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Dynamique des Bassins

1- Origine des Bassins Sédimentaires • Déformation lithosphérique: forçages internes • Sédimentation : forçages externes • Bassins Sédimentaires et ressources naturelles 2- Cadre géodynamique des Bassins Sédimentaires • Analyse de la subsidence • Bassins liés à la divergence

- rifts - marges passives

• Bassins liés à la convergence - bassins foreland

• Autre types de bassins 3- Évolution post-dépôt des Bassins Sédimentaires • Compaction - Diagenèse • Circulation des fluides • Cas de la matière organique - systèmes pétroliers

Michel Séranne Bat 22, 3eme Étage Gauche Page perso: www.gm.univ-montp2.fr/MichelSeranne

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2 © NASA

1- Origin of Sedimentary Basins 1.1 Lithospheric deformation: Internal forcings

1.2 Sedimentation: External forçings 1.3 Sedimentary basins & societal issues

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Distribution of sedimentary basins (sediment accumulation > 1km)

=> Study of sedimentary basins = analysis of processes responsible for the origin of: 1- the depression (mostly controlled by internal forcings «  Earth machine ») 2- the sedimentary-fill (controlled by interaction of internal and external forcing)

What is a sedimentary basin ? : it’s a depression filled with sediments

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=> The Earth’s interior is composed of number of compositional and rheological zones. ⇒ The main compositional zones are the crust (low density rocks + sedim. cover), mantle (olivine) and core (metallic : iron & nickel).

atmosphere

Lithosphere

mantle

Outer core

Molten outer.C. Solid inner C.

Solid crust

Rigid Lithosphere mantle

Struture and reology of the Earth envelopes

Basin forming driving mechanisms are related to processes within the rigid, cooled thermal boundary layer of the Earth known as the Lithosphere.

1.1.Lithospheric deformation: Internal forçings

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Basics about the Lithosphere • Definitions

Definition of the outer envelopes of the Earth that interact to form sedimentary basins

• Sedimentary basins are formed between solid and fluid envelopes of the Earth.

• Continental & oceanic crusts are compositionally different from the underlying mantle

• The outer mantle and the crust makes the lithosphere (rheological unit)

• The outer mantle has the same compostion as the underlying convective mantle (asthenosphere)

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6 Characterization of the different layers of the lithosphere. Deformation of the lithosphere induces

the formation of sedimetary basin.

Basics about the Lithosphere • parameters controling lihosphere rheology

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Continent (low density)

Mountain root

Mantle (high density)

Ocean

Depth of equal pressure

Basics about the Lithosphere • Principle of isostacy

mountain

The Airy hypothesis: Blocks of the same density (material), but different thickness, floating about an equilibrium surface => uneven Moho (roots beneath mountains and rises beneath basins) .

Pratt model blocks of differing density (lighter beneath mountains and denser beneath basins) => flat Moho.

Not

verified

by data

basin

« anti-root »

• Total mass of each column must be equal.

Yes!

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Basics about the Lithosphere • Principle of isostacy

load balanced vertically, beneath the load => lithosphere behaves like independant columuns => no rigidity

Regional isostacy:model = trampoline Local isostacy : model = snow cover

Load distributed over a wide area => each segment of the lithosphere is linked to the next => flexural rigidity

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weight of a lithosphere column before basin formation = weight of a column after basin formation

Only if

Locally

compensated !

Basics about the Lithosphere • Principle of isostacy

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Basics about the Lithosphere • Principle of isostacy

Considering that seismic data provides the depth of basement beneath the basin (5km) , and that Initial crust thickness = 30km Density of crust = 2.7 t/m3

Density of sediments = 2.2 t/m3 Density of mantle = 3.3 t/m3

Considering isostatic equilibrum, what is the depth of the Moho beneath this basin ?

moho

Basin

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Glob

al H

eat

Flow

Map

• Energy of accretion at the time of its formation ; • Energy related to formation of iron-rich core ; • Energy from decay of radioactive elements (mostly in the crust)

=> Responsible for mantle dynamics (convection) => Makes the plates moves at the surface => Energy loss to space = surface heatflow

