Depositional Environments and Sedimentary Facies12_G435.pps
Modern Gulf of Mexico
(a river dominated delta)
velocity slows
sediments are deposited.
Herodotus (c. 400 BC) - thought the alluvial plain at mouth of Nile looked like a D
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The Nile- Original D
Coal, Oil, and Natural Gas
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Nile River Delta (Med Sea)
(an engineered, wave/river dominated delta)
Tigris&Euphrates River Delta (Persian Gulf)
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Isopach thick... major stratigraphic component of (Terrigenous Clastic) sedimentary basin fill
Mississippi Delta
Regressive - Progradational successions
Abandonment – Transgressive Stage
Contemporaneous non-marine - marginal marine - to basinal depositional systems
Numerous sub-environments (each of a scale similar to that of most other depositional systems)
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Course bedload most proximal
Fines more distal from point source
Overall pattern:
leads to COARSENING UPWARDS
cross-section results as clastics are deposited in the sub environments
sediments builds out
PROGRADES INTO BASIN
Elongate
little reworking of sediments; levies form, builds out into basin
Lobate
Cuspate
each ridge is built as it moves out and progrades
Delta Morphology
strongly progradational/regressive
Lobate – Elongate
Destructional Deltas
Cuspate (transitional to interdeltaic systems)
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Climate
Relief
Sediment load and type
Delta Channels
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Vegetated
interdisciplinary bays
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Forms sub-aqueous mouth bar
water often brackish
finest grained sediments
aided by plume of sediment rich water that extends across delta front
blankets area with fine grains
suspended sediments
Delta front environments
Slope delta front is related to grain size
Coarse grains make steep slope
up to 35° angle of repose
Fine grains (silty clay) is <1° slope
Fines increase away from river
Delta front environments
fluvial dominated (sediment input)
wave dominated (wave Energy)
tidal dominated (tidal Energy)
River Dominated
fresh water lakes
bays
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Normal Marine Shelf
High biological productivity
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affects mouth bars in basin and mouth of river
modifies river –dominated delta
bedload is immediately reworked
if waves hit obliquely (and usually do), get lateral migration of sediments and development of spits
beach and mouth bars form // to coast
waves sort grains
Wave dominated deltas
High wave energy, open coasts, strong longshore currents
Non-marine, swamp to Eolian dune
Arcuate to strand-parallel sand dominated facies, barrier island sequences
Rhone River Delta (Med)
(a wave dominated delta)
mouth bars build to form new beaches
River mouth bars aren’t as continuous and have more overbank deposits
probably similar delta slope and front
Wave dominated deltas
very different features
Mud lenses as suspended sediments settles out in slack tide
lots of sediment in surface in form of tidal flats
lobate shape to mouth bars; perpendicular to shore
look for bi-directional flow indicators
can confuse with estuarine systems
look at over all sequences
delta is progradational; estuary often retogradational
Tide dominated deltas
High Tidal Range
Shore perpendicular, elongate sand dominated facies, tidal channel deposits
Ganges - Brahmaputra River Delta (Indian Ocean)
(a tide dominated delta)
Coarse grained deltas
bodies of gravelly detritus that form on margins of lakes and seas
needs braided river or alluvial fan
Tide dominated deltas
Damming, Dredging, Diverting