EAE2522 - Topic 2 - 1 Flashcards

Question 1

Q

Underpinning principles

What is the Principle of Uniformitarianism?

Answer

A

The present is the key to the past. Processes we observe operating today also operated in the past at comparable rates.

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Question 2

Q

Underpinning principles

What is the Principle of Superposition?

Answer

A

In a sequence of undeformed sedimentary (or volcanic) rocks, the oldest layers are at the base and the youngest layers are at the top.

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Question 3

Q

Underpinning principles

What is the Principle of Original Horizontality?

Answer

A

Sediments settle out a fluid gravitationally to form layers that are horizontal. If sedimentary layers are found to be folded and tilted, it follows that the deformation responsible for this reorientation post-dates deposition.

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Question 4

Q

Underpinning principles

What is the Principle of Original Continuity?

Answer

A

Sediments generally accumulate in laterally continuous sheets. If today you find a sedimentary layer cut by a canyon or valley, it can be assumed that the layer once spanned the canyon but was later eroded.

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Question 5

Q

Underpinning principles

What is the Principle of Faunal Succession?

Answer

A

Groups of fossil plants and animals occur in the geological record in a definite, determinable order. The Periods of geological time can be recognised by their fossil content.

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Question 6

Q

Field Geology Principles

What are the Principle of Cross-Cutting Relationships?

Answer

A

If one geological feature cuts another, the feature being cut is older. For example, igneous intrusions and fractures (e.g., faults) are younger than the rocks they cut

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Question 7

Q

Field Geology Principles

What is the Principle of Inclusion?

Answer

A

A fragment of one rock incorporated into another rock is older than the host rock.

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Question 8

Q

Field Geology Principles

What are the Principle of Baked Contacts?

Answer

A

An igneous intrusion "bakes" (metamorphoses) surrounding rocks. The baked rock must be older than the intrusion.

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Question 9

Q

Field Geology Principles

What is the Succession in Landscape Development?

Answer

A

Landforms evolve through a definite series of stages. Therefore, the degree of erosion is an indication of relative age.

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Question 10

Q

What are the Methods of age determination?

6 points.

Answer

A

<ul><li>Dendrochronology (wood, trees) </li><li>Tephrochronology (volcanic layers) </li><li>Varven(layers of sediment in lakes) </li><li>Index fossils </li><li>Paleomagnetic analyses </li><li>Isotopes</li></ul>

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Question 11

Q

Dendrochronology

4 points.

Answer

A

<ul><li>Each ring represents one year </li><li>Dating of natural events (fires, draughts etc) </li><li>Together with climate records absolute dating possible </li><li>Varven-and tephrochronology use the same principle</li></ul>

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Question 12

Q

Index fossils

3 points.

Answer

A

<ul><li>Some fossils are only found in defined stratigraphic layers </li><li>These species have only lived for a very short period in history </li><li>Only absolute in conjunction with other methods</li></ul>

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Question 13

Q

Isotopes!

3 points.

Answer

A

<ul><li>Widest used technique to get absolute ages </li><li>Isotope system used depends on the age of the specimen </li><li>Can be used to date fossils, minerals, rocks and events</li></ul>

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Question 14

Q

Stable vs radiogenic

<div>5 points.</div>

Answer

A

<ul> <li>Stable isotopes don't change their abundance over time</li> <li>Stable isotope ratios can be used as a marker for mainly biological processes</li> <li>Radiogenic isotopes are not stable over time</li> <li>They decay into another isotope of the same element, or an isotope of another element</li></ul>

<div>→ Abundance of radiogenic isotopes does change over time and therefore be used to date rocks and minerals</div>

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Question 15

Q

Elements

4 points.

Answer

A

<ul> <li>118 elements in total</li> <li>26 elements are monoisotopic (one stable isotope, e.g. Na, Al)</li> <li>21 elements are mononuclidic (only one isotope in total, e.g., Au)</li> <li>For all others: Usually one isotope is far more abundant that all others</li></ul>

<div>Example Oxygen = 3 isotopes (16,17,18) but ¹⁸O is 99.76% of occurence</div>

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Question 16

Q

What is Stratigraphy?

Answer

A

Subdividing a rock succession into distinctive rock units and understanding the 4-D spatial and age relationships between those rock units/bodies and their components_{EAE2522 2ap}

Question 17

Q

What are the hierarchy of stratigraphic units?

Answer

A

Bed → Member → Formation → Group (largest)

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Question 18

Q

Hierarchy of Stratigraphic Units

What is the bed?

5 points.

