Deltaic Depositional Systems

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Deltaic Depositional Systems

• Modern and
• Ancient

Arno River Delta (Med) (a wave dominated and
engineered delta)
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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)
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Importance Of Deltas

• Site of substantial fossil fuel resource
  accumulation
• Coal, Oil, and Natural Gas

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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)
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Main Geological Characteristics Of Deltas

• Isopach thick... major stratigraphic component of
  (Terrigenous Clastic) sedimentary basin fill

Mississippi Delta
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Main Geological Characteristics Of Deltas

• Regressive - Progradational successions
• Abandonment Transgressive Stage

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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)

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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)

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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

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Main Delta Sedimentary Facies

• Generic River-Dominated Delta Model
• large rivers
• broad shelf
• low wave energy
• low tidal range

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Main Delta Sedimentary Facies

• Generic River-Dominated Delta Model

• Upper Delta Plain
• above highest high tide
• low gradient/ meandering river systems
• fresh water lakes swamps

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Main Delta Sedimentary Facies

• Generic River-Dominated Delta Model

• Lower delta plain
• between the tides
• Distributary channels
• Inter-distributary bay fill
• levees

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Main Delta Sedimentary Facies

• Generic River-Dominated Delta Model

• Subaqueous Delta (Delta Front)
• below lowest low tide
• distributary mouth bar - bar finger sands
• bays

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Delta Front Progradation

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Main Delta Sedimentary Facies

• Generic River-Dominated Delta Model

• Prodelta
• Offshore transitional to open marine
• Normal Marine Shelf
• High biological productivity
• Abundant slumps and syndepositional deformation

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Generic Wave Dominated Delta Model

• High wave energy, open coasts, strong longshore
  currents

• Non-marine, swamp to Eolian dune
• Arcuate to strand-parallel sand dominated facies,
  barrier island sequences

Rhone River Delta (Med) (a wave dominated delta)
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Generic Tide Dominated Delta Model

• High Tidal Range

• Extensive lower delta plain/tidal mudflats
• Shore perpendicular, elongate sand dominated
  facies, tidal channel deposits

Ganges - Brahmaputra River Delta (Indian
Ocean) (a tide dominated delta)
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Transgressive Mississippi Delta Model

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Transgressive Mississippi Delta Model

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Transgressive Mississippi Delta Model

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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

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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 nations oil and natural gas
  supplies through the state

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Coastal Elevation in Louisiana
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Natures Revenge

• Louisianas vanishing wetlands