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Architecture des Bassins & Géomatique1- Origine des Bassins Sédimentaires • Déformation lithosphérique: forçages internes • Sédimentation : forçages externes • Importance des Bassins Sédimentaires
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
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2© NASA
1- Origin of Sedimentary Basins1.1 Lithospheric deformation: Internal forçings
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 iscomposed of number ofcompositional and rheologicalzones.
⇒The main compositional zonesare the crust (low density rocks +sedim. cover), mantle (olivine) andcore (metallic : iron & nickel).
atmosphere
Lithosphere
mantle
Outer core
Molten outer.C. Solid inner C.
Solid crust
Rigid Lithospheremantle
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 thatinteract to form sedimentary basins
• Sedimentary basins are formed betweensolid and fluid envelopes of the Earth.
• Continental & oceanic crusts arecompositionally different from theunderlying mantle
• The outer mantle and the crust makes thelithosphere (rheological unit)
• The outer mantle has the samecompostion as the underlying convectivemantle (asthenosphere)
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6Characterization 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)
Mountainroot
Mantle(high density)
Ocean
Depth ofequal pressure
Basics about the Lithosphere• Principle of isostacy
mountain
The Airy hypothesis:
Blocks of the same density (material), but different thickness, floating about an equilibriumsurface => uneven Moho (roots beneath mountains and rises beneath basins .
Pratt modelblocks of differing density (lighter beneath mountains and denser beneathbasins) => flat Moho.
Not verified
by data
basin
« anti-root »
• Total mass of eachcolumn must be equal.
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weight of a column of lithosphere 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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Earth internal dynamics as driving mechanisms for basin formation
=> The Earth System can be regarded as a thermo-mechanical machinewhich consumes, transforms and releases energy in order to maintain equilibrium conditions.
=> Sedimentary basins rocks are recording devices (and sediments the tapes or CD’s) which record(somewhat discontinuously) the equilibrium quest of the Earth system.
(Courtillot, 2003) (Don Anderson 2004)
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Internal driving forces of the Earth machine
Glob
al H
eat
Flow
Map
The internal heat is continuouslydissipated outwards from the centre ofthe Earth in 3 ways :
• Conduction : Thermal energy transmittedbetween atoms=> Internal solid Earth
• Advection : Movement of hot material tosurface=> Volcanoes and hot spot ;
• Convection : Movement of material in themantle and outer core by densitydifferentiation of the plastic material=> Plate tectonics
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Earth machine: mantle convection
Mantle convection with phase transition
(olivine -> spinel -> peroskivite
Mantle convection no phase transition
Sam Butler, www.usask.ca
subductionplume
avalanche
Uppermantle
Lowermantle
plume
subduction
Mantle one layer Mas
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• Earth internal energy = Energy of accretion at the time of its formation + Energy related to formation ofiron-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 anddeformation.
• Lithospheric plates movements (1000’s km laterally , 1000’s m vertically).
America Atlantic OceanW. Europe
Pacific Ocean
Subductionzone
Acretionaryridge
Convectioncells
Asthenosphere
Lithosphere
Relativemovement
Plate tectonics: lithosphere movements
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13Lithospheric surface of the Earth showing plate tectonics (plate boundaries, earthquakes and volcanoes).
Plate tectonics
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14Distribution of sedimentary basins (sediment accumulation > 1km) Continental passive margins , subductionzones, foreland of present or ancient mountain belts, centre of cratons.
Sedimentary basins and Plate tectonics
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How to create a depression ?
1- Cooling
2- Stretching/ thinning
3- Loading
-> 3 lithospheric processes account for subsidence
1300°C1300°C
20°C
1300°C
20°C
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0 80 180 Ma
Age of the oceanic Lithosphere(oceanic floor)Lithosphere emplaced at mid-oceanic ridges (accretion) andthen moves apart symetrically(seafloor spreading)
5km
2km
Bathymetry of the oceanicLithosphere (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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age
z
0°C
1300°C
geotherms
Sea level
• Cooling of oceanic lithosphere• Increasing bathymetry of oceanic floor• Increasing thickness of oc. lithosph.
