Delta structure, shape, classification, components, recognition

1. Submitted by –
Shibanee Naik
M.Sc. 1st year
Roll No.-22GEOL020

2.  INTRODUCTION
 DELTA STRUCTURE
 DELTA SHAPE
 CLASSIFICATION OF DELTA
 PHYSIOGRAPHIC AND SEDIMENT CHARACTER
 COMPONENT OF DELTA
 RECOGNITION
 CONCLUSION

3. • The term “delta” was first used by “Herodotus” to describe
triangular shape deposits found in river “NILE”.
• A delta is defined as a deposit, partly subaerial, built by a river
into or against a permanent body of water.
• A river moves more slowly as it nears its mouth, or end. This
causes sediment, solid material carried downstream by currents,
to fall to the river bottom.
• Formed at the mature stage of river
• Product of regressive coastline

4. Fig: Cross section of delta
TOPSET
FORESET
BOTTOMSET

5.  On the basis of shape:
Shape is like a claw
Delta formation is river dominated
proportion of suspended sediment carried
by the stream is high
Sedimentation at calm environment
•Bird’s foot delta
Fig : Missisipi river delta

6. • Arcuate
Fan shaped
Sedimentation at wave,
current or tide dominated areas
Composed of coarse porous
sand and gravel
Fig : Nile river delta

7. • Cuspate
Tooth shaped
Material spread evenly either
side of estuary
Sedimentation onto straight
shoreline with strong wave
Fig : Tiber river delta

8. •Lobate
•Fan-shaped delta
• Produced when a heavy
load of sediment is
discharged by a stream on
a plain of low gradient
•Not elongate
Fig: lobes at missisipi delta

9. (Fig: Variation of shapes of deltas as a function of sediment input,
wave energy flux, and tidal energy flux (after Galloway, 1975).

10.  On the basis of feeder system :
DELTA
ALLUVIAL
NON-
ALLUVIAL

11. ALLUVIAL DELTA
 River deltas - formed from deposits of
single river
 Braid plain deltas – formed from
deposits of braid plain stream
 Alluvial fan deltas – formed where
alluvial fan prograde into standing water
 Scree-apron deltas – formed where
scree deposit extend into water

12. Classification of alluvial delta:
Orton and Reading
(1993)
Classification

13.  On the basis of major process acting on them
ALLUVIAL
FAN
RIVER-
DOMINATED
WAVE-
DOMINATED
TIDE-
DOMINATED

14. River dominated delta:
• small tidal range
• weak storms
• High constructive
• Progradation of delta lobe
produces single coarsening up
succession.
• Transitional from muddier to
sandier facies.
eg : Ganges-Brahmaputra delta
Facies succession : River dominated delta

16. Wave dominated delta:
• Series of prograding beach ridge complexes.
• High destructive
• Delta front - coarsening upward shoreface facies
succession.
• Herringbone cross bedding and numerous reactivation
bounding surfaces indicate tidal influence.
• More lobate and have smooth, arcuate to cuspate
margins.
• Eg. Nile delta
Facies succession: Wave dominated delta

17. Tide dominated delta:
• Overall coarsening upward facies
succession.
• Sandbodies orientated parallel to
direction of tidal currents.
• Sandbodies often perpendicular to
coastline.
• Eg. Bengal delta
Facies succession: Tide dominated delta

18. NON ALLUVIAL DELTA:
 PYROCLASTIC DELTA
 LAVA DELTA

19. Controls on costal environment

20. Classification of modern deltas

21. PHYSIOGRAPHIC & SEDIMENT
CHARACTER:
• VARIATION IN DEPOSITIONAL FEATURES OF DELTAS IS DUE TO-
SEDIMENT INPUT
OUTFLOW VELOCITY
WAVE & CURRENT ENERGY

22. COMPONENT OF DELTA
DELTA
SUBAERIAL
COMPONENT
SUBAQUEOUS
COMPONENT

23. Fig.Components of delta

24. SUBAERIAL COMPONENT
DELTA
PLAIN
UPPER
DELTA
PLAIN
LOWER
DELTA
PLAIN

25. UPPER DELTA PLAIN
LIES ABOVE HIGH TIDE
LEVEL
SEDIMENTATION
PROCESSES-
– DISTRIBUTORY-
CHANNEL
– MIGRATION.
– CHANNEL & POINT
BAR DEPOSITION.
– OVERBANK
FLOODING.
– CREVASSING INTO
LAKE BASINS
Fig.Vertical succession of Upper delta plain

26. LOWER DELTA PLAIN
Lies between low tide
mark & upper limit of
tidal influence.
Sedimentation processes
-Distribution fill deposit
-Bay-fill deposits
Fig.Vertical succession of lower delta plain

27. SUBAQUEOUS COMPONENTS
SUBAQUEOUS
COMPONENT
DELTA FRONT PRODELTA
DELTA FRONT
Uppermost part of
subaqueous delta upto 10m
depth
PRODELTA
This is the seaward part of
subaqueous delta
Fig.Delta front in the deltas of Sweden coast

28. RECOGNITION OF ANCIENT DELTAIC DEPOSITS
Geometry
Sedimentary structure and
fossils
Close association of
marine and continental
depositional environment
Relationship with other
facies
Fig. An overall coarsening-upward succession of regressive fluvio-deltaic system

29. CONCLUSION
• Delta marks for largest resting place for clastic sediments.
• Progradation produces coarsening upward succession.
• Ancient deltaic deposits are major source of coal, petroleum
and gas.
• Pinching sand bodies, synsedimentary slum structures provide
trap rock situation for a petroleum reservoir.

30. REFERENCE
• Principles of sedimentology and stratigraphy by SAM
BOGGS JR
• Introduction to sedimentology by Supriya mohan
Sengupta
• Wikipidia
• ePG pathshala