Presentation is loading. Please wait.

Presentation is loading. Please wait.

GE Sedimentary processes and products

Similar presentations

Presentation on theme: "GE Sedimentary processes and products"— Presentation transcript:

1 GE0-3112 Sedimentary processes and products
Lecture 9. Deltas Geoff Corner Department of Geology University of Tromsø 2006 Literature: - Leeder Ch. 22. River deltas.

2 Contents 3.1 Introduction - Why study fluid dynamics
2.2 Material properties 2.3 Fluid flow 2.4 Turbulent flow Further reading

3 Importance of deltas Depocentres at the land-sea junction.
Source and reservoir for hydrocarbons. Sites of human habitation and resource utilisation.

4 What is a delta? A river delta is the sediment accumulation at the mouth of a river. A fan delta is the delta of an alluvial fan. NB. There is a gradation between river deltas and fan deltas in the sense that alluvial plains and alluvial only differ depositionally with respect to their degree of confinement. Alluvial - deltaic system Alluvial fans River Delta Fan delta

5 Eg of river and fan delta

6 Prerequisites for delta formation
Delta formation depends upon the balance between sediment supply by the river and removal by basinal processes. High constructive and destructive deltas.

7 High constructive and destructive deltas
High constructive (e.g. Mississippi) Low constructive (e.g. Amazon)

8 Factors influencing delta morphology
Supplying basin Discharge regime Sediment caliber Sediment volume Receiving basin Bathymetry Waves and tides Relative sea level Tectonics, isostasy Eustasy Climate

9 Delta subenvironments
Subdivision according to: Dominant process Delta plain (river) Delta front (river and basin) Prodelta (basinal) Morphology Delta plain (plain) Delta slope (slope) Prodelta (base) Delta slope or delta front or 'prodelta' Delta plain Delta front Prodelta Delta lip Delta toe

10 Prosesses at the river mouth
Outflow type Hypopycnal (less dense; buoyancy dominated) most marine deltas (coarse to fine) Homopycnal (equal density; friction dominated) suspension-rich flow into lakes and the sea Hyperpycnal (more dense; inertia dominated) 1) underflows in lakes 2) hyperconcentrated flows (flood discharge) in sea

11 Outflow jets and mouth bars
Inertia-dominated. Friction dominated. Buoyancy dominated.

12 Inertia-dominated jets
Homopycnal flow. Turbulent diffusion. Deep water Lunate mouth bar.

13 Friction-dominated jets
Shallow water. Frictional drag with bottom. Homo-/hypo-/hyperpycnal flows? Mid-ground distributary bars.

14 Buoyancy-dominated jets
Hypopycnal flows. Salt-wedge development. Crescentic mouth bar?

15 Wave and tide effects

16 Subaqueous processes Suspension settling from overflow/interflow plume. Underflows and turbidity currents Mass movement and slope failure Grain flows Debris flows Slumps Creep

17 Clastic and organic deposition

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

19 Delta case histories River-dominated Mixed wave-tide dominated
Mississippi Mixed wave-tide dominated Niger Wave-dominated Nile Tiber Tide-dominated Ganges-Brahmaputra Mahakam Fly Fjord deltas

20 Mississippi delta River-dominated regime.
Birdfoot morphology (modern delta). Well-developed buoyancy forces. Low tidal range (c. 0.3 m); moderate wave energy. Fine-grained sediment load. Gentle near-shore gradient. Several Holocene progradational lobes.

21 River-dominated deltas
Low-moderate wave energy, micro- to mesotidal Lobate to birdsfoot Examples: Mississippi Braidplain deltas Some fjord deltas

22 Mississippi – progradation history
Seven Holocene delta lobes: 1 Maringouin/Sale Cypremont (7,5-5 ka) 2 Cocordie 3 Teche (5,5-3.8 ka) 4 St. Bernard (4-2 ka) 5 Lafourche ( ka) 6 Plaquemine 7 Balize (1-0 ka) Achafalaya (50 – 0 yrs)

23 Modern birdsfoot delta

24 Delta lobe development

25 Mixed wave-tide dominated deltas
High wave energy, mesotidal Lobate shape Barrier beach and tidal channels Examples: Niger

26 Niger delta Mixed tide/wave-dominated regime.
Braided R.Niger divides into tide-dominated distributary channels. Deep offshore. Cenozoic history (9-12 km thick).

27 Niger delta subenvironments
Upper deltaic floodplain. Lower deltaic mangrove swamps. Tidal channels/ mouth bar sands. Coastal barrier sands. Offshore/prodelta mud.


29 Niger delta facies NB. Numerous growth faults at depth

30 Niger delta structure & development
Highstand Transgression Lowstand

31 Wave-dominated deltas
High-wave energy, microtidal. Lobate to cuspate shape. Fringing barrier-beach system. Examples: Nile, Egypt Tiber, Italy Rhône, France Rhone delta, France

32 Nile delta Wave-dominated (eastflowing currents and longshore drift).
Microtidal. Lobate-shaped with cuspate outlet cones. Aswan dam (1964) halted sediment supply – coastal erosion and land reclamation. Complex L. Pleistocene - Holocene history.

33 Nile delta subenvironments and facies
500 km long barrier-beach complex. Cuspate oulet lobes (Rosetta and Damietta). Back-barrier lakes and lagoons.



36 Nile delta progradation history
LGM (20 ka) – sandy incised braidplain on shelf. after 8 ka – postglacial transgression and floodplain deposition. several prehistoric abandoned distributary courses. 1 Early Holocene (c. 10 ka) 3 Historical 2 Modern

37 Tiber delta Wave-dominated regime. Cuspate shape.
Bay-head delta before postglacial s.l. rise. Rapid progradation last yrs (5 km).

38 Tide-dominated deltas
Macrotidal coasts (range >4 m). Dense network of tidal channels. Coast-normal, linear, tidal current ridges offshore. Examples: Ganges-Brahmaputra, Bangladesh Mahakam, Indonesia Fly, Gulf of Papua Irrawaddy delta, Myanmar

39 Ganges- Brahmaputra, Bangladesh

40 Mahakam, Indonesia

41 Fjord deltas Coarse-grained, steep faced (Gilbert deltas)
Confined to unconfined (straight fronted to lobate). Mixed fluvial-wave-tide influenced. Examples: Alta delta (unconfined, moderate wave energy) Tana (semi-confined, moderate wave energy) Målelv (confined, low wave-energy).

42 Alta delta

43 Tana delta

44 Photo: Raymond Eilertsen 2000
Målselv delta Photo: Raymond Eilertsen 2000

45 Målselv delta

46 Fjord-delta structure and facies
Topset-foreset units in a gravelly fjord-head delta

47 Further reading

Download ppt "GE Sedimentary processes and products"

Similar presentations

Ads by Google