Déformation lithosphérique: forçages internes

Transcription

Dynamique des Bassins
Michel Séranne
1
1- Origin of Sedimentary Basins
1.1 Lithospheric deformation: Internal forcings
1.2 Sedimentation: External forçings
1.3 Sedimentary basins & societal issues
2
© NASA
Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
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
Bat 22, 3eme Étage Gauche
Page perso: www.gm.univ-montp2.fr/MichelSeranne
What is a sedimentary basin ? : it’s a depression filled with sediments
Distribution of sedimentary basins (sediment accumulation > 1km)
3
=> 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)
1.1.Lithospheric deformation: Internal forçings
Struture and rheology 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.
Lithosphere
mantle
=> 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).
Solid crust
Rigid Lithosphere
mantle
Outer
core
Molten outer C.
Solid inner C.
4
atmosphere
• 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)
Definition of the outer envelopes of the Earth that
interact to form sedimentary basins
5
Basics about the Lithosphere
• Definitions
Characterization of the different layers of the lithosphere. Deformation of the lithosphere
induces the formation of sedimetary basin.
6
• parameters controling lihosphere rheology
• Principle of isostacy
mountain
Continent
(low density)
• Total mass of each
column must be equal.
« anti-root »
Mantle
(high density)
Mountain
root
Depth of
equal pressure
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) .
!
Yes
Pratt model
blocks of differing density (lighter beneath mountains and denser beneath
basins) => flat Moho.
Not d
fie
veri ta
a
d
y
b
7
Ocean
basin
Local isostacy : model = snow cover
load balanced vertically, beneath the load
=> lithosphere behaves like independant
columuns => no rigidity
Regional isostacy:model = trampoline
Load distributed over a wide area
=> each segment of the lithosphere is
linked to the next => flexural rigidity
8
c
y if
Onl
lly
loca ated !
s
n
e
omp
9
weight of a lithosphere column before basin formation = weight of a column after basin formation
e
rcis
Basin
moho
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 ?
10
e xe
Internal driving forces of the Earth machine
Global Heat 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
Nataf & Sommeria, 2000
11
The Earth internal flux of energy = sum of:
The internal heat is continuously
dissipated outwards from the centre of
the Earth in 3 ways :
•  Conduction : Thermal energy
transmitted between atoms
⇒  Inner core and Lithosphere
•  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
12
Internal driving forces of the Earth machine
Plate tectonics: lithosphere movements
Subduction
zone
America
Relative
Atlantic Ocean
movement Acretionary
ridge
W. Europe
Lithosphere
Asthenosphere
Convection
cells
• 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).
13
Pacific Ocean
Lithospheric surface of the Earth showing plate tectonics (plate boundaries, earthquakes and volcanoes).
14
Plate tectonics
Distribution of sedimentary basins (sediment accumulation > 1km) Continental passive margins , subduction
zones, foreland of present or ancient mountain belts, centre of cratons.
15
Sedimentary basins and Plate tectonics
www.marlimillerphoto.com/
Fort Proctor Louisiana (Gulf of Mexico):
-  subsidence > 1 m since1850
16
How to create a depression ?
How to create a depression ?
20°C
20°C
1- Cooling
1300°C
1300°C
2- Stretching/
thinning
3- Loading
Any sedimentary basin subsidence results from one of these 3 processes or a combination of them
17
-> 3 lithospheric processes account for subsidence
Stretching/Thinning
Sand-box
Analog
modeling
© Michon, 2000
Reflexion seismic - North Sea Rift
Copyright © 2008 Virtual Seismic Atlas
Marsden et al.'s (1990) interpretation of BIRPS' NSDP84-1 deep seismic line. MARSDEN, G, YIELDING, G, ROBERTS, A &
KUSZNIR, N. 1990
18
Stretched lithosphere is thinned because of mass conservation
- faulting in upper crust,
- rising of basal lithosphere
Age of the oceanic Lithosphere
(oceanic floor)
Lithosphere emplaced at midoceanic ridges (accretion) and then
moves apart symetrically (seafloor
spreading)
0
80
180 Ma
2km
Bathymetry of the oceanic Lithosphere
(oceanic floor)
increases away from oceanic ridges
5km
http://jules.unavco.org/Voyager/Docs/EarthScope
19
http://topex.ucsd.edu/WWW_html/mar_topo.html
Cooling: example
Accretion
Very high
geotherm
• Cooling of oceanic lithosphere
• Increasing bathymetry of oceanic floor
• Increasing thickness of oc. lithosph.
