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GEOL109 > Lecture 13 > Flashcards

Lecture 13 Flashcards

1
Q

What is relative time?

A

Order of deposition of a body of rock based on position

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2
Q

What is absolute time?

A

A number representing the time a body of rock was deposited.

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3
Q

What is stratigraphy?

A

Study of stratified rocks, especially their geometric relations, compositions, origins, and age relations.

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4
Q

Because sedimentary rocks are deposited, they naturally form horizontal layers called___.

A

straga

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5
Q

What is strata?

A

Units of rock with a distinct upper and lower surface distinguished by some physical, chemical, or paleontological property.

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6
Q

What allows geoscientists to determine relative ages of layers?

A

stratification

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7
Q

There is a natural sequence to___, and therefore the fossils found within these layers are also of utility for determining relative age.

A

deposition

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8
Q

What does Stratigraphy, strata, and stratification from?

A

The basic Principles of Stratigraphy

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9
Q

What are the three principles of stratigraphy developed by Nicholas Steno?

A

1) Principle of Original Horizontality
2) Principle of Superposition
3) Principle of Lateral Continuity

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10
Q

What is the principle of original horizontality?

A
  • because strata are deposited under the flow of gravity, they form horizontal layers
  • if strata are no longer horizontal, something has disturbed them after they are deposited
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11
Q

What is the principle of superposition?

A
  • unless they have been disturbed, the strata at the bottom were deposited first, and the ones on top of that are the next oldest, and so on and so forth
  • youngest strata will be the layer that is on top
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12
Q

What is the principle of lateral continuity?

A

Sediments extend laterally in all directions until it thins and pinches out or terminates against the edge of the depositional basin.

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13
Q

What did Steno and others find as they mapped stratigraphic units?

A

They found that there were gaps or breaks int eh layers

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14
Q

What do unconformities represent?

A

Periods of erosion or non deposition.

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15
Q

Who terms uniformitarianism?

A

Hutton

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16
Q

What did Hutton recognize about layers of rocks?

A

That they represent aspects of relative time

17
Q

What are the 3 main kinds of unconformities?

A
  • Disconformity
  • Angular unconformity
  • Nonconformity
18
Q

What is a disconformity?

A

Surface erosion/non-deposition is parallel with bedding planes

19
Q

What are bedding planes?

A

The surface that separates one stratum, layer, or bed of stratified rock from another.

20
Q

What is angular unconformity?

A
  • surface erosion which cuts across the bedding plane of lower strata
  • indicates that the rocks beneath were tilted or uplifted prior to erosion
21
Q

What is nonconformity?

A
  • erosional surface that downcuts into a crystalline rock

- this is non-sedimentary, such as metamorphic or igneous rocks

22
Q

What did Hutton add from unconformities?

A

additional Principles of Stratigraphy

23
Q

What is the Principle of Cross-Cutting Relationships?

A

Any structure (fold, fault, weathering surface, igneous intrusion, etc.) that cuts across another or otherwise deformed strata is necessarily younger than the rocks and structures it cuts across or deforms.

24
Q

What is the Principle of Inclusions?

A

Any rock fragments included as a sediment or xenoliths in a unit are from an older rock unit that the one in which it was included.

25
Q

What did early geologists use the Principles of Stratigraphy for?

A

Early geologists were able to figure out the sequence in which sediments and the environments they are deposited changed over time.

26
Q

What are relative ways of dividing up the geologic record?

A
  • Lithostratigraphy
  • Biostratigraphy
  • Chronostratigraphy
27
Q

What is lithostratigraphy?

A

Physical attributes of the rock.

28
Q

What is biostratigraphy?

A

By using fossils

29
Q

What is chronostratigraphy?

A

By time of deposition

30
Q

In lithostratigraphy, each formation is given a___.

A

name

31
Q

Lithostratigraphy: what are ‘members’?

A

laterally continuous distinct strata within a formation

32
Q

Lithostratigraphy: What are ‘groups’?

A

Several distinct, continuous bu related formations may be combined into a formal Group

33
Q

Lithostratigraphy: describe boundaries.

A
  • It was originally thought that boundaries between formations represented a single point in time, no matter where in space you were (Isochronous).
  • Biostratigraphy and radiometric dating later showed that many boundaries represent different times at different places (diachronous).

GEOL109 (18 decks)

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