Astronaut photo of Delta

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

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

Modern Deltas

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

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

Bird’s Foot Delta

Mississippi through Louisiana

Nile Satellite Photo

Ganges Delta

Landsat--Ganges

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

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.

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

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

Constructional Phase

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

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

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

Flooded Mississippi

Mississippi Crevasse Splay

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

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...

Bioturbation

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

B) Vertical Sequence C) Sed Structures 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

Growth faults--Mississippi

Mississippi Sediment

Mississippi Land Loss

Mississippi Land Use

Wave dominated Delta

Wave Dominated Brazil

Ord Delta

Sand Abundance

Stop Here

Nile Delta

Spit due to Reworking

Ebro Delta

Niger Delta Facies/Environments