sedimentology- pak sugeng
TRANSCRIPT
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PRINCIPLES OFPRINCIPLES OFSEDIMENTOLOGYSEDIMENTOLOGY
Dr.Dr. SugengSugeng SS Sur Sur j jonoono
[email protected]@ugm.ac.id
Lab. Sedimentografi
Jurusan Teknik Geologi, Fakultas Teknik
Universitas Gadjah Mada
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IntroductionIntroduction
DefinitionsDefinitions
•• SedimentologySedimentology = the study of the processes of= the study of the processes of
formation, transport and deposition of material whichformation, transport and deposition of material which
accumulates as sediment in continental and marineaccumulates as sediment in continental and marine
environments and eventually forms sedimentary rocksenvironments and eventually forms sedimentary rocks
•• StratigraphyStratigraphy = the study of rocks to determine the= the study of rocks to determine the
order and timing of events in Earth historyorder and timing of events in Earth history
•• SedimentarySedimentary geologygeology ≈≈ sedimentologysedimentology ++
stratigraphystratigraphy
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SEDIMENTARY CICLES
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Sedimentary ciclesSedimentary cicles
WeatheringWeathering
(Erosion)(Erosion)
TransportationTransportation --DepositionDeposition Lithification (diagenesis)Lithification (diagenesis)
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WeatheringWeathering
Physical Weathering
• Frost wedging: caused by freezing and thawing of water in rockfractures.
• Alternate expansion and contraction of rock surfaces as a result of
diurnal changes in temperature
• Release of overburden pressure owing to erosion to overlying stratacauses the development of rock fractures
Chemical Weathering
It involves changes that can alter both the chemical andmineralogical composition of rocks. Minerals in the rocks areattacked by water, oxygen and carbon dioxide of the atmosphere,causing some component of the minerals to dissolve and be removein solution.
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Sedimentary ciclesSedimentary cicles WeatheringWeathering
(Erosion)(Erosion)
TransportationTransportation DepositionDeposition
Lithification (diagenesis)Lithification (diagenesis)
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EROSI
Proses lepasnyasuatubagianbatuandari tubuhbatuan induknya.Bagianyang terlepas tersebut bisamerupakanbagianyang lapuk
ataupunyang masihsegar, akibat benturan, hempasan, goresan
danataukorosi
HASIL EROSI :
Erosi menghasilkanmaterialhancuran
yang teronggokdekatdenganbatuan induknya : ENDAPAN KLASTIK
Endapanklastik dipindahkandari tempat asalnyake tempat lain
olehprosesyang disebut prosesTRANSPORTASI
AGEN EROSI :
AIR MENGALIR
ANGIN BERTIUP
GLETSER YANG BERGERAK
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Sedimentary ciclesSedimentary cicles
WeatheringWeathering ((ErosionErosion))
TransportationTransportation -- DepositionDeposition Lithification (diagenesis)Lithification (diagenesis)
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Sediment transportSediment transport
mechanismmechanism
CurrentsCurrents
WavesWaves
TidesTides
GravityGravity
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Sediment transportSediment transport
mechanismmechanism
CurrentsCurrents
WavesWaves
TidesTides
GravityGravity
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in laminar flow , waterparticles are all movingnearly parallel to eachother downflow
Two types of flows: Laminar and turbulent flows
in turbulent flow , waterparticles are movingmore chaotically, wherein local areas watermight be moving up,
down, in, out, or evenupstream
Highly turbulent water masses are referred to as eddies
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LAMINAR VS TURBULENT FLOW
Schematic representation of laminar vs turbulent fluid flowa) Laminar flow over a smooth stream bedb) Laminar flow over a spherical particle on a smooth bedc) Turbulent flow over a smooth bed. The arrows indicate flow
paths of the fluid
Boggs, 1995
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Reynolds numberReynolds number (laminar vs. turbulent flow)(laminar vs. turbulent flow)
u=flow velocity; l=characteristic length (flow depth);u=flow velocity; l=characteristic length (flow depth); υυ==kinematickinematic
viscosity (dynamic viscosity/fluid density)viscosity (dynamic viscosity/fluid density)
•• Turbulence is promoted by high flow velocities and flowTurbulence is promoted by high flow velocities and flow
depths, and low viscosities (Re>2000); laminar flowdepths, and low viscosities (Re>2000); laminar flow
occurs when the reverse is the case (Re<500)occurs when the reverse is the case (Re<500)•• Air and water are nearly always turbulent Air and water are nearly always turbulent
υ
ulRe =
