Dr. EHAB M. ASSAL
Damietta University
Depositional Environments Lec. 8 Submarine fan systems
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Submarine Fans
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Monterey Bay
Monterey submarine
canyon
fault-controlled
topography
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Outline
The Reef Mosaic1
2 Reef Growth
3 Shallow-water Reefs
4 Zonation of A Reef
5 Deep-water Reefs
Submarine Fans
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“fan-shaped” wedgeof sediment
siliciclastic (delta-canyon source) or
carbonate! (reef)
transport mechanism
Turbidity currents
plus or minus
pelagic sediment
plus or minus large
slumps, slide, debris
submarine canyons
conduit to the deep ocean
lobe building
analogous to alluvial fans and deltas
lobe avulsion, progradation inherited structural /
geomorphic control
continental margin edge
faults, unconformities
Geomorphic Control on submarine fans
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Computer model of the Los Angeles shelf edge.
note many canyons cut (and maintained?) by turbidity
currents corresponding sediment lobes downstream
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The continental edge,modified by sedimenttransport and deposition
Monterey Bay
Monterey
submarine
canyon
fault-
controlled
topography
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Cenozoic marine
sediments in
yellow, tan,
brown
off-shore is notnecessarily oceanic crust!
Deep part of canyon is
Mesozoic granite
Faults cut across seafloor
Experimental turbidity current
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The BOUMA SEQUENCE (1962)
The model is based on outcrop observations
in the Tertiary Annot Sandstone (Maritime Alps)
Historical introduction and early models
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The model describes a typical turbidite
bed consisting of 5 depositional divisions
(Ta-e). Base-missing sequences develop
in a downcurrent direction.
The depositional cone implicitly interprets
a turbidity current as a non-uniform flow
with decreasing velocity and compence
with distance (proximal vs distal) as well
as an unsteady flow with decreasing
velocity and competence with time (graded
beds)
Classic Bouma facies as recognition criteria
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Sediment transport: turbidites (review)Classic Bouma facies as recognition criteria
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the flow
pause between flows
Typical turbidites
erosive base
pelagic top
may be missing lower or
upper Bouma facies (or both)
but
Bouma facies are always
in order!
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Idealized fan system
link sediment source to fan
submarine canyon
fan constructed at canyon mouth
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Posamentier & Walker (2006)
Inner submarine fan
submarine canyon mouth “point source”
deeply channelized flows, erosion of channel
walls
coarse, thick, debris-flow deposits in channels, finer
upward as channels are abandoned, channel wall
slumps
overbank deposits (interchannel) include fine mud and
coarse turbidites
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Dana Pt. basal conglomerate
Montecello Dam basal debris flows
Channel eroded into inter-channel fine and thin turbidites
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Sediments in the canyon floor:
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3D seismic oblique view image of channel system
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ExxonMobil image, from AAPG Explorer
Channel is 1/2 mile wide
3D seismic image processing
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Sand contrasts acoustically with mud, signal processing shows different attributes. Pleistocene, Gulf of Mexico; Davies & Posamentier, 2005
Role of submarine canyons
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Distribution of sediments todistal parts of the fan
Reworking of proximal
sediments
Mauritania example
Detailed thalweg transect:
depth range 0 - 3300 m east to west; 120 nautical milesacross
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Channel details
depth range 0 - 3300 m east to west; 120 nautical milesacross
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Note abandoned meanders, channel gradient
overbank deposits
fine top of flow can escape the channel and flow out
across the interchannel area
this “flow stripping” is especially likely at
meander bends
result outside the channel:
thin, base-missing turbidites
interbedded with pelagic and hemipelagic fines more
numerous flows than distal thin turbidites
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Evolving channel/lobe system
progressively stronger flows modify and fill the lobe
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USC image
Interlobe fines
starved ripples interpreted as “stripped” base-missingturbidites
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Great Valley Sequence, CA
The role of large slumps/slides
the Pleistocene Storegga slide in the North Sea
300 x 800 km slide,20 meter tsunami
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Large-scale slope failure, Amazon fan
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Reis et al., 2010, Geol. Soc. London
Mid-fan sediments
distributary lobes with channel systems, moderate channel relief
lobe building by progradation of lobe system,sequences thicken and
coarsen upward
avulsion - lobe-switching ends progradation,muds bury old lobe sands,
channels fill in
new lobe somewhere ...
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A single unconstrained lobe
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note thickness distribution of final deposit
deposit changes down the lobegenerally thinner and finer outward
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CTU cycles = prograding lobes,each flow goes farther,is thicker
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Boxer Ss. CA coast range
J. Trexler
stacked lobe sequences
top to left,note prograding,coarser and thicker beds
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review of prograding lobe strata
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Outer fan sediments
smooth, low-angle slope, channels are small and not
incised much
thin, blanketing turbidites interbedded with thick
mud sections
coarsening and thickening upward sequences
as distal lobes build outward
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Outer fan sediments thin,“base missing” turbidites no topography,sandy sheet-like
turbidites
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Great Valley Sequence
image: J Trexler
stacking patterssome expected architecture on different parts of the submarine fan
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lobe building
SEPM website
channel cut t ing, f i l ling, and abandonment
Controls on terrigenous sediment supply to fan
River/delta system point source supply
– climate, discharge, uplift of hinterland, etc.
