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