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Types of particle movements in a turbulent currentTypes of particle movements in a turbulent current
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FroudeFroude numbernumber ((subcriticalsubcritical vs. supercritical flow)vs. supercritical flow)
u=flow velocity; d=flow depth;u=flow velocity; d=flow depth; √√gdgd=celerity (wave velocity)=celerity (wave velocity)
•• Flow velocities exceeding wave propagation velocitiesFlow velocities exceeding wave propagation velocities(Fr>1) yield supercritical flow, lower velocities (Fr<1)(Fr>1) yield supercritical flow, lower velocities (Fr<1)
causecause subcriticalsubcritical flowflow
••
A spatial transition from A spatial transition from subcriticalsubcritical to supercritical flowto supercritical flow(or vice versa) is characterized by a(or vice versa) is characterized by a ‘ ‘hydraulic jumphydraulic jump’ ’
gd
uFr =
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StokesStokes’ ’ LawLaw (settling velocity in a static fluid)(settling velocity in a static fluid)
vvgg=settling velocity; D=grain diameter;=settling velocity; D=grain diameter; ρρgg=grain density;=grain density;
ρρf f =fluid density;=fluid density; µµ=dynamic viscosity=dynamic viscosity
•• StokesStokes’ ’ Law only applies to fine (<100Law only applies to fine (<100 µµm)m), quartz, quartz--
density grains in waterdensity grains in water
µ18)ρ(ρgDv f g
2
g −=
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Based on the equation and realize: a slight increase ingrain size leads to normal grading an increase in viscosity
and/or an increase in ρρf can lead to a matrix-supported
deposit (i.e. large clasts appear to be floating in a matrixof fine grained mud) as opposed to grain-supported
deposit where each large clast is resting on another large
clast.
Suspended Load vs. Bed Load: grains will stay in
suspension if the upward motion of water, due to
turbulence, is larger than the grain's settling velocity.
Therefore, the smaller or less dense grains will tend to by
carried in a flow up in suspension and settle down to the
bed, to become bedload, once the flow's turbulence
becomes less (i.e. the flow slows down).
StokesStokes’’ LawLaw
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•• TheThe BernouilliBernouilli effecteffect is the reduction of pressure,is the reduction of pressure,
proportional to the increase of flow velocity as the flowproportional to the increase of flow velocity as the flow
encounters an obstacle (sediment particle), leading to aencounters an obstacle (sediment particle), leading to alift force and entrainment of the particlelift force and entrainment of the particle
•• Drag forces and lift forces act together to causeDrag forces and lift forces act together to cause
entrainment of sediment grainsentrainment of sediment grains
•• TheThe boundary layerboundary layer is that part of the flow influencedis that part of the flow influenced
by frictional effectsby frictional effects
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Transport modes in a turbulent fluidTransport modes in a turbulent fluid
Coarse sediment (sand and gravel) moves on or very close to thebed during transport : bedload.
Finer material (clay to silt) carried higher up in the main flow abovethe bed makes up the suspended load
Types of bedload transport:
•• TractionTraction (rolling over the(rolling over the
bed surface)bed surface)
•• SaltationSaltation (jumping over(jumping overthe bed surface)the bed surface)
SuspensionSuspension (permanent(permanent
transport within the fluid)transport within the fluid)
PARTICLE TRANSPORT BY FLUIDS
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PARTICLE TRANSPORT BY FLUIDSHjulstrom Diagram : show the critical current velocity and sedimenterosion, transport and deposition (deduced experimentally from flows required to
move quartz grain on a plane bed at a water depth of 1 m
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Flow Competence: faster moving flows cancarry larger particles
Flow Capacity : faster moving flows can also
carry more particles
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Current ripplesCurrent ripples
•• Once movement of sand grains (<0.7 mm) occurs, current ripples aOnce movement of sand grains (<0.7 mm) occurs, current ripples arereformed as a result of boundary layer separation, commonlyformed as a result of boundary layer separation, commonly
accompanied by a separation vortexaccompanied by a separation vortex
•• Current ripples have aCurrent ripples have a stossstoss side (erosion and transport) and lee sideside (erosion and transport) and lee side
(deposition), the latter with a slope of ~30(deposition), the latter with a slope of ~30°° (angle of repose)(angle of repose)•• Current ripples only form under moderate flow velocities, with aCurrent ripples only form under moderate flow velocities, with a graingrain