Relative sea level
– low-stand: erosion of delta front and delivery of
sediment to distal fan
– high-stand: drowning of delta, shut off sediment supply to
fan
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Controls on carbonate sediment supply to fan
River/delta system point source supply
– climate, discharge, uplift of hinterland, etc.
Relative sea level
– low-stand: erosion of delta front and delivery of
sediment to distal fan
– high-stand: drowning of delta, shut off sediment supply to
fan
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Recognition of submarine-fan rocks
recognizing turbidites
– Bouma facies
recognition of system architecture
– lobe sequences coarsen up
– channel systems fine up
– down-fan fining and thinning of facies
prograding or regressing?
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submarine fan architecture much of what we know is from seismic stratigraphy very large scale
disconnect with outcrop
preservation bias
problem: very large submarine fan systems will not be deposited on
continental crust
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LATER DEVELOPMENTS
Historical introduction and early models
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One of the main issues remains how to correctly use the wealth of information gathered from outcrop studies over the years to better understand the increasing complexityemerging from deep- watersedimentation of continental marginsas depicted by oil exploration and marine geology studies
Nonetheless, even in most recent literature, deep-water sedimentation is still considered essentially dominated by turbidity currents within the framework of canyon- or channel-fed submarine fan models
The foredeep basin turbidites of thrust-and-fold belts
WHAT DO WE REALLY KNOW ABOUT TURBIDITES OF THRUST-AND-
FOLD BELTS FROM WHERE WE STARTED ?
Ancient exposed turbidites are primarily the fill of elongate and highly
subsiding troughs, called foredeeps, which are part of the foreland domaindeveloped in front of an advancing and growing orogenic wedge
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The foredeep basin turbidites of thrust-and-fold beltsFOREDEEP TURBIDITES
The best known examples of this kind of sedimentation are the Miocene
Marnoso-arenacea (northern Apennines) and the Eocene Hecho Group
(south-central Pyrenees) where excellent exposures, detailed mapping, and
the occurrence of numerous and distinctive key-beds (calcareous
megaturbidites) permit the tracing of individual sandstone beds and
packages of beds over considerable distances parallel to basin axis
(e.g., Ricci Lucchi and Valmori, 1980 for the MA and Mutti et al., 1988,
1999, for the Hecho Group)
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The spectacular exposures
of the Marnoso-arenacea
No doubt, foredeep turbidites are
essentially sheet-like deposits consisting of
outer-fan sandstone lobes passing distally
into basin-plain deposits as originally
described by Mutti and Ricci Lucchi
(1972). Sediments of this kind can only be
deposited by highly efficient, large-volume
and sustained turbidity currents.
Regional cross-section of the Miocene Marnoso-arenacea (MA)
roughly parallel to basin axis (paleocurrents from left to right). Note the
main key-beds.
From Mutti et al. (2007). Data from P.Muzzi and R. Tinterri.
The foredeep basin turbidites of thrust-and-fold belts
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0
Casaglia
1000
Main200
0
3000
m
60
KmTotal bed-by-bed measured sections: ~
6500m
NW1
2 3 4 and 5 6
Nasset
o
Acquadalt
o
Monte Nero
Thrust
S
E
faultChaotic unit
measure
dsections Vergheret
o
The Contessa key-
bed
Italy
( person for
scale)
FACIES, FACIES ASSOCIATIONS AND FACIES TRACTS
Mainly stemming from the Bouma sequence and from the proximal vs
distal concept (Parea, 1965, Walker, 1967), early attempts to develop
facies classification schemes were mainly descriptive (Mutti and Ricci
Lucchi, 1972, Walker and Mutti, 1973)
Later,facies classifications started to be process-oriented aiming at
developing schemes within which conglomerates, sandstones and
mudstones could be viewed as part of the same facies spectrum (Mutti and
Ricci Lucchi, 1975, Walker, 1975, Mutti, 1979, Lowe, 1982) (see Pickering
et al, 1989 for an extensive review).
Most concepts were derived from outcrop (rocks) observations.
This phase of research was strongly influenced by the seminal
paper of Middleton and Hampton (1973) on sediment gravity
flows.
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Detailed bed-by-bed regional cross-section of the MA
showing stratal correlations over a distance of some 60 km (From Muzzi
and Tinterri, 2011)
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More recently, spectacular bed-by-bed correlations have
been provided by Amy and Talling (2006), Tinterri and
Muzzi (2010) and Muzzi and Tinterri (2011) for the
Marnoso-arenacea and by Remacha and Fernandez
(2003) and Remacha et al. (2005) for the Hecho Group.
