Lecture 6: Weathering & Sedimentary Rocks Flashcards
What is weathering of rocks?
Weathering breaks down the rock by either mechanical or chemical weathering so they can be transported by agents of erosion
What are the two types of weathering?
Mechanical and physical
Define and give an example of mechanical weathering
The physical breakup of bigger rocks into smaller ones due to wind, water, ice, etc.
Ex. Sand
Define and give an example of chemical weathering
Breakdown or decomposition of minerals due to chemical reactions with water or gas
Ex. Rust
How are sedimentary rocks formed?
By the accumulation and hardening of sediment
This is possible because of weathering & erosion
What is the difference between weathering and erosion?
Weathering breaks down the rock, while erosion transports it
What are the three types of sedimentary rocks?
- Clastic sediment
- Chemical sediment
- Biochemical sediment
What is clastic sediment?
It consists of solid, small pieces of rock, that were derived from previous rocks
What is chemical sediment?
Consists of mineral matter precipitated from a solution
Ex. Salt
What is biochemical sediment?
Consists of material produced by organisms.
Ex. Bones, shells, teeth
How do you measure (estimate) a rocks susceptibility to weathering?
Through bowens reaction series!
It has the same order as first to crystallize (least resistant) and last to crystallize (most resistant)
Why is the order of crystallization and resistance to weathering similar? (BRS)
Because minerals that crystallize at a low temperature are more stable at earths surface
Give 4 example of ferromagnesian minerals and define what a ferromagnesian mineral is.
- olivine
- pyroxene
- amphibole
- biotite mica
A ferromagnesian silicate is a silicate mineral that contains ions of iron and magnesium
What are the products of chemical weathering?
- Residual minerals - sediment particles
2. Free ions - dissolved in water
What is the order of the horizons for the soil profile?
O,A,B,C,BEDROCK
What does the O-Horizon consist of?
Loose, partly decayed matter, decomposed humus
What does the a-horizon consist of?
Mixture of mineral matter and humus
What does the b-horizon consist of?
Accumulation of clay and oxides
What does the c-horizon consist of?
Broken down bedrock
What is deposition?
When the sedimentary particles come to rest once the transporting medium can no longer carry them.
Ex. Lighter particles are more uniformly rested (sand)
Heavier particles are deposited in an agitated way (house fragments from a mudslide)
How are clastic sedimentary rocks formed?
Through lithification (sediment -> sedimentary rock)
The sediment type of: gravel
Turns into:
(Clastic sedimentary rocks)
The sediment type of: gravel
Turns into: conglomerate (rounded pebbles throughout) or breccia (angular rocks throughout)
The sediment type of: sand
Turns into:
(Clastic sedimentary rocks)
The sediment type of: sand (particles are seen to be like grains of sand)
Turns into: sandstone
The sediment type of: silt
Turns into:
(Clastic sedimentary rocks)
The sediment type of: silt (particles barely seen)
Turns into: siltstone
The sediment type of: clay
Turns into:
(Clastic sedimentary rocks)
The sediment type of: clay (particles too small to be seen)
Turns into: shale (fissile, splits easily) or mudstone (massive structureless)
How are chemical sedimentary rocks formed?
- Water contains ions from weathered minerals and volcanic gases
- Because of evaporation, the dissolved ions become too concentrated for the water to hold
- The ions join together and precipitate as minerals
What are evaporites?
When water is too highly concentrated in salt (still ocean water) is crystallizes into halite or gypsum
What are chemical limestones?
A type of chemical sedimentary rock.
Travertine is an example that forms in hot springs and caves
What do biochemical sedimentary rocks consist of?
They consist of materials that are produced by chemical processes (biological material, bones, shells, teeth)
What is fossilferous limestone?
Biochemical sedimentary rock, composed of calcite shells (fossils)
What is chalk?
Biochemical sedimentary rock, its a form of fossilferous limestone, composed of microscopic algae
What is reef limestone?
Biochemical sedimentary rock, when older coral reefs build up limestone over the existing coral.
What is chert?
Biochemical sedimentary rock.
- When an organism (in the ocean) has a skeleton of silica
- Silica dissolves in the water and forms a gel on the sea floor
- The gel solidifies and forms chert
What is coal?
Biochemical sedimentary rock, composed of organic plant matter
What is dolostone?
Biochemical sedimentary rock, forms from the evaporation of limestone that solidified.
