EAE 07 Sedimentery Rocks (11)

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 water
• Many types, depending on:
  
  • what they are made of
  • where they formed
  • how they formed

_{EAE 9aa}

Question 2

How do you make a sediment?

Answer 2

The basic steps in the formation of sedimentary rocks:

* Weathering
* Erosion
* Transportation
* Deposition
* Lithification weathering

_{EAE 9ab}

Question 3

What types of weathering are there?

Answer 3

• Physical Weathering
• Chemical Weathering

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Question 4

How does physical weathering occur?

Answer 4

“mechanical” weathering breaks rocks apart

Produces detritus (fragments of pre existing rocks)

* "patterned ground" caused by freeze thaw
* Frost wedging (e.g. Antarctica)

_{EAE 9ad}

Question 5

How does Chemical weathering occur?

Answer 5

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

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Question 6

What is erosion?

Answer 6

Physical processes that loosen rock or regolith, separates it from the substrate, and carries it away

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Question 7

What are the agents of erosion?

Answer 7

• Heat & cold - expansion and contraction break surfaces
• Wind - erodes surfaces and removes fines
• Water - erodes surfaces and removes blocks and detritus
• Ice - erodes surfaces and removes everything in its path
• Gravity - causes things to fall

_{EAE 9ag}

Question 8

What is the grain size of boulders?

Answer 8

>256 mm

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Question 9

What is the grain size of cobbles?

Answer 9

64~256 mm

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Question 10

What is the grain size of pebbles?

Answer 10

2~64 mm

_{EAE 9aj}

Question 11

What is the grain size of sand?

Answer 11

2 ~ ¹⁄₁₆ mm

_{EAE 9ak}

Question 12

What is the grain size of silt?

Answer 12

¹⁄₁₆ ~ ¹⁄₂₅₆ mm

_{EAE 9al}

Question 13

What is the grain size of clay?

Answer 13

< ¹⁄₂₅₆ mm

_{EAE 9am}

Question 14

What impacts the transport of sediment?

Answer 14

Grain shape

* angularity or roundness

Grain size

* finer grain means it can travel farther from its source

_{EAE 9an}

Question 15

What does transportation of sediment influence?

Answer 15

Causes sorting of grains →

• Uniformity of grain sizes

“Maturity” of the sediment →

• Removal of easily weatherable sediments over time
• Think of Bowen’s Reaction Series

_{EAE 9ao}

Question 16

How does the wind transport sediment?

Answer 16

Generally transports only fine particles (sand, silt, clay)

Produces well sorted deposits = “aeolian”

_{EAE 9ap}

Question 17

How does the water transport sediment?

Answer 17

• Transports all sizes of material
• Produces a range of deposits, generally well sorted

    * Sorting improves with distance transported
    * For rivers and streams it "**fluvial**" transport

_{EAE 9aq}

Question 18

How does the ice transport sediment?

Answer 18

Ice = Glaciers

• Transport all sizes of material
• Produce poorly sorted deposits “glacial till”

_{EAE 9ar}

Question 19

How does gravity transport sediment?

Answer 19

• Transports all sizes of material
• Produces poorly sorted deposits “slumps” or “slides”

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Question 20

What are Clastic sediments?

Answer 20

• Fragments of pre existing rocks
• Deposited from: Wind, Water, Ice, Gravity
• When the transport system is no longer able to carry them away

_{EAE 9at}

Question 21

What are Chemical sediments?

Answer 21

• Form by over saturation of minerals in water = Chert
• Form by evaporation of water = “Evaporites”, e.g., rock salt

_{EAE 9au}

Question 22

What are depositional environments?

Answer 22

• Fluvial (stream)
• Deltaic
• Lacustrine (lake)
• Desert
• Beach
• Coastal swamp
• Coral reef
• Continental shelf
• Ocean basin … etc.

_{EAE 9av}

Question 23

What are the methods of lithification?

Answer 23

• Compaction = Grains are compressed and pore space is reduced
• Cementation = Growth of new minerals binds the grains together

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Question 24

What are the types of Sedimentary Rocks?

Answer 24

• Biochemical
• Organic
• Chemical
• Clastic/detrital

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Question 25

Describe ## Footnote **Biochemical Sedimentary Rocks**

Answer 25

Composed of skeletal or shell fragments ## Footnote * Limestone * Chalk * Chert _{EAE 9ay}

Question 26

Describe ## Footnote **Organic Sedimentary Rocks**

Answer 26

Made up of carbon rich plant material ## Footnote * Coal = ancient swamp * Oil shale = ancient lake or ocean basin _{EAE 9az}

Question 27

Describe ## Footnote **Chemical Sedimentary Rocks**

Answer 27

Composed of minerals that precipitate (crystallize) from water solutions i.e. salt lakes, caves ## Footnote * travertine * rock salt * gypsum _{EAE 9ba}

Question 28

Describe ## Footnote **Clastic Sedimentary Rocks**

Answer 28

Composed of grains of pre existing rocks ## Footnote * Shale * Siltstone * Sandstone * Conglomerate _{EAE 9bb}

Question 29

Describe ## Footnote **Shale**

Answer 29

Shale is made of clay ## Footnote The grains are too small to see ∴ ancient lake or ocean _{EAE 9bc}

Question 30

Describe ## Footnote **Claystone (mudstone)**

Answer 30

Like shale, the clay size grains are too fine to see Claystone has a massive habit, rather than layered ∴ river or swamp _{EAE 9bd}

Question 31

Describe ## Footnote **Siltstone**

Answer 31

Similar to shale, the grains are too fine to see, but it has a gritty texture ∴ river or swamp ## Footnote _{EAE 9be}

Question 32

Describe ## Footnote **Sandstone**

Answer 32

Sand size fragments (grains) ∴ beach, desert, river ## Footnote _{EAE 9bf}

Question 33

Describe ## Footnote **Breccia**

Answer 33

Angular fragments of pre existing rocks ∴ mountain river or stream ## Footnote Some fragments (grains) are pebble, cobble, or boulder size "Breccia" means *broken rock* _{EAE 9bg}

Question 34

Describe ## Footnote **Conglomerate**

Answer 34

Rounded fragments of pre existing rocks ∴ plains river or stream ## Footnote Some fragments (grains) are pebble, cobble, or boulder size Grain size reflects the energy of the transportation and deposition of these sediments _{EAE 9bh}

Question 35

Core Term ## Footnote **Deposition of Sediments**

Answer 35

* Sediments are deposited in layers, or beds = "*strata*" * Beds tend to be relatively flat, or horizontal, when deposition occurs ## Footnote _{EAE 9bi}

Question 36

Key points ## Footnote **The Principle of Superposition**

Answer 36

In a stack of sedimentary rocks, the rock layer on top is younger than the one below it. ## Footnote The lower layer had to be there before something could be deposited on top. _{EAE 9bj}