Astronaut photo of Delta

1. Astronaut photo of Delta

2. I) Intro • A. Transitional marine env. • B. High to low energy • C. Intermittent to subaerial exposure

3. II) Deltas • A. Delta construction by fluvial outbuilding • 1 mostly in passive margins • 2. oil and gas potential Dr. Paul Liu

4. Modern Deltas

5. B. Sedimentation Processes • 1) morphology & sedimentology related to: • i) climate, water, sed discharge, waves, tides, currents, winds • 2) other factors • i) shelf slope, subsidence rates, tectonic activity • 3) most important factors: • i) sed input • ii) wave energy • iii) tidal flux

6. Delta Types • 4) Deltas classified according to • i) wave-dominated • ii) tide dominated • iii) fluvial-dominated

7. Bird’s Foot Delta

8. Mississippi through Louisiana

9. Nile Satellite Photo

10. Ganges Delta

11. Landsat--Ganges

12. III. Fluvial dominated deltas • A) dominated by river processes • B) flow-types • 1) homopycnal • 2) hyperpycnal • 3) hypopycnal • C) Miss is birdsfoot-type delta Figure 1. Comparison between hypopycnal (A, inflow density < reservoir) and hyperpycnal (B, inflow density > reservoir) flows (original concept by Bates, 1953). Note that in the case of the hyperpycnal flow the fluvial discharge sinks below the water body continuing its travel basinward as a quasi-steady underflow. Figure 1B was redrawn from a pioneer work after Knapp (1943).www.searchanddiscovery.net/.../images/fig01.htm

13. Tide Dominated Ord Delta • IV) Tide-Dominated Delta • A. tidal currents>river outflow • 1 bidirectional redistribution of sed • 2. sand-filled, funnel-shaped distributaries • 3. linear ridges • 4. Ganges-Brahamaputra is tidal-dominated; tidal range 4m • 5. get braided, channel-fill sands, levees, tidal flats etc.

14. Nile • V) Wave-Dominated Delta • A) longshore currents rework mouth bars • B) form beaches, barrier bars & spits • C) delta may have arcuate shape

15. VI) Constructional vs. Destructional Phases • A) constructional = active growth of delta • B) destructional = erosion by tides and waves • C) growth cyclical, get coarsening upward • D) Lobe abandonment or transgression = destructive phase • E) Delta cycle=50-150 m pubs.usgs.gov/ha/ha730/ch_f/F-text3.html

16. Constructional Phase

17. VII) Physiographic & Sediment Characteristics • A) Subaerial component • 1) upper delta plain- mostly above high tide, fluvial dominated • 2) lower delta plain-exposed by low tide & covered by high; • i.fluvial and marine influences

18. B) Subaqueous DeltaPlain • 1) seaward of lower delta plain, below low tide • 2) upper part = delta front • 3) seaward part = prodelta

19. C) Upper delta plain sediments • 1) distributary channels and fluvial seds, get channels, bars, overbank fines, crevassing • 2) Depositional environments • i) braided, meandering rivers • ii) swamps & marshes • iii) seds are sands muds and gravels

20. Flooded Mississippi

21. Mississippi Crevasse Splay

22. D) Lower-Delta Plain • 1) abandoned distributary fill deposits • 2) channels, levees, crevasses splay, marshes • 3) stacks of bay-fill sand bodies separated by mud

23. F) Subaqueous Delta-Plain • 1) extends km & up to 300m in depth • 2) form base over which subaerial deposits prograde • 3) distributary mouth deposits grade to f. sands, silts of distal bars • 4) may get delta front sheet sands, wave reworking & mud diapirs • Paleozoic pro-delta facies siltstones and sandstones of the Gull Island Formation, capped by the sandstones and silts of the Tullig Cyclothem. At this locality the cliff shows synsedimentary slumping and faulting in its lower part. Ireland. www.gsi.ie/Publications+and+Data/Maps/Geology...

24. Bioturbation

25. VIII) Ancient Deltaic Deposits • A) General Characteristics • 1) Geometry-triangular & wedge-shaped in x-section • 2) Lateral Facies relationships • i) non-marine sands to deep marine seds • ii) complicated small-scale lateral facies relationship • iii) delta plain- marsh, interdistributary bay, lacustrine & dist. channel deposits • iv) coarse delta front seds may grade to prodelta muds/silts which grade to shelf muds

26. B) Vertical Sequence • 1) progradation get coarsening upward sequence-delta front sands over prodelta silts & clays • 2) local fining upward sequence e.g. channel fills • 3) lithologies, seds, structures depend on delta type • C) Sed Structures • 1) numerous & variable; x-beds,ripples, slumps, bioturbation • 2) fluvial=unidirectional, tidal=bidirectional

27. Growth faults--Mississippi

28. Mississippi Sediment

29. Mississippi Land Loss

30. Mississippi Land Use

31. Wave dominated Delta

32. Wave Dominated Brazil

33. Ord Delta

34. Sand Abundance

35. Stop Here

36. Nile Delta

38. Spit due to Reworking

39. Ebro Delta

40. Niger Delta Facies/Environments