Studied by 8 people
What is the distinction between weathering and erosion?
Weathering is the breakdown of rocks while erosion is the removal from its location
what are the two types of weathering?
Physical weathering and chemical weathering
How do mechanical weathering and chemical weathering enhance eachother?
mechanical weathering breaks down rocks into smaller pieces with greater surface area.
clues left by weathering
differential weathering
rounding
weathered surface on a rock
mechanical weathering
pressure release
frost wedging
plant growth
animal burrowing
thermal cycles
salt growth
why do granite outcrops form a dome shape when exposed to the surface?
exfoliation
atoms
smallest assemblies of matter
electrons
positively charged particles
protons
negatively charged particles
ion
an atom that has an excess or deficiency of electrons in the outer shell relative to number of protons in the neucleus
cations
positively charged ions
anions
negatively charged ions
chemical weathering agents
oxygen
acids
strong acids
give off large quantities of hydrogen ions (H+)
weak acids
give off low quantities of hydrogen ions (H+)
Olivine
With water→limonite
without water→hematite
feldspar
kaolinite (clay mineral)
calcite
ions in solution
in what part does chemical weathering take place?
Fission a nuclear reaction in which an atomic nucleus
sediment
an accumulation of loose grains
cementation
the phase of lithification in which cement, consisting of minerals that precipitate from ground water, partially or completely fills the spaces between clasts and attaches each grain to its neighbor
lithification
the transformation of loose sediment into solid rock through compaction and cementation
detrital rocks
consisting of cemented-together detritus derived from the weathering of pre-existing rock: produced from eroded mineral grains
bioclastic rocks
produced directly by accumulation of organic remains of plants or animals
chemical rocks
produced by precipitation of dissolved ions in water
sediment sizes of detrital sediments
gravel-sized grains
sand-sized grains
silt-sized grains
clay-sized grains
compaction
a shift to a tighter packing of the grains due to increasing overburden
crystallization
precipitation of minerals from solution
what happens to sediment when it is transported?
rounding: grains display more rounding further from the source
sorting: sediment grains are separated according to size and shape. sediment sizes decrease with increased transport distance
why are sedimentary structures important to recognize?
what are rock contacts?
where two different types of rock touch each other
metamorphic textures
slaty foliation → metamorphism
schistose foliation → more heat and/or pressure
gneissic foliation → temperature change
regional metamorphism
high pressure
differential stress
results in foliated texture
occur in wide temperature range
hydrothermal metamorphism
precipitated from or altered by hot water
metasomatism: water adds new atoms to the rock
partial melting metamorphism
produces migmatites: exhibit both intrusive igneous and foliated metamorphic textures
shock metamorphism
produced by rapid application of extreme pressure
contact metamorphism
due to proximity to or contact with an igneous intrusion
prograde metamorphism
a metamorphic rock re-crystallizes into a higher-grade metamorphic rock
shale→slate→phyllite→schist→gneiss→migmatite→granite
what is a parent rock?
original rock before metamorphism
radioactivity
radiometric dating (isotopic dating)
determining the absolute age of an igneous rock through its radioactive elements
isotopes
an element with the same number of protons but different number of neutrons
same atomic number, different atomic mass
radioactive decay
the spontaneous nuclear loss or gain of protons or neutrons at a constant and measurable rate
parent isotope
the original isotope before radioactive decay
daughter isotope
the product of radioactive decay
half-life
the time required for half of the parent isotopes to decay into daughter isotopes
stable isotopes
unstable isotopes
alpha decay
daughter nucleus has atomic number 2 less and mass number 4 less than parent nucleus
beta decay
daughter nucleus has atomic number 1 higher than parent nucleus. no change in mass number
electron capture
daughter nucleus has atomic number 1 lower than parent nucleus. no change in mass number
why is it a reliable time piece for age dating igneous rocks?
it is consistent
closure temperature
the temperature of an igneous melt at which it becomes a closed system
closed system
melt is sealed off so neither parent or daughter isotopes can leave
different isotopic pair
has different closure temperatures
what isotope is used for radiocarbon dating?
Carbon-14
how long is Carbon-14’s half-life?
5,730 years
about how long is carbon dating accurate for?
40,000 years
what is carbon dating more useful for than geology?
paleontology
disconformity
an unconformity between parallel layers of sedimentary rocks which represents a period of erosion or non-deposition
nonconformity
the contact surface between younger sedimentary beds and eroded older intrusive igneous or metamorphic rocks
Angular unconformity
contact between rock layers where the lower, underlying rocks are tilted and the younger, overlying rocks are flat
Law of original horizontality
beds that are deposited in deep, calm water formed horizontal or near horizontal layers
Law of superposition
in a sequence of undisturbed beds, the oldest is at the bottom and the the beds get progressively younger and upward
Law of lateral continuity
sedimentary or volcanic layers extend laterally until it tapers out or hits an obstruction
Law of inclusion
any clast that has become included into another rock must be older than the rock into which it has been incorporated
Law of cross-cutting
any geologic feature that cuts across another geologic feature must be younger than that which it cuts through
conformable sequence
sequence of sedimentary rock with complete record of depositional history
unconformities
erosional contact between rock layers that represent a gap in geologic time (lost time)
Index fossil
a fossil used to date a geologic structure
index fossil requirements
short geologic timespan
broad geographic range
sedimentary structures
features found within sedimentary rocks that form during or after deposition but before lithification
deformational structures
features that result from the deformation of the earth’s crust after lithification
compressional stress
forces push the rock together from opposite directions
tensional stress
forces pulling away from each other in opposite directions
shear stress
stresses act parallel to a plane
elastic phase of strain
deformed material that recovers its original shape after stress is reduced or removed
ductile phase of strain
material will bend while under stress but will NOT return to its original shape after stress is removed
brittle phase of strain
material fractures at stresses higher than the strength of the material
Tilted sedimentary bed (strike measurement)
a line formed by the intersection of an inclined bedding plane with a horizontal plane perpendicular to the dip direction
angle: how many degrees off due north
direction: what direction off of due north
Tilted sedimentary bed (dip measurement)
angle that a bedding plane dips below the earth’s surface
angle: number of degrees
direction: compass direction the bed dips
anticline fold
folds shaped like an arch
oldest rocks in center of the fold getting progressively younger toward the edge
bed dips away from hinge line
syncline fold
fold shaped like a trough
youngest rock are in the core of the fold and get progressively older toward the edge
rock beds dip toward the hinge line
structural domes
folds in which the bed dips away from a center point
oldest rocks are exposed at the core and get progressively younger toward the edge
structural basin
folds in which the beds dip toward a center point
youngest rocks are exposed at the core
Dip-slip faults
movement is parallel to dip direction
normal dip-slip fault
hanging wall down relative to foot wall
tensional stress
reverse dip-slip fault
hanging wall moves up relative to the foot wall
compressional stress
strike-slip fault
movement is parallel to the strike of the fault
horizontal or lateral faults
shear stress
right-lateral strike-slip fault
If the block opposite an observer looking across the fault moves to the right
left-lateral strike-slip fault
If the block opposite an observer looking across the fault moves to the left
oblique-slip fault
dip-slip and strike-slip components of movement
clues of fault movement
fault-zone
slickensides
drag folds
fault-zone
zone of broken rock that was ground up by fault movement
slickenside
polished and striated rock surface
drag folds
minor folds produced by movement