size <0.7 mmsize <0.7 mm
•• Height: 0.5Height: 0.5 – –3 cm; wavelength: 53 cm; wavelength: 5 – –40 cm40 cm
DunesDunes
•• Dunes are distinctly larger than current ripplesDunes are distinctly larger than current ripples
•• There is a relationship between boundaryThere is a relationship between boundary--layer thickness (layer thickness (≈≈flow depth in rivers) and the dimension of dunesflow depth in rivers) and the dimension of dunes
•• Dunes only form in grain sizes >0.2 mmDunes only form in grain sizes >0.2 mm
•• Sand waves constitute the largest category ofSand waves constitute the largest category of subaqueoussubaqueous
dunesdunes
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Current ripples (gelembur gelombang)
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Sediment transport mechanismSediment transport mechanism
CurrentsCurrents WavesWaves
TidesTides GravityGravity
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WavesWaves
Waves are windWaves are wind--generated oscillatorygenerated oscillatory
motions of watermotions of water Wave height is dependent on windWave height is dependent on wind
strength and fetchstrength and fetch
The depth to which the oscillatoryThe depth to which the oscillatorymotion due to wave action extends ismotion due to wave action extends isknown as theknown as the wave basewave base; shallow; shallowwater leads to breaking waveswater leads to breaking waves
Wave ripples are distinct from currentWave ripples are distinct from currentripples due to their symmetry, andripples due to their symmetry, andinclude lowinclude low--energyenergy ‘ ‘rolling grain ripplesrolling grain ripples’ ’ and highand high--energyenergy ‘ ‘vortex ripplesvortex ripples’ ’
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Tidal currentsTidal currents
Tides are formed by theTides are formed by the
gravitational attraction of the Moongravitational attraction of the Moonand Sun on the Earth, combinedand Sun on the Earth, combined
with the centrifugal force causedwith the centrifugal force caused
by movement of the Earth aroundby movement of the Earth aroundthe center of mass of the Earththe center of mass of the Earth--
Moon systemMoon system
•• SemiSemi--diurnal or diurnal tidal cyclesdiurnal or diurnal tidal cycles
•• NeapNeap--spring tidal cyclesspring tidal cycles
•• Annual tidal cyclesAnnual tidal cycles
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Ocean currentsOcean currents•• The circulation of sea water in the worldThe circulation of sea water in the world’ ’ ss
oceans is driven by wind and contrasts inoceans is driven by wind and contrasts in
density due to variable temperature anddensity due to variable temperature and
salinity (salinity (thermohalinethermohaline circulation),circulation),
combined with thecombined with the CoriolisCoriolis effecteffect•• Ocean currents transport clay and silt inOcean currents transport clay and silt in
suspension, and sand as bed load, andsuspension, and sand as bed load, and
their effects are especially important intheir effects are especially important indeep waters, where storms and tides aredeep waters, where storms and tides are
less importantless important
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Sediment transport mechanismSediment transport mechanism
CurrentsCurrents
WavesWaves
TidesTides
GravityGravity
PARTICLE TRANSPORT BY SEDIMENT GRAVITY FLOWS
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•• Debris flowsDebris flows have a high (>50%) proportion of sediment tohave a high (>50%) proportion of sediment to
water and can be both subaerial andwater and can be both subaerial and subaqueoussubaqueous
•• Low Reynolds numbersLow Reynolds numbers
•• Turbidity currentsTurbidity currents have a higher proportion of water, arehave a higher proportion of water, are
alwaysalways subaqueoussubaqueous, and move due to density contrasts, and move due to density contrasts
•• Higher Reynolds numbersHigher Reynolds numbers
PARTICLE TRANSPORT BY SEDIMENT GRAVITY FLOWS
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Below left: Ideal Bouma Sequence On right: Illustration of concept that with
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Below left: Ideal Bouma Sequence. On right: Illustration of concept that with
increasing distance downflow, the lower parts of the Bouma Sequence are
not found.
DiagenesisDiagenesis
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sediment is covered by successive layer of younger sediment;increased temperature and pressure leading to consolidation andlithification of the sediment into sedimentary rocks
diagenesis is anychemical, physical, orbiological changeundergone by
sediments after itsinitial deposition andduring and after itslithification, exclusiveof surface alteration
(weathering) andmetamorphism.
