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Sedimentology > FINAL (theory) > Flashcards

FINAL (theory) Flashcards

1
Q

Lithostratigraphic vs
Chronostratigraphic units

A

Lithostratigraphic: Older rocks under younger rocks

Chronostratigraphic: Uses absolute or relative dating methods to date the rocks.

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2
Q

A delta complex is an example of a…

A

Clastic wedge

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3
Q

Limestones are especially vulnerable
to what kind of change?

A

Diagenetic change (chemical
processes that occur post-deposition).

After burial, they can start dissolving allochems and precipitating cement.

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4
Q

What environment are stromatolites found in?

A

Subtidal environments with high salinity.

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5
Q

What is river avulsion?

A

The abandonment of one river and the formation of a new one in a different area.

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6
Q

Types of Tides/Tidal Environments

A
  1. Flood Tide: Incoming tide (landward direction)
  2. Ebb Tide: Outgoing tide (seaward direction)
  3. Slackwater: Period between flood and ebb tide where flow velocity is almost zero
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7
Q

Estuary

A

BANANA!

An embayed coastline with fluvial AND marine sediment sources.

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8
Q

Tripartite Zonation

A

Bayhead delta at the head, central basin in the middle, barrier with inlets at the mouth.

Sand –> mud –> sand pattern

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9
Q

Wave- vs Tide- Dominated Estuaries

A

Wave-Dominated Estuaries
- Higher fluvial energy
- Landward = high fluvial energy, low energy in central basin, near barrier = high marine energy
- Sediment from rivers is trapped in the estuaries and lagoons

Tide-Dominated Estuaries
- Tidal flats can flank the central basin
- Less energy than wave-dominated because flow is “channelized”
- Less defined tripartite facies (because less energy)

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10
Q

Hemipelagic Sediment

A

Terrigenous mud (delivered by rivers) deposited far from the coast with other pelagic sediment.

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11
Q

Debrites vs Turbidites vs Tempesites

A

Debrites: Deposits from debris flows

Turbidites: Deposit from turbidity current

Tempesites: Waves & currents from a storm

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12
Q

How does wind move grains?

A
  1. Saltation: Key mode of transport; sand-sized grains
  2. Creep: Grains rolling along the surface under pressure of wind or impacts from saltating grains; larger grains
  3. Suspension: Smaller grains light enough to be carried by turbulent air, scattered as dust
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13
Q

Progradation vs Retrogradation in cross-section

A

Progradation = SHALLOWING
- Increasing energy
- Getting coarser

Retrogradation = DEEPENING
- Decreasing energy
- Getting finer

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14
Q

Proximal vs Distal

A

Proximal = channels

Distal = floodplains

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15
Q

Crevasse Splays

A

Fan-shaped material formed by breaching a levee during flood. Exhibits the fining upwards of a fan.

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16
Q

What is a floodplain? What are natural levees? What is the whole region called?

A

Floodplain: The WIDE PLAIN of a river, finer-grained material (silt and clay) deposits dropped from floodwaters.

Natural Levees: Fine sands dropped NEAR to the channel due to a sudden loss of competence.

The whole region is called the “Overbank Region”.

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17
Q

Point bar migration creates…

Chutes (cutoffs) result in…

A

Scroll bars (inner scroll scars)

Oxbow lakes (C shape river)

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18
Q

What is a channel thalweg?

A

An imaginary line drawn through the LOWEST points in the channel, which marks the path of FASTEST flow.

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19
Q

Types of Rivers (Classifications)

A
  1. Straight - a stick (single-thread)
  2. Meandering - squiggly (single thread)
  3. Braided - inter-tangled (multi thread)
  4. Anastomosing - vegetated islands in between (multi thread)
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20
Q

What controls rates of weathering?

A

Surface Area: As mechanical weathering breaks rocks into smaller bits, more surface area is exposed to chemical weathering– faster weathering)

Mineral Resistance: Harder minerals with fewer planes of weakness will resist weathering. Note the most physically stable mineral is quartz!

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21
Q

Two Types of Weathering

A
  1. Physical Weathering
  2. Chemical Weathering
    They work at the same time and together!
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22
Q

Types of Physical Weathering

A
  1. Stress Release (me): Overlying rock erodes to uncover balloon-like pluton that “rebounds” up.
  2. Volume Changes: Bunch of types…
  3. Bio Agents: Little animals digging holes, tree roots breaking rocks!
  4. Abrasion (key): Transported grains (by one method or another) bash against each other, become more rounded, and break down.
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23
Q

Types of Physical Weathering: Volume Changes

A

A. Insolation: Repeated heating and cooling over daily cycles to break apart rock.

B. Freeze-Thaw: Water seeps into cracks, freezes and expands cracks, melts, and the process repeats until these cracks break the rock apart.

