Depositional environments Flashcards
Hvad er eksempler på kontinentelle depositionel enviroments
Gletsjer, aeolian
Hvad kaldes deposits direkte fra is
Till - hvis det ikke er sammenpresset
Tillite - hvis det er consolideret/lithithied
Hvilke typer gletsjere findes der
Poler, polytherman, temperate
Hvad er moræne
Till der er samlet i kanten af en gletsjer
Hvordan dannes et till sheet under floating ice sheet
Noget is smelter og sedimenter ryger fra ice sheet ned på bunden af havet
Dette kan også sker under flydende isbjerge kaldes dropstone
Hvad er en Loess
Fragmenter (clastic) primært på størrelse med silt
blæses sammen
Hvilke strukturer ses i aeolian miljø
Sand dune
Alluvial fans
Dry alluvial plain
ephemeral lake
Hvordan dannes mushroom rock
Vinden er stærkest et bestemt sted over jorden - her vil der ske meget erosion pga vinden
Hvilke bedforms ses i aeolian miljøer
Ripple 1-64 cm
Dune 10-640 m
Draa fiels 640 - < 2,5 km
Største bedforms i verden
Hvad ses i bedforms i aeolian miljøer
Større fragmenter i toppen af dunen - finere på bunden
Hvordan ser man forskel på aeolien og sub-aquarius dunes
I aeolian er der grain-flow tounges i bunden af dunen
Hvilke ting er karakteristiske for aeolian dunes
Well-sorted and well-rounded sand grains are mostly deposited by aeolian dunes (wind cannot move pebbles!).
Grain-flow tongues at the foot of aeolian dunes help to distinguished them from subaqueous bedforms.
Wind ripples oriented perpendicular to the dune cross lamina is also characteristic for aeolian dunes.
Hvordan adskiller en sø sig fra havet
Ingen tidevand
Stille vand
River deposits
Konglomarater
Sand and pebbles:
Deposited by flowing waters
within or in the vicinity of river
channels
Mud (mostly clay):
Deposited by stagnant water in
floodplain (sometimes also in
abandoned channels)
Hvornår dannes leeves
I floder på ydersiden dannes der en lille banke
Levees form when flood waters rapidly deposit sediment close to the bank and crevasse
splays are created when the levee is breached.
Hvad er den største morfologiske karakteristik ved braided river
Mid-cannel bars
Hvilken forskel ses vertikel i aflejring mellem braided og meandering floder
Braided har mindre lag af mudder på toppen
Større lag under med sand
Braided er aglamated
Hvad er calcreres
calcium-rich duricrust, a hardened layer in or on a soil
Ses i bunden af floder - mellem flod og grundvand
Tykke lag er calcretes indikerer well-developed soil profile
Tynde lag af calcretes kan grundvand løbe gennem
Hvilke fysiske ting kontrollerer en flod
Principal physical controls on river type:
- Sediment load
- Slope
- Seasonality of runoff
- Baseline
Hvad er en point bar og hvordan dannes den
Den inderste del af en sving i en meandering flod
Sedimenter aflejres i svinget
Modsat i svinget ligger et cutoff
Hvad er foreshore
Strand
Her ses sand
Mellem mean high water og mean low water
Alle sedimenter vil blive reworked af bølger
Sand her vil blive aflejret som wave ripple, cross-lamination og horizontal stratification
Mudder vil ligge i flaser beds aflejret i perioder med mindre bølge energi
- de bliver mere almindelige i lidt dybere vand
Wave ripples vil blive mindre almindelige jo tættere man kommer på fair weather wave base
Hvad er shore fase
Mellem mean low water og fair weather base
Her ses sand
Alle sedimenter vil blive reworked af bølger
Sand her vil blive aflejret som wave ripple, cross-lamination og horizontal stratification
Mudder vil ligge i flaser beds aflejret i perioder med mindre bølge energi
- de bliver mere almindelige i lidt dybere vand
Wave ripples vil blive mindre almindelige jo tættere man kommer på fair weather wave base
Hvad er offshore-transition
Mellem fair weather base og storm wave base
Her ses mudder og tynde lag af sand sten med HCS
Sand aflejres og reworks af storm
Proximal tempestites have erosive bases and are composed of coarse detritus,
whereas the distal parts of the bed are finer-grained laminated sands: hummocky and swaley cross-stratification occurs in the sandy parts of tempestites.
