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EASC 201 Post Midterm Notes

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EASC 201: POST-MIDTERM MATERIALS

LECTURE 5: CONTINENTAL FACIES MODELS

Four major groups:

1) Fluvial Deposits

2) Desert (Eolian)

3) Lacustrine Deposits

4) Glacial Deposits.

*only fluvial and eolian covered in lecture- refer to text for information

• Continental deposits tend to be dominated by siliciclastic material, rather than by carbonates. Contain

significant oil and gas, coal, oil shale and uranium.

FLUVIAL SYSTEMS

Includes all sedimentary media generated by the activities of rivers, streams, and associated sediment gravity-

flow processes.

• 3 broad settings:

1) Alluvial Fans

2) Braided Rivers

3) Meandering Rivers

• May be inter-related and overlapping

 (e.g., braided rivers may occur on alluvial fans)

• Proximal to distal trend common: alluvial fans tend to pass into braided rivers and change distally to

meandering rivers.

Alluvial Fans

Setting:

• shape resembles a segment of a cone

• Typically occur in areas of high relief,

 Base of a mountain range (abrupt change in slope)

 Where an abundant supply of sediment is available

• Tend to be sparsely vegetated, and common to arid or semi-

arid settings

• Common in glacial settings- develop outwash fans in front of

melting glaciers

• If an alluvial fan builds out into a body of water – it forms a

Fan-Delta

Processes:

• stream-flow, debris-flow, mud-flow, landslides

• Types of processes vary greatly, depending on the fan types, climate controls, etc.

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• Humid Fans are dominated by stream flow: 3 main types

1) Stream Channel: flow confined within the

channels

- Deposits are long narrow bodies and

typically consist of the coarsest and most

poorly sorted breccias and conglomerates

2) Sheet-flood deposits: formed by sediment-laden

flows that become unconfined and spread out

from the ends of channels. Includes

hyperconcentrated flows!

- Sheet-like deposits of gravel, sand or silt

- Tend to be well sorted (or at least better

sorted), and may be cross-bedded,

laminated or structureless

3) Sieve deposits: formed as lobes on the fan

where the sediment source has little sand, silt or

clay to serve as the matrix. Not abundant!

- Flows percolate through the gravel, because

there is no matrix, and coarser clasts get

held back.

- Forms an open framework conglomerate or

breccia

• Arid fans: are dominated by debris flows and mud flows

 Rainfall is infrequent but violent, slopes are

steep, and vegetation sparse.

 Stream flow is locally important. Sediment

transport is markedly periodic.

1) Debris flow deposits:

- Poorly sorted and typically lack sedimentary

structures

- Reverse grading may occur near the bases of

beds (kinetic sieving).

- Pronounced range in grain sizes: boulders >

house-sized to clay

- Clay matrix tends to make these units impermeable

2) Mud flow deposits: similar to debris-flows but consist mainly of sand-sized and finer grained materials

3) Landslides: important but deposits can be difficult to tell from debris-flows.

Characteristics of Alluvial Fan Deposits

Geometry:

• Cone-shaped to arcuate in plan view

• May have well-developed system of braided distributary channels across fan

• Longitudinal profile: fan grouped into upper fan, mid fan and distal fan

Facies:

• Pronounced proximal to distal fining

• Upper fan: coarsest sediment, extremely poorly sorted, few sedimentary structures.

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EASC 201: POST-MIDTERM MATERIALS LECTURE 5: CONTINENTAL FACIES MODELS Four major groups: 1) Fluvial Deposits 2) Desert (Eolian) 3) Lacustrine Deposits 4) Glacial Deposits. *only fluvial and eolian covered in lecture- refer to text for information • Continental deposits tend to be dominated by siliciclastic material, rather than by carbonates. Contain significant oil and gas, coal, oil shale and uranium. FLUVIAL SYSTEMS Includes all sedimentary media generated by the activities of rivers, streams, and associated sediment gravityflow processes. • 3 broad settings: 1) Alluvial Fans 2) Braided Rivers 3) Meandering Rivers • May be inter-related and overlapping  (e.g., braided rivers may occur on alluvial fans) • Proximal to distal trend common: alluvial fans tend to pass into braided rivers and change distally to meandering rivers. Alluvial Fans Setting: • shape resembles a segment of a cone • Typically occur in areas of high relief,  Base of a mountain range (abrupt change in slope)  Where an abundant supply of sediment is available • Tend to be sparsely vegetated, and common to arid or semiarid settings • Common in glacial settings- develop outwash fans in front of melting glaciers • If an alluvial fan builds out into a body of water – it forms a Fan-Delta Processes: • stream-flow, debris-flow, mud-flow, landslides • Types of processes vary greatly, depending on the fan types, climate controls, etc. • • Humid Fans are dominated by stre ...
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Tags: continental facies models Fluvial Deposits Lacustrine Deposits Alluvial Fans Braided Rivers