1

1 Mas

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Sedimentation on passive margins

2 Mas

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rift

Break-up

Young margin

Mature margin

Sedimentation is controled by continental margin geodynamic evolution

Tectonic-sedimentation relationships at passive margin scale

2

3 Mas

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Stage « rift »

Syntectonic sedim. Outward drainage

=> Starved basin

Lithosphere stretching

Axial lake (restricted) ⇒ M.O. preserved

thermal anomaly

Tectonic-sedimentation relationships on passive margins

4 Mas

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Model: East African rift

3

5 Mas

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Stage « break-up »

Oceanic accretion => Extensional stress stops => Fault activity stops

Transgression => evaporites

Thermal anomaly ⇒  cooling

cooling => densification => subsidence

Tectonic-sedimentation relationships on passive margins

Young (hot) ocean. lithosph. ⇒ Sub-horizontal ⇒ basement

6 Mas

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Model: Afar & Red Sea

Afar

Marge continentale d’Aden

Rift

4

7 Mas

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Differential Subsidence

=> tilting

Sed = Accom => aggradation

Gravitational Tectonics

Stage « young margin »

Differential accomm. Proximal->distal facies

Tectonic-sedimentation relationships on passive margins

8 Mas

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Stage « mature margin »

progradation Deep-sea fan

Reduced thermal subsidence

Added sediment load => Subsidence (flexure)

Terrigenous sediment flux

Tectonic-sedimentation relationships on passive margins

Flexural uplift

5

9 Mas

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- + - +

Acc > Sed

Acc = Sed

Sed > Acc

Sed > Acc

Acc >> Sed

Synrift subsidence

Thermal postrift Subsidence

Water depth Subsidence

0 marin

0 lacustre

Synthetic log of passive margins

Break-up unconf

10 Mas

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Oligocene-Present isopachs

4.5km 4

3

2

1

0km

Rust & Summerfield 1990, Anka 2004

Congo deep-sea-fan

• Angola: thick and focused deposits extensive continental watershed

• Africa SW: distributed and thin deposits

little continental erosion

Integrated study of passive margins « source-to-sink »

Congo

Orange

Watershed - depocentre relationship

6

11 Mas

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Long-term evolution of W. Africa deep-sea fans

• Congo-Angola: Cenozoic deep-sea-fan

• South-Africa : late Cretaceous margin + deep-sea-fan

Oceanic crust Cont. crust

Syn-rift+SDR

seamount

Cont. Cr.

synrift

Oceanic crust

50km

50km

5km

0km

10km

Séranne &Anka 2005,

12 Mas

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Onset of Cenozoic deep-sea-fan deposition

Base Oligocene

Top Turonian

Miocene latest

0.5

s

1 km

NE SW

Aptian salt SB

Progradation of Tertiary DSF Condensed surface

Tur.

Down lap

On lap

Top Oc. Cr.

7

13 Mas

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? ?

Condensed interval

Rust & Summerfield 1990, Anka 2004, Leturmy & Lucazeau 2003

14 Mas

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terr

igeo

us

terrigenous

carbonates

Evaporites

mar

ls

terrigenous = syntectonic sedimentation

Con

tinen

tal e

rosi

on

Red

uced

con

tinen

tal

eros

ion

8

15 Mas

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Record of Climate change on passive margins

Climate change (icehouse) => increased continental erosion => increase terrigenous flux

16 Mas

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Deep sea fans on mature margins Oceanic crust

Continental crust

0-10Ma

100-120Ma

65-100Ma

40-65Ma

10-25Ma

20km

Gravitational tectonics

Rifted Continental Crust Oceanic crust

• Terrigenous sediments over oceanic crust • Huge depocenter => burial + gravitational tectonics • Large sediment flux => large watershed and intense erosion • Sedimentation rate increases in Miocene

Lopez, 1996

Amazon example

DS

F lo

ad

9

17 Mas

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Flexural loading of Amazon DSF

Watts, 2009

Extra-subsidence (>2km at the center of load)

Flexural uplift (<40m) around the load

Characterizing and computing the extra-subsidence due to the lithosphere flexure in response to the load of the Amazon DSF

18 Mas

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Deep-sea fan : Congo

Angola

Escarpement

(Lopez, 2000)

Congo Turbidite deep-sea-fan (800 km) Margin

10

19 Mas

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Geometry of Congo DSF

(Anka, 2004)

Isopach map of Oligocene - Present

20 Mas

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Congo watershed

med

io-A

tlant

ic r

idge

Niger fan

Congo fan

Sedimentary load => flexure of the oceanic lithosphere

Modifié d �après Uchupi, 1992

Effect of Congo DSF on the passive margin

11

21 Mas

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Flexural loading of Congo DSF

Te=20km (Anka, 2004)

Flexural uplift (<70m)

Subs. >2km

22 Mas

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Interactions Margin-DSF

(Seranne Anka, 2005)

⇒ DSF sedimentary record complements that of the margin; ⇒  DSF depocentres are as big as margin�s depocentre, ⇒  Loading increases subsidence in mature margins AND flexural uplift of oshore margin; ⇒  Continental drainage concentrates in few major rivers ⇒ DSF record processes active on continent