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Sedimentære strukturer Flashcards

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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
Hvornår dannes imbricated pebbles
Når flow er en retning
26
Low-angle planar cross-bedding
Strand Lower flow regime
27
Hvornår ses et bouma sequence
describes a classic set of sedimentary structures in turbidite beds deposited by turbidity currents at the bottoms of lakes, oceans and rivers.
28
Hvad er Load Cast
Man ser også flame structure Dannes når to typer materialer presses sammen - f.eks muddersten og sadsten Nedefra ligner det lidt flutecast
29
Overturned cross-bedding
Når sedimentet udsættes for shear stress ovenfra
30
Hvad er convolute lamination
Plastic deformation of partially liquefied sediment, usually occurring soon after deposition. Liquefaction can be spontaneous as well as externally triggered
31
Hvad er en slump
sedimentær foldning, der påvirker mange lag
32
Hvordan kan man se at en slump ikke er af tektonisk karakter
Limited in vertical space! ➙ comprised in between unfolded rocks Signature for a syn-sedimentary process
33
Påvirkes sand af mudcracks
Nææh
34
Hvad betyder syn sedimantations strukturer
Dannet under sedimentering
35
Hvilken slags struktur er stromatolitter
Biologicallyinduced structures Også Thrombolites - cyanobakterier
36
Hvad er oncoids
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
Bioherm
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
Biostrome
structure built by similar organisms that is bedded but not moundlike.
39
Carbonate mud mounds
carbonate mud-dominated deposits with topographic relief and few or no stromatolites, thrombolites or in place skeletons.
40
Patch reef:
small isolated bioherm
41
Hvilke dyr har gennem tiden bygget rev
Rudister, lithioids, orme (serpulids)
42
Hvilken slags struktur er en teepee
Chemical precipitation structure
43
Hvad er bioturbations
Dyr graver- spiser - lever - det udfyldes
44
Hvad er de vigtigste bioturbations
Thalassonoïdes og Chondrites Diplocraterion - orme-gangde der udvides som ormen vokser
45
Hvad er en ichnofacies
En samling fossilspor, der indikerer miljøet hvor sedimenterene er aflejret
46
What is the difference between stromatolites and thrombolites
Stromatolites has lamination. Thrombolites doesn't
47
Laminar flow
Laminar flow: At all points in the flow all molecules are moving downstream. Molecules move parallel to each other.
48
Turbulent flow
Turbulent flow: At any point in the flow, a molecule may be moving in any direction, but the net flow is downstream.
49
Convolute lamination
Disrupted layering by liquefication during or after deposition
50
Mention the symmetrical ripple forms
Wave ripple, Rolling grain ripple, Vortex
51
Mention the asymmetrical ripple forms
Current ripple
52
Define planar cross-lamination
Are created at low flow velocities. Sand on the lee slope is not reworked
53
trough cross-lamination
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
Trough cross bedding
Formed by the migration of sinuous subaqueous dunes. Typically has asymptotic bottom contacts and an undulating lower boundary.
55
What does mud drapes indicate?
Indicates tidal influence of transport and deposition
56
What is Flaser, wavy and lenticular lamination associated with?
Tidlly influenced environment
57
What are the two types of diapirism?
Salt and mud diapirism
58
Ways for a particles to move
Rolling, Saltation and suspension
59
What is the difference between 2D and 3D dunes?
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
The Froude number
The Froude number is a relationship between the flow velocity (v) and the flow depth (h), and the acceleration due to gravity (g).
61
Characteristics of a fluid
Density, effective density and viscosity
62
Reynolds number
Reynolds number is a dimensionless quantity that indicates the extent to which a flow is laminar or turbulent.
63
Re > 2000 (high value)
Turbulent flow indication
64
Re < 500 (low value)
Laminar flow indication
65
Hvad indikerer andre skrukturer ovenpå en dune - f.eks en dune med ripples på
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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