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

EAE 07 Sedimentery Rocks (11) Flashcards

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

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2
Q

How do you make a sediment?

A

The basic steps in the formation of sedimentary rocks:

* Weathering
* Erosion
* Transportation
* Deposition
* Lithification weathering

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3
Q

What types of weathering are there?

A
  • Physical Weathering
  • Chemical Weathering

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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)

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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

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6
Q

What is erosion?

A

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

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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

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8
Q

What is the grain size of boulders?

A

>256 mm

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9
Q

What is the grain size of cobbles?

A

64~256 mm

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10
Q

What is the grain size of pebbles?

A

2~64 mm

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11
Q

What is the grain size of sand?

A

2 ~ ¹⁄₁₆ mm

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12
Q

What is the grain size of silt?

A

¹⁄₁₆ ~ ¹⁄₂₅₆ mm

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13
Q

What is the grain size of clay?

A

< ¹⁄₂₅₆ mm

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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

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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

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16
Q

How does the wind transport sediment?

A

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

Produces well sorted deposits = “aeolian”

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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

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18
Q

How does the ice transport sediment?

A

Ice = Glaciers

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

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19
Q

How does gravity transport sediment?

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

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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

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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

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22
Q

What are depositional environments?

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

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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

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24
Q

What are the types of Sedimentary Rocks?

A
  • Biochemical
  • Organic
  • Chemical
  • Clastic/detrital

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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

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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

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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

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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

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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

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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.

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LPC 2020 S2 - EAE1012 - Earth Science 2 (18 decks)

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