Weathering and SEDIMENTARY Rocks Flashcards
being exposed to weather
weathering
2 types of weathering
Physical and Chemical
process that transform rocks into soil, fractures and exposes more surface area of the rock for chemical weathering
physical weathering
destroys mineral structures to weaken rocks for physical weathering to be easier
chemical weathering
When the material over a rock is weathered and transported over time, the rock gets exposed and this also REDUCES the pressure the rock experiences.
exfoliation
Forces due to ice and root wedging.
Plants growing through rock cracks further expanding the crack.
Water freezing inside rock cracks further expands when becomes ice
Disrupting forces
Salt water infiltrates rocks, as the water dries, the salt crystals grow in the rock and crack it.
crystal growth
Bending of rocks due to unequal heating and cooling may cause rocks to break
unequal temperature
2 main types of chemical weathering
minerals into other minerals
minerals getting dissolved into a solution
chemical weathering agents
carbonic acid h2co3
oxidation
removal of weathered materials
erosion
agents of erosion
gravity
wind
water
waves
animals
movement of sediment and/or dissolved ions from point A (point where it was eroded) to point B (point where it will be deposited)
transportation
Transportation stops and sediments are deposited.
deposition
6 terrestrial depositional environments
glacial
alluvial
fluvial
lacustrine
evaporitic
aeolian
8 marine depositional environments
tidal
deltaic
beach
lagoonal
reef
shallow water marine
deep water marine
submarine fan
main depositional environments
see picture
formed from the lithification of sediments
sedimentary rocks
For the weathered materials to become rocks, the following must occur (in order):
burial, compaction, cementation
2 classifications of sedimentary rocks
clastic or chemical
made up of sediments that were transported as solid
fragments
clastic
made up of sediments that were transported as ions in solutions
chemical
clasts biggest to smallest
boulders, cobbles, pebbles, sand, silt, clay
5 clastic sedimentary rock groups
Mudrock, sandstone, conglomerate, breccia, coal
has at least 75% silt or clay composition and form in very low-energy environment (lakes, deep parts of the ocean)
mudrock
has beddings/lamination,
shale
Made up mostly of sand
sandstone
Silt and clay <15%
clean sandstone / arenite
silt and clay is >15%
wacke
if the clasts are rounded (formed in high energy environments like swift rivers, hence the more rounded shape)
conglomerate
if the clasts are angular (formed in environments where clasts not transported significantly, hence little effect on shape)
breccia
often classified as organic sedimentary rock due to its composition of decayed material (peat moss and humus)
coal
5 chemical sedimentary rocks
limestone, chalk, dolomite rock, chert, evaporites
composed mostly of the minerals: calcite and aragonite, the crystal form of calcium carbonate
limestone
A limestone composed of calcite minerals made from biochemical processes.
chalk
recrystallization of older limestones
dolomites
Some organisms like radiolarians and diatoms use silica to make their shell. When they die, the shells settle down and become
chert
In dry areas, when waters in lakes and rivers evaporate, they become concentrated with dissolved ions which then crystallize.
evaporites
composed mainly of halite
rock salt
composed mainly of gypsum
rock gypsum
4 Geological Principles for Sedimentary Structures
Original Horizontality
Superposition
Inclusions
Faunal Succession
layering of sediments that can be seen in changes in texture, color, composition, etc. It indicates changes related to the deposition of materials that may be due to seasonal, climates, or tectonic changes among others
bedding
are narrow gaps in between layers shown in a bedding. These may indicate periods with no deposition
partings
Bedding that has angled layers within horizontal beds. This forms due the sediments being deposited by water or wind
cross-bedding
Sediments in a flowing water body may become IMBRICATED – they tile towards one direction, with their tops tilting towards the direction of a flow
ripples
A bed where gradation/gradual change of grain size from large to small is seen as from bottom to top (known as normal graded beds). Some have large grains at the top and finer grains at the bottom known as reverse/inverse graded bed.
graded bedding
when a shallow body of water dries up, the mud at its bottom dries up and cracks due to the clay in the mud shrinking as it dries.
mudcrack
deterioration of a rock after exposure, often by excavation.
slaking
topography formed from dissolution of soluble rocks. It is characterized by underground drainage with sinkholes and caves.
karst
depression or hole in the ground caused by some form of collapse of the surface layer.
sinkhole