Mellem storme aflejres mudder.
Disse fine korn kommer fra floder og ender hele vejen nede i offshore-stransition
Storm deposits er derfor adskilt af mudderlag. Medmindre mudderet eroderes væk
Hvad er offshore
Under storm wave base
Her aflejres primært mudder. Ikke engang storme påvirker dette område - ekseptionelle storme kan måske aflejret noget sand her
Grå sedimenter - intet oxygen
Hvad ses ofte i carbonate shallow miljøer
Tropiske steder - varmt - henrys lov
Tropisk koral rev
Ooids
Hvad er Symbiotic photozoan organisms
Koraller lever i symbiose med photozoan- beskyttelse for ekstra energi/O
Shallow water tropical corals (and some
other organisms) live in symbiosis with
zooxanthellae, which are single-celled
protozoans (dinoflagellates)
Kold vandkoraller lever ikke i symbiose med zooxanthella.
Hvilke faktorer kontrollerer miljøet i lavvands carbonate
Lys
Hvilke organismer der producerer sedimanter alt efter dybde
Hvad ses ofte i mudder dominerede siciliclastisk hav
Bioturmation
Hvilke photozoan findes der
Grønne alger - Calcareous green algae
Røde alger - Calcareous red algae = Rhodolith
HvilkeSymbiotic photozoan organisms findes der
Orbitolina
Nummulitetter
Rudister
Hvad er Heterozoan organisms
Ingen symbiose
Kold vandskoraller
Bryozoans
Echinoderms
Brachiopods
Hvilke organismer producerer sediment, når der er lys
Koraller
Grønne alger
Rudister
Stromatoporider
Hvilke organismer producerer sediment, når der er lidt lys
Større foraminiferer
Røde alger
Hvilke organismer producerer sediment, når der ikke er lys
Bryozoer
Mollusker
Chrinoids
Sponges
Hvad kaldes de forskellige lyszoner
Høj til lav
Eutrophic
Mesotrophic
Oligotrophic
Hvad danner carbon i koldt vand
Heterotrophic
Hvad danner carbon i varmt vand
autotrophic
Hvad er de to ekstremer for carbonate platforms
Homoclinal - lige rampe
Rimmed shelf - rampe med en klump på
What are the 6 parameters required to fully
characterize the Seawater carbonate system?
Nutrience, Salinity, Temperature, Depth, Type of organisms, Sunlight
Hvilke slags deltaer findes der
Tide dominated - Tidal power
River dominated - mellem tide og river
Wave dominated - River power
Hvilke slags estuary findes der
Tide dominated - Tidal power
Wave dominated - Mellem tide og river
Lagoon - River power
Hvilke controls er der på deltaer
Climate
Tektonics
Eustatic sea level
Delta deposition - river dominated
Delta Top
- channel og overbank
- her kan være meget vegetation
- sediment aflejringer ligner fluvial
channel udmunder i bird’s foot
i bays her er fine sedimenter
Delta Front
Hvad karakteriserer river dominated delta
Der er noget der stopper bølgerne fra når kystlinjen
Low-energy, interdistributary bays are a characteristic of river-dominated deltas.
Interdistributary = omsluttet af en bay - en lille lomme
Bird’s foot pattern
Der er en lobe i bunden af floden - disse bliver ikke reworked af bølger
Denne flod kan skifte position når floden ændrer kanal
Hvad karakteriserer wave dominated delta
A wave-dominated delta formed where wave activity reworks the sediment brought
to the delta front to form coastal sand bars and extensive mouth-bar deposits
Der sker ikke meget prodegation fordi bølgerne hurtigt piller ved sedimenter i udmundingen
prodagation sker fordi bølgerne ikke kan flytte sedimenterne væk
Sedimenter kan migrere lateralt pga vind
Der dannes sandbunker, der er parallele med kysten
Bølger er gode til at sortere grans
Hvilken forskel ses mellem wave og river dominated deltaes
River = mindre kontinuerlig mouth bars, mere channel og overbank.
