Exam II review This is only a partial review in Power Point format. Please use the on- line Exam II review pages.
Dec 31, 2015
Exam II review
This is only a partial review in Power Point format.
Please use the on-line Exam II review pages.
II. Mechanical Weathering: breaks a mineral or rock into smaller pieces without changing their chemical makeup
Creates more surface area.
III. Chemical Weathering: Alters the composition of rocks and minerals, usually through chemical reactions involving water
Water is the most important factor controlling the rate of chemical weathering!
IV. Factors affecting weathering
A. Climate—water drives all chemical weathering
1. wet more chemical weathering2. hot (dry) more mechanical
weathering (heat helps break bonds)
B. Organisms—burrow and churn up the surface exposing unweathered minerals to the atmosphere
C. Time: more time = more weathering
D. Composition of minerals: some minerals more resistant to weathering than others
Weathering
B. Sediment Transport and Deposition
1.DetritalGenerally move from high ground to low ground by the pull of gravity (assisted by water, wind, or glacial ice)
Deposited when the carrying material loses it’s capacity to carry the sediment
2. Chemicalions remain in solution until there’s a change in the water’s temperature, pressure, or chemical composition and then the ions precipitate
Sediments
C. Sediment Texture: Detrital sediment are based on grain size; chemical sediment are classified based on composition.
1. Grain sizeGrain composition - some
minerals are stronger than others.
a. Distance - smaller grains travel longer distances.
b. Energy of the transportation medium - high energy environment moves larger grains.
Sediments
2. Shape: round vs angular grains.
3. SortingRelated to the carrying
capacity of the transport medium
II. Turning sediments into rock
Eventually accumulated sediment turns into rock
A. Diagenesis: All the chemical, physical, and biological changes that take place after sediments are deposited.
Burial
Alteration by groundwater
Lithification: occurs within the upper few kilometers of the crust at temperatures < 200C (400F)
Sediments and DiagenesisII. Turning sediments into rock
B. Lithification: the process by which unconsolidated sediments are transformed into solid sedimentary rocks (part of diagensis)
1. Compaction: pressure (from overlying sediment) reduces the volume of sediment—
Compaction forces out air and water and packs grains together.
2. Cementation
Cements grains together - ions dissolved in water by chemical weathering may be deposited by groundwater circulating through the sediment.
III. Types of Sedimentary rocks
A. Detrital Sedimentary rocks: made of sediment that is transported as solid particles
Particle size is the primary basis for distinguishing various detrital sedimentary rocks.
Sediments and Diagenesis
III. Types of Sedimentary rocks
A. Detrital Sedimentary rocks: made of sediment that is transported as solid particles
1. Shale (mudstone, siltstone)
>50% of all sedimentary rocks:
Need quiet water depositional setting
III. Types of Sedimentary rocks
A. Detrital Sedimentary rocks
2. Sandstone: sand sized particles (1/16 – 2 millimeters)
~25% of all sedimentary rocks
Shape and sorting important for determining depositional environment.
Sorting: well sorted = wind & wavespoorly sorted = streams
Shape: well rounded = water or wind transported over long distances
Angular = glacier or debris flow
III. Types of Sedimentary rocks
A.Detrital Sedimentary rocks
3. Conglomerate and Breccia—
Composed of gravels (pea to large boulders, >2 mm)
Conglomerate: composed of rounded grains of difference sizes.
Formed in energetic mountain streams or coasts (storm deposits)
Breccia: composed of angular pieces.
Did not travel far: glaciers, landslides
Sediments and Diagenesis
Sedimentary Rocks
III. Types of Sedimentary Rocks
B. Chemical Sedimentary Rocks
Interlocking crystals forming from precipitation
Either inorganic or organic from organisms secret CaCO3
minerals
1. Limestone (inorganic)(10% of all sedimentary rocks)
composted of calcite, CaCO3
2. Hot spring deposits
B. Chemical Sedimentary Rocks
Organic:
Marine organisms extract the ions from the water to form their shells
When they die, the shells accumulate on the bottom of the ocean
Compaction, recrystallization, & cementation
Microscopic algaeForaminifera (forams)Microscopic animals
Sedimentary Rocks
2. Chert (jasper, flint, agate)—SiO2
Inorganic: can precipitate from silica-rich water
Organic: some marine organisms make their shells of silica
Radiolaria: single celled animalsDiatomsSingle-celled plantsMarine sponges & larger animals
