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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

A

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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