EAE 07 Sedimentery Rocks (11) Flashcards Preview

LPC 2020 S2 - EAE1012 - Earth Science 2 > EAE 07 Sedimentery Rocks (11) > Flashcards

Flashcards in EAE 07 Sedimentery Rocks (11) Deck (36)
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1
Q

What is a Sedimentary Rock?

A
  • 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

2
Q

How do you make a sediment?

A

The basic steps in the formation of sedimentary rocks:

* Weathering
* Erosion
* Transportation
* Deposition
* Lithification weathering

EAE 9ab

3
Q

What types of weathering are there?

A
  • Physical Weathering
  • Chemical Weathering

EAE 9ac

4
Q

How does physical weathering occur?

A

“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

5
Q

How does Chemical weathering occur?

A

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

EAE 9ae

6
Q

What is erosion?

A

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

EAE 9af

7
Q

What are the agents of erosion?

A
  • 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

8
Q

What is the grain size of boulders?

A

>256 mm

EAE 9ah

9
Q

What is the grain size of cobbles?

A

64~256 mm

EAE 9ai

10
Q

What is the grain size of pebbles?

A

2~64 mm

EAE 9aj

11
Q

What is the grain size of sand?

A

2 ~ ¹⁄₁₆ mm

EAE 9ak

12
Q

What is the grain size of silt?

A

¹⁄₁₆ ~ ¹⁄₂₅₆ mm

EAE 9al

13
Q

What is the grain size of clay?

A

< ¹⁄₂₅₆ mm

EAE 9am

14
Q

What impacts the transport of sediment?

A

Grain shape

* angularity or roundness

Grain size

* finer grain means it can travel farther from its source

EAE 9an

15
Q

What does transportation of sediment influence?

A

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

16
Q

How does the wind transport sediment?

A

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

Produces well sorted deposits = “aeolian

EAE 9ap

17
Q

How does the water transport sediment?

A
  • 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

18
Q

How does the ice transport sediment?

A

Ice = Glaciers

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

EAE 9ar

19
Q

How does gravity transport sediment?

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

EAE 9as

20
Q

What are Clastic sediments?

A
  • 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

21
Q

What are Chemical sediments?

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

EAE 9au

22
Q

What are depositional environments?

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

EAE 9av

23
Q

What are the methods of lithification?

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

EAE 9aw

24
Q

What are the types of Sedimentary Rocks?

A
  • Biochemical
  • Organic
  • Chemical
  • Clastic/detrital

EAE 9ax

25
Q

Describe

Biochemical Sedimentary Rocks

A

Composed of skeletal or shell fragments

  • Limestone
  • Chalk
  • Chert

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26
Q

Describe

Organic Sedimentary Rocks

A

Made up of carbon rich plant material

  • Coal = ancient swamp
  • Oil shale = ancient lake or ocean basin

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27
Q

Describe

Chemical Sedimentary Rocks

A

Composed of minerals that precipitate (crystallize) from water solutions i.e. salt lakes, caves

  • travertine
  • rock salt
  • gypsum

EAE 9ba

28
Q

Describe

Clastic Sedimentary Rocks

A

Composed of grains of pre existing rocks

  • Shale
  • Siltstone
  • Sandstone
  • Conglomerate

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29
Q

Describe

Shale

A

Shale is made of clay

The grains are too small to see ∴ ancient lake or ocean

EAE 9bc

30
Q

Describe

Claystone (mudstone)

A

Like shale, the clay size grains are too fine to see

Claystone has a massive habit, rather than layered ∴ river or swamp

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31
Q

Describe

Siltstone

A

Similar to shale, the grains are too fine to see, but it has a gritty texture ∴ river or swamp

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32
Q

Describe

Sandstone

A

Sand size fragments (grains) ∴ beach, desert, river

EAE 9bf

33
Q

Describe

Breccia

A

Angular fragments of pre existing rocks ∴ mountain river or stream

Some fragments (grains) are pebble, cobble, or boulder size

“Breccia” means broken rock

EAE 9bg

34
Q

Describe

Conglomerate

A

Rounded fragments of pre existing rocks ∴ plains river or stream

Some fragments (grains) are pebble, cobble, or boulder size

Grain size reflects the energy of the transportation and deposition of these sediments

EAE 9bh

35
Q

Core Term

Deposition of Sediments

A
  • Sediments are deposited in layers, or beds = “strata
  • Beds tend to be relatively flat, or horizontal, when deposition occurs

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36
Q

Key points

The Principle of Superposition

A

In a stack of sedimentary rocks, the rock layer on top is younger than the one below it.

The lower layer had to be there before something could be deposited on top.

EAE 9bj