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Earth Science - Fall 2015 > Sedimentary Rocks > Flashcards

Sedimentary Rocks Flashcards

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1
Q

What is a Sedimentary Rock?

A

They are products of mechanical and chemical weathering.

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2
Q

How much of Earth is made up of Sedimentary Rocks?

A

5% of Earth’s outer 16 km is Sedimentary.

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3
Q

Why are Sedimentary Rocks important to study?

A

They contain evidence of what the environment was like in the past. It can tell us about sedimentary transport and they commonly contain fossils.

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4
Q

How is Sedimentary Rock formed?

A

Through transport via wind, water or ice.

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5
Q

Why are Sedimentary rocks important economically?

A

They may contain coal, petroleum and natural gas, or sources of iron, aluminum, manganese, fertilizer, and raw materials for the construction industry.

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6
Q

How does sediment become Sedimentary rocks?

A

Weathered debris are swept from bedrock, carried away, and deposited in lakes, river valleys, seas, and countless other places where it undergoes Diagenesis.

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7
Q

What is Diagenesis?

A

All of the chemical, physical, and biological changes that take place after sediments are deposited. This occurs prior to metamorphism.

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8
Q

Where does Diagenesis occur and at what temperature?

A

It occurs within the upper few kilometers of the Earth’s crust, at temperatures generally less than 200C.

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9
Q

What is Re-crystallization?

A

A type of Diagenesis that involves the development of mroe stable minerals from less stable ones.

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10
Q

What is an example of Re-crystallization?

A

Aragonite is secreted by many marine organisms to produce hard parts such as shells. In some environments, large quantities of these solid materials accumulate as sediment. As burial takes place, the aragonite re-crystallizes to the more stable form of calcium carbonate, calcite (the main part of the sedimentary rock, limestone)

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11
Q

What is Lithification?

A

Unconsolidated sediments that are transformed into solid sedimentary rock by compaction and cementation. Most sedimentary rocks are lithified.

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12
Q

What is Compaction?

A

Compaction occurs as sediment accumulates and the weight of overlying material compresses the deeper sediments. The deeper the sediment, the more it becomes compacted, and the firmed it becomes.

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13
Q

How does Compaction work?

A

As grains of sediment are pressed closer and closer together, there is a considerable reduction in pore space, the open space between rock particles. As pore space decreases, much of the water that was trapped in the sediments is driven out.

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14
Q

What is Cementation?

A

It is a chemical diagentic change that involves the precipitation of minerals among the individual sediment grains. The cementing materials are carried in solution by water gradually filters through the pore spaces between particles. The addition of cement into a sedimentary deposit reduces the pores.

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15
Q

What are the most common cements used in cementation?

A

Calcite, Silica, and Iron Oxide

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16
Q

How do you identify the material that is cementing?

A

Calcite bubbles in dilute hydrochloric acid. Silica is the hardest cement and produces the hardest sedimentary rock. If there is a orange or dark red colour, that means the cement was iron oxide.

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17
Q

Is it common for crystalline sedimentary rocks to be porous?

A

No, because crystals grow until they fill all available space, pores are frequently lacking in crystalline sedimentary rocks.

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18
Q

What is an Environment of Deposition or Sedimentary Environment?

A

A Geographical setting where sediment is accumulating. Each site is characterized by the a particular combination of geologic processes and environmental conditions.

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19
Q

How do environmental conditions determine the nature of the sediment that accumulates?

A

Depending on the environment, the properties of sediment will vary in grain size, grain shape, colour, and what it’s made of.

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20
Q

What can we learn about the environment from a sedimentary rock?

A

We can learn what kinds of animals, plants, rocks, and minerals are in the area where the rock was found. However this isn’t always true. Often sediment will be carried far distances by some combination of gravity, water, wind and ice.

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21
Q

How can sedimentary rocks tell us about the past. What is this theory called?

A

By applying what we know about sedimentary rocks that are made recently, we can imagine what the world looked like in the past. If we know that a certain type of sediment forms in a specific environment, we can reconstruct ancient environments by looking at ancient sedimentary layers composition.

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22
Q

What are the types of sedimentary environments?

A

Continental, Transitional (shoreline), Marine.

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23
Q

In cold regions, what is the dominant way sediment is created and moved?

A

By the moving masses of glacial ice.

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24
Q

What are the primary ways sediment is created in continental environments?

A

Erosion, and deposition associated with streams.

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25
Q

In arid and some coastal regions, what is the dominant way sediment is created and moved?

A

Wind.

26
Q

How do glaciers move sediment?

A

In frigid high-latitude or high altitude settings, glaciers pick up and transport huge volumes of sediment.

27
Q

How can you tell if sediment was moved by a glacier?