Delta lobes
Deposits mellem de to ligner hinanden
Hvad karakteriserer tidal dominated delta
Der dannes aflange aflejringer væk fra kysten. Tidal sand bars
Intertidal zone
Tidevandsaflejringer
Perioder udenbevægelse - mudder
Hvordan kender man forskel på tidal dominated delta og estuary
Delta har karakteristisk “coarsening-up”
- Sedimenterne bliver grovere længere væk fra havet
The main
distinguishing feature is that a delta is always a
progradational feature, whereas an estuary commonly
forms as part of a retrogradational, or transgressive,
succession
Hvad er en esturary
Del af havet der modtager sedimenter fra både floder og hav
Bliver påvirket af flod, tidevand og bølger
Transgressive
Er tredelt
Hav del - sedimenter går ind ad - bølger
Mellem del - ikke meget energi - tidevand
Flod del - sedimenter går mod hav
Hvad er en lagune
shallow body of water partly or completely
separated from a larger body of water by a barrier, which can be a bioconstructed reef, a clastic beach barrier or hard rocks ridge.
Hvilke to slags siliciclastiske strande (littoral) findes der
Dissipative
. bred surf zone
- typisk sand
Refrective
- stejl
- lille surfzone
- sand og grus
What is a beach berm?
Berm er et stykke af stranden der adskiller foreshore fra backshore
What characterizes lagoonal facies?
A lagoonal succession is typically
mudstone, often organic-rich, with thin,
wave-rippled sand beds
Ligner en sø
- marine forssiler kan fortælle der er en lagune
Hvilke slags sedimentære processer sker på det dybe hav
Mass-flow processes.
debris flows, density
flows and turbidity
currents
Bouma sequence
Hvordan starter massflow processes
Trigger - jordskælv, seismisk aktivitet
For meget sediment samlet på shelfen
Store strom bølger
Meget sediment fra floder
A fall in sea level exposes shelf
sediments to erosion, more storm effects
and sediment instability that result in
increased frequency of turbidity currents.
Hvad er et hyperpycnal flow
Turbidity flow der fortsætter - sker pga forhøjet sedimenter fra flod
Hvad er contourites
Sediment aflejringer på bunden af havet
Dannes af vanden der strømmer på bunden
Parallele med konturer på havbunden
Kontinuerlige i stedet for single event som tubidite
Hvad er pelagic sediment
pelagite
Fine sedimenter der samles på bunden fra det åbne hav
Der er tre typer siliceous oozes, calcareous oozes, and red clays.
Hvad er ooze
pelagic sediment
> 30% mikrospiske carbon er si rig planktoniske organismer
Resten er ler
Hvilke fire faktorer kontrolerrer pelagic sedimenters komposition
- Distance from major landmasses (affects dilution from terrigenous and other land-derived sediments)
- Water depth (affects preservation of both siliceous- and calcareous biogenic particles that settle to the ocean bottom)
- Oceanic fertility (controls the amount of biogenic particles produced in surface waters)
- Bottom currents (affects preservation of pelagic sediments due to erosion, reworking and re-deposition)
Hvad er CCD
Carbonate compensation debth
Grænsen hvor carbonater opløses
Hyper concentrated flow
Density flow
turbidity flow
Creates bouma sequence. The most common clastic deposit
Why are bouma sequences rarely complete?
Because of nonuniform grain size distribution and flow transformations
Hvad er forskellen mellem et tubidity flow og en bourma sequence
Bourma er kun en retning
Turbidite er interference
Deep clastic sea lithologies
Mud, sand and gravel
Deep clastic sea mineralogy
Arenites - may be lithic or arkosic (feldspar rich)
Deep clastic sea texture
Variable. Some turbidites. Poorly sorted.
Deep clastic sea Bed geometry
Mainly thin sheet beds
Deep clastic sea sedimentary structures
Graded turbidite beds with some horizontal and ripple lamination
Deep clastic sea paleocurrents
Bottom structures and ripple lamination in turbidites show flow direction.
Deep clastic sea paleocurrents
Examples of pelagic life
Diatom, radiolaria, forarminifera
“layer cake” stratigraphy
What important stratigraphy feature from the pelagic open ocean is this?
Horizontal layeringer with a small tilt
Hvad er CCD
carbonate compensation depth (CCD)
the ocean depth below which the seawater is sufficiently undersaturated with calcium carbonate that calcium carbonate shells and skeletons dissolve
What chemical compound in the ocean reachts with CaCO3 and dissolves the shells?
