Presentation on theme: "GE Sedimentary processes and products"— Presentation transcript:
1 GE0-3112 Sedimentary processes and products Lecture 9. DeltasGeoff CornerDepartment of GeologyUniversity of Tromsø2006Literature:- Leeder Ch. 22.River deltas.
2 Contents 3.1 Introduction - Why study fluid dynamics 2.2 Material properties2.3 Fluid flow2.4 Turbulent flowFurther 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 systemAlluvial fansRiverDeltaFan delta
9 Delta subenvironments Subdivision according to:Dominant processDelta plain (river)Delta front (river and basin)Prodelta (basinal)MorphologyDelta plain (plain)Delta slope (slope)Prodelta (base)Delta slope or delta front or 'prodelta'Delta plainDelta frontProdeltaDelta lipDelta toe
10 Prosesses at the river mouth Outflow typeHypopycnal (less dense; buoyancy dominated)most marine deltas (coarse to fine)Homopycnal (equal density; friction dominated)suspension-rich flow into lakes and the seaHyperpycnal (more dense; inertia dominated)1) underflows in lakes2) 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 waterLunate mouth bar.
29 Niger delta faciesNB. Numerous growth faults at depth
30 Niger delta structure & development HighstandTransgressionLowstand
31 Wave-dominated deltas High-wave energy, microtidal.Lobate to cuspate shape.Fringing barrier-beach system.Examples:Nile, EgyptTiber, ItalyRhône, FranceRhone 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 Historical2 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, BangladeshMahakam, IndonesiaFly, Gulf of PapuaIrrawaddy delta, Myanmar