GE0-3112GE0-3112 Sedimentary processes and products Sedimentary processes and products

Lecture 9. DeltasLecture 9. Deltas

Geoff CornerGeoff CornerDepartment of GeologyDepartment of GeologyUniversity of TromsøUniversity of Tromsø20062006

Literature:Literature:- Leeder 1999. Ch. 22. - Leeder 1999. Ch. 22. River deltas.River deltas.

ContentsContents

►3.1 Introduction - Why study fluid 3.1 Introduction - Why study fluid dynamicsdynamics

►2.2 Material properties2.2 Material properties►2.3 Fluid flow2.3 Fluid flow►2.4 Turbulent flow2.4 Turbulent flow►Further readingFurther reading

Importance of deltasImportance of deltas

►Depocentres at the land-sea Depocentres at the land-sea junction.junction.

►Source and reservoir for Source and reservoir for hydrocarbons.hydrocarbons.

►Sites of human habitation and Sites of human habitation and resource utilisation.resource utilisation.

What is a delta?What is a delta?

►A A river deltariver delta is the sediment is the sediment accumulation at the mouth of a river. accumulation at the mouth of a river.

►A A fan deltafan delta is the delta of an alluvial fan. is the delta of an alluvial fan. NB. There is a gradation between river deltas and fan NB. There is a gradation between river deltas and fan

deltas in the sense that alluvial plains and alluvial deltas in the sense that alluvial plains and alluvial only differ depositionally with respect to their degree only differ depositionally with respect to their degree of confinement.of confinement.

Alluvial - deltaic systemAlluvial - deltaic system

Alluvial fans

River

Delta

FanFan deltadelta

►Eg of river and fan deltaEg of river and fan delta

Prerequisites for delta Prerequisites for delta formationformation

►Delta formation depends upon the Delta formation depends upon the balance between sediment supply by balance between sediment supply by the river and removal by basinal the river and removal by basinal processes.processes.

►High constructive and destructive High constructive and destructive deltas.deltas.

High constructive and High constructive and destructive deltasdestructive deltas

►High constructive (e.g. Mississippi)High constructive (e.g. Mississippi)►Low constructive (e.g. Amazon)Low constructive (e.g. Amazon)

Factors influencing delta Factors influencing delta morphologymorphology

► Supplying basinSupplying basin Discharge regimeDischarge regime Sediment caliberSediment caliber Sediment volumeSediment volume

► Receiving basinReceiving basin BathymetryBathymetry Waves and tidesWaves and tides

► Relative sea levelRelative sea level Tectonics, isostasyTectonics, isostasy EustasyEustasy

► ClimateClimate

Delta subenvironmentsDelta subenvironments

Dominant processDominant process► Delta plain (river)Delta plain (river)► Delta front (river and Delta front (river and

basin)basin)► Prodelta (basinal)Prodelta (basinal)

MorphologyMorphology► Delta plain (plain)Delta plain (plain)► Delta slope (slope)Delta slope (slope)► Prodelta (base)Prodelta (base)

Subdivision according to:

Delta plain

Delta front

Delta slope or delta front or 'prodelta'

Prodelta

Delta lip

Delta toe

Prosesses at the river mouth Prosesses at the river mouth

► Outflow typeOutflow type Hypopycnal (less dense; buoyancy dominated)Hypopycnal (less dense; buoyancy dominated)

► most marine deltas (coarse to fine)most marine deltas (coarse to fine)

Homopycnal (equal density; friction dominated)Homopycnal (equal density; friction dominated)► suspension-rich flow into lakes and the seasuspension-rich flow into lakes and the sea

Hyperpycnal (more dense; inertia dominated)Hyperpycnal (more dense; inertia dominated)► 1) underflows in lakes1) underflows in lakes► 2) hyperconcentrated flows (flood discharge) in sea2) hyperconcentrated flows (flood discharge) in sea

Outflow jets and mouth barsOutflow jets and mouth bars

► Inertia-dominated.Inertia-dominated.►Friction dominated.Friction dominated.►Buoyancy dominated.Buoyancy dominated.

Inertia-dominated jetsInertia-dominated jets

►Homopycnal flow.Homopycnal flow.►Turbulent diffusion.Turbulent diffusion.►Deep waterDeep water►Lunate mouth bar.Lunate mouth bar.