C. Salt: Rock disintegration by salts crystallizing in cracks during salt water evaporation, breaking the rock apart.

D. Wetting/Drying: Clays expand when wet and contract when dry- these cycles lead to cracks.

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24
Q

Types of Chemical Weathering

A
  1. Simple Solution: Mineral dissolves completely (ie halite).
  2. Hydrolysis: Hydrogen ion replaces other positive ions to dissolve ions and solid products (ie k-feldpsar). Clays (ie kaolinite) are main product.
  3. Redox: Reduction (addition of electrons) and oxidation (removal of electrons) of a substance (ie pyrite).
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25
Q

What indicates provenance?

A

Grain size and composition indicate:
- composition of source
- transport distance and processes
- local climate

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26
Q

Types of Sedimentary Rocks

A
  1. Silici-clastic: Made from clasts (fragments) of older rocks (ie sandstone)
  2. Carbonaceous: Accumulation of organic debris (ie coal)
  3. Chemical/Biochemical: Precipitation of minerals from water (ie limestone)
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27
Q

What are the ingredients for our “Carbonate Factory”?

A
  • Water clarity
  • Sunlight
  • Nutrient levels
  • Salinity
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28
Q

What do we use to classify SILICICLASTIC rocks?

A

Grain size, shape, and sorting.
- Transport distances
- Transport processes

Grain composition.
- Source area
- Transport processes

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29
Q

Rounding and sorting increases with ________________ and ______________________.

A

Transport DISTANCE and ENERGY of transport (processes).

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30
Q

Reynold’s Number vs Freud’s Number

A

Reynolds: The ratio of inertial forces to viscous forces.
- High R = turbulent flow
- Low R = laminar flow

Freuds: The ratio of flow inertia to external field.
- High Fr = supercritical
- Low Fr = subcritical

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31
Q

Shields stress & Critical shear stress

A

Shields Stress: Uses the balance of DRIVING vs RESISTING forces to tell us if a grain will move or not.

Critical Shear Stress: The shear stress at the moment of particle entrainment.

32
Q

Why is water better at moving sediment than air?

A

More flow, and more turbulent flow to overcome resisting forces.

33
Q

Hydraulic Jump

A

When a flow goes from supercritical to subcritical.

34
Q

As velocity increases, we move through different bedforms. Explain this.

A

From LOWEST to highest flow VELOCITY…

LOWER FLOW REGIME
1. Lower plane beds: flat
2. Current ripples: mini dunes
3. Dunes

UPPER FLOW REGIME
4. Upper plane beds: dunes are wiped out
5. Antidunes: dunes in opp direction!
6. Chutes and pools: short-lived and unstable forms

35
Q

What creates bedding?

A
  1. Physical Processes: Changes in sediment transport conditions.
  2. Chemical Processes: Changes in temp, CO2, ion concentrations.
  3. Biological Processes: Changes in biota.
  4. Diagenesis: Post-depositional changes.
36
Q

How is cross bedding created?

A

Landform migration.

37
Q

Upper plane beds generate ___________________________, top surfaces shows ________________________.

A

Parallel laminations
Parting lineations

38
Q

What’s the difference between fluvial and tidal flow?

A

Fluvial: Unimodal
Tidal: Stops and reverses (tides cause flow reversal!)

39
Q

Bimodal dips of dune and ripple foresets due to tidal/flow reversal is called…

A

Herringbone Cross-Stratification

40
Q

Walther’s Law

A

A vertical succession of facies represents migration LATERALLY ADJACENT depositional environments (unless there is evidence of erosion!)

41
Q

Gamma ray logs vs Resistivity logs

A

Gamma Ray Logs: Provide insight into lithology

Resistivity Logs: Provide insight into fluid properties

42
Q

Conformity:
Disconformity:
Angular Unconformity:
Nonconformity:

A

Conformity: Surface separates older and younger layers.

Disconformity: Erosion layer of missing time.

Angular Unconformity: Older strata at an angle to flat younger strata.

Nonconformity: Igneous or metamorphic rocks under younger strata.

43
Q

Sequence Boundary

A

The unconformity generated during sea level fall.

44
Q

Coarsening upward is an indication of…

A

Progradation

45
Q

Parasequences are always progradational, but they can stack together to create what types of stacking patterns?

A
  1. Retrogradational: Long-term accommodation > sedimentation
  2. Progradational: Long-term accommodation < sedimentation
  3. Aggradational: Each parasequence is roughly equal
  4. Degradational: Units are shifted downward to due base-level fall (forced regression)
46
Q

Parasequence

A

Shallowing upward cycles bound by flooding surfaces (ie peritdal cycle).

47
Q

Explain and go through the steps of a Base Level Cycle (systems tract).

A
  1. Highstand Systems Tract: Sea level is constant, sediment input = progradation (seaward direction).
  2. Falling Stage Systems Tract: Sea level falls, coast moves seaward = unconformity (due to base level erosion).
  3. Lowstand Systems Tract: Rate of sea level fall slows, and then slowly begins to rise again.
  4. Rising Stage/Transgressive Systems Tract: Sea level rises so accommodation creation is higher than sediment input = forces transgression (landward direction). Capped by Maximum Flooding Surface.

When it reaches the next Highstand, transgression stops and regression resumes.

48
Q

Gypsum begins to precipitate after seawater has been evaporated down to __% of its original volume.

