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
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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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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
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
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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?
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
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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