Lecture 6: Weathering & Sedimentary Rocks

Question 1

What is weathering of rocks?

Answer 1

Weathering breaks down the rock by either mechanical or chemical weathering so they can be transported by agents of erosion

Question 2

What are the two types of weathering?

Answer 2

Mechanical and physical

Question 3

Define and give an example of mechanical weathering

Answer 3

The physical breakup of bigger rocks into smaller ones due to wind, water, ice, etc.
Ex. Sand

Question 4

Define and give an example of chemical weathering

Answer 4

Breakdown or decomposition of minerals due to chemical reactions with water or gas
Ex. Rust

Question 5

How are sedimentary rocks formed?

Answer 5

By the accumulation and hardening of sediment

This is possible because of weathering & erosion

Question 6

What is the difference between weathering and erosion?

Answer 6

Weathering breaks down the rock, while erosion transports it

Question 7

What are the three types of sedimentary rocks?

Answer 7

1. Clastic sediment
2. Chemical sediment
3. Biochemical sediment

Question 8

What is clastic sediment?

Answer 8

It consists of solid, small pieces of rock, that were derived from previous rocks

Question 9

What is chemical sediment?

Answer 9

Consists of mineral matter precipitated from a solution

Ex. Salt

Question 10

What is biochemical sediment?

Answer 10

Consists of material produced by organisms.

Ex. Bones, shells, teeth

Question 11

How do you measure (estimate) a rocks susceptibility to weathering?

Answer 11

Through bowens reaction series!

It has the same order as first to crystallize (least resistant) and last to crystallize (most resistant)

Question 12

Why is the order of crystallization and resistance to weathering similar? (BRS)

Answer 12

Because minerals that crystallize at a low temperature are more stable at earths surface

Question 13

Give 4 example of ferromagnesian minerals and define what a ferromagnesian mineral is.

Answer 13

• olivine
• pyroxene
• amphibole
• biotite mica

A ferromagnesian silicate is a silicate mineral that contains ions of iron and magnesium

Question 14

What are the products of chemical weathering?

Answer 14

1. Residual minerals - sediment particles

2. Free ions - dissolved in water

Question 15

What is the order of the horizons for the soil profile?

Answer 15

O,A,B,C,BEDROCK

Question 16

What does the O-Horizon consist of?

Answer 16

Loose, partly decayed matter, decomposed humus

Question 17

What does the a-horizon consist of?

Answer 17

Mixture of mineral matter and humus

Question 18

What does the b-horizon consist of?

Answer 18

Accumulation of clay and oxides

Question 19

What does the c-horizon consist of?

Answer 19

Broken down bedrock

Question 20

What is deposition?

Answer 20

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)

Question 21

How are clastic sedimentary rocks formed?

Answer 21

Through lithification (sediment -> sedimentary rock)

Question 22

The sediment type of: gravel
Turns into:
(Clastic sedimentary rocks)

Answer 22

The sediment type of: gravel

Turns into: conglomerate (rounded pebbles throughout) or breccia (angular rocks throughout)

Question 23

The sediment type of: sand
Turns into:
(Clastic sedimentary rocks)

Answer 23

The sediment type of: sand (particles are seen to be like grains of sand)
Turns into: sandstone

Question 24

The sediment type of: silt
Turns into:
(Clastic sedimentary rocks)

Answer 24

The sediment type of: silt (particles barely seen)

Turns into: siltstone

Question 25

The sediment type of: clay
Turns into:
(Clastic sedimentary rocks)

Answer 25

The sediment type of: clay (particles too small to be seen)

Turns into: shale (fissile, splits easily) or mudstone (massive structureless)

Question 26

How are chemical sedimentary rocks formed?

Answer 26

1. Water contains ions from weathered minerals and volcanic gases
2. Because of evaporation, the dissolved ions become too concentrated for the water to hold
3. The ions join together and precipitate as minerals

Question 27

What are evaporites?

Answer 27

When water is too highly concentrated in salt (still ocean water) is crystallizes into halite or gypsum

Question 28

What are chemical limestones?

Answer 28

A type of chemical sedimentary rock.

Travertine is an example that forms in hot springs and caves

Question 29

What do biochemical sedimentary rocks consist of?

Answer 29

They consist of materials that are produced by chemical processes (biological material, bones, shells, teeth)

Question 30

What is fossilferous limestone?

Answer 30

Biochemical sedimentary rock, composed of calcite shells (fossils)

Question 31

What is chalk?

Answer 31

Biochemical sedimentary rock, its a form of fossilferous limestone, composed of microscopic algae

Question 32

What is reef limestone?

Answer 32

Biochemical sedimentary rock, when older coral reefs build up limestone over the existing coral.

Question 33

What is chert?

Answer 33

Biochemical sedimentary rock.

1. When an organism (in the ocean) has a skeleton of silica
2. Silica dissolves in the water and forms a gel on the sea floor
3. The gel solidifies and forms chert

Question 34

What is coal?

Answer 34

Biochemical sedimentary rock, composed of organic plant matter

Question 35

What is dolostone?

Answer 35

Biochemical sedimentary rock, forms from the evaporation of limestone that solidified.