12 1.2. Sedimentation: External forcings

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Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
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)
Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
• Tidal sediments =
Sediment deposition controled by the tides
(cyclic phenomenon).
24
Present: Baie du Mont Saint Michel
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
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Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
Energ
y
tilt
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’s energy
n
he Su
rom t ergy
f
y
g
Ener 000 x en rth
a
= 10
nal E
inter
m
o
r
f
NO tilt
• No seasonal variation of insolation
• Increased yearly average temperature
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Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
Insolation : sun’s energy
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)
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Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
T= tilt or obliquity
insolation => climate => sedimentation
Atmosphere
Hydrosphere
Biosphere
©ArthusBertrans
Temperature, pluviometry, seasonnallity, …
Erosion, weathering, life, river transport, ocean circulation…
sedimentation
©NASA
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Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
Sun energy
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
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Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
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
• Signals of different time/
space scale => record of
stacked (nested) cycles
- several nested sequences in
the stratigraphic record
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Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
• Periodic (or not) changes in the controlling processes => record cycles
re
iai
t
r
Te
ét
Cr
é
ac
© M. Séranne
Chicxulub impact
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Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
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.
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Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
Volcanism -> ashes in atmosphere -> modify climate
Volcanism -> ashes -> widespread & contemporaneous deposits -> correlation & dating
Sediment or not sediment ?
Stratigraphy (≠ sedimentology) = study of sediment stacking pattern
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Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
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…
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Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
Deposits age (Ma)
Sediment thickness (m)
Sediment
thickness (m)
Observed
Exercise : Sediment accumulation rate
Languedoc
Synthetic lithostratigraphy and tectonic evolution of Languedoc
140Ma
Slope
Berriasian
Bathonian
Dogger
"Marly" Lias
190Ma
"Calcareous"
Lias
200Ma
2
1
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
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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Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
0
Carbonate ramp
Bajocian
0
gravitational
listric faulting
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
50
rifting
145Ma
E.Pyrenean
unconformity
Fluviatile/lacustrine
Sediment thickness (km)
Early
Cretaceous
(Neocomian)
Alluvial fans
100
Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
Lacustrine
Lutetian
150
Pyrenean
foreland basin
Alluvial fans
Bartonian
50Ma
E. Eocene
60Ma Paleocene
Late
70Ma
Cretaceous Maastrichtian
100Ma
130Ma
rifting
unconformity
Deposits age (Ma)
200
Vocontian period
Fluviatile
Compare sediment record and time: construct the
accummulation curve for the Languedoc area
"Bassin du Sud-Est" (Tethyan aborted rift)
Priabonian
North Tethyan Margin
30Ma
continental
Alluvial fans
L. Rupelian
Marine
2
break-up
unconformity
cont.
Oligocene
Eocene
2.5
20Ma
Aquitanian
3
Messinian
erosion
Mediterr.
desiccation
Thermal subsidence
Shoreface
E. Miocene
shallowing-up
¹3ÏRANNE
Burdigalian
Rifting
Langhian
16Ma
3.5
Thrusting &
growth strata
Gilbert-deltas
Tectonics
Thermal subsidence
5Ma
Discontinuities
inversion
Sedimentary
environments
Fluviatile
Pliocene
cont.
Lithographic
column
0Ma
marine
Stratigraphy
Pliocene
marine
approx.
thickness
km
Base-level
upstream
1
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.
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Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
downstream
Available space => Accommodation
2
Basin
subsidence
Eustacy
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.
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Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
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
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Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
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, mantleconvection induced uplift,…) or of the volume of water in the World Ocean (growth or decay of polar icecaps, 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
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Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
progradation
Sedimentation pattern of
Neogene passive margins
0
-50
Eustacy
0
+50 +100
Slope shales
Reworked
clastics 10
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
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Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
Fluvial & delta
Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
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
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Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
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.
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Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
synthesis
1.3.Sedimentary basins & societal issues
Salt
Geothermy
Aquifers
Stones
Natural resources
Iron ore
Fossil energy
Gas storage
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Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
es
l
sequestration Argi
es
abl
mé
r
e
imp
Natural Reactor = ore formation
Dissolved metallic ion
s
Sediments
Sediment deposition
& ions precipitation
ores
© P.J.Combes
subsidence
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Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
erosion & weathering
eosion &
weathering
Natural Reactor = hydrocarbons generation
Organic mater
(anoxiclake)
sol
© M. Séranne
migra
tion
soil
oil
burial
Maturation f(temperature, pressure, time):
Organic matter -> kerogene -> Oil -> gas!
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Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
Biosphere
Biosphere
(Carbon)
Ressources minérales
eau
Énergie fossile
La vaste majorité des ressources naturelles provient des bassins sédimentaires
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Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
Consommation ressources naturelles /an / personne
51
Réserves mondiales de Charbon
Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
(estimations en 2000)
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
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Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne
conventionnel