A

Materials deposited directly from ice are typically poorly sorted mixtures of particles that range in size from clay to boulders.

28
Q

How can glaciers sort sediment better?

A

When they melt, water transports and re-deposits some of the glacial sediment, creating well sorted accumulations.

29
Q

What has a strong influence on the nature of the sediments deposited in continental environments?

A

Climate

30
Q

What do you call an environment dominated by erosion and deposition through a stream?

A

Fluvial

31
Q

What kinds of sediment particles will be deposited by steams?

A

The sediment particles will be separated according to density and grain size due to the water motion.

32
Q

Why are streams the dominant agent of landscape alteration?

A

Because they erode more land as the flow, transporting and depositing more sediment than any other process.

33
Q

What happens to the type of sediment deposited by a steam when the waters are particularly turbulent?

A

It will be dominated by gravel.

34
Q

What happens to the type of sediment deposited by a steam when the waters are fairly calm?

A

It will be dominated by mud.

35
Q

What is an Alluvial fan?

A

A distinctive cone-shaped build up of sediment where a steam emerges from a mountainous region onto a flatter one.

36
Q

What happens to lowlands distant from Alluvial fans?

A

Significant volumes of mud and sand settle out from flood waters that overwhelm flat areas of land called floodplains.

37
Q

The work of wind and it’s resulting deposits are referred to as ______.

A

Aeolian

38
Q

How well sorted are particles deposited by wind?

A

Well sorted, wind can only life fine dust.

39
Q

Why is the wind able to transport sediment deposits long distances?

A

Because the wind is strong and there is little to no vegetation rooting sand to the ground, it is able to lift it up into the air.

40
Q

What happens to sand that is transported close to the ground?

A

The sand accumulates into dunes.

41
Q

Where are you likely to see dunes?

A

Deserts and coasts.

42
Q

What are playa lakes?

A

Large holes that are dried lakes that will occasionally fill up with water again. They often form during heavy rains of periods of snowmelt in adjacent mountains. They rapidly dry up again.

43
Q

What could happen when a playa lake dries up?

A

It could leave behind mudflats, evaporites, and other deposits.

44
Q

What are quiet lakes in humid regions good for, and why?

A

Sediment traps. Small deltas, beaches, and bars form of sediment along the lakeshore, with finer sediments resting on the lake floor.

45
Q

How are tidal flats made?

A

Low gradients or quiet water conditions, when fine grained sediment is deposited under shallow sheets of water and exposed to air.

46
Q

What happens in transitional environments where the shoreline is characterized by energetic waves and current action.

A

Sediments are rapidly sorted and deposited to produce a sand or gravel beach.

47
Q

What does reworking and redistribution of sand by waves and currents along a shoreline produce?

A

Linear sand bodies, such as spits, bars, and barrier islands.

48
Q

What is a lagoon?

A

A slightly salty water area that develops behind an offshore bar or reef. These will be in sheltered areas with calm water and mine-grained sediment deposits.

49
Q

What is one of the most significant deposits associated with transitional environments?

A

Deltas

50
Q

What are deltas?

A

Complex accumulations of sediment built outwards into the sea when rivers experience an abrupt loss of velocity and drop their load of debris.

51
Q

List off the transitional shoreline sedimentary environments.

A

Tidal flats, Beaches, Spits, Bars, Barrier Islands, Lagoons, Deltas

52
Q

How are marine sedimentary environments categorized?

A

By depth.

53
Q

What is classified as a shallow marine environment?

A

Shallow marine environments reach depths of about 200 meters, and extend from the shore to the outer edge of the continental shelf.

54
Q

What is classified as a deep marine environment?

A

Deep marine environments lie seaward of the continental shelf in waters deeper than 200 meters.

55
Q

Where might you find shallow marine environments?

A

Shallow marine environments border all of the world’s continents.

56
Q

How wide can shallow marine environments get?

A

They vary. They can be as extensive as 1500km, and much shorter in others. The average size is 80kms wide.

57
Q

What kind of sediment deposits are in shallow marine environments?

A

This depends on several factors, including the distance from shore, the elevation of the adjacent land area, the water depth, water temperature, salinity, and climate.

58
Q

How does sediment enter shallow marine environments?

A

The ocean erodes the adjacent landmass and receives huge quantities of sediment

59
Q

What is the predominant sediment in shallow marine environments and why.

A

Carbonate rich muds are the predominant sediment in shallow marine environments, because the influx of sediment is small and seas are relatively warm.

60
Q

What does carbonate rich mud consist of?

A

Most of this material consists of skeletal debris of carbonate-secreting organisms mixed with inorganic precipitates.

Earth Science - Fall 2015 (9 decks)

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