Answer

A

<ul> <li>Single layer (or stratum; plural is strata), millimetres to metres thick, representing a single sedimentation event</li> <li>The thickness of a bed is not a reflection of the duration of a depositional event or time (e.g., 2m thick turbidite sandstone versus 20 cm thick mudstone)</li> <li>Usually local in extent (e.g. in a river channel), but</li> <li>May be regionally extensive (e.g. volcanic ash fall layer, turbidity current deposit)</li> <li>Tops and bottoms may represent long time breaks</li></ul>

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Question 19

Q

Hierarchy of Stratigraphic Units

Member

<div>3ʳᵈ biggest stratigraphic unit</div>

Answer

A

<ul> <li>Distinctive part of formation</li> <li>Slightly different from rest of formation</li> <li>Single or several beds</li> <li>Local or regional</li> <li>Formation may be subdivided into none, one or more members</li></ul>

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Question 20

Q

Hierarchy of Stratigraphic Units

Formation

<div>2ⁿᵈ biggest stratigraphic unit</div>

Answer

A

<ul> <li>Fundamental map unit depicted on geological maps </li> <li>Usually a package of many beds </li> <li>Usually 10's to 100's metres thick </li> <li>Regionally extensive </li> <li>Usually a diachronous rock unit </li> <li>Distinguished from other formations by distinctive lithological character </li></ul>

<div>e.g., limestone, mudstone, volcanics, turbidites</div>

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Question 21

Q

Hierarchy of Stratigraphic Units

Group

<div>Largest stratigraphic unit</div>

Answer

A

<ul><li>An association of two or more formations </li><li>Distinguished from adjacent groups or formations by distinctive lithologies</li></ul>

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Question 22

Q

What is stratigraphic correlation?

3 points.

Answer

A

<div>Establishing equivalence of stratigraphic units or elements between two separate localities</div>

<ul> <li>Lithostratigraphic unit correlation</li> <li>Biostratigraphic zone/stage correlation</li> <li>Chronostratigraphic (age) correlation - establishing age equivalence</li></ul>

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Question 23

Q

Understanding Age Relationships

2 points.

Answer

A

<ul> <li>A vertical succession of different stratigraphic units at one locality records a succession of different depositional events, (sub)environments, or conditions at that locality through time</li> <li>If the same succession of facies/rock units occurs regionally over a large area, each unit may either</li></ul>

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Question 24

Q

Describe

Facies concept

3 points.

Answer

A

<ul> <li>A body of sediment characterised by specific textural, structural and compositional properties</li> <li>Each facies corresponds to a specific sedimentary environment characterised by a particular suite of physical, chemical and biological processes. E.g., shoreline facies (Swamp,floodplain, sand & silt, shale, carbonate).</li> <li>Facies associations: depositional systems in which different facies are formed at the same time.</li></ul>

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Question 25

Q

Lateral Facies Changes

What is Transgression?

3 points.

Answer

A

Sea level rise

<ul> <li>Lateral facies changes during transgression will produce a vertical sequence of facies representing progressively deeper water environments (a deepening-upward sequence).</li> <li>A transgressive sequence will have finer-grained facies overlying coarser-grained facies</li> <li>Sometimes referred to as an onlap sequence.</li></ul>

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Question 26

Q

Lateral Facies Changes

What is Regression?

3 points.

Answer

A

Sea level fall

<ul> <li>A regression will produce a vertical sequence of facies representing progressively shallower water environments (a shallowing-upward sequence).</li> <li>A regressive sequence will have coarser-grained facies overlying finer-grained facies</li> <li>Sometimes referred to as an offlap sequence.</li></ul>

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Question 27

Q

What is Walther’s Law?

Answer

A

<div>Walther's Law states that a vertical succession of facies reflects lateral changes in environment. </div>

<div>Conversely, it states that when a depositional environment "migrates" laterally, sediments of one depositional environment come to lie on top of another. </div>

<div>A classic example of this law is the vertical stratigraphic succession that typifies marine trangressions and regressions.</div>

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Question 28

Q

What factors control the rise and fall of 
sea level?

3 points.

Answer

A

<ul> <li>Eustasy - global changes in sea level</li> <li>Tectonics</li> <li>Sediment Supply</li></ul>

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Question 29

Q

What are Unconformities?

5 points.

Answer

A

Unconformities are stratigraphic boundaries that may be concordant or discordant relative to underlying strata

<ul><li>They represent significant time breaks </li><li>They are regionally extensive surfaces </li><li>They represent considerable periods of erosion &/or non-deposition </li><li>They are produced by regional scale tectonic uplift or sea level fall </li><li>They are NOT faults or intrusive contacts</li></ul>

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Question 30

Q

What are Angular unconformities?

3 points.

Answer

A

<ul> <li>Older strata truncated by erosion surface at considerable angle</li> <li>Indicate a major tectonic deformation, uplift & erosion of an older rock succession, before deposition of a younger sedimentary or volcanic rock succession commences</li> <li>Major time break</li></ul>

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Question 31

Q

What is a Disconformity?

2 points.

Answer

A

<ul> <li>Strata above & below the erosional surface are parallel, but the unconformity is irregular</li> <li>Indicates regional block uplift without folding or tilting, or rapid sea-level fall and erosion, before sedimentation recommences</li></ul>

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Question 32

Q

What are Paraconformities?

Answer

A

All strata & the unconformity are parallel indicating a period of no deposition, no erosion

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Question 33

Q

What are Non-conformities?

2 points.

Answer

A

<ul> <li>Contact between old uplifted, weathered & eroded plutonic or metamorphic rocks & younger sediments</li> <li>Represent a significant time break</li></ul>

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EAE2522 - Topic 2 - 1 Flashcards

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