Sedimentary Rocks

Question 1

What are two groups sedimentary rocks can be divided into?

Answer 1

They can be subdivided into either detrital (clastic) or chemical-based on its texture (grain size), mineralogy, and chemical composition.

Question 2

What are sedimentary rocks?

Answer 2

Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at the Earth’s surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles to settle in place.

Question 3

How are detrital (clastic) sedimentary rocks formed?

Answer 3

Detrital (clastic) sedimentary rocks are formed by mechanical transport and deposition of fragments of pre-existing rocks. They then go through a process of lithification to form rock.

Question 4

How are chemical sedimentary rocks formed?

Answer 4

They are precipitated from solution (non-clastic) meaning they are evaporated out. They are derived from the material that is carried in the solution to lakes/seas (e.g shells).

There are two types; physical and biochemical

Question 5

What is an example of a detrital (clastic) sedimentary rock?

Answer 5

Quartz (common) is resistant to chemical weathering due to being extremely durable.

Question 6

What are the two types of chemical sedimentary rocks?

Answer 6

1. Physical (evaporation, hydrothermal).

2. Biochemical (shells, wood, organism, e.g limestone and coal).

Question 7

What is an example of a biochemical (chemical) sedimentary rock?

Answer 7

Limestone and coal.

Question 8

How are sedimentary rocks formed generally?

Answer 8

Sedimentary rocks are formed by moving particles from one another.

Sediments form LAYERS (strata) which contain the majority of fossils and information about Earth’s history.

Question 9

What can fossils in sediments tell us?

Answer 9

Fossils in the sediments tell us the time WHEN they were EXPOSED.

E.g A pebble’s shape tells us how it was transported and can then interpret the story of what happened during that time.

Question 10

Can we match (strata) layers from different areas/countries?

Answer 10

Yes, we can match (strata) layers from different countries and areas to each other.

Question 11

What are the four different textures given to sedimentary rocks?

Answer 11

1. Course (over 2mm) = Gravel (rounded) = E.g conglomerate and Gravel (angular) = E.g Berrica
2. Medium (1/16-2mm) = Sand (if abundant feldspar is present) = E.g Sandstone
3. Fine (1/16-1/256) = Mud = E.g siltsone
4. Very fine (less than 1/256) = Mud = E.g shale