechanically altering the size of materials.  Physical forces break down materials.  


What is exfoliation dome?



If you want to learn more check out pharmacology exam 3

Oxidation- rock will rust due to iron minerals that break down when  exposed to oxygen.  

parent material –the original rock

pressure release –type of mechanical weathering where energy is  released by outward expansion  

regolith –layers of weathering products on Earth’s surface.  Unconsolidated rock (broken down rock), mineral fragments, and soil.  salt crystal growth- type of mechanical weathering where salt  crystals grow and expand in cracks of rock. Happens in salty areas like  desserts and beaches.

soil- organic-bearing regolith that supports plant life.  soil degradation- any process that leads to loss in soils fertility  including: Erosion, contamination with pollutants, and the destruction  of nutrients.  


What is frost action?



We also discuss several other topics like gastrodermis jellyfish

soil horizon-distinct layers of soil that differ in texture, structure,  composition, and color.  

solution- type of chemical weathering where rocks will dissolve in a  liquid substance, like water or acidic solutions.

spheroidal weathering- angular rocks (square/jagged edged) tend to round during chemical weathering  If you want to learn more check out chem 232 sdsu

thermal expansion and contraction weathering- type of  mechanical weathering where extreme heating and cooling cracks  rocks and physically breaks them down into smaller pieces by  expansion and contraction.  

Relationship between chemical and mechanical weathering Weathering is an essential part of the rock cycle. It is responsible for the formation of soil.

Mechanical weathering-pieces keep composition and increase  surface area. The more surface area available the more chemical  weathering can happen.

Greater surface area=greater mechanical weathering.  

Types of mechanical weathering

Frost Action (water freezes in cracks)

Pressure Release (sheets of rock will fall off due to a decrease in  pressure) Thermal Expansion and Contraction (heat of the sun  causes expansion and contraction that eventually breaks rock)  Growth of Salt Crystals (salt forms in cracks and grows which cracks the rock)

Activities of Organisms (animals that burrow or plant roots) All of these forces can work together, and often do.  

Types of chemical weathering We also discuss several other topics like ucr ee

Solution (rocks dissolve) and Oxidation (rocks rust).

Chemical weathering operates on surface particles from the outside  in. It will change the rock’s composition.

What is soil and how does it form?

Soil is organic-bearing regolith that supports plant life, meaning it  houses living organisms. Soil is formed from weathered materials  (broken down rock). It is formed from the top down. If you want to learn more check out ttu advertising

Order and composition of soil horizons

Orange Apes Eat Boston Crème (Donuts.) –Order of horizons (Figure in powerpoint is very helpful)

Factors that control soil formation

- Climate and Soil- climate is the most important factor of soil  formation. Chemical processed operate faster where it is warm and wet (because those factors support chemical weathering).  Tropics will have the thickest amount of soil, where deserts/the  artic will have the least amount.  

- Parent Material- chemically stable rock will have less soil (Like  Quartz)

- Organic Activity- Humus comes from organic activity.  (microorganisms/plant root nutrients)

- Relief/Slope- if there is a slope, soil will be less likely to form  there bc of gravity.  

- Time- More time=more erosion/weathering=more soil Dust Bowl – causes and solutions

The cause was a severe drought a failure to apply dry land farming  methods to prevent wind erosion.

Trees were planted to hold down soil and block the wind. They also  paid farmers $1 an acre to practice better farming techniques. Reading assignment

(It would probably be a good idea to read over your summary of the hw assignment)

Chapter 7

biochemical sedimentary rocks –rocks that are formed from  sediment derived from biological processes. If you want to learn more check out What is the meaning of protein quality?

evaporite –a natural salt or mineral deposit left after the evaporation  of a body of water. (ex. salt or gypsum)

Rounding- the father away a grain goes from its source area, the  rounder it will be

carbonate rock –Calcite, made of calcium carbonate. The larger  grouping of rocks that we refer to Limestone.  

fossil-tangible remains and traces of ancient life. Usually formed only  in sediments and sedimentary rocks. Important for determining  depositional environments.  

sediment- any solid that settles to the bottom of a liquid cementation- glues sediments together

graded bedding –upward decrease in grain size. Smaller grains at  top, bigger grains at the bottom.  

sedimentary facies –bodies of sediment each possessing distinctive  physical, chemical, and biological attributes.  

chemical sedimentary rock- precipitate or are extracted by  organisms

lithification –sediment becomes sedimentary rock by compactation,  cementation, or both.  

sedimentary rock- products of mechanical and chemical weathering. Compaction- the volume of sediment decreases  

marine regression –sea level decreases, the rock facies will be  deeper into the water.  

sedimentary structure- features within sedimentary rocks that  formed at the time of deposition and represent the physical and  biological processes that operated in depositional environments.  cross-bedding –angled with respect to dispositional surface (due to  wind/water)

marine transgression – sea levels rise and the rock facies will move  more towards land with the water.  

sorting –the further away the rock is from the source, the more sorted it will be.  

depositional environment –places where sediments are deposited.  Where places would have certain grain characteristics.  mud crack –sedimentary structures formed as muddy sediment dries  and contracts (common in desert)

strata (beds) –layers of rock

detrital sedimentary rock- rock that derives from weathering of  preexisting rock.  

ripple mark- small scale alternating ridges and troughs. Made by the  current (asymmetric ripple marks) or waves (symmetrical ripple  marks).  

