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

Astronaut photo of DeltaAstronaut photo of Delta

I) IntroI) IntroA. Transitional marine env. A. Transitional marine env.

B. High to low energy B. High to low energy

C. Intermittent to subaerial exposureC. Intermittent to subaerial exposure

II) DeltasII) DeltasA. Delta construction A. Delta construction by fluvial outbuildingby fluvial outbuilding

1 mostly in passive 1 mostly in passive marginsmargins2. oil and gas 2. oil and gas potentialpotential

Dr. Paul Liu

Modern DeltasModern Deltas

B. Sedimentation ProcessesB. Sedimentation Processes1) morphology & sedimentology related to:1) morphology & sedimentology related to:

i) climate, water, sed discharge, waves, i) climate, water, sed discharge, waves, tides, currents, windstides, currents, winds

2) other factors2) other factorsi) shelf slope, subsidence rates, tectonic i) shelf slope, subsidence rates, tectonic

activityactivity

3) most important factors: 3) most important factors: i) sed inputi) sed inputii) wave energyii) wave energyiii) tidal fluxiii) tidal flux

Delta TypesDelta Types

4) Deltas classified according to4) Deltas classified according toi) wave-dominatedi) wave-dominatedii) tide dominatedii) tide dominatediii) fluvial-dominatediii) fluvial-dominated

Bird’s Foot DeltaBird’s Foot Delta

Mississippi through LouisianaMississippi through Louisiana

Nile Satellite PhotoNile Satellite Photo

Ganges DeltaGanges Delta

Landsat--GangesLandsat--Ganges

III. Fluvial III. Fluvial dominated deltasdominated deltas

A) dominated by A) dominated by river processesriver processes

B) flow-typesB) flow-types1) homopycnal1) homopycnal

2) hyperpycnal2) hyperpycnal

3) hypopycnal3) hypopycnal

C) Miss is birdsfoot-C) Miss is birdsfoot-type deltatype 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

IV) Tide-Dominated DeltaIV) Tide-Dominated DeltaA. tidal currents>river A. tidal currents>river outflow outflow

1 bidirectional 1 bidirectional redistribution of sedredistribution of sed2. sand-filled, funnel-2. sand-filled, funnel-shaped distributariesshaped distributaries3. linear ridges3. linear ridges4. Ganges-Brahamaputra 4. Ganges-Brahamaputra is tidal-dominated; tidal is tidal-dominated; tidal range 4mrange 4m5. get braided, channel-fill 5. get braided, channel-fill sands, levees, tidal flats sands, levees, tidal flats etc.etc.

Tide Dominated Ord DeltaTide Dominated Ord Delta

NileNile

V) Wave-V) Wave-Dominated DeltaDominated Delta

A) longshore A) longshore currents rework currents rework mouth barsmouth bars

B) form beaches, B) form beaches, barrier bars & spitsbarrier bars & spits

C) delta may have C) delta may have arcuate shapearcuate shape

VI) Constructional vs. VI) Constructional vs. Destructional PhasesDestructional Phases

A) constructional = A) constructional = active growth of deltaactive growth of delta

B) destructional = B) destructional = erosion by tides and erosion by tides and waveswaves

C) growth cyclical, get C) growth cyclical, get coarsening upwardcoarsening upward

D) Lobe abandonment D) Lobe abandonment or transgression = or transgression = destructive phasedestructive phase

E) Delta cycle=50-150 E) Delta cycle=50-150 mm

pubs.usgs.gov/ha/ha730/ch_f/F-text3.html

Constructional PhaseConstructional Phase

VII) Physiographic VII) Physiographic & Sediment & Sediment CharacteristicsCharacteristics

A) Subaerial A) Subaerial componentcomponent

1) upper delta 1) upper delta plain- mostly plain- mostly above high tide, above high tide, fluvial dominatedfluvial dominated2) lower delta 2) lower delta plain-exposed by plain-exposed by low tide & low tide & covered by high;covered by high;

i.fluvial and i.fluvial and marine marine influencesinfluences

B) Subaqueous B) Subaqueous DeltaPlainDeltaPlain

1) seaward of lower 1) seaward of lower delta plain, below low delta plain, below low tidetide

