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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