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
?
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
flow
up
Sedimentary Structures & Environments
Sedimentary Structures & Environments
?
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
2a. Asymmetrical ripples:
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Flow Direction?
Sedimentary Rock Types
2a. Asymmetrical ripples:
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Flow Direction?
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:
map view
FlowDirection?
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Sedimentary Rock Types
2b. Symmetrical ripples:
map view
FlowDirection?
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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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