Lec 8: Sedimentary Rocks

Question 1

Lecture’s goals:

1_ Describe the ways sedimentary rocks form

2_ Compare and contrast the texture and composition of sedimentary rocks

3_ Define facies (pronounced Fay She’s) and describe how they might change (e.g. due to sea level rise/fall)

4_ Describe how oil is formed and trapped

5_ List and describe some hazards of designing on or in sedimentary rocks

Answer 1

Lecture’s goals:

1_ Describe the ways sedimentary rocks form

2_ Compare and contrast the texture and composition of sedimentary rocks

3_ Define facies (pronounced Fay She’s) and describe how they might change (e.g. due to sea level rise/fall)

4_ Describe how oil is formed and trapped

5_ List and describe some hazards of designing on or in sedimentary rocks

Question 2

Lecture’s goals:

1_ Describe the ways sedimentary rocks form (hint:2)

Answer 2

Sedimentary rocks form by

_deposition (laying down of material or precipitation from solution)
or
_ lithification (=compaction+cementation)

Question 3

Lecture’s goals:

2_ Compare and contrast the texture and composition of sedimentary rocks

Answer 3

1_ Clastic (fragments or particles)
-> composed of fragments of weathered and eroded rocks

3 main categories according to origin:

1_ clastic (detrital) = fragments or particles

2_ chemical (evaporites) -= formed by precipitation from solution

3_ organic (biogenic) = formed from previously living organisms

Question 4

Which clastic sedimentary rock is composed of grains that have been transported the least distance from the source?

Answer 4

The one that has the most angular grains

The more distance of transport from sediment source, the more rounded and fined the grains look

Question 5

Lecture’s goals:

3_ Define facies (pronounced Fay She’s) and describe how they might change (e.g. due to sea level rise/fall)

Answer 5

Facies is a distinctive rock unit that forms under certain conditions of sedimentation, reflecting a particular process or environment

Marine transgression: sea level rises relative to land surface
Marine regression: sea level falls relative to land surface

Note: to know which one is which, when given the cross-section of the sample, the one that looks like wall bricks first, and the smoothest one at the bottom is transgression, reverse is regression

Question 6

Lecture’s goals:

4_ Describe how oil is formed and trapped

Answer 6

Oil is from organic-rich sediments that settle on the ocean floor

For oil to be trapped, the reservoir has to be capped by an impermeable (not allow fluid to pass) rock

Question 7

Lecture’s goals:

5_ List and describe some hazards of designing on or in sedimentary rocks

Answer 7

_ Bedding planes are potential zones of weakness

_ Bedding orientation can influence on slope stability

_ Sedimentary rocks are susceptible to weathering and/or abrasion (the process of wearing away)