12III. Fluvial dominated deltas A) dominated by river processes B) flow-types1) homopycnal2) hyperpycnal3) hypopycnalC) Miss is birdsfoot-type deltaFigure 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
13Tide Dominated Ord Delta IV) Tide-Dominated DeltaA. tidal currents>river outflow1 bidirectional redistribution of sed2. sand-filled, funnel-shaped distributaries3. linear ridges4. Ganges-Brahamaputra is tidal-dominated; tidal range 4m5. get braided, channel-fill sands, levees, tidal flats etc.
14Nile V) Wave-Dominated Delta A) longshore currents rework mouth bars B) form beaches, barrier bars & spitsC) delta may have arcuate shapeNile
15VI) Constructional vs. Destructional Phases A) constructional = active growth of deltaB) destructional = erosion by tides and wavesC) growth cyclical, get coarsening upwardD) Lobe abandonment or transgression = destructive phaseE) Delta cycle= mpubs.usgs.gov/ha/ha730/ch_f/F-text3.html
22D) Lower-Delta Plain 1) abandoned distributary fill deposits 2) channels, levees, crevasses splay, marshes3) stacks of bay-fill sand bodies separated by mud
23F) Subaqueous Delta-Plain 1) extends km & up to 300m in depth2) form base over which subaerial deposits prograde3) distributary mouth deposits grade to f. sands, silts of distal bars4) may get delta front sheet sands, wave reworking & mud diapirsPaleozoic 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.
25VIII) Ancient Deltaic Deposits A) General Characteristics1) Geometry-triangular & wedge-shaped in x-section2) Lateral Facies relationshipsi) non-marine sands to deep marine sedsii) complicated small-scale lateral facies relationshipiii) delta plain- marsh, interdistributary bay, lacustrine & dist. channel depositsiv) coarse delta front seds may grade to prodelta muds/silts which grade to shelf muds
26B) Vertical Sequence C) Sed Structures 1) progradation get coarsening upward sequence-delta front sands over prodelta silts & clays2) local fining upward sequence e.g. channel fills3) lithologies, seds, structures depend on delta typeC) Sed Structures1) numerous & variable; x-beds,ripples, slumps, bioturbation2) fluvial=unidirectional, tidal=bidirectional