Classification of Deltas. Deltas are a good sink/reservoir for Hydrocarbons; they also important Ecotones for various forms of living organisms. Presented here are the mechanisms responsible for shaping of deltas around the world.

1. Department of GeologyDepartment of Geology
UIUI
A Presentation on Processes
Responsible for Delta Formation
BY
Fatai Olabanji BALOGUN

2. OUTLINE
• Introduction
• Delta classification
•Types of Delta
• Deltaic Deposits
• Economic Importance

3. INTRODUCTION
• The word Delta (Δ) was coined by Herodotus.
• Deltas are formed where rivers enter oceans,
semi-enclosed seas
• A delta is divided into two parts -: subaqueous
and subaerial
• Subaerial (delta plain) -----» characterized by
fine sands and sometimes coarse sediments.
• Subaqeous (Delta front) -----» Characterized
by silt and clay deposits.
(Source: Google images)

4. CLASSIFICATION OF DELTAS
• One way of classifying deltaic form is by the controlling energy
factors. (River, waves and Tide).
• This classification was done by Galloway (1975)
•River Dominated
•Wave Dominated
• Tide Dominated
• Deltas can also be on the basis of the grain size of the sediments they
deposit.

5. MISSISSIPI RIVER DELTA (River-dominated Delta)
• River-dominated deltas have irregular shorelines.
• Distributaries will prograde as finger-like extensions.
• There must be high fluvial discharge, sediment load, low wave , tide activity, and a shallow basin.

6. NILE RIVER DELTA (Wave-dominated Delta)
• wave activity dominates fluvial input into the basin.
• Tidal range over the delta is moderated.
• Are characterized by mouth bars reworked into shore-parallel sand bodies and
beaches.

7. GANGES-BRAHMAPUTRA DELTA (Tide-dominated)
• When tidal currents are stronger than river flow.
• Currents redistribute river mouth sediments producing sand-filled, funnel
distributaries.
• Exhibit tidal mudflats and mouth bars that are reworked into elongate sand bodies
perpendicular to the shoreline. Conditions that favor tide-dominated deltas include
low fluvial discharge and sediment load, high tide, low to moderate wave activity,
an embayed coast, and a shallow basin.

8. Source : Google images
Galloway (1975) classification of deltas

9. • The second acceptable classification of deltas was done by Coleman&Wright
(1975)
• The classification is based on the combined effect of Fluvial, Tidal and wave
processes.
•Deltas were grouped into 6 types based on this. They are;
• River dominated
• River-dominated/ Tide influenced
• Tide-dominated/ Wave influenced
•Wave-dominated
• Wave-dominated/River influenced
• Wave dominated/ Tide influenced

10. River-dominated River-dominated/tidally-
influenced
Tide-dominated/wave-influenced
Wave-dominate Wave-dominated/river-influenced Wave-dominated/tide-influenced
HYBRID DELTAS
Most Deltas are a mixture of fluvial, tidal and wave dominance

11. .

12. Source: (Google images)
Classification of deltas based on deltaic front processes and
distribution of grain size (After Orton et al 1991)

13. TYPES OF DELTA
•There are about 4 types of deltas: Elongate, Arcuate, Cuspate and Lobate.
•Deltas can also be divided into highly constructive and highly destructive deltas.
•Highly constructive deltas : develop when fluvial action and depositional process
dominate the system. Examples are the Elongate and Lobate types.
• Highly destructive deltas : form where the shoreline energy is high and much of the
sediment delivered by the river is reworked by wave. Examples are Arcuate and Cuspate.

14. Elongate (“Birds foot” delta)
Fingers of deposition
build out into the sea along the
distributaries channels, giving appearance
like a birds claw. This delta typically is
predominated by fine sediments.
Example is the Mississippi River Delta.

15. ARCUATE DELTA
This is the most common shape of
delta. It is characterized by curving
shoreline (smoothed by long shore
drift), distinct pattern of drainage
(branching of distributaries), and
typically more ‘gravely’ deposits.
Example is the Nile River Delta in
Egypt.

16. CUSPATE DELTA
A cuspate delta is shaped like
a tooth by gentle but regular
opposing currents in the water
body the river flows into, or
longshore drift.
An example is the Ebro River
Delta

17. LOBATE ???
Results from the process of
Avulsion (Delta switching)

18. Hyperpycnal Flow Hypopycnal Flow
If stream flow density is > that of
the basin, the flow remains in
contact with the basin floor,
eroding the previous surface and
forming turbidite-like deposit.
If stream flow density is < that of
the basin, after dropping the coarse
load fraction, fine sediment spreads
across the sea surface, slowly
settling to the sea floor.
DELTAIC DEPOSITS

19. Deltaic deposits
Factors controlling Deltas and their deposits

20. DELTAIC DEPOSITS (River dominated deltas)
River-dominated deltaic facies coarsen-upward from offshore and prodelta mud through
distributary and beach or barrier sand to mixed fluvial and splay deposits
Source: Adapted from sedimentology and stratigraphy by Nicols Gray

21. (Wave-dominated delta deposits)
Wave-dominated deltaic facies coarsen-upward from offshore and prodelta mud through
distributary and beach or barrier sand mixed with lagoonal, washover, and tidal deposits.

22. (Tide-dominated Delta deposits)
Tide-dominated deltaic facies coarsen-upward from offshore and prodelta mud to sandy
distributary and tidal bar deposits.
Source: sedimentology and stratigraphy by Nicols Gary

23. IMPORTANCE OF DELTAS
•Deltas are incredibly important depositional
environment where petroleum is sourced. i.e
(They are petroliferous)
•They are important places for trade and
commerce. For example Vancouver has one of
the busiest, most cosmopolitan ports in the
world.
•Deltas are also very important in the area of
Agriculture. For example, in the Mekong and
Nile river delta.

24. The Okavango Delta

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