Depositional environmentsDepositional environments
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Depositional environmentsDepositional environments
Fluvial environmentsFluvial environments
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•• Bedrock riversBedrock rivers essentially do not contribute to the stratigraphicessentially do not contribute to the stratigraphicrecord, contrary torecord, contrary to alluvial riversalluvial rivers
•• Alluvial fans Alluvial fans are relatively steep (>1are relatively steep (>1--22°°) cones consisting of) cones consisting of
coarsecoarse--grained facies and constitute the most proximal fluvialgrained facies and constitute the most proximal fluvial
depositional environments (usually at the break of slope on thedepositional environments (usually at the break of slope on theedge of a floodplain)edge of a floodplain)
•• Debris flows dominate on small and steep alluvial fansDebris flows dominate on small and steep alluvial fans
•• SheetfloodsSheetfloods are common on larger and gentler alluvial fansare common on larger and gentler alluvial fans
•• Ephemeral rivers are dry during a significant part of the year,Ephemeral rivers are dry during a significant part of the year,
contrary to perennial riverscontrary to perennial rivers
•• Floodplains are the areas occupied by river channels, as well asFloodplains are the areas occupied by river channels, as well as
the surrounding, flat (the surrounding, flat (overbank overbank ) areas that are subject to flooding) areas that are subject to flooding•• Discharge is confined to the channel untilDischarge is confined to the channel until bankfullbankfull discharge isdischarge is
reached; from that point onreached; from that point on overbank overbank flow can occur, submergingflow can occur, submerging
the entire floodplainthe entire floodplain
Fluvial environmentsFluvial environments
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Fluvial environmentsFluvial environments
•• Channel patterns (fluvial styles) are commonlyChannel patterns (fluvial styles) are commonlyclassified as:classified as:•• Braided riversBraided rivers
•• Meandering riversMeandering rivers•• Straight riversStraight rivers
•• Anastomosing Anastomosing riversrivers
•• Fluvial style is primarily controlled by specific streamFluvial style is primarily controlled by specific stream
power (W mpower (W m--22) and grain size, but also by bank) and grain size, but also by bankstability and the amount of bed loadstability and the amount of bed load
ρρ=fluid density; Q=discharge; s=slope (gradient); w=channel=fluid density; Q=discharge; s=slope (gradient); w=channelwidthwidth
w
ρgQsω =
Fluvial environmentsFluvial environments
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Fluvial environmentsFluvial environments
•• BarsBars are sandy or gravellyare sandy or gravelly macroformsmacroforms in channelsin channels
that are emergent, mostlythat are emergent, mostly unvegetatedunvegetated features atfeatures at
low flow stage, and undergo submergence and rapidlow flow stage, and undergo submergence and rapid
modification during high dischargemodification during high discharge
•• Point barsPoint bars form on inner banks and typically accreteform on inner banks and typically accrete
laterally, commonly resulting in laterallaterally, commonly resulting in lateral--accretionaccretion
surfaces; midsurfaces; mid--channel orchannel or braid barsbraid bars accrete bothaccrete bothlaterally and downstreamlaterally and downstream
•• Braided rivers are characterized by a dominance ofBraided rivers are characterized by a dominance of
braid bars; meandering rivers primarily contain pointbraid bars; meandering rivers primarily contain pointbars; in straight (and mostbars; in straight (and most anastomosinganastomosing) rivers bars) rivers bars
are almost absentare almost absent
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Fluvial environmentsFluvial environments
•• Channel beltsChannel belts consist ofconsist of channelchannel--barbar andand channelchannel--fillfill
depositsdeposits; the proportion of the two generally decreases; the proportion of the two generally decreases
markedly from braided rivers to straight ormarkedly from braided rivers to straight or anastomosinganastomosing
riversrivers•• The geometry of a channel belt (width/thickness ratio) is aThe geometry of a channel belt (width/thickness ratio) is a
function of the channel width and the degree of lateralfunction of the channel width and the degree of lateral
migration; values are typically much higher for braidedmigration; values are typically much higher for braided
systems (>>100) than for straight orsystems (>>100) than for straight or anastomosinganastomosing
systems (<25)systems (<25)
•• ResidualResidual--channel depositschannel deposits are predominantly muddyare predominantly muddy
(occasionally organic) deposits that accumulate in an(occasionally organic) deposits that accumulate in anabandoned channel where flow velocities are extremelyabandoned channel where flow velocities are extremely
smallsmall
Fluvial environmentsFluvial environments
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•• Overbank Overbank environmentsenvironments are dominated byare dominated byfinefine--grained facies (predominantlygrained facies (predominantly mudsmuds))•• NaturalNatural--levee depositslevee deposits are wedges of sedimentare wedges of sediment
that form adjacent to the channel, dominated bythat form adjacent to the channel, dominated byfine sand and silt exhibiting planar stratification orfine sand and silt exhibiting planar stratification or(climbing) ripple cross stratification(climbing) ripple cross stratification
•• CrevasseCrevasse--splay depositssplay deposits are usually cones ofare usually cones of
