Presentation on theme: "GE0-3112 Sedimentary processes and products Lecture 9. Deltas Geoff Corner Department of Geology University of Tromsø 2006 Literature: - Leeder 1999. Ch."— Presentation transcript:
GE Sedimentary processes and products Lecture 9. Deltas Geoff Corner Department of Geology University of Tromsø 2006 Literature: - Leeder Ch. 22. River deltas. River deltas.
Contents ► 3.1 Introduction - Why study fluid dynamics ► 2.2 Material properties ► 2.3 Fluid flow ► 2.4 Turbulent flow ► Further reading
Importance of deltas ► Depocentres at the land-sea junction. ► Source and reservoir for hydrocarbons. ► Sites of human habitation and resource utilisation.
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
► Eg of river and fan delta
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.
High constructive and destructive deltas ► High constructive (e.g. Mississippi) ► Low constructive (e.g. Amazon)
Delta subenvironments Dominant process ► Delta plain (river) ► Delta front (river and basin) ► Prodelta (basinal) Morphology ► Delta plain (plain) ► Delta slope (slope) ► 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 ► 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
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
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.
Nile delta subenvironments and facies ► 500 km long barrier-beach complex. ► Cuspate oulet lobes (Rosetta and Damietta). ► Back-barrier lakes and lagoons.
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