1. Delta Environments
Nile Delta
Mississippi Delta

2. Discrete shoreline protuberances, partly subaerial and partly submarine, built by rivers into a body of permanent water

3. Delta plain: mostly subaerial part of delta complex (dominated by fluvial processes)
Distributary channels
Interdistributary bay
Delta front: shallow subtidal part of delta, above wave base (mix of fluvial and wave/tide processes)
Prodelta: deeper subtidal part of delta, below wave base

4. Progradation of relatively steep delta front (1-10°) produces a type of bed geometry called a clinoform
Topset
Foreset
Toeset
Bottomset
Delta front foresets

5. Prodelta (sub-wave base) generally resembles fine-grained offshore facies
Slumps may occur due to steeper prodelta slopes and rapid sedimentation rate

6. May have characteristics of wave or tide influence
Delta front sediments occur as coarsening-upward succession over prodelta
May have characteristics of wave or tide influence
Transgressive lag
Delta Plain
Delta Front
Delta Front
Prodelta P

7. Hypopycnal plume
Density < seawater
Relatively continuous
Deposition from suspension (=hemipelagic sedimentation)
Hyperpycnal plume
Density > seawater
Episodic, lasts hours-days
Deposition from suspension, modified by traction

8. Waxing/waning flow Inverse-normal grading
Hemipelagic sediments
Finely laminated or bioturbated mud
Suspension deposition
Normal grading

9. Delta plain: mostly subaerial part of delta complex (dominated by fluvial processes)
Distributary channels
Interdistributary bay
Delta front: shallow subtidal part of delta, above wave base (mix of fluvial and wave/tide processes)
Prodelta: deeper subtidal part of delta, below wave base

10. By definition, fluvial influence is important in deltas
Waves or tides can also rework delta plain deposits

11. Fundamental sedimentological unit of a delta is the distributary mouth bar, formed where sediment is rapidly deposited after rivers enters basin

12. High sedimentation rates during river flood events
Traction deposition with significant contribution from suspension settling
Climbing ripples

13. Interdistributary bay
Atchafalaya River, Louisiana
Distributary channel
Interdistributary bay

14. Cycles of interdistributary bay filling and abandonment, with crevasse-splay type deposits, organic-rich muds, rippled fluvial channel sands, coal
Delta plain sediments may be finer-grained (coal, interdistributary bay mudstone, etc.) than delta front sands

15. In wave-dominated deltas, mouth bars modified by wave action into linear beach ridge sand bodies
Tiber delta, Italy

16. Tide-dominated deltas contain mouth bars that are molded into elongate, shore-perpendicular sand bodies by tidal currents
Fly River delta, Papua New Guinea

17. Abandoned subsiding lobe
“Lobe switching” cycles may be autocyclic (inherent due to delta processes) rather than allocyclic (due to external forces like base level)
Abandoned subsiding lobe
Active delta lobe