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!
Weathering
IV. Factors affecting weathering
A. Climate—water drives all chemical
weathering
1. wet  more chemical weathering
2. 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
Sediments
B. Sediment Transport and
Deposition
1.Detrital
Generally 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. Chemical
ions 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.
2. Shape: round vs angular
grains.
1. Grain size
Grain composition - some
minerals are stronger than
others.
3. Sorting
Related to the carrying
capacity of the transport
medium
a. Distance - smaller grains
travel longer distances.
b. Energy of the
transportation medium high energy environment
moves larger grains.
Sediments and Diagenesis
II. Turning sediments into rock
II. Turning sediments into rock
Eventually accumulated sediment turns
into rock
B. Lithification: the process by
which unconsolidated sediments
are transformed into solid
sedimentary rocks (part of
diagensis)
A. Diagenesis: All the chemical,
physical, and biological changes
that take place after sediments are
deposited.
1. Compaction: pressure (from
overlying sediment) reduces the
volume of sediment—
Burial
Compaction forces out air and water
and packs grains together.
Alteration by groundwater
2. Cementation
Lithification: occurs within the upper
few kilometers of the crust at
temperatures < 200C (400F)
Cements grains together - ions
dissolved in water by chemical
weathering may be deposited by
groundwater circulating through the
sediment.
Sediments and Diagenesis
III. Types of Sedimentary rocks
III. Types of Sedimentary rocks
A. Detrital Sedimentary rocks:
made of sediment that is
transported as solid particles
A. Detrital Sedimentary rocks
Particle size is the primary basis
for distinguishing various detrital
sedimentary rocks.
2. Sandstone: sand sized particles
(1/16 – 2 millimeters)
~25% of all sedimentary rocks
III. Types of Sedimentary rocks
Shape and sorting important for
determining depositional
environment.
A. Detrital Sedimentary rocks:
made of sediment that is
transported as solid particles
Sorting: well sorted = wind & waves
poorly sorted = streams
1. Shale (mudstone, siltstone)
>50% of all sedimentary rocks:
Need quiet water depositional setting
Shape: well rounded = water or wind
transported over long distances
Angular = glacier or debris flow
Sediments and Diagenesis
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
Sedimentary Rocks
III. Types of Sedimentary
Rocks
B. Chemical Sedimentary Rocks
Organic:
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
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 algae
Foraminifera (forams)
Microscopic animals
Sedimentary Rocks
III. Types of Sedimentary Rocks
B. Chemical Sedimentary Rocks
3. Evaportites: form when ionrich water evaporates and
leaves minerals behind.
Salt - NaCl
Gypsum - CaSO4 + 2 H2O
Sylvite KCl
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 animals
Diatoms
Single-celled plants
Marine sponges & larger animals
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
C. Mudcracks
A. Bedding (stratification):
B. Ripple Marks
Ripples at top of deposit - records
direction of flow
Wet fine-grained sediment exposed
to the air, it dries out and
shrinks.
Indicates wet environment that dried
up.
Metamorphism and Metamorphic Rocks
I. Factors controlling
metamorphism
B. Metamorphism
Heat, pressure, and chemical
reactions deep within the
Earth alter the mineral content
and/or structure of preexisting
rock without melting it
I. Types of Metamorphism:
heat, pressure, and fluids interact
differently in different geological
settings to produce different
metamorphic rocks
A.
B.
C.
D.
Contact Metamorphism
Regional Metamorphism
Subduction zone
Hydrothermal
Metamorphism and plate tectonics
A. Heat: most important factor this
drives chemical reactions
1. Bury Rocks
2. Near heat sources (plutons, dikes,
etc…
B. Pressure
Confining versus directed
pressure
C. Circulating Fluids
Increases potential for
metamorphic reactions
Metamorphic rocks
Slate, phyllite, schist, and
gneiss
I. Principles of Numerical Dating
D. Dating minerals in rocks
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
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
I. Principles of Numerical Dating
II. Types of Isotope Dating
Using minerals in rocks
1. Uranium-thorium-lead
(granite)
2. Rubidium-Strontium
plagioclase feldspar (igneous
and metamorphic rocks)
3. Potassium-Argon
lots of minerals (plagioclase,
biotite, muscovite, amphibole)
II. Types of Isotope Dating
Organic material
4. Carbon 14 (radiocarbon
dating)
14C  14N
5730 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)
I.Principles of Numerical Dating B. Varve chronology (lake deposits)
III. Other Dating Techniques:
Besides minerals
Lakes produce annual layers of sediment similar
to tree rings
A. Dendrochronology (Tree-ring
dating)
Spring & summer  high sediment input  thick,
coarse, light-colored layers
Trees grow rings for each year
We 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
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)
I. Principles of Relative Dating
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. Deformation
 Stress
 Strain
 Types of differential stress
o Compressional stress
o Tensional stress
o Shear 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
Faulting
 Hanging wall and foot wall
definitions
 Normal fault
 Reverse fault
 Strike-slip fault
Folds
 Fold Geometry
 Fold type