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SoS > Sedimentære strukturer > Flashcards

Sedimentære strukturer Flashcards

1
Q

Hvilke tre overordnede ting påvirker sedimentære strukturer

A

. Induced by physical processes

  • Biologically induced
  • Chemically induced
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2
Q

Hvad er flutecast

A

Erosionsstruktur

Markeringer når sand eller silt deposeres på mudder og vandet/flow eroderer der undeliggende mudder

Scour & Tool marks

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3
Q

Hvad er eksempler på flute cast/sole marks

A

Rill marks
Obstacle scour

Prod marks
Groove marks

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4
Q

Hvad dannes med et Froude tal under 0,7 (lav sediment koncentration)

A

Dunes

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5
Q

Hvad dannes med et Froude tal mellem 0,7 og lidt over 1 (lav sediment koncentration)

A

Plane bed

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6
Q

Hvad dannes med et Froude tal over 1,1 (lav sediment koncentration)

A

Antidunes

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7
Q

Hvordan dannes cross-stratification

A

Sediment aflejres i dunes
- Dette ses som forskellig størrelse grains i en aflejring/sortering

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8
Q

Hvad kendetegner 3D dunes

A

Trough cross-stratification

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9
Q

Hvad kendetegner 2D dunes

A

Planar cross bedding

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10
Q

Hvilken størrelse har dunes

A

Over ca 10 cm

Bølger over 1 m

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11
Q

Hvad kendetegner ripples i et miljø med høj energi

A

Runde crests
- Eddys samler sediment op og afrunder ripples

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12
Q

Hvad kendetegner ripples i et miljø med lav energi

A

Skarpe crests

Grains ruller

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13
Q

Hvilke to typer ripples findes der

A

Symmetrisk og asymmetrisk

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14
Q

Hvad kendetegner sinous ripples

A

Kurvet cross-stratification

Trough cross-stratification

Current med en retning

All laminae formed under this type of ripple dip at an angle to the flow as well as downstream.

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15
Q

Hvad kendetegner Linguoid ripples

A

Bugter i flere retninger end sinuos

Linguoid ripples have lee slope surfaces that are curved generating a laminae similar to caternary and sinuous ripples.

Linguoid ripples generate an angle to the flow as well as downstream. Linguoid ripples have a random shape rather than a “W” shape, as described in the catenary description. Lunate ripples, meaning crescent shaped ripples, are exactly like linguoid ripples except that the stoss sides are curved rather than the lee slope. All other features are the same.

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16
Q

Hvad kendetegner ladder rippes og hvornår depositeres de

A

Symmetriske ripples med mindre ripples, der går på tværs mellem dem

Tidevandmiljø

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17
Q

Hvad er climbing ripples

A

Når lagene mellem ripples ikke er horisontelle, men ligger skrå

Increased rates of aggradation over
progradation

Danner en Stross side (lang side) og en Lee side (kortt)

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18
Q

Hvad står HCS og SCS for

A

Hummocky cross stratification

Swaley cross stratification

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19
Q

Hvad kendetegner HCS og SCS

A

Product of strong and complex wave activity, mainly in areas
below fair-weather wave base.
Typically interpreted as produced by storm activity.

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20
Q

Hvad aflejres i hhv. et lower og upper flow regime

A

Upper Fr>1 Plane bed + antidune
Lower Fr<1 Ripples + dunes

Increasing energy
Rippler - dunes - plane beds - antidunes

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21
Q

Hvad kendetegner Antidunes

A

Upper flow regime

Rarely preserved in the rock record
Most examples are from volcanoclastic setting (very
high velocity and large sediment load during
pyroclastic surges)

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22
Q

Hvornår dannes herringbone crossing

A

Tidevandsmiljøer

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23
Q

Hvad kendetegner Descending cross-bedding

A

Produced by small dunes descending the leeside of a larger dune

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24
Q

Hvilke tre slags lamination hører sammen med tidevandsmiljøer

A

Flaser
Wavy
Lenticular

Rhythmic variation of mud-tosand ratio.

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25
Q

Hvornår dannes imbricated pebbles

A

Når flow er en retning

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26
Q

Low-angle planar cross-bedding

A

Strand
Lower flow regime

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27
Q

Hvornår ses et bouma sequence

A

describes a classic set of sedimentary structures in turbidite beds deposited by turbidity currents at the bottoms of lakes, oceans and rivers.

28
Q

Hvad er Load Cast

A

Man ser også flame structure
Dannes når to typer materialer presses sammen - f.eks muddersten og sadsten

Nedefra ligner det lidt flutecast

29
Q

Overturned cross-bedding

A

Når sedimentet udsættes for shear stress ovenfra

30
Q

Hvad er convolute lamination

A

Plastic deformation of partially
liquefied sediment, usually
occurring soon after deposition.

