CHPTR 5/6 Sedimentary Rocks Flashcards
weathering
physical /chemical breakdown of rock at or near the surface of the Earth to produce sediment
mass wasting
transfer of material downhill under influence of gravity
Transport of sediment types
mass wasting
erosion
lithification
sediment turns into sedimentary rock
erosion
movement by water, ice or wind
deposition
sediment reaching a location where it accumulates
detrital sediment
final product of mechanical weather
3 types of mechanical weathering
frost wedging, sheeting, biological activity
how does mechanical weathering affect chemical weathering
mechanical weathering creates more surface area which makes chemical weathering more effective
frost wedging
water enters the cracks of rocks and expands by 9% when it freezes
- this creates pressure and causes the rocks to break
talus
broken rock that has fallen from mountains because of frost wedging
sheeting
mechanical weathering where the rock breaks into sheets - granite at the surface
what causes sheeting
pressure releases
temp. cycle from day to night and winter to summer
biological activity
tree roots, geology students, etc
3 types of chemical weathering
dissolution, oxidation, hydrolosis
end result of chemical weathering
ions dissolved in water - chemical sediment
dissolution
chemical weathering where the water molecules are polar, electrostatic forces allow ions to be removed from solid
thus water dissolves rock
what acid is in acid rain and how is it relevant to chemical weathering
carbonic acid H2CO3 - acid increases the effects of dissolution
oxidation
rusting -
chemical weathering where rocks containing iron minerals breakdown when exposed to the atmosphere - the atoms dissociate
hydrolysis
hydrogen ions react with and replace positioive ions in potassium feldspare.
what does hydrolysis form
clay minerals and potassium and silica in a solution
3D framework > sheet silicate
feldspar > kaolinite
what is kaolinite used for
(mineral) used in China pots
spheroidal weathering
in chemical weathering, sharp corners have more surface area so weathering will occur faster there. This leads to rounded shapes
Bowen’s Reaction series
high to low melting temperature
(first to crystallize)
olivine
pyroxene/calcium feldspar
amphibole
biotite/sodium feldspar
potassium feldspar
muscovite
quartz
Order of mineral’s suseptibilitiy to chemical weathering
Bowen’s reaction series
least resistant to most
olivine
pyroxene/calcium feldspar
amphibole
biotite/sodium feldspar
potassium feldspar
muscovite
quartz
effects of climate on type of weathering
strong chemical - hot and wet
strong mechanical - cold and wet
boulder size range
> 256mm
cobble/gravel size range
64 - 256mm
pebble size range
4-64mm
granule
2-4mm
sand size range
1/16 - 2mm
silt/mud size range
1/16 - 1/256mm
clay size range
<1/256mm
what particle sizes form conglomerate and breccia
boulder
cobble
pebble
granule
what particles sizes form sandstone
sand
what particle sizes form mudrocks
silt/mud and clay
most common minerals for clasts
quartz, feldspar, clay minerals
sorting
poorly sorted - many sizes in one sample
very well sorted - all same sizes in one sample
how is sediment affected by transportation
sorting improves - heavies particles drop sooner
roundness increases - grains abrade each other
continental depositional environments
glacial deposits, streams - alluvial fans, wind - sand dunes, salt lakes
transitional depositional environments
tidal flats, beaches, spit, lagoons, deltas
marine depositional environments
continental shelf - shallow
continental slope - deep
colluvial sediments + features
transported by gravity
- poorly sorted
- angular
alluvial sediments + features
transported by water
- well sorted
- rounded
aeolian sediments + features
transported by wind
- well sorted
- heavier particles are distributed first
loess
a structure made up of wind-blown dust that’s mostly silt-sized particles
glacial sediments
transported by ice
glacial till
clay formed under glacier ice
morraine
mixture of boulders, gravel, sand, and clay carried on top of ice (poorly sorted)
soil formation depends on (5)
- parent material
- time
- climate
- plants and animals
- topography
unconfined compressive strength of bedrock
> 1 MPa
unconfined compressive strength of regolith
< 1 MPa
regolith
unconsolidated sediments (“engineering soil”), grains not connected, formed locally or transported from elsewhere through erosion
soil + ideal composition
combination of mineral and organic material
50% mineral/humus
25% air
25% water
where is regolith thickest
sedimentary basins and along major rivers
where is regolith thinnest
the Arctic
bedrock
residual soils
unconsolidated material
transported soils
how does parent material affect soil formation (from sediment)
parent rock is bedrock - slower formation of soil
parent rock is unconsolidated material - faster formation of soil
chemistry of the parent material controls chemistry of soil and fertility
how does time affect soil formation (from sediment)
initially soil composition depends on parent material
as time progresses climate begins to control composition
how does climate affect soil formation
determines temperature and amount of precipitation
how could plants and animals affect soil formation
high organic content in forest or bog
low organic content in desert
fungi, bacteria, worms all increase the rate of formation of soil
how does topography affect soil formation
- low moisture content on a steep slope
- soil gets moved downhill by erosion so area no longer has soil
- lowlands have higher moisture and more time for soil to develop
if i have 50% mineral, 25% air, 25% water, what is the porosity of my sample
50% - half of the gaps are just filled with water
most important factor of soil formation
climate
downward sequence of soil horizons
O, A, E, B, C
o horizon
Organic. varies from dead leaves to decomposed material. full of microscopic life
a horizon
mineral matter - up to 30% humus
E horizon
lEached horizon. light coloured layer with little organic material. Percolation of water causes eluvation. Other chemicals transported through leaching
B horizone
subsoil. material from E- horizon is deposited here
C horizon
altered parent material
which soil layers are the top soil
O and A
pedalfer
soil type
precipitation greater than evaporation+transpiration (wet/humid)
(think of the Boreal forest)
enough vegetation to produce acid conditions for leaching
pedocal
soil type
precipitation less than evaporation+transpiration (dry/grassland)
what happens to calcium carbonate in pedocal
not leached downwards, can be drawn upwards and precipitated
what happens to calcium carbonate in pedalfer
vegetation produces acid conditions that allow the calcium carbonate to be leached downwards
laterite
soil type
develops in hot, wet tropical climates
what happens to calcium carbonate in laterite
very intense leaching
what colour is laterite and how is it agriculturally
red due to concentrated aluminum and iron.