Mantle convection 3D simulation

The Earth internal flux of energy = sum of:

Internal driving forces of the Earth machine

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Internal driving forces of the Earth machine

The internal heat is continuously dissipated outwards from the centre of the Earth in 3 ways : •  Conduction : Thermal energy transmitted between atoms => Internal solid Earth •  Advection : Movement of hot material to surface => Volcanoes and hot spot ; •  Convection : Movement of material in the mantle and outer core by density differentiation of the plastic material => Plate tectonics

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• Earth internal energy = Energy of accretion at the time of its formation + Energy related to formation of iron-rich core + Energy from decay of radioactive elements => dissipated at surface = heat flux. •The heat flux propagated by convection in the plastic upper mantle is converted into mechanical energy (and localized partial melting) at the base of the Lithosphere and dissipated by plate motion and deformation. • Lithospheric plates movements (1000’s km laterally , 1000’s m vertically).

America Atlantic Ocean W. Europe

Pacific Ocean

Subduction zone

Acretionary ridge

Convection cells

Asthenosphere

Lithosphere

Relative movement

Plate tectonics: lithosphere movements

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14 Lithospheric surface of the Earth showing plate tectonics (plate boundaries, earthquakes and volcanoes).

Plate tectonics

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15 Distribution of sedimentary basins (sediment accumulation > 1km) Continental passive margins , subduction zones, foreland of present or ancient mountain belts, centre of cratons.

Sedimentary basins and Plate tectonics

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16 Fort Proctor Louisiana (Gulf of Mexico):

-  subsidence > 1 m since1850

How to create a depression ?

www.marlimillerphoto.com/

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How to create a depression ?

1- Cooling

2- Stretching/ thinning

3- Loading

-> 3 lithospheric processes account for subsidence

1300°C 1300°C

20°C

1300°C

20°C

Any sedimentary basin subsidence results from one of these 3 processes or a combination of them

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Stretching/Thinning

© Michon, 2000

Marsden et al.'s (1990) interpretation of BIRPS' NSDP84-1 deep seismic line. MARSDEN, G, YIELDING, G, ROBERTS, A & KUSZNIR, N. 1990

Stretched lithosphere is thinned because of mass conservation - faulting in upper crust, - rising of basal lithosphere

Copyright © 2008 Virtual Seismic Atlas

Sand-box Analog

modeling

Reflexion seismic - North Sea Rift

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0 80 180 Ma

Age of the oceanic Lithosphere (oceanic floor) Lithosphere emplaced at mid-oceanic ridges (accretion) and then moves apart symetrically (seafloor spreading)

5km 2km

Bathymetry of the oceanic Lithosphere (oceanic floor) increases away from oceanic ridges

http://jules.unavco.org/Voyager/Docs/EarthScope http://topex.ucsd.edu/WWW_html/mar_topo.html

Cooling: example

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• Cooling of oceanic lithosphere • Increasing bathymetry of oceanic floor • Increasing thickness of oc. lithosph.

Accretion Very high geotherm

0°C

1300°C

geotherms

age & distance

z

Sea level

-2km

-5km

Thermal contraction of the Oceanic Lithosphere

Depth or subsidence of oceanic lithosphere = f[lithosphere age] 1/2

Carlson&Johnson, 1994

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Sedimentary load of the Congo deep-se-fan ( > 5km thick) => Deflexion by flexure of the oceanic lithosphere (subsidence)

Modifié d ’après Uchupi, 1992

Loading of the lithosphere => flexure

Congo drainage area

Atlan

tic

accr

etiona

ry r

idge

Niger fan

Congo fan

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Plume

Hawai

flexure

load

flexure

flexure

Uplift (Plume)

500km

Loading of the lithosphere => flexure

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23 Different types of basins according to plate tectonic setting: spatial and temporal evolution from one type to another

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1.2. Sedimentation: External forcings

• Tidal sediments = Sediment deposition controled by the tides (cyclic phenomenon). • Tides results from combined attraction of the Moon and the Sun on the oceans (& on the crust). • Sedimentation records variations of parameters external to the Earth

Burdigalian (Digne foreland Basin)

Present: Baie du Mont Saint Michel