sandy tosandy to siltysilty facies with both coarseningfacies with both coarsening--upwardupwardand finingand fining--upward successions, and are formed byupward successions, and are formed bysmall, secondary channels during peak flowsmall, secondary channels during peak flow
•• FloodFlood--basin depositsbasin deposits are the most distal facies,are the most distal facies,consisting entirely of sediments deposited fromconsisting entirely of sediments deposited fromsuspension, and are volumetrically very importantsuspension, and are volumetrically very important(mainly in low(mainly in low--energy fluvial settings)energy fluvial settings)
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Fluvial environmentsFluvial environments
•• PaleosolsPaleosols (well drained conditions) and(well drained conditions) and peatspeats
(poorly drained conditions) occur frequently(poorly drained conditions) occur frequentlyinin overbank overbank environments and are importantenvironments and are important
indicators of variations ofindicators of variations of clasticclastic aggradationaggradation
rates and the position relative to activerates and the position relative to activechannelschannels
•• LacustrineLacustrine deposits can be important indeposits can be important in
overbank overbank environments characterized by highenvironments characterized by highwater tables, and are also found in distalwater tables, and are also found in distal
settingssettings
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Fluvial environmentsFluvial environments
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•• Avulsion Avulsion is the sudden diversion of a channel to ais the sudden diversion of a channel to a
new location on the floodplain, leading to thenew location on the floodplain, leading to the
abandonment of a channel belt and the initiation of aabandonment of a channel belt and the initiation of a
new onenew one
•• Alluvial architecture Alluvial architecture refers to the threerefers to the three--
dimensional arrangement of channeldimensional arrangement of channel--belt depositsbelt deposits
andand overbank overbank deposits in a fluvial successiondeposits in a fluvial succession•• The nature of alluvial architecture (e.g., theThe nature of alluvial architecture (e.g., the
proportion of channelproportion of channel--belt tobelt to overbank overbank deposits) isdeposits) is
dependent on fluvial style,dependent on fluvial style, aggradationaggradation rate, and therate, and the
frequency of avulsionfrequency of avulsion
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Deltaic environmentsDeltaic environments
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Deltaic environmentsDeltaic environments
•• Deltas form where a river enters a standing body ofDeltas form where a river enters a standing body ofwater (ocean, sea, lake) and forms a thick deposit thatwater (ocean, sea, lake) and forms a thick deposit thatmay or may not form protuberancesmay or may not form protuberances
•• TheThe delta plaindelta plain is theis the subaerialsubaerial part of a deltapart of a delta(gradational upstream to a floodplain); the(gradational upstream to a floodplain); the delta frontdelta front(delta slope and(delta slope and prodeltaprodelta) is the) is the subaqueoussubaqueous componentcomponent
•• Delta plains are commonly characterized by distributariesDelta plains are commonly characterized by distributariesand flood basins (upper delta plain) orand flood basins (upper delta plain) or interdistributaryinterdistributarybays (lower delta plain), as well as numerous crevassebays (lower delta plain), as well as numerous crevassesplayssplays
•• Upper delta plains containUpper delta plains contain faciesfacies assemblages that areassemblages that arevery similar to fluvial settingsvery similar to fluvial settings
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GED2008
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Deltaic environmentsDeltaic environments
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Deltaic environmentsDeltaic environments
•• Mouth barsMouth bars form at the upper edge of theform at the upper edge of the
delta front, at the mouth of distributaries; theydelta front, at the mouth of distributaries; they
are mostly sandy and tend to coarsen upwardsare mostly sandy and tend to coarsen upwards
•• TheThe delta slopedelta slope is commonly 1is commonly 1--22°° and consistsand consists
of finer (usuallyof finer (usually siltysilty)) faciesfacies; the most distal; the most distalprodeltaprodelta is dominated by even finer sedimentis dominated by even finer sediment
•• ProgradationProgradation ((basinwardbasinward building) of deltasbuilding) of deltas
leads to coarseningleads to coarsening--upward successions, andupward successions, andprogradationprogradation rates depend on sediment supplyrates depend on sediment supply
and basin bathymetry (water depth)and basin bathymetry (water depth)
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GED2008
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Deltaic environmentsDeltaic environments
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Deltaic environmentsDeltaic environments
•• Delta morphology reflects the relativeDelta morphology reflects the relativeimportance of fluvial, tidal, and wave processes,importance of fluvial, tidal, and wave processes,
as well as gradient and sediment supplyas well as gradient and sediment supply•• RiverRiver--dominated deltasdominated deltas occur inoccur in microtidalmicrotidal settingssettings
with limited wave energy, where deltawith limited wave energy, where delta--lobelobe
progradationprogradation
is significant and redistribution of mouthis significant and redistribution of mouth
bars is limitedbars is limited
•• WaveWave--dominated deltasdominated deltas are characterized byare characterized bymouth bars reworked into shoremouth bars reworked into shore--parallel sand bodiesparallel sand bodies
