CEE 598, GEOL 593

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CEE 598, GEOL 593 TURBIDITY CURRENTS
MORPHODYNAMICS AND DEPOSITS
LECTURE 3 MORPHOLOGIES CREATED BY (AND
ASSOCIATED WITH) TURBIDITY CURRENTS
Seascape north of Monterey, California
outer shelf
rise
slope
Courtesy MBARI
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WHAT ARE WE LOOKING AT?
Seascape north of Monterey, California
outer shelf is planed off
canyon
gullies
Courtesy MBARI
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WHY IS THE SHELF SO FLAT?
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CONTINENTAL MARGIN STRUCTURE
The basic structure of a continental margin is
like this.
A
A
Note that the shelf is mildly tilted
seaward. Shelves are usually shallow enough so
that they feel the effect of waves during
storms. The waves are not felt in deeper water.
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SHELVES, SLOPES AND WAVE BASE
Sediment can be planed off the shelf and
delivered offshore by wave-current action.
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IF THERE WERE NO SHELF, SEDIMENT WOULD DEPOSIT UP
TO WAVE BASE AND FORM ONE
Adriatic coast of Italy. Image courtesy F.
Trincardi
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ALONGSHELF WAVE-CURRENT ACTION ACTS TO SMEAR THIS
TABLE OUT INTO A CONTINUOUS SHELF
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HOW IS THE SLOPE CONSTRUCTED?
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WAVE-SUPPORTED SHEET TURBIDITY CURRENTS THAT DIE
ON THE SLOPE
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WAVE-SUPPORTED SHEET TURBIDITY CURRENTS
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SUCH CURRENTS BUILD OUT A CLINOFORM
Migrating clinoform
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THE CLINOFORM THUS BUILDS OUTWARD, EXTENDING THE
SHELF
Wave resuspension Diluted muddy turbidity
currents
Late Holocene Adriatic clinoform
Your first seismic image!
1 km
10 ms
Slide courtesy F. Trincardi
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GANGES-BRAHMAPUTRA DELTA
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GANGES-BRAHMAPUTRA CLINOFORM KUEHL ET AL. (1997)
Topset deposit deposit on shelf Foreset
deposit deposit on slope
Bottomset deposit deposit on slope base/rise
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THE SLOPE OFTEN HAS GULLIES, CARVED OUT OR
DEPOSITED BY TURBIDITY CURRENTS
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GULLIES ON THE CONTINENTAL SLOPE OFF NEW JERSEY
Dissected passive siliciclastic margin.
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GULLIES ON THE SLOPE OF THE EEL RIVER MARGIN,
NORTHERN CALIFORNIA
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GULLIES ON THE CONTINENTAL SLOPE OFF SANTA
BARBARA, CALIFORNIA
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GULLIES MAY BE MAINTAINED THROUGH EITHER ENHANCED
EROSION OR SUPPRESSED DEPOSITION
Focusing of a sheet turbidity current can lead to
incipient channels. This focusing can result in
enhanced erosion or suppressed deposition in the
channels/gullies.
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Suppressed deposition in gullies
Enhanced erosion in gullies
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MUDDY SHEET TURBIDITY CURRENTS AND
NET-DEPOSITIONAL GULLLIES ON THE BRUNEI MARGIN
Muddy deposits uniformly blanket zone of mud
diapirism at base of margin
Straub, Mohrig and Pirmez in progress
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MUD DRAPES THE ENTIRE TOPOGRAPHY, INCLUDING THE
GULLIES
Seafloor C.I. 8m
Slightly suppressed deposition in the lows allows
for channels to be constructed in a
net-depositional environment!
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WITH ENOUGH FOCUSING, A GULLY CAN ERODE INTO THE
SHELF, CAPTURE A SEDIMENT SOURCE AND EXCAVATE
ITSELF INTO A SUBMARINE CANYON
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GULLIES AND CANYONS OFF NORTHERN CALIFORNIA
Monterey Submarine Canyon
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Monterey Submarine Canyon
SUBMARINE CANYONS PROVIDE DIRECT CONDUITS TO
CARRY TERRESTRIAL SEDIMENT INTO DEEP WATER
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A RECENT SUCCESS IN MEASURING TURBIDITY OCCURE
FREQUENTLY, AND HAVE BEEN SUCCESSFULLY MEASURED
IN MONTEREY SUBMARINE CANYON
Xu, Noble, Rosenfeld, Paull (USGS, NPS, MBARI)
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VIEWS OF HEAD OF MONTEREY SUBMARINE CANYON
Canyon is about 1 km wide
Heads of Monterey Canyon
This and next two images courtesy D. Smith, USGS
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VIEWS OF HEAD OF MONTEREY SUBMARINE CANYON
Tall terrace in middle is about 25 m m tall.
