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Sedimentology > Week 2 > Flashcards

Week 2 Flashcards

1
Q

Stratigraphy =

A

Study of vertical sequence of strata and lateral variations of individual beds on a regional basin

  • stratum
  • bedding planes (bounding surfaces)
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2
Q

Sharp boundaries represent

A

Period of non-deposition

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3
Q

Lithostratigraphy =

A

Study of PHYSICAL relationship among rock units

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4
Q

Biostratigraphy (concept)

A

:) Shorter lifespan = more precisely correlated
:) Rapidly evolving
:) Broad distribution

e.g. Graptolites, lower Palaeozoic correlate to 100,000 year time frame

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5
Q

Chemostratigraphy (concept)

A

U/Th/K

Gamma rays, consistent with certain lithologies
- low for sand, high for mud

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6
Q

Allostratigraphy =

A

Uses discontinuities:

  • unconformities
  • omission surfaces
  • ravinement surfaces
  • flooding surfaces
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7
Q

Ravinement surface =

A

Erosional!

1st surface due to flooding (increasing SL)

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8
Q

Flooding surface =

A

Separates young/old and obvious change in SL

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9
Q

Facies =

A

Distinctive packet of sedimentary rock with specific sedimentary features FROM DEPOSITIONAL ENVIRONMENT

e.g. “deltaic” facies

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10
Q

Lithofacies =

A

Based on grain size/mineralogy

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11
Q

Biofacies =

A

Based on fossils

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12
Q

Walthers Law =

A

Concept that vertical succession of facies represents lateral changes in environment

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13
Q

What controls accommodation space?

A

SEA SURFACE
- eustasy = global SL from datum

SEA FLOOR
- tectonics

RATE OF SEDIMENT ACC

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14
Q

Sea level falls =

A

Sea cuts down and incises
Regression
Coarsening upwards/prograding sequence

Foreshore material steps over and works its way towards the sea

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15
Q

Sea level rises =

A

Sediment deposited further up near river
Transgression
Fining upwards sequence

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16
Q

Mechanisms of SL change

A

Varying ice volume (global/regional)

Varying ridge volume

  • slow spreading = decrease (steeper = more vol so requires “more sea”
  • fast spreading = increases

Tectonic effects

  • plate convergence
  • continental collision
17
Q

Systems tracts =

A

Heterogeneous sedimentary units produced by contemporaneous depositional systems during specific phases of basal level variation

18
Q

TST

A

Transgressive

Increase in SL

19
Q

RST

A

Regressive

Decrease in SL

20
Q

Parasequence =

A

~conformable succession of genetically related beds/bedsets bounded by marine flooding surfaces and their correlative surfaces

Together form a sequence with unconformities as boundaries

21
Q

Progradational parasequence

A

Decreasing SL

22
Q

Aggradational parasequence

A

Static SL

23
Q

Retrogradational parasequence

A

Increasing SL

24
Q

Subaerial unconformity =

A

Formed through subaerial exposure and erosion including downcutting rivers/soil/karst processes

25
Q

Allocyclic controls =

A

External to system

TECTONICS

CLIMATE

BASE LEVEL

26
Q

Allocyclic TECTONICS

A

Accommodation space

Sediment flux direction

Uplift = erosion

Slope/stream power

Facies distribution

27
Q

Allocyclic CLIMATE

A

Weathering

Rainfall

Glaciation

Climatic belts (arid/tropical etc)

28
Q

GR: even block with sharp top and base “cylindrical”

A

Aggrading

Eolian
Braided fluvial
Channel fill
Submarine-canyon fill
Carbonate shelf margin
Evaporite fill of basin
29
Q

GR: coarse up and sharp top “funnel”

A

Prograding

Crevasse splay
River mouth bar
Delta front
Shoreface
Submarine fan lobe
Change from clastic to carbonates
30
Q

GR: fine up and sharp base “bell”

A

Retrograding

Fluvial point bar
Tidal point bar
Deep-tidal channel fill
Tidal flat
Transgressive shelf
31
Q

GR: hourglass “symmetrical”

A

Prograding and retrograding

Reworked offshore bar
Regressive to transgressive shore face delta

32
Q

GR: saw teeth “serrated”

A

Aggrading

Fluvial floodplain
Storm-dominated shelf
Distal deep-marine slope

33
Q

When does a greater occurrence of turbidites in deepwater occur?

A

During lowstand rather than highstand

Sedimentology (9 decks)

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