Lecture Eighteen

Question 1

What is a sedimentary rock?

Answer 1

Any rock that has formed out of fragments of pre-existing rocks or minerals, or has precipitated from dissolved minerals. 
Many types depending on: 
What they are made of. 
Where they formed. 
How the formed.

Question 2

How is a sediment made?

Answer 2

Weathering –> Erosion –> Transportation –> Deposition –> Lithification.

Question 3

Explain the process of weathering.

Answer 3

Physical weathering: 
Mechanical weathering. 
Produces detritus (fragments of pre-existing rocks). 

Chemical weathering:
Chemical reactions change or destroy minerals within a rock, generally when it is in contact with water or air.

Question 4

Explain the process of erosion.

Answer 4

Physical precesses that loosen rock or regrowth, separate it from the substrate and carry it away.
Agents of erosion:
Heat and cold - expansion and contraction break surfaces.
Wind - erodes surfaces and removes fines.
Water - erodes surfaces an removes blocks and detritus.
Ice - erodes surfaces and removes everything in its path.
Gravity - causes things to fall.

Question 5

Explain the process of transportation of sediments.

Answer 5

The way in which a sediment is transported influences:
Sorting of grains - uniformity of grain sizes.
Maturity of the sediment - Removal of easily weather-able sediments over time (Bowen’s Reaction Series).
Wind - generally transports only fine particles, and produces well-sorted deposits “aeolian.”
Water - transports all sizes, produces a range of deposits, generally ell sorted (improves with distance travelled).
Ice - Transports any sizes, produces poorly sorted deposits “glacial till.”
Gravity - Transports all sizes, produces poorly sorted deposits.

Question 6

Explain the process of deposition of sediments.

Answer 6

Clastic sediments:
fragments of pre-existing rocs.
Deposited from - Wind, water, ice, and/or gravity.
When the transport system is no longer able to carry them away.

Chemical sediments:
Form by over saturation of minerals in water = chert.
Form by evaporation of water = evaporites.

Question 7

Explain the process of lithification.

Answer 7

Compaction:
Grains are compressed and pore space is reduced.
Cementation:
growth of new minerals binds the grains together.

Question 8

What are the types of sedimentary rocks?

Answer 8

Biochemical:
Composed of skeletal or shell fragments.

Organic:
Made up of carbon-rick plant material.

Chemical:
Composed of minerals that precipitate (crystallise) from water solutions.

Clastic/detrital:
Compose of grains of pre-existing rocks.