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1 Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne 2- Geodynamics of Sedimentary Basins Master1 Réservoirs Géologiques Architecture des Bassins - Michel Séranne http://earth.imagico.de/main.php 2 Master1 Géologie des Réservoirs Dynamique des Bassins - Michel Séranne 2.1 Basins due to divergence - Rifts - Subsidence analysis - Passive continental margins Lakes Tanganyika & Victoria Gulf of Suez & Red Sea USA Atlantic Margin

2- Geodynamics of Sedimentary · PDF fileExercise: Viking Graben ... Thin-skinned vs thick-skinned extensional tectonics - Rift geometry . Master1 Géologie des Réservoirs Dynamique

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2- Geodynamics of Sedimentary Basins

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http

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de/m

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php

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2.1 Basins due to divergence - Rifts - Subsidence analysis - Passive continental margins

Lakes Tanganyika & Victoria Gulf of Suez & Red Sea USA Atlantic Margin

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2.1.1. Rifts a. stretching Subsidence analysis b. kinematics of rifting c. Rift basin architecture

http

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a. Stretching

Extension => deformation = stretching

Stretching <=> thinning (volume conservation)

thinitial

linitial

lfinal

thfinal

Stretching factor (β): lfinal/linitial (always >1) Thinning factor: thfinal/thinitial (always <1)

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Stretching (extensional stress)

a)  Stretching => thinning b)  Deformation = Normal faults in upper crust and

uplift of Lithos/asthenos boundary c)  N. Faults => initial subsidence d)  LAB isotherm uplift =>increased geotherm

a)  Stop of extensional stress => and faults b)  Cooling of thinned lithosphere c)  Cooling => density increase => subsidence d)  Subsidence => sediment deposition

Considered

instantaneous

10’s Millions

of years

Lithospheric Stretching

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Rifting and subsidence processes

Cooling

Stretching/ thinning

Loading

Rifting (lithosphere stretching and thinning) involves the 3 basic subsidences processes,

simultaneously or successively. 0°C

1300°C

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Geological example of a rift : Viking Graben

Moho

Thinned cont. Crust (lithosph. also affected)

Synrift sequence (initial subsidence)

Postrift sequence Rift axis

Postrift basin

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How does it work ? -> the McKenzie model = Subsidence Analysis

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Computing the value of initial subsidence

local

isostacy

instantaneous

Mass

Conservation

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Sediment-fill = load => extra-subsidence

Subsidence without

sediment

sediment

Subsidence with sediment

Extra Subsid. due to

sediment load

local

isostacy

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Computing the subsidence due to Sediment-load

3.15

2.3

1

Sload = 0.60 hs

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subsidence in rift basins

Temporal subdivision

Processes

Driving mechanisms

Syn-rift

(intantaneous, initial)

+ Post-rift (long-term)

Fault activity

+ Thermal recovery

Sediment load + Geodynamics

(“tectonic”)

Total subsidence in rift basins (measured in borehole)

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(“tectonic”)

12 True for any

type of basin

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Exercise: Viking Graben

• Considering a pre-rift crustal thickness of 35km, what is the total subsidence at points A, B, C ? • Same question, considering that Trias + U. Palaeozoic belong to pre-rift. • What are the stretching and thinning factors at each point?

A B C

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Subsidence evolution of sedimentary basins

g h+ag udv br �

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udcal br � g a++hd�

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nar w&+dbl h�

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vna+hiudg h� r adoul a+h� �vna+hiudg h� r adoul a+h� �

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&nuvh�

g adn&� � � &bn+&��

+wdobpb+h&� r al l hn&�

2 a+hd�2 a+hd�

� b+ unuc4�

130My ago

Deposits at

Surface

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� �

g h+ag udv br �g h+ag udv br �

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Today,

basement at

10km depth

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Exercices: subsidence evolution of basins

15

Plot the total subsidence curve from different types of data

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inw0ban� &al p&+ul h&�

h0avudb+h&�

vna+hiudg h� r adoul a+h� �

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� �

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Measuring Subsidence in sedimentary basins

Subsidence : Amount of downward vertical movement of the sedimentation surface 

= burial of top of the basement = depth of the basement = thickness of sediments and/or water

Data from: • borehole data (stratigraphic) • seismic reflection or refraction • sediment sections measured in the field

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and/or water

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Initial position

must be known

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Synr

ift

Postrift

Prer

ift

time

Sedi

men

t th

ickn

ess fast subsidence

= synrift

postrift subsidence: cooling of the lithosphere

Previously thinned

Subsidence in rift basins

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Postrift subsidence = lithosphere thermal recovery

Theoritical evolution of thermal subsidence for different amounts of stretching, using McKenzie’s model

Following rifting, the stretched mantle lithosphere gets cooler. As it gets cooler, the density increases, and subsides (principle of isostacy) = « thermal subsidence » Subsidence due to sedimentary loading has been removed

geodynamic

subsidence

Exercise: determine initial and thermal tectonic subsidence for a rift basin formed in Late Jurassic (considered instantaneous); Basin is 5km thick, Moho at 25km depth

10

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Backstripping : geodynamics from total subsidence

Basement burial = total subsidence

Remove effect of sediment loading = backstripping

Computed « geodynamic » subsidence

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Backstripping : 1D modeling softwares

Données pour Backstripping Le puits Chote Name Base Ageb SLb WDb Top Aget SLt Wdt c C o type