age & distance
Sea level
-2km
-5km
0°C
Carlson&Johnson, 1994
z
1300°C
geotherms
Depth or subsidence of
oceanic lithosphere =
f[lithosphere age] 1/2
20
Thermal contraction of the Oceanic Lithosphere
Loading of the lithosphere => flexure
Congo
drainage area
Atlantic accre
Congo fan
Sedimentary load of the Congo deep-se-fan ( > 5km thick)
=> Deflexion by flexure of the oceanic lithosphere (subsidence)
Modifié d ’après Uchupi, 1992
21
tionary ridge
Niger fan
Loading of the lithosphere => flexure
load
flexure
flexure
Uplift
(Plume)
flexure
Hawai
Plume
22
500km
23
Different types of basins according to plate tectonic setting: spatial and temporal evolution from one type to another
1.2. Sedimentation: External forcings
• 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)
24
Present: Baie du Mont Saint Michel
• Tidal sediments =
Sediment deposition controled by the tides
(cyclic phenomenon).
y
External forcings
• Periodic changes in the Earth’s orbital parameters affect the amount of radiation from the
Sun.
• The energy dissipated by the Sun varies with time => variation in radiation received by the
Earth.
⇒ The total amount of solar radiation received on the Earth’s surface governs
long-term
(100’s of millions of years) and short-term (10-1000’s years) temperature of the atmosphere
and hydrosphere. Through complex feedback
loops, this has direct and indirect
consequences on Climate and associated
exogenic transfer processes.
=> Climate forcing affects the way the sedimentary basins are filled
25
Energ
Insolation : sun’s energy
Sun’s energy
45°
1.41 m2 ->242W/m2
90°
1m2 ->342W/m2
• High latitudes receives less energy than
inter-tropical areas
• Insolation seasonal variation
Sun =
m the from
o
r
f
y
Energ 0 x energy
10 00 rnal Earth
inte
Sun’s energy
NO tilt
• No seasonal variation of insolation
• Increased yearly average temperature
26
tilt
Milankovitch cycles
P = precession
E = eccentricity
• 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 through time.
• During Quaternary, Milankovitch cycles are particularly well expressed (Glaciations stages)
27
T= tilt or obliquity
insolation => climate => sedimentation
Sun energy
©ArthusBertrans
Temperature, pluviometry, seasonnallity, …
Erosion, weathering, life, river transport, ocean circulation…
sedimentation
28
©NASA
Atmosphere
Hydrosphere
Biosphere
Hettangian (S-Cevennes) records cyclic flooding
and desiccation of shallow carbonate platform.
Sedimetary record counts tens of cycles subdivided
into 5 smaller cycles; interpreted as eccentricity
(100ky) combined with precession (20ky) forcing
© M. Séranne
© Y. Hamon
Oligocene evaporites
(Portels/Corbières) record
of seasonnal, cyclic
desiccation of lagoon
© Y. Hamon
29
Periodic changes in forcings => sedimentary cycles
Periodic changes in forcings => cycles
• Combination of stacking of several
signals => complex stratigraphic
record
-  Basin analysis aims at deciphering
these signals
-  sedimentary basinfill contains these
signals => Archives
- several nested sequences in
the stratigraphic record
Guillocheau 2000
• Signals of different time/space
scale => record of stacked
(nested) cycles
30
• Periodic (or not) changes in the controlling processes => record cycles
r
iai
rt
Te
e
ac
ét
Cr
é
© M. Séranne
Chicxulub impact
31
Non-periodic changes in forcings => catastrophic events
Non-periodic changes in forcings => record of events
Tonga, March 2009
One cinerite bed (ashes layer)
interbeded the continental cyclic
lacustrine siltites of the Permian
Lodève Basin.
32
Volcanism -> ashes in atmosphere -> modify climate
Volcanism -> ashes -> widespread & contemporaneous deposits -> correlation & dating
Sediment or not sediment ?