bad for agriculture due to minimal humus
chernozemic
grassland soil - pedocal
luvisolic
boreal forest - pedalfer
cryosolic
permafrost - mature soil does not develop - tundra
diagenesis
change in rock temperature within 150 - 200 degrees C - one type is lithification
lithification
compaction then cementation
compaction
the volume of a deposit of sediment decreases as the weight of overlying sediment causes a reduction in pore space
what rock can be formed purely by compaction
mud into shale
cementation
new mineral between grains of sediment
most common cementation elements
calcium, carbonate, silica, iron oxide
most common type of sedimentary rock
shale/mudrocks
- more than half of all sedimentary rocks
shale/mudrocks features
- fine grains that cannot be seen
- brittle
- low permeability
second most abundant sedimentary rock
sandstone
sandstone features
poorly sorted to very well sorted
sharp edges
made of quarts, feldspars, lithic fragments
arenite
quartz sandstone
arkose
> 25% feldspar sandstone - found near granite was weathered
greywacke + sorting
quartz, feldspar, lithic fragments make up the sandstone - associated with turbidity currents
poorly sorted
conglomerate
> 2mm rock fragments in cement - rounded
breccia
> 2mm rock fragments in cement - angular
3 inorganic mechanisms to convert chemical sediment into sedimentary rocks
evaporation, dripping, chemical processes
organic mechanism to convert chemical sediment into sedimentary rocks (biochemical)
aquatic organisms
what % of sedimentary rocks is limestone
10% + most abundant chemical sedimentary rock
is limestone a chemical or mechanical sedimentary rock
chemical and organic
types of organic limestone
fossiliferous, chalk
types of inorganic limestone
travertine, oolitic
what is the highest mineral percentage in limestone
Calcite
what forms fossiliferous limestone
polyps (reefs) turn CaCO3 into shells.
chalk is formed by + features + what does chalk form
formed as microorganisms shed small plates
porous and resistant to erosion
forms steep cliffs
travertine
limestone formed along streams, when CaO3 is is deposited when the water is evaporated, leaving a supersaturated solution
oolitic limestone
limestone made of spherical grains of CaO3
dolostone formation
direct precipitation from seawater
chert
silica + quartz dissolved in water
plankton convert into rocks
evaporites
as concentration of salt increases, crystal precipitated in sequence
1. carbonates (calcite, dolomite)
2. sulphates (gypsum, anhydrite)
3. halite
4. potassium salts (sylvite)
(least to most bitter)
when water is lost this mineral turns into anhydrite
gypsum
successive stages in the formation of coal
peat, lignite, bituminous, anthracite
peat
partially altered plant material
caused by burial in swamp environment
lignite
soft, brown coal
caused by compaction of peat
bituminous
soft black coalant
caused by greater compaction of lignite
anthracite
hard black coal
caused by metamorphism of bituminous
strata
horzontal lines - formed as sediments are most commonly deposited flat in water
bed
strata with a thickness > 1cm
laminae
strata with a thickness < 1cm
bedding plane
the separation of layers of strata
crossbedding
characteristic of sand dunes, river deltas.
preserves layers deposited at an angle
graded beds
continental shelf avalanche, largest particles settle first, smaller particles settle last. creates greywacke
ripple marks shallow water - back and forth current
symmetrical ripples
ripple marks deeps water - current
angled ripples
rythmites
thin and thick strips - tidal cycle causes a different layer per day
varves
rock stripes - coarse sediment in the summer, fine in the winter creates layers
crystalline basement
igneous and metamorphic rocks that underlay a surface layer of sedimentary rocks
mudcracks form only
above sea level
4 reasons sedimentary rocks are economically significant
- hydrocarbon resources
- hyrdologic resources
- uranium deposits
- iron
3 reasons sedimentary rocks are scientifically significant
- record of evolution by preserving fossils
- record past climate
- record past earthquakes
what percentage of the crust is sedimentary rocks by volume
5-10%
what percentage of the crust is sedimentary rocks by surface area
75%
order of mineral precipitation in evaporite formation
- Carbonates (dolomite, calcite)
- Sulphates (gypsum, anhydrite)
- Halites (rock salt)
- Potassium Salts (potash)
(gets more “salty”)
