What are the Methods of age determination?6 points.

Dendrochronology (wood, trees) Tephrochronology (volcanic layers) Varven(layers of sediment in lakes) Index fossils Paleomagnetic analyses IsotopesEAE2522 2aj

Widest used technique to get absolute ages Isotope system used depends on the age of the specimen Can be used to date fossils, minerals, rocks and eventsEAE2522 2am

Stable vs radiogenic5 points.

Stable isotopes don't change their abundance over time Stable isotope ratios can be used as a marker for mainly biological processes Radiogenic isotopes are not stable over time They decay into another isotope of the same element, or an isotope of another element → Abundance of radiogenic isotopes does change over time and therefore be used to date rocks and mineralsEAE2522 2an

118 elements in total 26 elements are monoisotopic (one stable isotope, e.g. Na, Al) 21 elements are mononuclidic (only one isotope in total, e.g., Au) For all others: Usually one isotope is far more abundant that all othersExample Oxygen = 3 isotopes (16,17,18) but ¹⁸O is 99.76% of occurenceEAE2522 2ao

EAE2522 - Topic 2 - 1 Flashcards by Andrew crisp

Underpinning principles

What is the Principle of Uniformitarianism?

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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Underpinning principles

What is the Principle of Superposition?

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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Underpinning principles

What is the Principle of Original Horizontality?

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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Underpinning principles

What is the Principle of Original Continuity?

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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Underpinning principles

What is the Principle of Faunal Succession?

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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Field Geology Principles

What are the Principle of Cross-Cutting Relationships?

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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Field Geology Principles

What is the Principle of Inclusion?

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

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Field Geology Principles

What are the Principle of Baked Contacts?

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

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Field Geology Principles

What is the Succession in Landscape Development?

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

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What are the Methods of age determination?

6 points.

<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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Dendrochronology

4 points.

<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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Index fossils

3 points.

<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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Isotopes!

3 points.

<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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Stable vs radiogenic

<div>5 points.</div>

<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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Elements

4 points.

<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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What is Stratigraphy?

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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}

What are the hierarchy of stratigraphic units?

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Bed → Member → Formation → Group (largest)

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Hierarchy of Stratigraphic Units

What is the bed?

5 points.

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<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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Hierarchy of Stratigraphic Units

Member

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

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<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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Hierarchy of Stratigraphic Units

Formation

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

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<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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Hierarchy of Stratigraphic Units

Group

<div>Largest stratigraphic unit</div>

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<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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What is stratigraphic correlation?

3 points.

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<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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Understanding Age Relationships

2 points.

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<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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Describe

Facies concept

3 points.

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<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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Lateral Facies Changes

What is Transgression?

3 points.

Sea level rise

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

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Lateral Facies Changes

What is Regression?

3 points.

Sea level fall

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

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What is Walther’s Law?

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

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

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

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What factors control the rise and fall of
sea level?

3 points.

Eustasy - global changes in sea level
Tectonics
Sediment Supply

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What are Unconformities?

5 points.

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

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

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What are Angular unconformities?

3 points.

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

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What is a Disconformity?

2 points.

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

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What are Paraconformities?

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

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What are Non-conformities?

2 points.

Contact between old uplifted, weathered & eroded plutonic or metamorphic rocks & younger sediments
Represent a significant time break

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EAE2522 - Topic 2 - 1 Flashcards

(33 cards)