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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 MexicoAnd 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 nation’s oil and natural gas supplies through the state

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Coastal Elevation in Louisiana

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Nature’s Revenge

• Louisiana’s vanishing wetlands