Stratigraphy (≠ sedimentology) = study of sediment stacking pattern
thickness
Time
control
Time
control
33
distance
Sediments are deposited and preserved in some parts of the basins,
not everywhere, not at all time
⇒  incomplete and inhomogeneous record related to basin depositional evolution
⇒  Basin dynamics accounts for sediment distribution in space and time
Sediment accumulation rate
Sedimentary deposits are an uncomplete and distorted record of time
Deposits age (Ma)
Modeled from
several datings
hiatus
Time hiatus = no
deposit correlates
with this time
interval => Eroded
or never
deposited?
Slow accumul. rate
Fast accumul.
rate
•Sediment accummulation
rate varies through time in
basins.
• Depends on sedimentary
processes, paleogeography,
sediment flux, subsidence…
=> Part of the record of
Basin dynamics
34
Deposits age (Ma)
Sediment thickness (m)
Sediment
thickness (m)
Observed
Exercise : Sediment accumulation rate
Languedoc
Synthetic lithostratigraphy and tectonic evolution of Languedoc
Lacustrine
Lutetian
50Ma
E. Eocene
Slope
Berriasian
190Ma
"Calcareous"
Lias
200Ma
0
Aalenian
Toarcien
Domerian
Carixian
Sinemurian
Lagoonal platform
0
Hettangian
Late Triassic
Triassic
250Ma
Early Triassic
Variscan basement
Sabkha
Fluviatile
onset of
Tethyan rifting
35
sandstone
lacustrine
limestone
dolomite
marly limestone
bioclastic
limestone
conglomerate
marl & silts
evaporites
limestone
grainstone
Sediments 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
Sediments 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.
36
0
1
Bajocian
50
gravitational
listric faulting
"Marly" Lias
Carbonate ramp
2
Thermal subsidence
Bathonian
Dogger
175Ma
0.5
L. Oxfordian
Callovian
deepening-up
1
Gulf of Lion Margin
Emmersion
Reef platform
Kimmeridgian
160Ma
Renewed
subsidence
Basin
150Ma
Malm
3
mid-Cretaceous
Erosion
e
Valanginian
Portlandian
1.5
uxit
ba
140Ma
145Ma
E.Pyrenean
unconformity
Fluviatile/lacustrine
100
rifting
Early
Cretaceous
(Neocomian)
Alluvial fans
Sediment thickness (km)
60Ma Paleocene
Late
70Ma
Cretaceous Maastrichtian
100Ma
130Ma
150
Alluvial fans
Bartonian
rifting
unconformity
Marine
Eocene
Fluviatile
North Tethyan Margin
Priabonian
continental
30Ma
Deposits age (Ma)
200
Pyrenean
foreland basin
Alluvial fans
L. Rupelian
cont.
Oligocene
2.5
2
break-up
unconformity
Vocontian period
20Ma
Aquitanian
3
Messinian
erosion
Compare sediment record and time: construct the
accummulation curve for the Languedoc area
"Bassin du Sud-Est" (Tethyan aborted rift)
Shoreface
E. Miocene
shallowing-up
¹3ÏRANNE
Burdigalian
Mediterr.
desiccation
Thermal subsidence
Langhian
16Ma
3.5
Rifting
Gilbert-deltas
Tectonics
Thrusting &
growth strata
5Ma
Discontinuities
inversion
Sedimentary
environments
Fluviatile
Pliocene
cont.
Lithographic
column
0Ma
marine
Stratigraphy
Pliocene
marine
approx.
thickness
km
Base-level
upstream
Base level (Wheeler, 1964) :
•  is an abstract, non physical dynamic surface ; can be assimilated to an upstream-downstream profile
in 2D sections
•  is above the earth surface where deposition occurs, below where erosion occurs, and equal to the
earth srface where there is an equilibrium (e.g., bypass) ;
•  represents the surface where sediment flux would be constant (i.e., a balance would exist between
sediment supply 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.
37
downstream
Available space => Accommodation
Eustacy
Basin
subsidence
Intraplate
deformation
Accommodation : it is the rate (measured in m/Ma) at which space is being made available for
sediments to be trapped in the basin. It is the result of the vertical movements of the basement
(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 of sediment 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.