CO2
How can calcite be deposited, when there is a CCD?
The topography of the ocean bottom may result in calcite being deposited, as some areas lie above the CCD
What does the depth of the CCD tell us about the ocean?
How acidic it is. The closer the CCD is to the ocean water surface, the more acidic is the water. Likewise is the CO2 concentration also important.
What can still be found below CCD?
silliceous ooze and clay
What are the main depositioal environments?
Continental, transitional, marine, volcanic, lacustrine, river.
Amphidromic point
A point which the tidal wave rotates around. At this point, there is no change in water level during the tidal cycle, and there are no tides.
Density flow
Mixtures of detritus and fluid that move under gravity, are known as density flows / currents (debris flow).
Turbidity currents
gravity-driven turbid mixtures of sediment suspended in water. They are less dense mixtures than debris flows and has a high Reynolds number. Often turbulent flow. The name comes from being mixtures of opaque mixtures of sediment and water (turbid), and not from turbulent flow.
Why are pelagic sediments so boring?
The pelagic sediments depend on nutrients of the water, and the deposits reflect topography. For instance: Radiolarian ooze is primarily found at the equator and the west coast of continents, because the water is rich in nutrients.
This means, that types of pelagic sediments are quite uniform, but the type of sediment depend on the environment.
They are also boring because they are made of only CaCO3
How are carbonate ramps divided?
Offshore, deep subtidal and shallow subtidal
Depositional environment of offshore and deep subtidal
Thin packstone storm beds in lime mudstone. May be graded or contain HCS and sole marks.
Depositional environment of Shallow subtidal (above FWWB)
Large sandbars. Large subaqueous dune. Cross bedding made of ooids and skeletal fragtments. May also have wave ripples and parallel beach laminations
Teepee structures
Dessiccation (= drying out) cracks are formed by wetting, drying and thermal contraction during a tidal cycle. VERY COMMON for peritidal deposition - often seen as polygonal desiccation cracks (like mud cracks). · Continued wetting and drying of cessiccation cracks can deform the lamination upwards, which creates the teepee structure.
Carbonate platform
Low gradient to flat, shallow, broad top with very steep slope. May have platform-edge barrier (reef or shoals)
(un)Rimmed platform
When there is a barrier present = rimmed
Platforms without a barrier = unrimmed
Energy distribution on a rimmed platform
we find the energy maximum at the reef boundary (the platform edge). The interior has low energy.
Energy distribution on an unrimmed platform
have an energy maximum at the margins (platform edge) because of the wave focusing as the water abruptly shallows at the edge of the platform. As the water slows across the platform (frictional energy loss), will it lose energy from friction.
Berm formation
Dissipative coast and reflective coast
Coastal plain
Land area that lies adjacent to the max tide level
strand plain
Sandy coastline where an extensive area of beach deposits lies directly adjacent to the coastal plain.
Lagoonal succesion
Typically, mudstone, often organic rich, with wave-rippled sand beds. The fossil assemblage may indicate a marine influence. A restricted fauna may provide evidence of brackish or hypersaline water.
Littoral Clastic coast bed geometry
Elongate lenses
Littoral Clastic coast Sedimentary structures
Low angle stratification and wave reworking
Littoral Clastic coast Paleocurrents
Mainly wave formed structures
Shoreface stratigraphy
Wave ripple, low angle ripples, bioturbation, wave ripple cross lamination and horizontal stratification. Flaser beds.
Sedimentary structures of the offshore transition zone
Tempestites, finer-grained laminated sands, HCS, SCS. Alternation layers of sand and mud.
Characteristics of tide-dominated successions
Large sand ridges with moderately well sorted, medium grained sand. Deposits may include clay laminae deposited during slack phases. Likely cross bedded and cross laminated sandstone.
Characteristics of tide-dominated successions
Large sand ridges with moderately well sorted, medium grained sand. Deposits may include clay laminae deposited during slack phases. Likely cross bedded and cross laminated sandstone.
Why are reefs located the way they are?
