! 4-Fluvial Deltaic Sedimentation 1-40
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Transcript of ! 4-Fluvial Deltaic Sedimentation 1-40
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FLUVIAL DELTAICFLUVIAL DELTAICSEDIMENTATIONSEDIMENTATION
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FLUVIAL-DELTAICDEPOSITIONAL ENVIRONTMENT
A delta is formed by the accumulation offluvial sediment at a river mouth, either on alacustrine/lake or marine coastline
Fluvial systems are the primary agents forcollecting sediment which has beenweathered from continental highlands andtransporting it into lacustrine and marinebasins
Delta Mahakam
Delta
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FLUVIAL SYSTEM
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( 3%>) Low Bed load/Total load ratio High (>11%)Small Sediment size LargeSmall Sediment load LargeLow Flow velocity HighLow Gradient High
LOW
HIG
H
LO
WSI
NU
OSI
TY
Bra
ided
Mea
nder
ing
St
raig
ht
SEDIMENTMud – rich Sand - rich
Channel BoundaryFlowBars
LOW
REL
ATIV
ESTA
BIL
ITY
HIG
H
( 3%>) Low Bed load/Total load ratio High (>11%)Small Sediment size LargeSmall Sediment load LargeLow Flow velocity HighLow Gradient High
( 3%>) Low Bed load/Total load ratio High (>11%)Small Sediment size LargeSmall Sediment load LargeLow Flow velocity HighLow Gradient High
LOW
HIG
H
LO
WSI
NU
OSI
TY
Bra
ided
Mea
nder
ing
St
raig
ht
SEDIMENTMud – rich Sand - rich
Channel BoundaryFlowBars
LOW
REL
ATIV
ESTA
BIL
ITY
HIG
H
Channel patterns displayed by dingle-channel segments and the spectrum of associated variables. (modified from Schumm, 1981)
Fluvial Characterization
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CH
ANN
ELG
RAD
IEN
T
$L
CH
ANN
ELG
RAD
IEN
T
$LDELTA FLUVIAL SYSTEM FANSuspended Load Mixed Load Suspended Load Mixed Load Bed Load
Contact Plain Piedmont Riverine Plain Montane PlainDistributaries Distributaries
Tributaries Continous CHANNEL FLOW FlashyShallow Intermediate WATER TADLE Shallow Deep
y y y yy y y
DELTA FLUVIAL SYSTEM FANSuspended Load Mixed Load Suspended Load Mixed Load Bed Load
Contact Plain Piedmont Riverine Plain Montane PlainDistributaries Distributaries
Tributaries Continous CHANNEL FLOW FlashyShallow Intermediate WATER TADLE Shallow Deep
y y y yy y y
Hypothetical fluvial system traversing a montane basin and associated riverine plain, and then debouching onto a prograding, deltaic coastal plain. The trunk channel evolves through bed-load, mixed-load suspended-load styles as sediment-load, gradient, and discharge vary along the system.
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Generalized depositional model, verticalsequences of grain size and sedimentarystructures, and electric (S.P.) log profilesproduced by a low--sinuosity, braided channel.Sequence A is dominated by migration of agravelly longitudinal bar. Sequence B recordsdeposition of successive transverse bar cross-bed sets upon a braid channel fill.
Generalized depositional model, verticalsequences, and electric (S,P.) log profiles of ameanderbelt sand body produced by a high-sinuosity channel. Sequence A illustrates acomplete fining-upward sequence typical of themid-or downstream point bar. Section Billustrates the truncated vertical sequencecommonly found in the upstream end of the bar.
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CHANNELTYPE
COMPOSITION OFCHANNEL FILL
CROSS SECTION MAP VIEW SAND ISOPACH SEDIMENTARY FABRIC VERTICAL SQUENCELATERAL
RELATIONSCHANNEL GEOMETRY INTERNAL STRUCTURES
BED
LOAD
CHA
NNEL
MIXE
D LO
AD C
HANN
ELSU
SPEN
DED
LOAD
CHA
NNEL
CHANNELTYPE
COMPOSITION OFCHANNEL FILL
CROSS SECTION MAP VIEW SAND ISOPACH SEDIMENTARY FABRIC VERTICAL SQUENCELATERAL
RELATIONSCHANNEL GEOMETRY INTERNAL STRUCTURES
BED
LOAD
CHA
NNEL
MIXE
D LO
AD C
HANN
ELSU
SPEN
DED
LOAD
CHA
NNEL
Dominant Sand
Straight to slightlysinuous broad continous bed
Bed accretion dominatesSediment infill
Irregular, fining up,poorly developed
Multyhistory channel fill,encased in abundant overbank mud & claySequence dominated by
fine material, this verticaltrends may be obscure
Bank accretion (either symetrical or asymetrical) dominatessediment in fill
High width / depth ...