AccretionVery high geotherm
-2km
-5km
Thermal contraction of the Oceanic Lithosphere
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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 Application of the flexural cantilever simple-shear/pure-shear model to the north sea. In: Blundell, D &Gibbs, A (eds). Tectonic Evolution of the North Sea Rifts. Oxford University Press, Oxford.
La lithosphère étirée s’amincit - failles dans la croûte supérieure, - remontée manteau sous la zone amincie
Copyright © 2008 Virtual Seismic Atlas
Sand-boxAnalog
modeling
Reflexion seismic - North Sea rift
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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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20Different 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 attractionof the Moon and the Sun on the oceans (&on the crust).
• Sedimentation records variations ofparameters external to the Earth
Burdigalian (Digne foreland Basins)
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• Periodic changes in the Earth’s orbital parameters affect the amount of radiationfrom the Sun.• The energy dissipated by the Sun varies with time => variation in radiation received bythe Earth.
=> The total amount of solar radiation received on the Earth’s surface governs long-term (100’s of millions of years) or on short-term (10-1000’s years) temperature of the atmosphere and hydrosphere. Through complex feedbackloops, this has direct and indirect consequences on Climate and associatedexogenic transfer processes.
=> Climate forcing affect the way the sedimentary basins are filled
EnergyEnergy
External forcings
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Sun’s energySun’s energy
1m2 ->342W/m2
1.41 m2 ->242W/m245°
90°
tilt
NO tilt• No seasonal variation of insolation• Increased yearly average temperature
• High latitudes receives less energythan inter-tropical areas• Insolation seasonal variation
Insolation : sun’s energy
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Milankovitch cycles
T= tilt or obliquity
E = eccentricity
P = precession
• Orbital parameters of the Earth have been acting over the whole history of the planet(albeit changes in periodicity and amplitude).• Milankovitch cycles have been recorded in sediments with different intensity throughtime.• During Quaternary Milankovitch cycles are particularly well expressed (Glaciations stages)
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Sediment accumulate in basins if:1- there is a gravity-driven flux of sediment (erosion/ transport/ deposition)
=> base level 2- there is space available to trap the sediment
=> accommodation space
Sediment are generated if:• Deformation of the topographic surface of the lithosphere induced by internal forcing(mountain-building, volcanism, thermal uplift…).⇒ Erosion of the topography, mobilization of detritals, transport, deposition.⇒ All processes governed by gravity.⇒ Processes strongly dependent on external forcing (climate…).
• Biological activity contributes to sediment flux.⇒ in-situ carbonate production in favourable environments (« carbonate factory » in ocean,lakes) -> climate-dependent⇒ reworked carbonates behaving as detritals⇒ plants residues (coal)
• (Bio-) Chemical activity = weathering, alteration, evaporation, precipitation.
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Base-level
1
Base level (Wheeler, 1964) :• is an abstract, non physical, surface ;• is above the earth surface where deposition occurs, below where erosion occurs, and upon where there is anequilibrium (e.g., bypass) ;• represents the surface where sediment flux would be constant (i.e., a balance would exist between sedimentsupply and removal) ;• is a potentiometric surface (i.e., the surface along which the energy of sediment flux is minimized) ;• is a dynamic surface (i.e., it vibrates with respect to the physical surface in time and space) ;• exists in a system where space, energy and mass are conserved.
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Available space => Accommodation
Eustacy
IntraplatedeformationBasin
subsidence
accommodation
2
Accommodation : it is the rate (measured in m/Ma) at which space is being made availablefor sediments to be trapped in the basin. It is the result of the vertical movements of thebasement (subsidence + lithoshere deformation) and of eustacy (World ocean level).Sediment flux may or may not fill the availlable space. This is determined by the balance ofsediment rate and accommodation.
