Clastic sediments

Question 1

By what processes are clastic sediments derived by?

Answer 1

Weathering and erosion of subaerially exposed pre-existing rock

Question 2

How is rock made available to be weathered and eroded?

Answer 2

Uplift, exposure, tectonic, and volcanic processes

Question 3

What does weathering lead to the formation of?

Answer 3

Regolith and soil

Question 4

What factor controlled the rate of soil formation?

Answer 4

Climate

Question 5

What affects water availability, needed to mediate chemical weathering?

Answer 5

Faster reactions in areas of high rainfall. In colder areas, where the water is solid, it is unavailable.

Question 6

How does temperature affect the rate of chemical weathering reactions?

Answer 6

Higher temperatures increase the rate of chemical weathering reactions.

Question 7

Give three examples of physical weathering

Answer 7

Frost wedging, exfoliation, action of plants

Question 8

What is true of all chemical weathering processes?

Answer 8

They are all mediated by water

Question 9

What does chemical weathering involve?

Answer 9

Dissolution of minerals, for example by hydrolysis, hydration, ion exchange

Question 10

What does the development of thick regolith do and what is needed to prevent it?

Answer 10

Inhibits the access to water to fresh rock. Mechanism for its continuous removal is needed.

Question 11

Name four hill slope processes

Answer 11

Falls, landslides, creep, surface runoff

Question 12

What is the most common clast in clastic sediments?

Answer 12

Quartz

Question 13

Why does quartz not weather easily?

Answer 13

It is inert at the Earth’s surface and it has a hardness of Mohs 7.

Question 14

What are the breakdown products of feldspars and micas?

Answer 14

Clay and free ions (K, Ca, Na)

Question 15

Why are clays weak?

Answer 15

They are sheet silicates with one perfect cleavage. Mohs 1-2.5

Question 16

Why does the physical weathering of clay make different minerals difficult to identify?

Answer 16

Produces a fine matrix (mud) where particles cannot be discerned with the naked eye

Question 17

Describe shales

Answer 17

Mudstones that are mostly clays, with a matrix that holds clasts.

Question 18

Name the three types of processes that can erode weathered regolith and soil

Answer 18

Fluvial, wind, glacial

Question 19

Where can short-term storage of sediment occur?

Answer 19

Anywhere

Question 20

Where cam long-term storage of sediment occur?

Answer 20

Subsiding sedimentary basins

Question 21

Describe the characteristics of a texturally mature grain

Answer 21

Decreasing: size, angularity.
Increasing: sphericity, porosity of formation.

Question 22

What dictates grain sorting?

Answer 22

Rate of change of velocity

Question 23

Describe the characteristics of a chemically mature grain

Answer 23

Loss of feldspar, mica, and other clasts, in favour of clay, matrix, and quartz

Question 24

Define diagenesis

Answer 24

The conversion of a sediment into a sedimentary rock through burial

Question 25

Describe the growth of a cement during diagenesis

Answer 25

Crystals (usually quartz, clay, or calcite) precipitate from water/brine and are then circulated through the pore space

Question 26

What are the three components of clastic sediments?

Answer 26

Grains, matrix, and pore space

Question 27

What are the four components of clastic sedimentary rocks?

Answer 27

Grains, matrix (depositional), cement (diagenetic), and pore space