Low to moderate relief onBasal scour surface
Multilateral channel fillscommonly volumetricallyeroded overbank deposit
Mixed sand, silt,and mud
Moderate width / depthRatio
High relief on basal scoursurface
Sinuous Complex, typically “bedded” belt
Bank and bed accretionBoth preserved in sediment infill Variety of fining – up
Profiles well developed
Multistory channel fillsgenerally subordinate &surrounding overbankdeposits
Dominantly silt and mud
Low to very low … /Depth ratio
High-relief scour withStreep bonks, some seg-Ments with multiplethotwegs
Highly sinuous toanastomosing Shoestring or pod
Geomorphic and sedimentary characteristic of bed-load, mixed-load and suspended-load channelsegments and their deposits. (from Galloway, 1977)
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Fluvial Deltaic for Explorationist
AbandonedChannel
sequence
ActiveChannel
sequence
Sand deposite inactive braided channels Mudy deposition in
abandoned channels
2 M
AbandonedChannel
sequence
ActiveChannel
sequence
Sand deposite inactive braided channels Mudy deposition in
abandoned channels
2 M
Physiography and facies of a braided alluvial channel system
1. Braided channels system
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Nemec, 1992
1. Braided channels architecture
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Modern braided channels
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Mini Braided Channel
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Modern braided channels
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Block diagram Ideal of meandering system channel (from Walker, 1992)
2. Meandering channels system
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Meurebo River, Meulaboh, Aceh (Rimba 2005)
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2. Meandering channels architecture
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2. Meandering channels architectureThalweg
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Bojongmanik Fm, Rangkasbitung
2. Meandering channels architectureChannel Outcrop
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Cross section of ideal channel system with natural levees
Active Channel
Terrace (abondoned floodplain) DepositsFloodplain Deposits
Natural Levees
2. Meandering channels architectureNatural Levee
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2. Meandering channels architectureCrevasse Splay
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AVERAGEGRAIN SIZE
E-LOGPROFILE
Levee-Pedagonicstructures
Complexlamination
Mid bar
Trough cross-stratification
Lower bar andchannel floor
LagScoured base
A
CHANNEL FLOOR AND LAGPOINT BAR
LEVEE
A
Lateral Accretion
AVERAGEGRAIN SIZE
E-LOGPROFILE
Levee-Pedagonicstructures
Complexlamination
Mid bar
Trough cross-stratification
Lower bar andchannel floor
LagScoured base
AAVERAGE
GRAIN SIZEE-LOG
PROFILE
Levee-Pedagonicstructures
Complexlamination
Mid bar
Trough cross-stratification
Lower bar andchannel floor
LagScoured base
AVERAGEGRAIN SIZE
E-LOGPROFILE
Levee-Pedagonicstructures
Complexlamination
Mid bar
Trough cross-stratification
Lower bar andchannel floor
LagScoured base
Levee-Pedagonicstructures
Complexlamination
Mid bar
Trough cross-stratification
Lower bar andchannel floor
LagScoured base
A
CHANNEL FLOOR AND LAGPOINT BAR
LEVEE
A
Lateral Accretion
A profile illustrates a complete upward-fining sequence; typical of the lateral accretion (Galloway, 1989).
Point Bar (Lateral Accretion Surfaces)
2. Meandering channels system
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........
.......
........
.......
........
............
.......
...
1
1 2 3
. .... .
