sedimentary structures

Sedimentary Structures

Sedimentary Structures

Sedimentary Structures

Sedimentary Structures:

• Features that form within

sediment during accumulation

and before it is lithified.

Sedimentary Structures

Sedimentary Structures

Sedimentary Structures:

Sedimentary Structures

Uses of Sedimentary Structures

Sedimentary Structures & Environments

1. Paleoenvironmental indicators:

many features only form under

certain physical conditions.

Uses of Sedimentary Structures

Sedimentary Structures & Environments

1. Paleoenvironmental indicators:

many features only form under

certain physical conditions.

• on land• moving water• moving air• still water• event(s) vs. continous

Sedimentary Structures & Environments

From Shrock 1948

Sedimentary Structures & Environments

From Shrock 1948

Modern Raindrop Imprints on Clay

Uses of Sedimentary Structures

Sedimentary Structures & Environments

2. Paleo-current direction:

• some indicate direction of flow,

• may allow for regional interpretations

Late Paleozoic“Michigan River Delta”

Illinois

Indianaflow

directions

SW

NE

Late Paleozoic“Michigan River Delta”

Illinois

Indiana

flow directions

Uses of Sedimentary Structures

Sedimentary Structures & Environments

3. Stratigraphic “up” direction:

• indicates original orientation in tectonically deformed beds

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Examples of Sedimentary Structures

Sedimentary Structures & Environments

1. Bedding = stratification:

• Change or break in deposition

causes a marked plane.

Examples of Sedimentary Structures

Sedimentary Structures & Environments

1a. Massive bedding:

• thick uniform bedding

• constant conditions during deposition • relatively quite water

Examples of Sedimentary Structures

Sedimentary Structures & Environments

1b. Cross bedding:

• layers within bed are inclined at time of deposition (not horizontal)

• sand moving along as ripples or dunes

• formed by water or air

• restricted to moving water

Examples of Sedimentary Structures

Sedimentary Structures & Environments

1b. Cross bedding:

Sedimentary Structures & Environmentsh

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Sedimentary Structures & Environments

• truncated side = up,• forset in flow direction

Sedimentary Structures & Environments

• truncated side = up,• forset in flow direction

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Sedimentary Structures & Environments

Sedimentary Structures & Environments

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Sedimentary Structures & Environments

two directions = beach/tides

Sedimentary Rock Types

1c. Graded bedding:

• grain size decrease from bottom to the top of the bed.

• represents an event

Environmental significance of sandstones

Sedimentary Rock Types

1c. Graded bedding:

• grain size decrease from bottom to the top of the bed.

• represents an event

Environmental significance of sandstones

Sedimentary Rock Types

Sedimentary Rock Types

Graded beds of graywacke

Environmental significance of sandstones

Sedimentary Rock Types

2. Ripples and dunes:

two kinds

Sedimentary Rock Types

2a. Asymmetrical ripples:

Sedimentary Rock Types

2a. Asymmetrical ripples:

• long face and short face• short face points down current/wind

Sedimentary Rock Types

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Flow Direction?

Sedimentary Rock Types

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Sedimentary Rock Types

2b. Symmetrical ripples:

Sedimentary Rock Types

2b. Symmetrical ripples:

• back and forth, wave motion

• pointed crests rounded troughs

• directional indicator, crest UP

Sedimentary Rock Types

2b. Symmetrical ripples:

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Sedimentary Rock Types

2b. Symmetrical ripples:

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Sedimentary Rock Types

3. Mud cracks:

• series of polygonal desiccation cracks

• sediment accumulated in alternating wet and dry environment

Sedimentary Rock Types

3. Mud cracks:

• directional indicator, curl UP

Sedimentary Rock Types

Summary:

• massive beds: <environment>

• cross bed: <up>, <flow>, <environment>

• graded beds: <up>, <environment>

• asymmetrical ripple: <flow>

• symmetrical ripple: <up>

• mud cracks: <up>, <environment>

Sedimentary Rock Types

Other structures: (not on exam)

• Raindrop imprints: <up>, <environment>

Sedimentary Rock Types

Other structures: (not on exam)

• Fossil Burrows: <up>, <environment>

Sedimentary Rock Types

Other structures: (not on exam)

• Water escape: <up>

Sedimentary Rock Types

Other structures: (not on exam)

• load casts: <up>

bottom side of sandstone over mud

Sedimentary Rock Types

Other structures: (not on exam)

• load casts: <up>

bottom side of sandstone over mud

Sedimentary Rock Types

Other structures: (not on exam)

• sole marks: <up>, <flow>

bottom side of sandstone over mud

Sedimentary Rock Types

Other structures: (not on exam)

• sole marks: <up>, <flow>

bottom side of sandstone over mud

Sedimentary Rock Types

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