Warm water contains less CO2, which means it contains more carbonate iron.
euphotic zone
Upper layer of a body of water through which sunlight can penetrate and support photosynthesis. Supports life of corals, green algae and rudists
oligophotic zone
15 - 100 m water depth. A medium amount of sunlight penetrates, which supports the life of red algae and larger forarminifera.
aphotic zone
The deeper layer of ocean water that lacks sufficient sunlight for photosynthesis. Only supports life for heterozoan organisms. Bryozoans, mollusks, spongies.
What other than sunlight controls the life forms in the ocean?
Salinity and nutrience level
Hypertrophic
A lot of nutrience
Levels of nutrience
Oligitrophic, Mesotrophic, Eutrophic, Hypertrophic.
M factor
Mud-mound + Micrite: Microbes and mud
C factor
Cool-water + controlled precipitates: Heterozoans
T factor
Tropical + Topmost water: Mostly photozoan (autotrophic + Needs life (they need food)
Micritization
Endolithic (live inside the rock) microbes (algae, fungi, bacteria) bore into allochems and their tubes are later filled by micrite.
Micrite formation
Partly form by inorganic precipitation in the surface ocean (whitings)
Movement of temperate glaciers
Basal sliding and plastic deformation
Movement of cold glaciers
Plastic deformation
lateral moraine
A ridge of till along the sides of a valley glacier composed primarily of debris that fell to the glacier from the valley walls.
medial moraine
deposit of sediment formed when the lateral moraines of two glaciers meet
recessional moraine
Marks the pauses in the retreat of a glacier
terminal moraine (end moraine)
a type of moraine that forms at the snout (edge) of a glacier, marking its maximum advance
Creation of snowball earth
CO2 and water combines and weathers silicate rocks. Less CO2 in the atmosphere makes it colder. Ice is spreading. Large albedo effect. The earth freezes. Volcanoes erupts and emits CO2, which builds up. Ice melts, because of the greenhouse effect from CO2.
Loess
Aflejringer fra gletsjere
A wind-formed deposit made of fine particles of clay and silt
Windkanter
Dannes af aeolian - vind sliber kanter
Where is the maximum erosional potential? - Aeolian
About 1 meter above ground (max wind speed + max amount grains).
What happens during a storm in aeolian environments?
Large amounts of dust is blown away. Can be blown from Sahara to Bahamas for instance –> The reason for clay minerals. Also provides nutrience. Dust can be carried with the wind
What is desert varnish?
A dark, rusty-brown coating of iron oxide and magnesium oxide that accumulates on the surface of the rock, as very fine sand and particles are moved by the wind.
Define Star Dunes
Isolated hills of sand that exhibit a complex form, as wind has blown from all directions
Why are most dunes asymmetrical
Because they follow the prevailling winds, making the stoss side gentle in slope, and the lee side more steep (avalanching).
What is seen in aeolian dunes, but NEVER in marine?
Avalancing on the lee side of dunes
Define Barchan Dunes
Dunes shaped like crescents with the tips pointing downwind from where there is little sand and a flat surface. The crescent forms when the wind is stable and fixed.
Define Linear dunes
have their crests parallel to the wind direction. These
dunes frequently have a slipface on each side and are probably formed from winds that come from two close directions, say south and southwest. The dunes are aligned between the two directions. Because of the two wind directions, they often have two slipfaces. These dunes are frequently found in groups of parallel dunes, which can extend for hundreds of kilometers.
What is NOT found in aeolian environments?
Fossils
What is characteristic about about aeolian dunes?
The grainflow tongues out at the bottom of the dune, which subaqueous bedforms doesn’t.
You will also often find wind ripples orientated perpendicular to dune cross lamina.
What does lacustrine and ocean environments have in common?
Bedform (except tides)
Where do deltas form?
as a stream enters an ocean
How do seas and lakes differ?
Fauna and flora. Water chemistry. Certain physical processes of temperature and density stratification.
What controls the water level in a lake? And the water chemistry!
The balance between inflow, outflow, and evaporation.
Lake water stratification
Contrast in temperature, density and chemistry in the upper and lower part of the water body
Thermal stratification of (fresh) lakes
Oxic upper layer, and a colder, anoxic lower layer.
Hypolimnion
deeper water; cold, dense; low dissolved oxygen in a lake
Epilimnion
An upper layer of warm water with high levels of dissolved oxygen in a lake
Controls for sedimentation in a lake
Density stratification above and below the thermocline
Saline lakes cause
Salt lake; commonly caused by interior stream drainage in an arid environment
What does it mean, that a river always try to reach a equilibrium?