and beachesand beaches•• TideTide--dominated deltasdominated deltas exhibit tidal mudflats andexhibit tidal mudflats and
mouth bars that are reworked into elongate sandmouth bars that are reworked into elongate sandbodies perpendicular to the shorelinebodies perpendicular to the shoreline
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Deltaic environmentsDeltaic environments
•• CoarseCoarse--grained deltas are composed of gravellygrained deltas are composed of gravelly
faciesfacies and form where alluvial fans or relativelyand form where alluvial fans or relatively
•• steep braided rivers enter a water bodysteep braided rivers enter a water body
•• Delta cycles are the result of repetitive switchingDelta cycles are the result of repetitive switching
of delta lobes, comparable to avulsion in fluvialof delta lobes, comparable to avulsion in fluvial
environments; this leads to characteristic verticalenvironments; this leads to characteristic vertical
successions withsuccessions with progradationalprogradational faciesfacies andand
transgressivetransgressive faciesfacies
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GED2008
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GED2008
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Coastal environmentsCoastal environments
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•• ErosionalErosional coasts are commonly characterized by cliffs, whereascoasts are commonly characterized by cliffs, whereas
constructional coasts can be formed byconstructional coasts can be formed by clasticclastic, carbonate, or, carbonate, or
evaporiteevaporite faciesfacies
•• The morphology of constructional coasts is determined by sedimenThe morphology of constructional coasts is determined by sedimentt
supply, wave energy, and tidal range, as well as climate and seasupply, wave energy, and tidal range, as well as climate and sea--
level historylevel history
•• Beaches form when sand or gravel is available and wave energy isBeaches form when sand or gravel is available and wave energy is
significant, and result in lowsignificant, and result in low--angle crossangle cross--stratified deposits andstratified deposits andcross strata formed by wave ripplescross strata formed by wave ripples
•• Beaches can either be connected directly to the land and formBeaches can either be connected directly to the land and form
strand plainsstrand plains oror chenierchenier plainsplains (the latter consisting of beach(the latter consisting of beach
ridges separated byridges separated by mudsmuds), or be separated by), or be separated by lagoonslagoons oror tidaltidalbasinsbasins (the latter consisting of tidal channels, tidal flats, and salt(the latter consisting of tidal channels, tidal flats, and salt
marshes) and form eithermarshes) and form either spitsspits oror barrier islandsbarrier islands
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Coastal environmentsCoastal environments
•• Barrier islands are especially prolific in environments with a hBarrier islands are especially prolific in environments with a highigh
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wave energy and a limited tidal range, that have experiencedwave energy and a limited tidal range, that have experiencedtransgression (relative seatransgression (relative sea--level rise)level rise)
•• The tidal inlets between barrier islands are sites of deepThe tidal inlets between barrier islands are sites of deep erosionalerosional
scour and are associated with floodscour and are associated with flood--tidal deltas (tidal deltas (lagoonallagoonal side) andside) and
ebbebb--tidal deltas (seaward side)tidal deltas (seaward side)•• WashoversWashovers can form during major storm events, and are foundcan form during major storm events, and are found
elsewhere across barrier islandselsewhere across barrier islands
•• Coastal dunes are common features associated with sandy beachesCoastal dunes are common features associated with sandy beaches
•• EstuariesEstuaries are semiare semi--enclosed coastal water bodies where fluvialenclosed coastal water bodies where fluvial
and marine processes interactand marine processes interact
•• TideTide--dominated estuariesdominated estuaries have tidal channels with bars and tidalhave tidal channels with bars and tidal
mudflats that contain tidal sedimentary structures (e.g., tidalmudflats that contain tidal sedimentary structures (e.g., tidal bundles,bundles,heterolithicheterolithic stratification)stratification)
•• WaveWave--dominated estuariesdominated estuaries are partly enclosed by a coastal barrierare partly enclosed by a coastal barrier
and have welland have well--developed baydeveloped bay--head deltashead deltas
Coastal environmentsCoastal environments
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•• Carbonate coastal environments can exhibit comparableCarbonate coastal environments can exhibit comparable
characteristics ascharacteristics as clasticclastic coasts (i.e., barriers andcoasts (i.e., barriers and
lagoons), consisting of carbonate sands andlagoons), consisting of carbonate sands and mudsmuds,,
respectivelyrespectively•• StromatolitesStromatolites (algal or bacterial mats) commonly form on(algal or bacterial mats) commonly form on
carbonatecarbonate--rich tidal flatsrich tidal flats
•• Arid coastal environments are characterized by Arid coastal environments are characterized by sabkhassabkhas
andand salinassalinas, coastal plains frequently inundated by, coastal plains frequently inundated by
saline water andsaline water and hypersalinehypersaline lagoons, respectively,lagoons, respectively,
wherewhere evaporitesevaporites (notably anhydrite and gypsum) can(notably anhydrite and gypsum) canaccumulateaccumulate
Shallow marine environmentsShallow marine environments