2) upper part = delta 2) upper part = delta frontfront

3) seaward part = 3) seaward part = prodeltaprodelta

C) Upper delta plain C) Upper delta plain sedimentssediments

1) distributary channels 1) distributary channels and fluvial seds, get and fluvial seds, get channels, bars, overbank channels, bars, overbank fines, crevassingfines, crevassing

2) Depositional 2) Depositional environmentsenvironments

i) braided, meandering i) braided, meandering riversrivers

ii) swamps & marshesii) swamps & marshes

iii) seds are sands muds iii) seds are sands muds and gravelsand gravels

Flooded MississippiFlooded Mississippi

Mississippi Crevasse SplayMississippi Crevasse Splay

D) Lower-Delta D) Lower-Delta PlainPlain

1) abandoned 1) abandoned distributary fill distributary fill depositsdeposits2) channels, 2) channels, levees, crevasses levees, crevasses splay, marshessplay, marshes3) stacks of bay-3) stacks of bay-fill sand bodies fill sand bodies separated by mudseparated by mud

F) Subaqueous Delta-F) Subaqueous Delta-PlainPlain

1) extends km & up to 1) extends km & up to 300m in depth300m in depth

2) form base over which 2) form base over which subaerial deposits subaerial deposits progradeprograde

3) distributary mouth 3) distributary mouth deposits grade to f. sands, deposits grade to f. sands, silts of distal barssilts of distal bars

4) may get delta front 4) may get delta front sheet sands, wave sheet sands, wave reworking & mud diapirsreworking & mud diapirs

Paleozoic pro-delta facies siltstones and Paleozoic pro-delta facies siltstones and sandstones of the Gull Island Formation, sandstones of the Gull Island Formation, capped by the sandstones and silts of the capped by the sandstones and silts of the Tullig Cyclothem. At this locality the cliff Tullig Cyclothem. At this locality the cliff shows synsedimentary slumping and shows synsedimentary slumping and faulting in its lower part. Ireland. faulting in its lower part. Ireland. www.gsi.ie/Publications+and+Data/Maps/Geology... www.gsi.ie/Publications+and+Data/Maps/Geology...

BioturbationBioturbation

VIII) Ancient Deltaic VIII) Ancient Deltaic DepositsDeposits

A) General CharacteristicsA) General Characteristics1) Geometry-triangular & 1) Geometry-triangular & wedge-shaped in x-sectionwedge-shaped in x-section2) Lateral Facies 2) Lateral Facies relationshipsrelationships

i) non-marine sands to i) non-marine sands to deep marine sedsdeep marine sedsii) complicated small-ii) complicated small-scale lateral facies scale lateral facies relationshiprelationshipiii) delta plain- marsh, iii) delta plain- marsh, interdistributary bay, interdistributary bay, lacustrine & dist. channel lacustrine & dist. channel depositsdepositsiv) coarse delta front iv) coarse delta front seds may grade to seds may grade to prodelta muds/silts which prodelta muds/silts which grade to shelf mudsgrade to shelf muds

B) Vertical SequenceB) Vertical Sequence1) progradation get 1) progradation get coarsening upward coarsening upward sequence-delta front sequence-delta front sands over prodelta sands over prodelta silts & clayssilts & clays2) local fining upward 2) local fining upward sequence e.g. channel sequence e.g. channel fillsfills3) lithologies, seds, 3) lithologies, seds, structures depend on structures depend on delta typedelta type

C) Sed StructuresC) Sed Structures1) numerous & variable; 1) numerous & variable; x-beds,ripples, slumps, x-beds,ripples, slumps, bioturbationbioturbation2) 2) fluvial=unidirectional, fluvial=unidirectional, tidal=bidirectional tidal=bidirectional

Growth faults--MississippiGrowth faults--Mississippi

Mississippi SedimentMississippi Sediment

Mississippi Land LossMississippi Land Loss

Mississippi Land UseMississippi Land Use

Wave dominated DeltaWave dominated Delta

Wave Dominated BrazilWave Dominated Brazil

Ord DeltaOrd Delta

Sand AbundanceSand Abundance

Stop HereStop Here

Nile DeltaNile Delta

Spit due to ReworkingSpit due to Reworking

Ebro DeltaEbro Delta

Niger Delta Facies/EnvironmentsNiger Delta Facies/Environments