-How are the different types of sedimentary rocks formed?  Detrital: Are made from preexisting rock. They have a clastic  texture (meaning they are composed of clasts). Origins include  weathering, erosion, transportation, deposition, and lithification.  Classified by grain size. Conglomerate/Breccia are the largest.  Chemical and Biochemical: substances derived from solution  by inorganic or biochemical processes. They can have a  crystalized texture (composed of interlocking crystals) or clastic  texture (made up of fragments, like shells glued together.)  Chemical sedimentary rocks form from the precipitation of ions in solution. Classified by composition and texture. Ex. Limestone,  Chert, Rock Salt.  

-What is sediment?  

Sediment is any solid that settles to the bottom of a liquid.  

-Types of sediment and how they form - Rounding, sorting and  info about transportation and deposition (grain characteristics) Types of Sediment: Detrital/Chemical or Biochemical  

Smaller grains, more rounded, and better sorted will mean that  the rock is farther away from its source. (Chart in powerpoint)

Chemical Sedimentary Rocks  

Form from the precipitation of ions in solutions. (Limestone, Rock  Salt)

-Classification of Sedimentary Rocks  

Detrital rocks are classified by grain size. The biggest pieces  (grain size) of rocks you will find will be the closest to where they came from.  

Chemical/Biochemical sedimentary rocks are classified by  composition/texture.  

Sedimentary structures  

Sedimentary Structures are features within sedimentary rocks  that formed at the time of deposition and represent the physical and  biological processes that operated in depositional environments. They

include: Strata beds, Cross-bedding, Graded bedding, Ripple Marks,  and Mud cracks.  

Sedimentary Rocks Represent Past Environments Sedimentary rocks give us clues to the past environments of  Earth. By the sedimentary structures, fossils, and depositional  environments.  

Economic Geology

Many valuable resources are found in sedimentary deposits.  Placer deposits are surface accumulations from streams that are sorted by density. Coal, Water, Petroleum, Banded iron formations ect.  

Chapter 8

aureole –area of metamorphism surrounding an intrusion.  heat –the most common/important agent of metamorphism. Souces of heat include: Lava, Magma, Deep Burial-geothermal gradient metamorphism –the transitions of one rock into another by  temperatures and/or pressures unlike those in which it formed.  contact metamorphism – metamorphism due to contact with or  proximity to an igneous intrusion.  

index mineral- chart in powerpoint (metamorphic grades). You can  use the index mineral to determine how much temperature and  pressure (metamorphism) has occurred. Different metamorphic  minerals form from diff temps and pressure and can be put into an  index to figure out their composition.  

nonfoliated texture –metamorphic rock that lacks foliation.  differential pressure –not the same pressure on all sides. Ex. When a place converges together at a convergent plate boundary.  metamorphic grade –order of grade: Slate (Low grade), Phylite,  Schist, Gneiss (high grade)

protolith –parent rock

fluid activity –hydrothermal activity, chemically active fluids. Small  scale metamorphism caused by a migration of heated fluids through a  rock.  

metamorphic rock –Added heat/pressure to sedimentary rocks. They  are some of the oldest rocks on Earth.  

regional metamorphism –metamorphism that happens over a large  area. (High temperature and pressure associated with mountain  building or at a subduction zone.)  

foliated texture –any planar arrangement of mineral grains or  structural features within a rock (driven by compressional stress)

metamorphic zone- zones of higher grade meta and lower grade  exist.  

Agents of metamorphism  

The agents of metamorphism include: Heat, Pressure (increases  with depth/confining pressure is equal on all sides, differential pressure is not the same pressure on all sides), and Chemically active fluids  (that come from a plume underground, the fluids will be hot).  Causes of metamorphism

Temperature/Pressure (main causes) and Chemically Active Fluids (small scale)  

Protolith and metamorphic rock pairs  

Protolith is another word for parent rock. Mineral make up  determines the degree to which each metamorphic agent will cause  change.

Limestone-Marble is a metamorphic rock pair.  

Metamorphic Textures  

Foliated (Slate, Phylite, Schist, Gneiss) or Nonfoliated (Marble,  Quartzite, Anthracite.)

Texture: size, shape, and arrangement of grains within a rock.  Foliation: any planar arrangement of mineral grains or structural  features within a rock. Grains aligning themselves horizontally.  Can be:

1. Slaty Cleavage- closely spaced planar surfaced along  which rocks split. (Typically the low-grade  

metamorphosis of shale/slate)

2. Schistosity- platy mineral exhibits a planar or layered  structure. (middle-grade metamorphosis). A schist will  be shinier than slate.  

3. Gneissic- distinctive banded appearance. (high-grade  metamorphosis)

Metamorphic rocks can also be nonfoliated.  

Common Metamorphic Rocks  

Foliated: Slate, Phylite, Schist, Gneiss  

Nonfoliated: Marble, Quartzite, Anthracite  

(There is an important chart in powerpoint)

Metamorphic Environments  

 1. Contact or thermal metamorphism –magma or lava alters  country rock around it.  

 2. Hydrothermal metamorphism –water is heated enough to  metamorph the rocks.  

3. Burial metamorphism –rock gets buried under Earth’s surface  at a subduction zone where there is increased heat/pressure.

Can also happen where a basin subsides, causing rock to be  pushed lower into the ground.  

4. Regional Metamorphism –over a large area (subduction zone) Metamorphic Grades

Highest temperature/pressure happens at a meteorite impact.  Most metamorphism happens at subduction zones.  

Temperature beyond Gneiss will melt rock back to igneous. (Multiple diagrams explaining in powerpoint)

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