BA
Lateral Accretion
BA
BA
Point Bar (Lateral Accretion Surfaces)2. Meandering channels system
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Modern floodplain’s surfaces
Ancient Floodplain
2. Meandering channels architectureFlood Plain Deposit
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PRODELTAPRODELTA
DELTA FRONTDELTA FRONT
ALLUVIAL PLAINALLUVIAL PLAIN
DISTRIBUTARYDISTRIBUTARYDELTA PLAINDELTA PLAIN
PRODELTAPRODELTAPRODELTAPRODELTA
DELTA FRONTDELTA FRONTDELTA FRONTDELTA FRONT
ALLUVIAL PLAINALLUVIAL PLAINALLUVIAL PLAINALLUVIAL PLAIN
DISTRIBUTARYDISTRIBUTARYDELTA PLAINDELTA PLAIN
2. Meandering channels architectureDistributary Channel on Delta Plain
The processes are same with fluvial
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DELTA SYSTEM
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DeltaWhat is Delta ?
• Delta (noun) a triangular tract of sediment deposited at the mouth of a river, typically where it diverges into several outlets.
• ORIGIN mid 16th century: originally specifically as the Delta of the River Nile, from the shape of the Greek letter
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DeltaWhy Delta is unique ?
• Delta contains all the petroleum system components from Source Rock to Trap.
• Processes in Delta are composed of terrestrial processes & marine processes
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Dalrymple et al, 1992
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CoastTypes
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Prerequirement: 1. Fluvial/River.
2. Standing body of water.
3. Positive feature.
Sediment influx from aerial (aerial processes) is MORE dominant than sea erosion.
Fan shaped of deltas of the Mississippi river at Gulf of Mexico
Fan shaped of Mahakam Deltas
When Delta Formed ?:
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Fluvial / river
Standing Body of Water
Create Positif feature
RESULT
EstuarineAlluvial Fan
Tombolo, Barrier Bar, Spit bar
DELTA
Com
pone
nt
When Delta Formed ?
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When Delta Formed ?
Alluvial Fan Estuarine
Spit
TomboloEstuarine
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from Terrestrial to the Sea …
DeltaWhere is Delta forming ?
Alluvial Fan enter to the lake Called Fan Delta
Fan Delta (delta on terrestrial)
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MORPHOLOGY AND ENVIRONTMENT OF DELTA
- Delta Plain
Dominated by Fluvial Processes & all terrestrial characters (Subaerial Delta)
- Delta Front
Indicated by Fluvial & Marine Processes (Subaerial & Subaquaeous Delta)
- Pro Delta
Dominated by Marine Processes (Subaquaeous Delta)
Morphology and environment of delta (Allen, GP 1998)
MEANDERING / TRIBUTARY/ FLUVIAL
DELTA PLAIN
ALLUVIAL PLAIN
DISTRIBUTARY
PRODELTA
DELTA FRONT
INTER DISTRIBUTARY
HEAD OF PASSES
MOUTH BAR
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Head of passes of Mahakam Delta
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SEDIMENT INPUTSEDIMENT INPUT
MISSISSIPPI
MAHAKAM
DANUBA
SAO FRANSISCO
COPPERFLY
WAVE ENERGY FLUXWAVE ENERGY FLUX TIDAL ENERGY FLUXTIDAL ENERGY FLUX
FLIVIALDOMINATED
WAVEDOMINATED
TIDEDOMINATED
Yukon?
Mahakam
Talu
Calorado
Mekang
Ganges - BrahmaputraKlang - Langor
Niger
Nile
Ebra
Rhane
Kelantan
Sao FransiscoBrotos
Burdenia
Si Bernard(Miss)
Pa
Danube
Lefourch(Miss)
PraqueminesModern Miss
Fly
Cooper
Morphologic and stratigraphic classification of delta system based on relative intensity of fluvial and marine processes.
(Modified from Galloway, 1975)
Delta Classification
Based on domination of the energy:
• River-dominated– Small tidal range, weak
storms and large sediment flux build delta out into basin
• Tide-dominated– Large tidal ranges dominate
transport, deposition & geomorphology
• Wave-dominated– Strong and repeated storms
rework delta sediment
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Delta Morphology
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Note how sediment is carried by both river and ocean currents
Mississipi Delta
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Note black arrow showing sediments supply direction, McGeary 1996
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Delta ProcessesDelta Jetting Processes