View up canyon toward head. VE about 5?
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VIEWS OF HEAD OF MONTEREY SUBMARINE CANYON
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ZAIRE/CONGO SUBMARINE CANYON
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SUBMARINE FANS
As turbidity currents exit submarine canyons,
they can deposit huge submarine fans. The Ganges
submarine fan in particular is over 3000 km long.
Indus and Ganges Submarine Fans
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THE CONGO/ZAIRE CANYON/FAN SYSTEM
Focusing self-acceleration excavates a royal
pathway to deliver sand into deep water!
Savoye, Cochonat et al. (2000)
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CONGO/ZAIRE CANYON/FAN SYSTEM
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AMAZON SUBMARINE FAN
The Amazon Submarine Fan is another huge
submarine fan. The fan is built up over time by
channels that repeatedly aggrade and avulse.
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LONG PROFILE OF AMAZON RIVER, THEN DOWN THE
AMAZON CANYON AND ONTO THE SUBMARINE FAN
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LONG PROFILE OF AMAZON SUBMARINE CANYON, AND THE
MOST RECENT CHANNEL OF THE SUBMARINE FAN BELOW IT
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SMALL SUBMARINE FAN ON A STEPPED PROFILE ON THE
NIGER MARGIN, AFRICA
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CLOSEUP VIEW OF THE SAME FAN
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INCISED MEANDERING CHANNELS CREATED BY TURBIDITY
CURRENTS
Incised meandering channel on the continental
slope of the Niger Margin
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A COMPARISON BETWEEN THE SUBMARINE AND SUBAERIAL
WORLD
Subaerial
Submarine
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MEANDERING CHANNEL IN A VALLEY (FAIRWAY)
INCISED INTO THE SLOPE
An increasing body of evidence suggests that
submarine meandering channels do most of the
things that meandering rivers do (but in
different degrees).
Abreu, Sullivan, Pirmez, Mohrig (2006)
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MEANDERING CHANNELS ON SUBMARINE FANS
Mississippi Submarine Fan (Weimer, 1991).
Indus Submarine Fan (Kenyon et al., 1995)
Amazon Submarine Fan (Pirmez, 1995)
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CLOSER VIEW OF A MEANDERING CHANNEL ON THE AMAZON
SUBMARINE FAN
Meandering channel on Amazon Submarine Fan
(Pirmez, 1995)
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MEANDERING CHANNEL AND CUTOFFS ON THE GANGES
SUBMARINE FAN
Bengal Fan Schwenk, Spiess,Hubscher, Breitzke
(2003)
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LEVEES ON SUBMARINE CHANNELS
SELF-CONFINEMENT AND LEVEE CONSTRUCTION
Turbidity currents are adept at confining
themselves between levees.
Channel on Amazon Submarine Fan Damuth and Flood
(1985)
Toyama Submarine Channel Kubo and Nakajima (2002)
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SELF-CONTAINMENT BY LEVEES
Submarine meandering channels contain themselves
between levees over 100s 1000s of km and
scores 100s of bends.
Bengal Fan Schwenk, Spiess,Hubscher, Breitzke
(2003)
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MINIBASIN FIELDS
Here the continental slope is governed by salt
tectonics.
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THE RIDGES AND BASINS ARE CONNECTED BY A DRAINAGE
NETWORK OF TURBIDITY CURRENT CHANNELS.
From Liu and Bryant
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HOW WAS THIS BASIN-AND-RIDGE TOPOGRAPHY CREATED?
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THE CHANNEL PROFILE HAS BEEN SMOOTHED BY FILLING
IN THE BASINS AND INCISION IN THE RIDGES THE
LAST BASIN (4) HAS NO OUTLET
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SEDIMENT WAVES
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SEDIMENT WAVES
California margin image courtesy W. Normark
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DIFFERENT VIEW OF SAME SEDIMENT WAVES
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LEVEE OF OUTER BANK OF SHEPERD MEANDER, MONTEREY
SUBMARINE CHANNEL
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SEDIMENT WAVES ON THE OUTER LEVEE OF THE SHEPERD
MEANDER BEND
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THE SEDIMENT WAVES INVARIABLY MIGRATE UPSTREAM
IN ORDERLY TRAINS