Sed. Rate < Accomm => underfilled basin, water depth increases (starved basin, condensation surface)
Sed Rate = Accomm => basin remains at the same water-depth => persistance of sedimentary facies through time
Sed. Rate > Accomm => basin being filled, water-depth decreases, coarsening and shallowing up sequences. M
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« Eustacy » vs « Relative sea-level change »EustacyEustacy = variation of the global World Ocean (all seas & oceans being connected)this is due to changes in the shapes of the ocean floor ( variable rates of sea-floor spreading, mantle-convection induced uplift,…) or of the volume of water in the World Ocean (growth or decay of polar ice-caps, soil moisture, water thermal expansion…).
Haq Eustatic Curve
Relative Relative sea-level sea-level changechange = variation of water depth in one basin. It’s the combination of eustacy, and localconstraints: subsidence/uplift and sediment flux.
Several Eustatic Curveshave been compiled andprogressively improved(Haq, Miller, Kominz,…) .They can be appliedeverywhere.
Relative sea-level
Eustacy
Bst vertical mvt
sediment fluxRelative sea-level change in abasin can be approached byanalysis of the stratalarchitecture combined withsedimentary facies.
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Periodic changes in forcings => cycles• Periodic (or not) changes in the controlling processes => record cycles
• Signals of differenttime/space scale => record ofstacked (nested) cycles
- several nested sequences inthe stratigraphic record
• Combination of stacking of severalsignals => complex stratigraphicrecord
- Basin analysis aims at decipheringthese signals- sedimentary basinfill containsthese signals => Archives
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Stratal geometry
Canterbury Basin, New Zealandaggradation
progradation
Condensedsection
Aggradation:Sed. Rate ≤ Accomm
Progradation :Sed Rate ≥ Accomm
2 mains patterns: several possible causes f(subsidence, sediment flux, sea-level)
bathymetryDivergent: Differentialsubsidence
Down-lap
Onlap
Sed. Rate > Accomm Sed. Rate < Accomm
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Fluvial & deltaSlope shales Reworked
clastics
sequence boundary
MaximumFloodingSurface
Modifié d’après Bartek et al, 1991
0 +50 +100-500
20
30
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Oligocene
Miocene
Pliocene
EustacySedimentation pattern of Neogene passive margins
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32Valanginian, S. France
Orbitalparametersof the Earth
variable sunenergy
received
outerenvelopes
temperaturessedimentationclimate Stratigraphic
record
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Sedimentology : lithofacies
Lithofacies is the set of physical features of a sedimentary rock.Lithofacies provides info on depositional conditions.
Lithofacies =
Lithology
Texture
structure Geometry of thesedimentary body
Mode of association ofconstitutive elements
Mineralogy, granulo,morphometry
Hydrodynamics biochemicals,biological indicators
Mode of transport & deposition
Source, transport, duration,environment,bathymetry
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synthesis
Sedimentary basins result from the complex interaction of internal andexternal forcings_ “Reading” the sedimentary record allows to decipherthe controlling factors and their temporal evolution.
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35Fossil energy
Argiles imperméables
1.3.Sedimentary basins & societal issues
Geothermy
Iron ore
sequestration
Natural resources
Stones
Salt
Gas storage
Aquifers
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Distribution of sedimentarybasins (sediment accumulation >1km)
World distribution of population,mostly in sedimentary basins(favourable to agriculture, economicactivity and easy communication)
World population (1994)
Cropland (Jon Foley & al)
World distribution of cropland : Landuse for agriculture is prevalent insedimentary basins (West Americanforeland basin, Mississippi valley,Indian Foreland basins, continentalmargins of Asia and Australia, intracratonic basins of Europe andCanada,…). Note that this map partlymirrors the population distribution
Sedimentary basins
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erosion & weathering
eosion &weathering
Dissolved metallic ions
Sediments Sediment deposition & ions precipitation
© P
.J.C
ombe
s
Natural Reactor = ore formation
oressubsidence
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Organic mater(anoxiclake)
Biosphere(Carbon)
Biosphere
soilsol
Maturation f(temperature, pressure, time):Organic matter -> kerogene -> Oil -> gas!
burial
oil
migration
© M
. Sé
rann
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Natural Reactor = hydrocarbons generation
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Consommation ressources naturelles /an / personne
Ressources minérales
eauÉnergie fossile
La vaste majorité des ressources naturelles provient des bassins sédimentaires
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