Friction-dominated jetsFriction-dominated jets

►Shallow water.Shallow water.►Frictional drag with bottom.Frictional drag with bottom.►Homo-/hypo-/hyperpycnal flows?Homo-/hypo-/hyperpycnal flows?►Mid-ground distributary bars.Mid-ground distributary bars.

Buoyancy-dominated jetsBuoyancy-dominated jets

►Hypopycnal flows.Hypopycnal flows.►Salt-wedge development.Salt-wedge development.►Crescentic mouth bar?Crescentic mouth bar?

Wave and tide effectsWave and tide effects

Subaqueous processesSubaqueous processes

►Suspension settling from Suspension settling from overflow/interflow plume.overflow/interflow plume.

►Underflows and turbidity currentsUnderflows and turbidity currents►Mass movement and slope failureMass movement and slope failure

Grain flowsGrain flows Debris flowsDebris flows SlumpsSlumps CreepCreep

Clastic and organic Clastic and organic depositiondeposition

Delta types and classificationDelta types and classificationClassification criteria:Classification criteria:► Dominant process (river-wave-tide)Dominant process (river-wave-tide)► Shape (lobate, cuspate, birdfoot)Shape (lobate, cuspate, birdfoot)► Grain-size (coarse, fine)Grain-size (coarse, fine)

Delta case historiesDelta case histories

► River-dominatedRiver-dominated MississippiMississippi

► Mixed wave-tide dominatedMixed wave-tide dominated NigerNiger

► Wave-dominatedWave-dominated NileNile TiberTiber

► Tide-dominatedTide-dominated Ganges-BrahmaputraGanges-Brahmaputra MahakamMahakam FlyFly

► Fjord deltasFjord deltas

Mississippi deltaMississippi delta

► River-dominated regime.River-dominated regime.► Birdfoot morphology (modern delta).Birdfoot morphology (modern delta).► Well-developed buoyancy forces.Well-developed buoyancy forces.► Low tidal range (c. 0.3 m); moderate Low tidal range (c. 0.3 m); moderate

wave energy.wave energy.► Fine-grained sediment load.Fine-grained sediment load.► Gentle near-shore gradient.Gentle near-shore gradient.► Several Holocene progradational Several Holocene progradational

lobes.lobes.

River-dominated deltasRiver-dominated deltas

►Low-moderate wave energy, micro- to Low-moderate wave energy, micro- to mesotidalmesotidal

►Lobate to birdsfootLobate to birdsfoot►Examples:Examples:

MississippiMississippi Braidplain deltasBraidplain deltas Some fjord deltasSome fjord deltas

Mississippi – progradation Mississippi – progradation historyhistory

► Seven Holocene delta lobes:Seven Holocene delta lobes:1 Maringouin/Sale Cypremont (7,5-5 ka)1 Maringouin/Sale Cypremont (7,5-5 ka)

2 Cocordie2 Cocordie

3 Teche (5,5-3.8 ka)3 Teche (5,5-3.8 ka)

4 St. Bernard (4-2 ka)4 St. Bernard (4-2 ka)

5 Lafourche (2.5-0.8 ka)5 Lafourche (2.5-0.8 ka)

6 Plaquemine6 Plaquemine

7 Balize (1-0 ka)7 Balize (1-0 ka)

Achafalaya (50 – 0 yrs)

Modern birdsfoot deltaModern birdsfoot delta

Delta lobe developmentDelta lobe development

Mixed wave-tide dominated Mixed wave-tide dominated deltasdeltas

►High wave energy, mesotidalHigh wave energy, mesotidal►Lobate shapeLobate shape►Barrier beach and tidal channelsBarrier beach and tidal channels►Examples:Examples:

NigerNiger

Niger deltaNiger delta

►Mixed tide/wave-dominated regime.Mixed tide/wave-dominated regime.►Braided R.Niger divides into tide-Braided R.Niger divides into tide-

dominated distributary channels.dominated distributary channels.►Deep offshore.Deep offshore.►Cenozoic history Cenozoic history

(9-12 km thick).(9-12 km thick).