Liquefaction can be spontaneous
as well as externally triggered

31
Q

Hvad er en slump

A

sedimentær foldning, der påvirker mange lag

32
Q

Hvordan kan man se at en slump ikke er af tektonisk karakter

A

Limited in vertical space!
➙ comprised in between unfolded rocks
Signature for a syn-sedimentary process

33
Q

Påvirkes sand af mudcracks

A

Nææh

34
Q

Hvad betyder syn sedimantations strukturer

A

Dannet under sedimentering

35
Q

Hvilken slags struktur er stromatolitter

A

Biologicallyinduced structures

Også
Thrombolites - cyanobakterier

36
Q

Hvad er oncoids

A

Spherical or less wellrounded structures,
commonly up to 2-3
cm in diameter but
sometimes larger.
Lamination similar to
stromatolites

Oncoids - indeholder et lille stykke alge

37
Q

Bioherm

A

ancient organic reef of moundlike form (positive topography
over the sea floor) built by a variety of marine invertebrates, including
corals, echinoderms, gastropods, mollusks, and others…

38
Q

Biostrome

A

structure built by similar organisms that is bedded but not
moundlike.

39
Q

Carbonate mud mounds

A

carbonate mud-dominated deposits with
topographic relief and few or no stromatolites, thrombolites or in
place skeletons.

40
Q

Patch reef:

A

small isolated bioherm

41
Q

Hvilke dyr har gennem tiden bygget rev

A

Rudister, lithioids, orme (serpulids)

42
Q

Hvilken slags struktur er en teepee

A

Chemical precipitation structure

43
Q

Hvad er bioturbations

A

Dyr graver- spiser - lever - det udfyldes

44
Q

Hvad er de vigtigste bioturbations

A

Thalassonoïdes og Chondrites

Diplocraterion - orme-gangde der udvides som ormen vokser

45
Q

Hvad er en ichnofacies

A

En samling fossilspor, der indikerer miljøet hvor sedimenterene er aflejret

46
Q

What is the difference between stromatolites and thrombolites

A

Stromatolites has lamination. Thrombolites doesn’t

47
Q

Laminar flow

A

Laminar flow: At all points in the flow all molecules are moving downstream. Molecules move parallel to each other.

48
Q

Turbulent flow

A

Turbulent flow: At any point in the flow, a molecule may be moving in any direction, but the net flow is downstream.

49
Q

Convolute lamination

A

Disrupted layering by liquefication during or after deposition

50
Q

Mention the symmetrical ripple forms

A

Wave ripple, Rolling grain ripple, Vortex

51
Q

Mention the asymmetrical ripple forms

A

Current ripple

52
Q

Define planar cross-lamination

A

Are created at low flow velocities. Sand on the lee slope is not reworked

53
Q

trough cross-lamination

A

Sinuous and linguoid ripples have lee slope surfaces that are curved, which makes laminae that dip at an angle to the flow as well as downstream

54
Q

Trough cross bedding

A

Formed by the migration of sinuous subaqueous dunes. Typically has asymptotic bottom contacts and an undulating lower boundary.

55
Q

What does mud drapes indicate?

A

Indicates tidal influence of transport and deposition

56
Q

What is Flaser, wavy and lenticular lamination associated with?

A

Tidlly influenced environment

57
Q

What are the two types of diapirism?

A

Salt and mud diapirism

58
Q

Ways for a particles to move

A

Rolling, Saltation and suspension

59
Q

What is the difference between 2D and 3D dunes?

A

2D dunes har en lineær crest. 3D dunes har en sinius crest. Hvis du skærer en 2D dunes igennem, har det planar cross-stratifcation (horizontal laminations)
3D dunes har trough-stratification (Bended lamination).
Lower flow velocity = 2D dunes
Higher flow velocity = 3D dunes

60
Q

The Froude number

A

The Froude number is a relationship between the flow velocity (v) and the flow depth (h), and the acceleration due to gravity (g).

61
Q

Characteristics of a fluid

A

Density, effective density and viscosity

62
Q

Reynolds number

A

Reynolds number is a dimensionless quantity that indicates the extent to which a flow is laminar or turbulent.

63
Q

Re > 2000 (high value)

A

Turbulent flow indication

64
Q

Re < 500 (low value)

A

Laminar flow indication

65
Q

Hvad indikerer andre skrukturer ovenpå en dune
- f.eks en dune med ripples på

A

At der ikke er ligevægt
- unsteady flow (ikke uniform)
- der dannes en internal boundary layer på stoss siden af dunes

SoS (6 decks)

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