Halite precipitates from brines reduced to __% its original volume

A

Gypsum = 20%

Halite = 10%

49
Q

Explain the growth and different precipitation textures/stages of gypsum.

A
  1. Gypsum directly precipitating from seawater forms large SELENITE crystals.
  2. Gypsum can dehydrate to form ANHYDRITE, and rehydrate to form ALABASTER, fine-grained gypsum.

Nodal textures form when gypsum grows in carbonate or clay sediment:

  1. If the nodules grow large enough to interfere, it causes CHICKENWIRE TEXTURE.
  2. If more gypsum is added, the gypsum nodules fold over each other, forming an ENTEROLITHIC TEXTURE.
50
Q

Iron formation and phosphorite are what? Give examples of importance.

A

Bioelemental sediments.

Iron formation = Hemoglobin, etc

Phosphorite = DNA and ATP

51
Q

Highest grade Fe ore is…

Highest grade P ore is…

A

Pristine iron formation = taconite or DSO

Granular phosphorite = amalgamated storm beds

52
Q

Ages…
Iron formation =
Phsophorite =

A

Iron formation = Precambrian
Phsophorite = Phanerozoic

53
Q

What creates/destroys accommodation?

A
  1. Eustasy (changes in global sea-level) due to:
    - Global tectonics - e.g. mid-ocean ridge volume
    - Climate - ice mass
    - Climate - thermal expansion of water
  2. Tectonics
    - Subsidence
    - Uplift
54
Q

Base level

A

Sea level/lake level

55
Q

A change in accommodation can be driven by a change in…

A

base level or by subsidence (uplift).

56
Q

Dating/correlation techniques in stratigraphy

A
  1. Biostratigraphy (fossils)
  2. Absolute dating
  3. Magnetostratigraphy
  4. Chemostratigraphy (isotopes)
  5. Sequence stratigraphy
57
Q

Continental evaporites form thin deposits in…

Marginal marine evaporates are prevalent in…

Evaporite deposits hundreds of meters thick can form in…

A

Arid playa-lake settings.

Arid sabkha and salina settings.

Silled, arid marine basins.

58
Q

Stratigraphy

A
  • The study of larger successions of sedimentary rocks
  • The study of how TIME is recorded in rocks
59
Q

Playa Lakes vs Salinas vs Sabkhas

A

Playa lakes = salt pans in lake (smaller)

Salinas = arid lagoons and salt pans (larger)

Sabkhas = arid, supratidal mud flats

60
Q

Coccoliths produce ________.

A

Chalk

61
Q

When did the pelagic factor evolve? Any sediment before then must be what?

A

Jurassic. Any samples older are basically just periplatform (re-sedimented) ooze.

62
Q

What are the two sources of deepwater carbonate sediment?

A
  1. Pelagic Factory: Pelagic rain
  2. Periplatform: Gravity-driven transport downslope (re-sedimented)
63
Q

Explain the CCD

A

Carbonate Compensation Depth is the depth at which carbonate sediment no longer accumulates (the line where rate of accumulation = rate of dissolution).

64
Q

Increase in CO2 =
Decrease in CO2 =

Cold temps =
Warm temps =

A

Increase in CO2 = Dissolution (of CaCO3)
Decrease in CO2 = Precipitation (of CaCO3)

Cold temps = Dissolution (of CaCO3)
Warm temps = Precipitation (of CaCO3)

65
Q

Why does the Pacific (N. Pacific especially) have less calcareous deepwater sediment than the Atlantic?

A
  1. The Pacific has more CO2, meaning more acidic water, keeping the CaCO3 DISSOLVED
  2. Its CCD is deeper
  3. It’s also a deeper ocean
66
Q

Pelagic

A

Near the surface of the ocean

67
Q

What are the 3 reasons carbonate sediments are found in oceans?

A
  1. Solubility differences between carbonate minerals
  2. Ocean circulation
  3. Changes in seawater chemistry with depth
68
Q

Order of Evaporation

A
  1. Calcite
  2. Gypsum
  3. Halite
  4. K & Mg salts
69
Q

Stromatolitic reefs are the norm in…

A

subtidal environments with elevated salinity.

70
Q

What does “peritidal” mean?

A

Within and slightly outside of tidal influence.

71
Q

How does carbonate mud form?

A

Direct precipitation or breakdown of skeletal (usually algae) components.

72
Q

Intraclasts vs Extraclasts

A

Intraclasts: Fragments of lithic (stoned) sediment transported only a short distance.

Extraclasts: Transported far; foreign to depositional environment.

73
Q

Big 3 Carbonate Minerals

A
  1. Calcite
  2. Aragonite
  3. Dolomite
74
Q

Types of Ooids

A
  1. Oolites: 0.25-2 mm
  2. Pisolites: 2+ mm
  3. Oncoids: mm to cm
  4. Oncolites: cm
75
Q

What are allochems?

A

Carbonate grains.

A. Skeletal remains
B. Ooids
C. Intraclasts

76
Q

What are carbonate sediments?

A

Precipitates from organic material, like the skeletons and shells of organisms.

Sedimentology (4 decks)

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