38
accommodation
« Eustacy » vs « Relative sea-level change »
Several Eustatic Curves
have been compiled and
progressively improved
(Haq, Miller, Kominz,…).
They can be applied
everywhere.
Haq Eustatic Curve
Relative sea-level change = variation of water depth in one basin. It’s the combination of eustacy, and local
constraints: subsidence/uplift and sediment flux.
sediment flux
Relative sea-level change in a
basin can be approached by
analysis of the stratal architecture
combined with sedimentary facies.
Eustacy
Relative
sea-level
Bst vertical mvt
39
Eustacy = 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…).
Stratal geometry (for beginners…)
Condensed
section
aggradation
Canterbury Basin, New Zealand
2 mains patterns: several possible causes f(subsidence, sediment flux, sea-level)
Aggradation:
Sed. Rate ≤ Accomm
Divergent:
Differential
subsidence
Progradation :
Sed Rate ≥ Accomm
Onlap
Sed. Rate > Accomm
Sed. Rate < Accomm
gin
Mar
VS
in
Bas
bathymetry
Down-lap
40
progradation
Sedimentation pattern of
Neogene passive margins
-50
Eustacy
0
+50 +100
0
Slope shales
Reworked
10
clastics
Miocene
20
Maximum
Flooding
Surface
Modifié d’après Bartek et al, 1991
30
Oligocene
sequence boundary
41
Orbital
parameters
of the Earth
variable sun
energy received
outer envelopes
temperatures
climate
sedimentation
Stratigraphic record
Valanginian, S. France
42
Fluvial & delta
Pliocene
Sedimentology : lithofacies
Lithofacies =
Lithology
Mineralogy, granulo,
morphometry
Source, transport, duration,
environment,bathymetry
Texture
Mode of association of
constitutive elements
Mode of transport & deposition
structure
Geometry of the
sedimentary body
Hydrodynamics biochemicals,
biological indicators
43
Lithofacies is the set of physical features of a sedimentary rock.
Lithofacies provides info on depositional conditions.
Sedimentary basins result from the complex interaction of internal and
external forcings. “Reading” the sedimentary record allows to decipher the
controlling factors and their temporal evolution.
44
synthesis
Stratal geometry
NW
NW Marocco margin
Interpret the seismic profile (line-drawing)
45
SE
1.3.Sedimentary basins & societal issues
Salt
éab
es
les
im
Geothermy
Aquifers
Stones
Natural resources
Iron ore
Gas storage
Fossil energy
46
sequestration Argil
m
per
Natural Reactor = ore formation
s
Sediment deposition
& ions precipitation
Sediments
ores
© P.J.Combes
subsidence
47
Dissolved metallic ion
erosion & weathering
eosion &
weathering
Natural Reactor = hydrocarbons generation
Biosphere
Organic mater
(anoxiclake)
sol
migra
soil
tion
© M. Séranne
oil
burial
Maturation f(temperature, pressure, time):
Organic matter -> kerogene -> Oil -> gas!
48
Biosphere
(Carbon)
Ressources minérales
Énergie fossile
La vaste majorité des ressources naturelles provient des bassins sédimentaires
49
(estimations en 2000)
50
eau
Consommation ressources naturelles /an / personne
Réserves mondiales de Charbon
Réserves & ressources mondiales de
Pétrole et de Gaz
non-conventionnel
Pétrole
Ressource > 15000 Gtec ; Production = 5Gtec/an
Gtec: 109 tonnes équivalent charbon
Mauriaud & al, 2013 « La faim du pétrole »
Gaz
Pétrole : 2000 Gbep (dont 80% conventionnel)
Gaz : 2500 Gbep (dont 49% conventionnel)
Gbep: 109 barils équivalent pétrole
en 2010
Réserves mondiales de pétrole & gaz= 2665 Bboe
Bboe: Billion Barrel Oil Equivalent = 109 barils équivalent
pétrole
51
conventionnel
Mass of carbon estimated to be sequestrated as natural gas hydrates compared to other
carbon sources. Modified from various sources.
Beauchamp, 2004 Comptes Rendus Geoscience, Volume 336, Issue 9, July 2004, Pages 751-765
52
Gas hydrates

Déformation lithosphérique: forçages internes

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