Sedimentære strukturer Flashcards
Hvilke tre overordnede ting påvirker sedimentære strukturer
. Induced by physical processes
- Biologically induced
- Chemically induced
Hvad er flutecast
Erosionsstruktur
Markeringer når sand eller silt deposeres på mudder og vandet/flow eroderer der undeliggende mudder
Scour & Tool marks
Hvad er eksempler på flute cast/sole marks
Rill marks
Obstacle scour
Prod marks
Groove marks
Hvad dannes med et Froude tal under 0,7 (lav sediment koncentration)
Dunes
Hvad dannes med et Froude tal mellem 0,7 og lidt over 1 (lav sediment koncentration)
Plane bed
Hvad dannes med et Froude tal over 1,1 (lav sediment koncentration)
Antidunes
Hvordan dannes cross-stratification
Sediment aflejres i dunes
- Dette ses som forskellig størrelse grains i en aflejring/sortering
Hvad kendetegner 3D dunes
Trough cross-stratification
Hvad kendetegner 2D dunes
Planar cross bedding
Hvilken størrelse har dunes
Over ca 10 cm
Bølger over 1 m
Hvad kendetegner ripples i et miljø med høj energi
Runde crests
- Eddys samler sediment op og afrunder ripples
Hvad kendetegner ripples i et miljø med lav energi
Skarpe crests
Grains ruller
Hvilke to typer ripples findes der
Symmetrisk og asymmetrisk
Hvad kendetegner sinous ripples
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.
Hvad kendetegner Linguoid ripples
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.
Hvad kendetegner ladder rippes og hvornår depositeres de
Symmetriske ripples med mindre ripples, der går på tværs mellem dem
Tidevandmiljø
Hvad er climbing ripples
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)
Hvad står HCS og SCS for
Hummocky cross stratification
Swaley cross stratification
Hvad kendetegner HCS og SCS
Product of strong and complex wave activity, mainly in areas
below fair-weather wave base.
Typically interpreted as produced by storm activity.
Hvad aflejres i hhv. et lower og upper flow regime
Upper Fr>1 Plane bed + antidune
Lower Fr<1 Ripples + dunes
Increasing energy
Rippler - dunes - plane beds - antidunes
Hvad kendetegner Antidunes
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)
Hvornår dannes herringbone crossing
Tidevandsmiljøer
Hvad kendetegner Descending cross-bedding
Produced by small dunes descending the leeside of a larger dune
Hvilke tre slags lamination hører sammen med tidevandsmiljøer
Flaser
Wavy
Lenticular
Rhythmic variation of mud-tosand ratio.
Hvornår dannes imbricated pebbles
Når flow er en retning
Low-angle planar cross-bedding
Strand
Lower flow regime
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.
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
Overturned cross-bedding
Når sedimentet udsættes for shear stress ovenfra
Hvad er convolute lamination
Plastic deformation of partially
liquefied sediment, usually
occurring soon after deposition.
Liquefaction can be spontaneous
as well as externally triggered
Hvad er en slump
sedimentær foldning, der påvirker mange lag
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
Påvirkes sand af mudcracks
Nææh
Hvad betyder syn sedimantations strukturer
Dannet under sedimentering
Hvilken slags struktur er stromatolitter
Biologicallyinduced structures
Også
Thrombolites - cyanobakterier
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
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…
Biostrome
structure built by similar organisms that is bedded but not
moundlike.
Carbonate mud mounds
carbonate mud-dominated deposits with
topographic relief and few or no stromatolites, thrombolites or in
place skeletons.
Patch reef:
small isolated bioherm
Hvilke dyr har gennem tiden bygget rev
Rudister, lithioids, orme (serpulids)
Hvilken slags struktur er en teepee
Chemical precipitation structure
Hvad er bioturbations
Dyr graver- spiser - lever - det udfyldes
Hvad er de vigtigste bioturbations
Thalassonoïdes og Chondrites
Diplocraterion - orme-gangde der udvides som ormen vokser
Hvad er en ichnofacies
En samling fossilspor, der indikerer miljøet hvor sedimenterene er aflejret
What is the difference between stromatolites and thrombolites
Stromatolites has lamination. Thrombolites doesn’t
Laminar flow
Laminar flow: At all points in the flow all molecules are moving downstream. Molecules move parallel to each other.
Turbulent flow
Turbulent flow: At any point in the flow, a molecule may be moving in any direction, but the net flow is downstream.
Convolute lamination
Disrupted layering by liquefication during or after deposition
Mention the symmetrical ripple forms
Wave ripple, Rolling grain ripple, Vortex
Mention the asymmetrical ripple forms
Current ripple
Define planar cross-lamination
Are created at low flow velocities. Sand on the lee slope is not reworked
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
Trough cross bedding
Formed by the migration of sinuous subaqueous dunes. Typically has asymptotic bottom contacts and an undulating lower boundary.
What does mud drapes indicate?
Indicates tidal influence of transport and deposition
What is Flaser, wavy and lenticular lamination associated with?
Tidlly influenced environment
What are the two types of diapirism?
Salt and mud diapirism
Ways for a particles to move
Rolling, Saltation and suspension
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
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).
Characteristics of a fluid
Density, effective density and viscosity
Reynolds number
Reynolds number is a dimensionless quantity that indicates the extent to which a flow is laminar or turbulent.
Re > 2000 (high value)
Turbulent flow indication
Re < 500 (low value)
Laminar flow indication
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
