Deltaic Depositional Systems - PowerPoint PPT Presentation

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Deltaic Depositional Systems

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  1. Deltaic Depositional Systems Modern and Ancient Arno River Delta (Med) (a wave dominated and engineered delta)

  2. Deltaic Depositional Systems • Locus of voluminous terrigenous clastic sediment accumulation where fluvial dispersal systems encounter standing water • Most common in subsiding basin-settings (passive continental margins) where major river systems transport large volumes of sediment. Modern Gulf of Mexico And the Mississippi River Delta (a river dominated delta)

  3. Importance Of Deltas • Site of substantial fossil fuel resource accumulation • Coal, Oil, and Natural Gas

  4. Importance Of Deltas • Diverse and prolific ecosystems • Common site of large human population centers Nile River Delta (Med Sea) (an engineered, wave/river dominated delta) Tigris & Euphrates River Delta (Persian Gulf)

  5. Main Geological Characteristics Of Deltas • Isopach thick... major stratigraphic component of (Terrigenous Clastic) sedimentary basin fill Mississippi Delta

  6. Main Geological Characteristics Of Deltas • Regressive - Progradational successions • Abandonment – Transgressive Stage

  7. Main Geological Characteristics Of Deltas • Contemporaneous non-marine - marginal marine - to basinal depositional systems • Numerous sub-environments (each of a scale similar to that of most other depo systems)

  8. Delta Types • Constructional Deltas • Dominated by the fluvial system • strongly progradational/regressive • Lobate – Elongate • Destructional Deltas • Dominated by marine processes • common marine reworking with transgressive intervals • Cuspate (transitional to interdeltaic systems)

  9. Main Processes Influencing Delta Depositional Systems • Climate • Relief • Fluvial Discharge (water volume and time variation) • Sediment load and type • River mouth processes • Tidal Processes • Wave energy

  10. Main Delta Sedimentary Facies • Generic River-Dominated Delta Model • large rivers • broad shelf • low wave energy • low tidal range

  11. Generic River-Dominated Delta Model Upper Delta Plain above highest high tide low gradient/ meandering river systems fresh water lakes & swamps Main Delta Sedimentary Facies

  12. Generic River-Dominated Delta Model Lower delta plain between the tides Distributary channels Inter-distributary bay fill levees Main Delta Sedimentary Facies

  13. Generic River-Dominated Delta Model Subaqueous Delta (Delta Front) below lowest low tide distributary mouth bar - bar finger sands bays Main Delta Sedimentary Facies

  14. Delta Front Progradation

  15. Generic River-Dominated Delta Model Prodelta Offshore transitional to open marine Normal Marine Shelf High biological productivity Abundant slumps and syndepositional deformation Main Delta Sedimentary Facies

  16. High wave energy, open coasts, strong longshore currents Non-marine, swamp to Eolian dune Arcuate to strand-parallel sand dominated facies, barrier island sequences Generic Wave Dominated Delta Model Rhone River Delta (Med) (a wave dominated delta)

  17. High Tidal Range Extensive lower delta plain/tidal mudflats Shore perpendicular, elongate sand dominated facies, tidal channel deposits Generic Tide Dominated Delta Model Ganges - Brahmaputra River Delta (Indian Ocean) (a tide dominated delta)

  18. Transgressive Mississippi Delta Model

  19. Transgressive Mississippi Delta Model

  20. Transgressive Mississippi Delta Model

  21. Environmental Issues in Modern Deltas • Damming, Dredging, Diverting • Coastal Land loss (erosion/subsidence) • Coastal Pollution • Nutrient loading, • anoxic events • Petroleum contamination • Habitat Destruction • land loss, • contamination, and • development

  22. Environmental Issues in Modern Deltas • Mississippi Delta Coastal Land loss • Louisiana's coastal wetlands, a national resource supporting 30% of the nation's fisheries and most of the wintering ducks in the Mississippi Flyway, are at risk from the annual conversion of an estimated 35-45 mi2 of wetlands to open water. • Louisiana's wetland loss rate is the highest of any state in the nation. The processes causing wetland loss in coastal Louisiana are complex and varied. • Huge energy infrastructure • Louisiana roads, pipelines, and transmission and distribution systems transport more than 30 percent of the nation’s oil and natural gas supplies through the state

  23. Coastal Elevation in Louisiana

  24. Nature’s Revenge • Louisiana’s vanishing wetlands