weathering and sedimentary rocks (LEC 4) Flashcards
most common external processes,
hint: weathering
weathering
erosion
mass wasting (movement of rock/soil downslope)
what is weathering
breakdown of earth’s materials
when rocks are broken down, particle size ____________ and surface area _____________
words: increases, decreases
decreases
increases
what are the types of weathering
mechanical and chemical
what is mechanical weathering chemical weathering
*physical breakdown of rocks without changing the composition
*breakdown of rocks by chemical reactions mainly reactions with air
or water and resulted in one or more new compounds
examples of mechanical weathering
- frost action (freezing and thawing)
- pressure release (sheeting)
- biological activity
important agents of chemical weathering:
- atmospheric gases (mainly oxygen)
- water (the most important agent)
- organic acids (produced by plants and decaying of organic matter)
chemical weathering mechanisms (3)
- dissolution
- oxidation
- hydrolysis
sources of acids (3)
1) carbonic acid is produced from the CO2 in the atmosphere
2) sulphuric or nitrous acids are introduced in acid rains
3) various organic acids are released into soil as organisms decay
oxidation reactions are very slow in dry environments, what speeds up the oxidation reactions
water
factors affecting the chemical weathering rate (2)
rock characteristics
climate
___________ silicate in the rock, increases its resistance to weathering
high silicate content results in low rate of chemical weathering
increasing
high temperature = high/low weathering
dry climate = high/low weathering
high
low
old rocks > small particles > sediments > SOIL
slay
soil: parent materials can be either _________ (residual soil) or ________________ (transported soil)
bedrock; unconsolidated materials
climate is the most influential parameter for soil formation
hot, wet climate = ______ layer of chemically weathered soil
cold, dry climate = ______ layer of mechanically weathered soil
option: thin/thick
thick
thin
the optimum topography for soil formation is flat, why
because of low moisture content and high erosion in a steep slope will create poorly developed soil
soil horizons are separated layers that
differ from one another in _____, _______, _______, and _______
colour, texture, structure, and composition
define eluviation
when water percolates downward,
it carries FINE PARTICLES to a deeper zone
soil colour is generally a reflection of its composition:
high organic matter = what colour?
high Fe = what colour?
black or brown
red or yellow color
high particle size = high _________
leachate
which rocks are the only rocks that contain fossils
sedimentary rocks
calcite, iron oxide, silica, what are these?
the most common cements
identification of cements:
________ = bubble with dilute HCl
________ = the hardest cement
________ = orange or dark red color
calcite
silica
iron oxide
two main types of marines and their depths
shallow marine (less than 200 m depth)
deep marine (more than 200 m depth)
name the continental environments (3)
alluvial fan
sand dunes
playa lake
name the transitional environments (3)
tidal flats
beach
delta
sedimentary rocks are classified based on their composition into three main types:
*clastic (detrital) :pieces of rocks derived by mechanical or chemical weathering
*chemical (crystalline): dissolved compounds in solution precipitate due to evaporation or
oversaturation.
*biological (bioclastic): remains of living
organisms or plants or materials produced by
organic (biological) precipitation
three characteristics of clastic sedimentary rocks that can give us information about their deposition environment:
- particle size
- sorting
- roundness
the final deposit reflects the combined influence of environmental
energy and sediment availability
idk how to create a question from this……. LOL
well sorted sediment (the grains in the sample are about same size) = deposited by _______
poor sorted sediment (the grains in the sample are different sizes (mixture of
large and small sizes) = deposited by _______
options: water, wind
wind
water
main types of clastic sedimentary rocks (5)
- mudrocks
- shale
- sandstone
- conglomerate
- breccia
mudrocks are the _____ common type of sedimentary stone, they form from sediments deposited in a quiet water environment (lakes, lagoons, deep-ocean basin)
most
why is groundwater usually underlain by shale bed
shale consists of very small particles which result in microscopic pore spaces which don’t permit water to infiltrate, restricting the
movement of groundwater through the shale rock
types of sandstones (composition) (3)
- quartz sandstone
- arkose
- wacke
main types of clastic sedimentary rocks
conglomerate and breccia
precipitate can be inorganic or organic material:
inorganic = _____________
organic = _____________
chemical sedimentary rock
biological sedimentary rock
examples of:
chemical precipitates
biological precipitates
*ex. halite, calcite, and gypsum
halite: dissolved sodium and dissolved chloride, when concentrated enough, produce sodium chloride (halite).
*fossil remains of plants and animals
common chemical sedimentary rocks (4)
limestone
dolostone
chert
evaporites
_______ soluble minerals precipitate first
options: more/less
less
stages of coal formation:
(accumulation of plant remains) >
1. plant material (plants remains) >
(partial oxidation by bacteria) >
2. peat (soft brown materials) >
(shallow burial increase in T&P) >
3. lignite (soft brown coal) >
(deep burial, the water and volatiles are pressed out) >
4. bituminous [hard, more compacted black coal (rock)]
that was not a question :)
but just memorize it like so:
1. remains → partial oxidation
2. p(EAT) → soft brown
3. l(IGNITE) → brown coal
4. bit[(L)uminous] → black coal
carbon content in different coal stages
peat >
lignite (carbon content = 25 to 35%) >
bituminous (carbon content = 45 to 86%) >
anthracite (carbon content = 86 to 97%)
sedimentary structures are features formed from sediments during or shortly after deposition. common types of sedimentary structures:
- bedding
- mud cracks
- ripple marks
bedding: beds or strata are layers of sediments accumulated in various depositional environments. three main types of bedding:
- parallel-bedding
- cross-bedding
- graded-bedding
parallel-bedding: the layers are parallel and typically horizontal
so what is cross-bedding
when the layers are inclined to horizontal
what are graded-beds
when the particles within a single layer gradually change from coarse at the bottom to fine at the top
what are mud cracks
when wet mud is exposed to air and dries up, it cracks
what are ripple-marks
small waves of sand on the surface of a sediment layer by the action of moving water or air
fossils are the remains or traces of prehistoric life now preserved in rock
* fossils are generally found in _______ rock and rarely in _______ rock, but never in _______ rock
sedimentary
metamorphic
igneous
define leaching
when water percolates downward,
it carries dissolved INORGANIC MATTER to a deeper zone
