EESC > SedStrat Exam 3 > Flashcards

SedStrat Exam 3 Flashcards

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1
Q

Define stratigraphy.

A

The study of layered sedimentary rocks and the processes that form them.

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2
Q

What is lithostratigraphy?

A

Correlation and classification of rock layers based on physical characteristics.

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3
Q

What physical properties are used in lithostratigraphy?

A

Color, grain size, mineralogy, sedimentary structures, and texture.

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4
Q

What is the Law of Superposition?

A

In undisturbed strata, younger rocks overlie older rocks.

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5
Q

Define conformity.

A

A contact indicating continuous deposition without interruption.

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6
Q

Define unconformity.

A

An erosional surface representing missing geologic time.

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7
Q

Define gradational contact.

A

A slow transition from one rock type to another.

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8
Q

What is a formation?

A

A mappable rock unit with distinct lithologic characteristics.

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9
Q

What is direct correlation?

A

Physically tracing a rock layer across exposures.

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10
Q

What is indirect correlation?

A

Using logs, fossils, or polarity to correlate units.

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11
Q

What is lithocorrelation?

A

Matching rock units based on lithologic similarities.

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12
Q

What is biocorrelation?

A

Matching rock units using fossil content.

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13
Q

What is chronocorrelation?

A

Matching units based on geologic age.

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14
Q

What log measures natural radioactivity?

A

Gamma ray log.

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15
Q

What does a resistivity log measure?

A

How well a rock resists electrical current.

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16
Q

What does a sonic log measure?

A

The velocity of sound through a rock.

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17
Q

What is a marker bed?

A

A distinctive layer useful for correlation.

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18
Q

What is cyclostratigraphy?

A

Study of cyclic sedimentary patterns related to Milankovitch cycles.

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19
Q

What causes Milankovitch cycles?

A

Changes in Earth’s orbital eccentricity, obliquity, and precession.

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20
Q

What are small-scale sedimentary cycles called?

A

Parasequences.

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21
Q

What do repeating shale-sandstone cycles represent?

A

Climate-driven sedimentary changes.

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22
Q

Who first formalized early stratigraphic classification?

A

Johann Lehmann.

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23
Q

What is Walther’s Law?

A

Vertically adjacent facies were once laterally adjacent.

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24
Q

What is lateral facies change?

A

Changes in rock type across an environment.