Kimmer 3.063 145 .150 .300 2.824 140 .250 .300 2.6*103 .71 .70 0 Cal-argi Potlan 2.824 140 .150 .300 2.752 134 .250 .200 2.6 .71 .70 0 Cal-argi Kti 2.752 134 .150 .2 00 2.668 110 .150 .100 2.6 .71 .70 0 calc Uncon 2.668 110 .150 .100 2.668 64 .200 .200 Pchi 2.668 64 .200 1.200 2.546 60 .200 1.200 2.42 .39 .56 0 Sab-arg Pchm 2.546 60 .200 1.200 2.320 54 .200 .900 2.42 .39 .56 0 sab>argi Pchs 2.320 54 .200 .900 2.136 49 .200 .400 2.42 .27 .56 0 sab Eg 2.136 49 .200 .400 1.240 39 .200 .200 2.38 .51 .63 0 Argil Chapo 1.240 39 .200 .200 .988 36 .225 .100 2.38 .51 .63 0 Argil Horco .988 36 .225 .100 .831 30 .225 .50 2.42 .27 .49 0 sable Pri .831 36 .225 .050 .639 30 .200 .025 2.42 .27 .49 0 Sabl m Prs .639 30 .200 .025 .368 25 .150 .025 2.42 .27 .49 0 Sabl g Coatzi .368 25 .150 .025 0 22 .100 .010 2.38 .51 .63 0 argi

Data for backstripping Chote well (W. Gulf of Mexico)

Form

atio

n

age

Dep

th B

ase

Sea

leve

l

Bath

ymet

ry

dens

ity

Poro

sity

at

de

posi

tion

Com

pact

ion

fa

ctor

litho

logy

age

Dep

th B

ase

Sea

leve

l

Bath

ymet

ry

Top of formation Base of formation Formation physical properties

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Backstripping

Burial history for each stratigraphic interval Chote well (W. Gulf of Mexico)

Geodynamic subsidence = backstripped total subsidence computed

total subsidence = basement burial observed

Removal of

Sediment load

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b- Kinematics of rifting

-  Stretching in crust above stretching in the mantle, -  Postrift subsidence centred on the rift axis -  conjugate normal faults

-  Offset of stretching in crust and in the mantle -  surface uplift above mantle thining -  postrift subsidence offset -  Low-angle extensional detachment -  lower crust/mantle denudation

Symetrical (McKenzie, 1978)

Assymetrical (Wernicke, 1981)

uplift

2.1.1. Rifts a. stretching Subsidence analysis b. kinematics of rifting c. Rift basin architecture

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Viking Graben - seismic section

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- Geometry ? - synrift vs postrift ?

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Viking Graben - depth section M

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- Geometry ? -  synrift vs postrift ? -  approx. thinning ratio ? -  Prerift?

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c. Rift basin architecture

Tectonic-sedimentation relationships -  synrift sediment geometry -  Fault profile

Parallel reflections

Divergent reflections

Horizontal, onlap reflections

Rift basin formation

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25 Define prerift, synrift, postrift ?

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c. Rift basin architecture

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Relationships between : fault profile and basin-fill geometry

Thin-skinned vs thick-skinned extensional tectonics -  Rift geometry -  Measurement of extension and consequences on crustal thinning

Faure, 1989 Benedicto, 1996 cf cours P. Labaume

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Active rift basin = Death Valley

www.marlimillerphoto.com/

normal F.

Basement erosion

Alluvial fan in the basin

normal F.

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Active rift basin - Nevada

Basi

n bo

undi

ng f

ault

Small radius aggrading

alluvial fans

Sabkha or lake

Uplifted & eroded footwall

Hanging-wall

Axia

l dra

inag

e

wide radius prograding alluvial fans

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Sedimentary facies distribution ⇒ syn-tectonic sedimentation • Rapid facies change: proximal -> distal • Breccia along active faults - mudstone at rift axis • Growth structures/ progressive unconformities

Breccia against border fault

Sand & conglomerates channels (fluvial)

Lacustrine limestone

Benedicto , 1996

Benedicto , 1996

Fossil rift basin = Les Matelles

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Architecture of rift basin infill

Downlap + thinning away from fault => Proximal breccia -> distal fine clastics

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Prosser, 1993

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Copyright ©

2001. All R

ights Reserved.

Tectonic–sedimentation relationships in rift basin

Gawthorpe & Leeder, 2000

Rift initiation

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Copyright ©

2001. All R

ights Reserved.

Tectonic–sedimentation relationships in rift basin

Gawthorpe & Leeder, 2000

Rift development

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Copyright ©

2001. All R

ights Reserved.

Tectonic–sedimentation relationships in rift basin

Gawthorpe & Leeder, 2000

Rift climax

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Active rift basins : Gulf of Corinth

Acc = Sed

Acc > Sed

Acc < Sed

Acc << Sed

Continent.

marine

Rohais & al 2007

dap

rès

Flot

té &

al 2

003

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Type sequence of a rift basin

Synrift unconformity

Fluvial or littoral

Lake delta

Lake turbidites

Lacustrine blackshales (anoxic => organic matter)

Alluvial fan

fluvial

postrift unconformity

prerift

Rift initiation (sediment against

active faults)

Rift climax Accom >> Sedim

Starved basin

Filling sequence Accom < Sedim

End of rifting

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Model of an active rift basin

Erosion in watershed

Footwall

Hanging-wall

Narrow, thick, high accommodation alluvial fans close to border fault

Wide, thin, low accommodation alluvial fans above roll-over

fluvial/lacustrine axial facies

Listric normal fault

Roll-over

Progressive unconformities = growth structures

Footwall Rapid facies change

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Geological example : Moray Firth

W E

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Architecture of post-rift basin infill

Geometry of post-rift sequence = « steer-head » (Porcupine Basin)