A river will mostly erode the same during its run. On slopes will the erosion be controlled by the energy of the slope, and on flat ground is it the energy from the amount of water in the river.
What happens to the equilibrium, when you remove sediment from a river?
the energy of the river will be larger, and it will start to erode more, and thereby reach a new equllibrium.
Anabranching channel
multiple large channels are present across a vast floodplain
Braided river
Form when many small river channels interconnect between areas of abundant sediment deposition. Common where glaciers flow into valleys and release meltwater and abundant sediment.
Levees
Barriers composed of river sediments made on either side of a river due to flooding.
How does the water flow in a meandering river?
When water is flowing alongside a curve (and the Coriolis force deflect the water molecules), the water on the outer bend of the water, will flow faster than the inner bend of the curve.
Crevasse splays
are created when the levee is breached. –> Erosion makes a “hole” which makes a lot of sand flow out
River bars
An elevated region of sediment that has been deposited by the flow. Complex features, composed of stacked bedforms. The dimension of the bars is related to the channel width.
Amalgamated
Connected bodies of sand makes large reservoirs, but water may escape. There is also higher risk of pollution of the water
Non-amalgamated
May be good reservoirs, as sand-bodies are not connected. Sealing rock may be present.
Concretion
Hard, rounded mass that develops when a considerable amount of cementing material precipitates locally in a rock, often around an organic nucleus.
Often CaCO3
Concretion
Hard, rounded mass that develops when a considerable amount of cementing material precipitates locally in a rock, often around an organic nucleus.
Often CaCO3
The Neritic zone
In which deposits are waves and tides a great identification of a marine environment
From the coast and down to a depth of 200 meter (shallow water)
The Bathyal zone
The Bathyal zone
The Abyssal zone
What zone lies between 4000 m and 5000 meter water depth?
Mention the different “faces” of a marine environment
Offshore, Offshore-transition, shoreface, foreshore
Where lies storm wave base?
Between offshore and offshore-transition
Where lies fair weather wave base
Between offshore-transition zone and shoreface.
Where do we find mean high water and mean low water
Beyond and before the foreshore
Which parameters are used for describing transitional environments?
1) Transgression / regression
2) Is there a river nearby?
3) Main transport agent
Transitional environemnt without a river?
Tidal flat, strandplan, lagoon
Transitional environment with a river
Delta or Estuary
Delta formation
Deltas are formed when rivers propagate to the sea and deliver sediments.
What does a delta integrate?
Sea leve change, mountain building, waves, tides and climate.
What does the climate control in deltas?
Discharge
What do tectonics control in deltas?
Relief, slope and subsidence
What do eustatic sea level changes control in deltas?
Accommodation, waves and tides
What do discharge, relief and slope control in deltas?
Grain size
What do subsidence and accomodation control in deltas?
Depth
What do waves and tides control in deltas
Reworking of sediments
What mouth bar does fine-grained deltas have?
Small mouth bar
What mouth bar does Coarse-grained deltas have?
Larger mouth bars
Delta deposits that will move with time.
Lobes
When a delta channel avulses (adskilles), will the deposits (lobes) build out the new location of the delta mouth.
Sedimentary structures of tide deltas
River progrates into the ocean.
Herringbone cross stratification
Mud drapes
Neb-spring cycles
Flaser, wavy and lenticular lamination.
Interferece and ladder ripples.
Sedimentary structures of tide deltas
River progrates into the ocean.
Herringbone cross stratification
Mud drapes
Neb-spring cycles
Flaser, wavy and lenticular lamination.
Interferece and ladder ripples.
Sedimentary structures of wave deltas
Symmetrical ripple marks and HCS
Progradation
Seaward extension of the shoreline through deposition of sediment
Regression
Seaward extension of the shoreline through lowering of sealevel
auses for regression / progradation
Entering glacial period (less sea water), tectonic activity uplifts land, high sedimentation rate
transgression
Higher sea level (Shoreline moves landward)
Retrogradation
Subsidence of land (Shoreline moves landward)
Causes for transgression / retrogradation
Leaving glacial period (More sea water), tectonic activity lowers the land (from weight on top), low sedimentation rate, river that delivers sediments has been cut off (for example a meandering river)