Some of these correlations (Muzzi and Tinterri, 2010)
extend over 60 km and are based on more than 6500m
of measured sections.
The great variety of turbidite facies of foredeep basin fills
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FOREDEEP TURBIDITES ARE AN IDEAL NATURAL
LABORATORY
TO STUDY FACIES CHANGES AND FLOW
TRANSFORMATIONS OVER CONSIDERABLE
DISTANCES
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Inferred from basinwide detailed
correlations in the Hecho Group
(Pyrenees) and the MA Fm
(Northern Apennines) and
observations in many other
turbidite basins
The tract is interpreted as produced by downcurrent transformations of dense
frictional flows, impelled by inertia forces under conditions of excess pore pressure,
into turbulent flows. For the sake of simplicity and for practical purposes of basin
analysis the general terms turbidity currents and turbidites are here used to
define this broad spectrum of processes and resulting deposits respectively (Mutti,
1992; Mutti et al., 2003).
General Turbidite (facies tract)
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The characteristics of facies tracts
depend mainly on the textural
composition of parental flows,
amount of bed erosion, flow
efficiency, and basin configuration.
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Example of turbidite bed deposited by a bipartite turbiditycurrent
C : Impervious mudstone division
B : Fine-grained current-laminated division (mostly current ripples) deposited
by a dilute turbulent flow and plastically deformed by water escape moving
upward and laterally
A : Medium-grained structureless division with basal load features deposited
by an inertia-driven dense sandy flow under conditions of excess pore
pressure. Note the diapir-like features at the top of the division with
concentration of mudstone clasts and plant fragments floating at the top of the
dense flow (red arrows).
A
B
C
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AND WHAT ABOUT COEVAL FLUVIO-DELTAIC SYSTEMS?
Terms like “source-to-sink” and “staging areas” havebeen recently introduced to point out the problem that afull understanding of deep-water turbidite sedimentationcan only be achieved through a better knowledge of the coeval fluvial drainage basins (source) and related fluvio-deltaic systems (staging areas).
The importance of the problem was emphasized in theworkshop entitled “Turbidites: models and problems”which was held on May 21-25, 2002, at the University ofParma, Italy (see Mutti, Steffens, Pirmez and Orlando, Marine and Petroleum Geology,2003).
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AND WHAT ABOUT COEVAL FLUVIO-DELTAIC SYSTEMS?
Terms like “source-to-sink” and “staging areas” have beenrecently introduced to point out the problem that a fullunderstanding of deep-water turbidite sedimentation canonly be achieved through a better knowledge of the coevalfluvial drainage basins (source) and related fluvio-deltaicsystems (staging areas).
The importance of the problem was emphasized in theworkshop entitled “Turbidites: models and problems”which was held on May 21-25, 2002, at the University ofParma, Italy (see Mutti, Steffens, Pirmez and Orlando, Marine and Petroleum Geology,2003).
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In their vast majority, fluvio-deltaic systems of foreland and
tectonically active basins are dominated by facies and facies
associations related to rivers in flood with the extensive
development of delta-front sandstone lobes
Delta-front sandstone lobes of the Eocene
Santa Liestra Group (Pyrenees)
Jurassic Bardas Blanca
Neuquen Basin (Argentina)
Displaced sleletal debris
HC
S
Tabular geometry of
sandstone lobes
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Stratigraphic cross-section of the Eocene foreland basin of the S-central Pyrenees showing the relationship between basinal turbidites and fluvio-deltaic strata
Fluvio-
deltaic
systems
Occurrence of turbidites and their
shallower water “cousins”:
1 - Delta-front sandstone lobes
2 - Slope channels and thrust-
related piggy-back basins
or minibasins
3 - Basinal or foredeep turbidites
Foredeep
turbidites
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Facies distribution pattern of a turbidity current exiting a deep-water
conduit (A) and a dense sediment-laden flow exiting a river mouth
during a severe flood (B).
Except for water depth, fossil assemblages and the occurrence of HCS in (B), the
two patterns are essentially similar recording deposition from jet flows. Angle of
spreading depends on the local ratio between inertia and frictional forces
A B
CONCLUSIONS: Both flows are hyperpycnal because of
their excess density. Both flows decelerate with distance
and time. Both flows are sediment gravity flows. Their
deposits, produced by similar processes, should be
simply termed deep-water (basinal) and shallow-water
(delta front) turbidites.
FLUVIO-TURBIDITE SYSTEM
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It forms when highly catastrophic floods carry sediment directly from drainage
fluvial basins to deep waters eroding former alluvial and nearshore staging areas.
Note how transfer zones and staging areas vary during the evolution from A to C
THE MISSOULA FLOOD
Models from seismic stratigraphy
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www.du.edu.eg/faculty/sci
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