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)
TigrisEuphrates 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

• Topset deposits.
• Foresets deposits(1- Distributary channel , 2-
  Subaqueous Levees , 3 - Distributary mouth bar ,
  4 Distal bar).
• Bottomset deposits.

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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

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ANCIENT DELTAS
1 - The Pennsylvanian rocks of the Appalachian
Plateau of the eastern USA -contain some
classic examples of ancient deltaic sequences
(Perm, 1962, 1975 Ferm and Williams, 1963, 1964)
with extremely complex river channel
patterns associated within these deltas. 2 -
Another classic example is the Devonian of New
York whose deltaic origin was reognized near the
turn of this century by Barrel. 3 - The
Caseyville Formation, as well as other
Pennsylvanian units in the ) Illinois Basin,
is another example of a deltaic facies
(Wanless et al, 1970). 4 - The Cretaceous
appears to be Rocky Mountains of the USA
where, amongst many units, the Parkman
Sandstone of Wyoming (Hubert et al, 1972) and
the Frontier Formation of Wyoming have all
the classical coarsening-upward successions
predicted from the Mississippi .
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DELTAIC VERTICAL SEQUENCE
For most deltas, the vertical sequence of
sedimentary structures, lithologies and
textures is coarsening-upward (Figure ).
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Coarsening-upward sequence produced by
prograding delta, Frontier Formation
(Cretaceous), North Tisdale, Wyoming. 1- Delta
Plain distributary sandstone 2- Delta Front
3- Prodelta (reprinted by permission of the
Geological Society of America).
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Vertical and lateral distribution of sediments
on idealized delta based on vertical succession
of deltaic subenvironments (A) . (B) position of
vertical sequence on ideal delta in columns
C, D, E. (C) Mississippi Delta. (D) Niger
Delta. (E) Klang-Langat Delta (from Klein,
1974 reprinted by permission of the
Geological Society 'of America).