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•• Shallow seas can be subdivided intoShallow seas can be subdivided into clasticclastic andand
carbonatecarbonate--dominated systems, dependingdominated systems, depending
mainly on sediment supply and climatic settingmainly on sediment supply and climatic setting•• Idealized models predict a general decrease ofIdealized models predict a general decrease of
grain size with water depth (i.e., away from thegrain size with water depth (i.e., away from the
shoreline); however, this simple picture isshoreline); however, this simple picture iscomplicated by a large number of factors (e.g.,complicated by a large number of factors (e.g.,
shelf bathymetry)shelf bathymetry)
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Shallow marine environmentsShallow marine environments
SS d i dd i d l il i h lh l id ll hibiid ll hibi
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•• StormStorm--dominateddominated clasticclastic shelvesshelves ideally exhibit aideally exhibit atransition from predominantly wavetransition from predominantly wave--rippled sands in therippled sands in theupperupper shorefaceshoreface, to alternating sands and, to alternating sands and mudsmuds((tempestitestempestites with hummocky cross stratification) in thewith hummocky cross stratification) in the
lowerlower shorefaceshoreface, to muddy facies below storm wave base, to muddy facies below storm wave base•• TideTide--dominateddominated clasticclastic shelvesshelves may exhibitmay exhibit erosionalerosional
features, sand ribbons, and sand waves with decreasingfeatures, sand ribbons, and sand waves with decreasingflow velocities, commonly associated with mudflow velocities, commonly associated with mud--drapeddraped
subaqueoussubaqueous dunes; tidal sand ridges (tens of m high, manydunes; tidal sand ridges (tens of m high, manykm across) are characteristic of shelves with a high supplykm across) are characteristic of shelves with a high supplyof sandof sand
•• BioturbationBioturbation can obliterate many primary sedimentarycan obliterate many primary sedimentary
structures in shelf environmentsstructures in shelf environments
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•• Shallow seas within theShallow seas within the photicphotic zone are thezone are the
premierpremier ‘ ‘carbonate factoriescarbonate factories’ ’
•• Carbonate platformsCarbonate platforms can cover continentalcan cover continentalshelves orshelves or epicontinentalepicontinental seas, when theseas, when the
conditions for carbonate productionconditions for carbonate production
(temperature, salinity, light conditions) are(temperature, salinity, light conditions) are
favorablefavorable
•• Isolated platforms (atolls) are found in shallowIsolated platforms (atolls) are found in shallow
seas surrounded by deep water, like extinctseas surrounded by deep water, like extinctvolcanoesvolcanoes
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Shallow marine environmentsShallow marine environments
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•• Carbonate rampsCarbonate ramps exhibit processes and characteristicsexhibit processes and characteristics
comparable tocomparable to clasticclastic shelves, with carbonate sands andshelves, with carbonate sands and
mudsmuds ultimately producing a seaward transition fromultimately producing a seaward transition from
grainstonegrainstone to mudstone, commonly with similarto mudstone, commonly with similarsedimentary structuressedimentary structures
•• Rimmed carbonate shelvesRimmed carbonate shelves consist of a coral reef orconsist of a coral reef or
carbonate sand barrier at some distance from thecarbonate sand barrier at some distance from the
mainland; the shelf lagoon can be up to many tens ofmainland; the shelf lagoon can be up to many tens of
kilometers widekilometers wide
•• BoundstonesBoundstones dominate the reef faciesdominate the reef facies
•• Shelf lagoon facies are mostly fineShelf lagoon facies are mostly fine--grained and ultimately lead tograined and ultimately lead tothe formation of mudstones andthe formation of mudstones and wackestoneswackestones
Deep marine environmentsDeep marine environments
h l l f d fTh i l l i j f di f
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•• The continental slope is a major source of sediment forThe continental slope is a major source of sediment for
the deep sea, and is a setting where slumps can occurthe deep sea, and is a setting where slumps can occur
•• Debris flows and turbidity currents are the mainDebris flows and turbidity currents are the main
mechanisms of transport from the continental slope intomechanisms of transport from the continental slope intothe deep sea; these processes can be triggered bythe deep sea; these processes can be triggered by
external forcing (e.g., an earthquake) or by the slopeexternal forcing (e.g., an earthquake) or by the slope
reaching a critical state as a result of ongoing depositionreaching a critical state as a result of ongoing deposition
•• DebrisDebris--flow deposits andflow deposits and turbiditesturbidites are often geneticallyare often genetically
relatedrelated
•• TurbiditesTurbidites can be bothcan be both clasticclastic (commonly leading to the(commonly leading to the
formation offormation of wackeswackes) or calcareous) or calcareous
Deep marine environmentsDeep marine environments•• Submarine canyons at the shelf edge (commonlySubmarine canyons at the shelf edge (commonly
related to deltas) are connected torelated to deltas) are connected to submarinesubmarine
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related to deltas) are connected torelated to deltas) are connected to submarinesubmarinefansfans on the ocean flooron the ocean floor
•• Contrary to debris flows,Contrary to debris flows, turbiditesturbidites exhibit aexhibit a
