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Sedimentary basins—a primer
Goal is to develop an understanding of:
• Where sedimentary basins form
• Relation of tectonic setting to basin characteristics
• Three basin ‘flavors’ important to our discussion
Goose Creek Oil Field, Texas
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Sedimentary rocks and sedimentary basins
Formation of a sedimentary rock require two key ingredients
Sedimentary rocks form in sedimentary basins—regions
experiencing downward motion of the crust (subsidence)
Subsidence of the Earth’s crust
Supply of sediment (from uplifted continental terranes)
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Continental margins are the loci of sedimentary basin formation
Why?
Two requirements for a sedimentary basin?
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Here?
Here?
Here? (Lake Baikal)
Here? (Lake Malawi)
Quiz: Where on Earth are we ‘making’ sedimentary rocks today?
Here?
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Map of Relative Plate Motions
Horizontal plate motion: ~ 1 - 10 cm/yr
Vertical motion (uplift & subsidence): ~ 1 mm/yr
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Sedimentary basins are intrinsically linked to plate
tectonics via crustal subsidence
Useful conversion: 1 mm/a = 1 m/ka = 1 km/Ma
Considerable variability in subsidence rates
1 mm/a
0.1 mm/a
0.01 mm/a
Same rates apply to uplift / mountain building
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Plate tectonics and basin characteristics (‘flavor’)
Extensional (rifts & passive margins)
Collisional (flexural basins)
Intracratonic (‘middle’ of continents)
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Divergent plate boundaries: Rift basins & passive margins
Tim
e
• Lithospheric thinning
• Surface subsidence
• Asthenospheric upwelling
• Thermal anomaly
• Flank uplift
• Fault-bounded sub-basins
• Initially rapid subsidence
• Non-marine (fluvial) rocks
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Divergent plate boundaries: Rift basins & passive margins
• Continued thinning ruptures continental crust
• Forms a spreading center and new oceanic lithosphere
• ‘Trailing’ margin continues to subside via thermal decay
• Very long-lived process (100+ Ma)
Tim
e
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• e-folding time ~ 60 Ma
• Rifting began in the late
Triassic
• Margin age ~ 200 Ma
• Very thick sediment pile
• 15+ km in 200 Ma
Offshore
New Jersey
Depth
(km
)
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Extension and development of Midcontinent Rift System (MRS) ~1.1 Ga (or 1100 Ma)
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Swenson et al. (2004)
North shore, MN Keweenaw Peninsula, MI
• Notice reverse faults!
• Duluth is not ocean
front property
• MRS closed by collision
(Grenville Orogeny)
Note: Sedimentary package is mostly fluvial (rivers)
General lack of marine rocks Rift failure (partial closure)
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Plate tectonics and basin characteristics (‘flavor’)
Collisional (flexural basins)
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Convergent plate boundaries: Flexural (foreland) basins
• Plate collision / thrust faulting
• Lithospheric loading and associated flexure
• Primary basin (foredeep) immediately outboard of load
• Shorter lived (10s of Ma)
• Thinner sediment package (3 - 6 km)
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Flexural basins: Western Canada Sedimentary Basin
Alberta Geological Survey
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A’
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Thrust sheets = Load
• Subsidence rate decreases in mean transport direction
• Sediment package thins in mean transport direction
• Significant variability in subsidence rate
• Reflects complexity of loading history
• Cambrian – Mississippian rocks older passive margin
Image: Geological Society, London
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The Penokean Orogeny and the Animikie Basin (~1.8 Ga)
Schulz & Cannon (2007)
Removing Midcontinent Rift System (MRS) rocks isolates…
MRS
MRS
MRS
MRS
MRS
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Arrows reflect delivery of sediment
… the (older) Animikie Basin rocks
Basin formed during continent-continent collision of the Penokean Orogeny approximately 1800 Ma
Ojakangas et al. (2001)
Animikie Basin
Northwest-southeast compression
Mountains!
More sediment yield
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Animikie Basin stratigraphy
Mudstone (mostly)
• Deeper water deposition• Strongly deformed (folded)
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Plate tectonics and basin characteristics (‘flavor’)
Intracratonic (‘middle’ of continents)
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Far from plate boundaries: Intracratonic basins
• Subsidence mechanism poorly
understood
• Intraplate stresses
• Long-lived, slow subsidence
• 4 km in 200 Ma
• Sedimentation ~ subsidence
Michigan Basin
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Is Lake Superior a sedimentary basin?
Source: NASA
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