Niger delta subenvironmentsNiger delta subenvironments► Upper deltaic floodplain.Upper deltaic floodplain.► Lower deltaic mangrove Lower deltaic mangrove

swamps.swamps.► Tidal channels/ Tidal channels/

mouth bar sands.mouth bar sands.► Coastal barrier sands.Coastal barrier sands.► Offshore/prodelta mud.Offshore/prodelta mud.

Niger delta Niger delta faciesfacies

► NB. Numerous NB. Numerous growth faults at growth faults at depthdepth

Niger delta structure & Niger delta structure & developmentdevelopment

► HighstandHighstand

► TransgressionTransgression

► LowstandLowstand

Wave-dominated deltasWave-dominated deltas

►High-wave energy, microtidal.High-wave energy, microtidal.►Lobate to cuspate shape.Lobate to cuspate shape.►Fringing barrier-beach system.Fringing barrier-beach system.►Examples:Examples:

Nile, EgyptNile, Egypt Tiber, ItalyTiber, Italy RhRhôône, France ne, France

Rhone delta, France

Nile deltaNile delta

►Wave-dominated (eastflowing Wave-dominated (eastflowing currents and longshore drift).currents and longshore drift).

►Microtidal.Microtidal.►Lobate-shaped with cuspate outlet cones.Lobate-shaped with cuspate outlet cones.►Aswan dam (1964) halted sediment supply Aswan dam (1964) halted sediment supply

– coastal erosion and land reclamation.– coastal erosion and land reclamation.►Complex L. Pleistocene - Holocene history.Complex L. Pleistocene - Holocene history.

Nile delta subenvironments and Nile delta subenvironments and faciesfacies

► 500 km long barrier-beach complex.500 km long barrier-beach complex.► Cuspate oulet lobes (Rosetta and Damietta).Cuspate oulet lobes (Rosetta and Damietta).► Back-barrier lakes and lagoons.Back-barrier lakes and lagoons.

Nile delta progradation Nile delta progradation historyhistory

► LGM (20 ka) – sandy incised braidplain on shelf.LGM (20 ka) – sandy incised braidplain on shelf.► after 8 ka – postglacial transgression and floodplain deposition.after 8 ka – postglacial transgression and floodplain deposition.► several prehistoric abandoned distributary courses.several prehistoric abandoned distributary courses.

1 Early Holocene (c. 10 ka)

3 Historical2 Modern

Tiber deltaTiber delta

► Wave-dominated regime.Wave-dominated regime.► Cuspate shape.Cuspate shape.► Bay-head delta before Bay-head delta before

postglacial postglacial s.l. rise.s.l. rise.

► Rapid progradation last Rapid progradation last 500 yrs (5 km).500 yrs (5 km).

Tide-dominated deltasTide-dominated deltas

►Macrotidal coasts (range >4 m).Macrotidal coasts (range >4 m).►Dense network of tidal channels.Dense network of tidal channels.►Coast-normal, linear, tidal current Coast-normal, linear, tidal current

ridges offshore.ridges offshore.►Examples:Examples:

Ganges-Brahmaputra, BangladeshGanges-Brahmaputra, Bangladesh Mahakam, IndonesiaMahakam, Indonesia Fly, Gulf of PapuaFly, Gulf of Papua

Irrawaddy delta, Myanmar

Ganges- Ganges- Brahmaputra, Brahmaputra, BangladeshBangladesh

Mahakam, IndonesiaMahakam, Indonesia

Fjord deltasFjord deltas

► Coarse-grained, steep faced (Gilbert deltas)Coarse-grained, steep faced (Gilbert deltas)► Confined to unconfined (straight fronted to Confined to unconfined (straight fronted to

lobate).lobate).► Mixed fluvial-wave-tide influenced.Mixed fluvial-wave-tide influenced.► Examples:Examples:

Alta delta (unconfined, Alta delta (unconfined, moderate wave energy) moderate wave energy)

Tana (semi-confined, Tana (semi-confined, moderate wave energy) moderate wave energy)

Målelv (confined, Målelv (confined, low wave-energy). low wave-energy).

Alta deltaAlta delta

Tana deltaTana delta

Målselv deltaMålselv delta

Photo: Raymond Eilertsen 2000

Målselv deltaMålselv delta

Fjord-delta structure and Fjord-delta structure and faciesfacies

Topset-foreset units in a gravelly fjord-head delta

Further readingFurther reading