distinct proximal to distal finingdistinct proximal to distal fining•• Submarine fans share several characteristics withSubmarine fans share several characteristics with
deltas; they consist of a feeder channel thatdeltas; they consist of a feeder channel that
divides into numerousdivides into numerous distributarydistributary channelschannelsbordered by natural levees and are subject tobordered by natural levees and are subject toavulsionsavulsions•• Proximal fan (trunk channel)Proximal fan (trunk channel)
•• Medial fan (lobes)Medial fan (lobes)
•• Distal fanDistal fan
•• BasalBasal BoumaBouma--divisions have the highestdivisions have the highest
preservation potentialpreservation potential updipupdip; upper; upper BoumaBouma
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preservation potentialpreservation potential updipupdip; upper; upper BoumaBouma--divisions are more commondivisions are more common downdipdowndip
•• TurbiditeTurbidite lobes characterize the medial fan andlobes characterize the medial fan and
may exhibit the most completemay exhibit the most complete BoumaBoumasequencessequences
•• TheThe BoumaBouma--model is increasingly challenged,model is increasingly challenged,
because manybecause many turbiditesturbidites do not conform to itdo not conform to it(e.g.,(e.g., ‘ ‘highhigh--concentrationconcentration turbiditesturbidites’ ’ ))
•• ContouritesContourites are formed by ocean currents andare formed by ocean currents and
commonly represent reworkedcommonly represent reworked turbiditesturbidites
Deep marine environmentsDeep marine environments
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Deep marine environmentsDeep marine environments
•• Pelagic sedimentsPelagic sediments primarily have a biogenic originprimarily have a biogenic origin•• Calcareous ooze (e.g., foraminifera) forms above the calciteCalcareous ooze (e.g., foraminifera) forms above the calcite
compensation depth (CCD) at ~4000 m depthcompensation depth (CCD) at ~4000 m depth•• Siliceous ooze (e.g., radiolarians, diatoms) forms betweenSiliceous ooze (e.g., radiolarians, diatoms) forms between
the CCD and ~6000 m depth where silica dissolves; itthe CCD and ~6000 m depth where silica dissolves; itlithifieslithifies intointo chertscherts
•• HemipelagicHemipelagic sedimentssediments consist of fineconsist of fine--grainedgrained(muddy)(muddy) terrigenousterrigenous material that is deposited frommaterial that is deposited fromsuspensionsuspension•• EolianEolian dust is an important component (~50%) ofdust is an important component (~50%) of
hemipelagichemipelagic (and pelagic) facies(and pelagic) facies•• BlackBlack shalesshales have a 1have a 1--15% organic15% organic--matter content and formmatter content and form
in anoxic bottom watersin anoxic bottom waters
Facies and depositional environmentsFacies and depositional environments
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•• TheThe faciesfacies concept refers to the sum of characteristicsconcept refers to the sum of characteristicsof a sedimentary unit, commonly at a fairly small (cmof a sedimentary unit, commonly at a fairly small (cm--m)m)
scalescale•• LithologyLithology
•• Grain sizeGrain size
•• Sedimentary structuresSedimentary structures
•• ColorColor•• CompositionComposition
•• Biogenic contentBiogenic content
•• Lithofacies (physical and chemical characteristics)Lithofacies (physical and chemical characteristics)
•• BiofaciesBiofacies (macrofossil content)(macrofossil content)•• IchnofaciesIchnofacies (trace fossils)(trace fossils)
•• Facies analysisFacies analysis is the interpretation of strata in termsis the interpretation of strata in termsof depositional environments (or depositional systems),of depositional environments (or depositional systems),
commonly based on a wide variety of observationscommonly based on a wide variety of observationsFacies associationsFacies associations constitute several facies that occurconstitute several facies that occur
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commonly based on a wide variety of observationscommonly based on a wide variety of observations•• Facies associationsFacies associations constitute several facies that occurconstitute several facies that occur
in combination, and typically represent one depositionalin combination, and typically represent one depositionalenvironment (note that very few individual facies areenvironment (note that very few individual facies arediagnostic for one specific setting!)diagnostic for one specific setting!)
•• Facies successionsFacies successions (or facies sequences) are facies(or facies sequences) are faciesassociations with a characteristic vertical orderassociations with a characteristic vertical order
•• WaltherWalther’ ’ s Laws Law (1894) states that two different facies(1894) states that two different faciesfound superimposed on one another and not separatedfound superimposed on one another and not separated
by an unconformity, must have been deposited adjacentby an unconformity, must have been deposited adjacentto each other at a given point in timeto each other at a given point in time
•• Sedimentary logsSedimentary logs are oneare one--dimensional representationsdimensional representationsof vertical sedimentary successionsof vertical sedimentary successions
•• Facies modelsFacies models are schematic, threeare schematic, three--dimensionaldimensionalrepresentations of specific depositional environmentsrepresentations of specific depositional environmentsthat serve as norms for interpretation and predictionthat serve as norms for interpretation and prediction
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2008
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is it time for lunch??is it time for lunch??
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2008