3. Evaportites: form when ion-rich water evaporates and leaves minerals behind.
Salt - NaCl Gypsum - CaSO4 + 2 H2O Sylvite KCl
III. Types of Sedimentary Rocks
B. Chemical Sedimentary Rocks
4. Coal: made of terrestrial organic matter, leaves, bark, wood, plant matter
Dead organic matter accumulates in oxygen poor environments (swamps)
III. Types of Sedimentary rocks
IV. Sedimentary Structures in detrital sedimentary rocks
A. Bedding (stratification):
1. Graded Beds: within a layer, the sediments continuously change size
Produced by rapid deposition by water
Heaviest grains fall out first
2. Cross-bedding: sedimentary layers deposited at an angle
Forms when material dropped from a moving current
Sand dunes or ocean dunes or river dunes
Change in deposition direction Changes the direction of the beds
Represents lee side of dunes: records direction of flow
A. Bedding (stratification):
B. Ripple Marks
Ripples at top of deposit - records direction of flow
C. Mudcracks
Wet fine-grained sediment exposed to the air, it dries out and shrinks.
Indicates wet environment that dried up.
B. Metamorphism
Heat, pressure, and chemical reactions deep within the Earth alter the mineral content and/or structure of preexisting rock without melting it
Metamorphism and Metamorphic Rocks I. Factors controlling metamorphism
A. Heat: most important factor this drives chemical reactions
1. Bury Rocks2. Near heat sources (plutons, dikes,
etc…
B. PressureConfining versus directed pressure
C. Circulating FluidsIncreases potential for metamorphic reactions
I. Types of Metamorphism: heat, pressure, and fluids interact
differently in different geological settings to produce different metamorphic rocks
A. Contact MetamorphismB. Regional MetamorphismC. Subduction zoneD. Hydrothermal
Metamorphic rocksSlate, phyllite, schist, and
gneissMetamorphism and plate tectonics
C. Radioactive decay
1. Decay rates of radioactive atoms are constant
2. Half Life: time it takes for half the atoms of the parent isotope to decay, ranges from tens of billions of years to thousandths of a second.
Percentage of parent atoms that decay in each half life is the same (50%)
The actual number of atoms that decay with each passing half-life continually decreases
Increase in daughter = decrease in parent
I. Principles of Numerical DatingD. Dating minerals in rocks
1. Igneous rocks – the best! Dates when the minerals formed
2. Metamorphic: during metamorphism ions can migrate, so dating tells us when metamorphism ended.
3. Sedimentary rocks: more errors because it dates the age of the individual pieces, gives maximum age
II. Types of Isotope DatingUsing minerals in rocks
1. Uranium-thorium-lead (granite)
2. Rubidium-Strontiumplagioclase feldspar (igneous
and metamorphic rocks)
3. Potassium-Argonlots of minerals (plagioclase,
biotite, muscovite, amphibole)
I. Principles of Numerical DatingII. Types of Isotope DatingOrganic material
4. Carbon 14 (radiocarbon dating)
14C 14N5730 year ½ life
Useful between 100 and about 50,000 years old
Can date things that contain organic carbon (Used to be living): bones, shells, wood, charcoal, plants, paper, cloth, pollen, seeds)
III. Other Dating Techniques: Besides minerals
A. Dendrochronology (Tree-ring dating)
Trees grow rings for each yearWe can count rings to get ages of trees
Pronounced changes in climate (i.e. drought) causes distinct patterns that can then be correlated between trees
Useful for dating: landslides, avalanches, or mudflows or wooden artifacts
I. Principles of Numerical Dating B. Varve chronology (lake deposits)
Lakes produce annual layers of sediment similar to tree rings
Spring & summer high sediment input thick, coarse, light-colored layers
Winter little to no sediment, dark, thin layers
Useful for dating: landslides into the lake
C. Lichenometry
For similar rocks and similar climate: the larger the lichen colony, the longer the time since the growth surface was exposed
Develop a growth curve based on measuring lichen of known age (tombstones, buildings) then extrapolate/interpolate to age of unknown rock
Useful for dating: glacial deposits, rockfalls, mudflows (expose new rock to surface)
III. Other Dating Techniques: Besides minerals
C. Lichenometry (dating lichen colonies)
Lichen—simple plant-like colonies the grow on exposed rock
For similar rocks and similar climate: the larger the lichen colony, the longer the time since the growth surface was exposed
Develop a growth curve based on measuring lichen of known age (tombstones, buildings) then extrapolate/interpolate to age of unknown rock
Useful for dating: glacial deposits, rockfalls, mudflows (expose new rock to surface)
I. Principles of Relative Dating
Faulting Hanging wall and foot wall
definitions Normal fault Reverse fault Strike-slip fault
Folds Fold Geometry Fold type
I. Deformation
Stress Strain Types of differential stressoCompressional stressoTensional stressoShear stresses
Types of deformation Elastic Brittle Plastic (ductile)
Deformation styles
Factors that control deformation Heat Pressure Time dependence Rock composition
Plate tectonics, differential stress
II. Faulting and folding