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25
What limits direct bed tracing?
Poor exposure and pinch-outs.
26
What is sequence stratigraphy?
Study of sedimentary layers in relation to sea-level changes.
27
Define base level.
The surface to which erosion converges, essentially sea level.
28
Define accommodation space.
Space available for sediment deposition.
29
What controls accommodation?
Sea level changes and sediment supply.
30
What is a sequence?
A stratigraphic package formed during one sea-level cycle and bounded by unconformities.
31
What is a systems tract?
Sediment deposited during a specific phase of sea-level change.
32
Define Highstand Systems Tract (HST).
Deposits formed during high or slowly rising sea level.
33
Define Falling Stage Systems Tract (FSST).
Deposits formed as sea level falls and causes forced regression.
34
Define Lowstand Systems Tract (LST).
Deposits formed at the lowest sea level.
35
Define Transgressive Systems Tract (TST).
Deposits formed during rising sea level and increasing accommodation.
36
What is progradation?
Outbuilding of sediment seaward.
37
What is retrogradation?
Landward shift of depositional facies due to rising sea level.
38
What is aggradation?
Vertical stacking of sediment when accommodation and supply are balanced.
39
Define a parasequence.
Shallowing-upward sediment package bounded by flooding surfaces.
40
What is a flooding surface?
A surface marking an abrupt increase in water depth.
41
What is maximum flooding surface?
The surface marking peak transgression.
42
What does forced regression mean?
Seaward migration of shoreline due to sea-level fall.
43
What is a shelf-margin wedge?
Sediment body deposited at a shelf edge during lowstand.
44
What is a slope fan?
Sediments deposited along continental slopes during lowstand.
45
What is a basin-floor fan?
Deep-water sediment deposited far from shore during lowstand.
46
What is a Wheeler diagram?
A chronostratigraphic chart showing time vs deposition.
47
What is the purpose of sequence stratigraphy?
To provide a basin-wide chronological framework for sediment distribution.
48
What is onlap?
Sedimentary layers terminating landward against an inclined surface.
49
What is toplap?
Strata ending upward against a boundary due to nondeposition.
50
What indicates sea-level standstill?
Coastal onlap without major facies shift.
51
What is seismic stratigraphy?
Interpretation of subsurface layers using seismic reflections.
52
What produces seismic reflections?
Differences in acoustic impedance between rock layers.
53
What is acoustic impedance?
The product of rock density and seismic velocity.
54
What is a seismic reflector?
A boundary where seismic waves reflect because of property changes.
55
Why might thin beds not produce separate reflections?
Their reflections merge due to insufficient thickness.
56
What is two-way travel time?
Time for seismic waves to travel down and return to the surface.
57
What affects seismic velocity?
Rock density, lithology, porosity, and fluid content.
58
What are parallel reflectors?
Indicate uniform, continuous deposition.
59
What are prograding reflectors?
Show seaward outbuilding of sediment, typical of deltas.
60
What are chaotic reflectors?
Indicate disturbed deposits like slumps or debris flows.
61
What is reflection-free seismic character?
Represents homogeneous lithology with little layering.
62
What is truncation?
Reflectors cut off by erosion.
63
What is toplap?
Reflectors terminate upward due to nondeposition.
64
Define onlap in seismic terms.
Reflectors terminate updip onto an inclined surface.
65
Define downlap.
Reflectors terminate downdip onto a surface.
66
What are undaforms?
Flat-topped reflections representing shelf areas.
67
What are clinoforms?
Inclined reflections forming shelf-slope transitions.
68
What are fondoforms?
Flat basin-floor reflections.
69
What is seismic amplitude?
Strength of reflection, often tied to layer thickness or contrast.
70
What is seismic facies analysis?
Interpretation of reflection patterns to infer depositional environment.
71
What is a sequence boundary in seismic data?
A major unconformity recognized by reflection terminations.
72
What does divergent bedding indicate?
Variable subsidence or sediment supply during deposition.
73
What is a seismic line?
A 2-D cross section showing reflection geometry.
74
What is environmental interpretation in seismic?
Determining depositional settings based on reflection patterns.
75
Why is seismic stratigraphy useful?
It reveals basin-scale architecture unavailable from outcrop alone.
76
What is magnetostratigraphy?
Correlation and dating using magnetic polarity in rocks.
77
What creates Earth's magnetic field?
Flow of molten iron-nickel in Earth's outer core.
78
What is a magnetic reversal?
A switch where magnetic north and south poles flip.
79
What is thermal remanent magnetization?
Magnetic alignment preserved as igneous rocks cool.
80
What is detrital remanent magnetization?
Alignment of magnetic grains during sediment deposition.
81
What is declination?
Horizontal angle between ancient magnetic pole and geographic pole.
82
What is inclination?
Angle of magnetic field lines related to latitude.
83
What is normal polarity?
Magnetization pointing toward modern north magnetic pole.
84
What is reversed polarity?
Magnetization pointing toward modern south magnetic pole.
85
Why are magnetic reversals important?
They are synchronous worldwide and ideal for correlation.
86
What are magnetic anomalies?
Striped patterns of polarity on the seafloor.
87
What do magnetic anomalies reveal?
Seafloor spreading history.
88
What dating method pairs with magnetostratigraphy?
Radiometric dating.
89
What is the geomagnetic polarity timescale?
Record of magnetic reversals through time.
90
Why is magnetostratigraphy useful in loess?
Loess often lacks fossils, but preserves magnetic polarity.
91
How are magnetic measurements taken?
With magnetometers in laboratories.
92
Why is basalt good for magnetostratigraphy?
It preserves strong magnetic signatures when it cools.
93
What is a chrons?
A long interval of normal or reversed polarity.
94
What is a subchron?
A shorter polarity interval within a chron.
95
What is paleomagnetism?
Study of Earth's ancient magnetic field recorded in rocks.
96
What is a magnetic reversal boundary?
A contact marking a switch in polarity.
97
What does inclination close to 90 degrees indicate?
Formation near a magnetic pole.
98
What does inclination near 0 degrees indicate?
Formation near the magnetic equator.
99
What is correlation?
Matching rock layers from place to place using shared characteristics.
100
Why is magnetostratigraphy globally powerful?
Magnetic reversals occur simultaneously worldwide.
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