1. Sedimentary Structures

2. Sedimentary Structures
• Features that form within
sediment during accumulation
and before it is lithified.

3. Sedimentary Structures

4. Uses of Sedimentary Structures
Sedimentary Structures & Environments
Uses of Sedimentary Structures
1. Paleoenvironmental indicators:
many features only form under
certain physical conditions.

5. Uses of Sedimentary Structures
Sedimentary Structures & Environments
Uses of Sedimentary Structures
1. Paleoenvironmental indicators:
many features only form under
certain physical conditions.
• on land
• moving water
• moving air
• still water
• event(s) vs. continous

6. Sedimentary Structures & Environments
From Shrock 1948

7. Modern Raindrop Imprints on Clay
Sedimentary Structures & Environments
Modern Raindrop Imprints on Clay
From Shrock 1948

8. Uses of Sedimentary Structures
Sedimentary Structures & Environments
Uses of Sedimentary Structures
2. Paleo-current direction:
• some indicate direction of flow,
• may allow for regional
interpretations

9. “Michigan River Delta”
Illinois
Late Paleozoic
“Michigan River Delta” NE
flow directions
Indiana SW

10. “Michigan River Delta”
Illinois
Late Paleozoic
“Michigan River Delta”
flow directions
Indiana

11. Uses of Sedimentary Structures
Sedimentary Structures & Environments
Uses of Sedimentary Structures
3. Stratigraphic “up” direction:
• indicates original
orientation in
tectonically deformed
beds ?

12. Examples of Sedimentary Structures
Sedimentary Structures & Environments
Examples of Sedimentary Structures
1. Bedding = stratification:
• Change or break in deposition
causes a marked plane.

13. Examples of Sedimentary Structures
Sedimentary Structures & Environments
Examples of Sedimentary Structures
1a. Massive bedding:
• thick uniform
bedding
• constant conditions
during deposition
• relatively quite water

14. Examples of Sedimentary Structures
Sedimentary Structures & Environments
Examples of Sedimentary Structures
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

15. Examples of Sedimentary Structures
Sedimentary Structures & Environments
Examples of Sedimentary Structures
1b. Cross bedding:

16. Cross bedding Sedimentary Structures & Environments

17. flow erosion deposition Sedimentary Structures & Environments

18. flow erosion deposition Sedimentary Structures & Environments

19. flow up Sedimentary Structures & Environments

20. • forset in flow direction
Sedimentary Structures & Environments
• truncated side = up,
• forset in flow direction

21. up flow • truncated side = up, • forset in flow direction
Sedimentary Structures & Environments
• truncated side = up,
• forset in flow direction up
flow

22. Sedimentary Structures & Environments

23. Sedimentary Structures & Environments?

24. two directions = beach/tides
Sedimentary Structures & Environments
two directions = beach/tides

25. Environmental significance of sandstones
Sedimentary Rock Types
Environmental significance of sandstones
1c. Graded bedding:
• grain size decrease
from bottom to
the top of the bed.
• represents an event

26. Environmental significance of sandstones
Sedimentary Rock Types
Environmental significance of sandstones
1c. Graded bedding:
• grain size decrease
from bottom to
the top of the bed.
• represents an event

27. Sedimentary Rock Types

28. Environmental significance of sandstones
Sedimentary Rock Types
Environmental significance of sandstones
Graded beds of graywacke

29. Sedimentary Rock Types
2. Ripples and dunes:
two kinds

30. 2a. Asymmetrical ripples:
Sedimentary Rock Types
2a. Asymmetrical ripples:

31. 2a. Asymmetrical ripples:
Sedimentary Rock Types
2a. Asymmetrical ripples:
• long face and short face
• short face points down current/wind

32. 2a. Asymmetrical ripples:
Sedimentary Rock Types
2a. Asymmetrical ripples:
map view
Flow Direction?

33. 2a. Asymmetrical ripples:
Sedimentary Rock Types
2a. Asymmetrical ripples:
map view
Flow Direction?

34. 2b. Symmetrical ripples:
Sedimentary Rock Types
2b. Symmetrical ripples:

35. 2b. Symmetrical ripples:
Sedimentary Rock Types
2b. Symmetrical ripples:
• back and forth, wave motion
• pointed crests rounded troughs
• directional indicator, crest UP

36. 2b. Symmetrical ripples:
Sedimentary Rock Types
2b. Symmetrical ripples:
map view
Flow
Direction?

37. 2b. Symmetrical ripples:
Sedimentary Rock Types
2b. Symmetrical ripples:
map view
Flow
Direction?

38. 3. Mud cracks: • series of polygonal desiccation cracks
Sedimentary Rock Types
3. Mud cracks:
• series of polygonal desiccation cracks
• sediment accumulated in alternating
wet and dry environment

39. Sedimentary Rock Types
3. Mud cracks:
• directional indicator, curl UP

40. • massive beds: <environment>
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>

41. • Raindrop imprints: <up>, <environment>
Sedimentary Rock Types
Other structures: (not on exam)
• Raindrop imprints: <up>, <environment>

42. • Fossil Burrows: <up>, <environment>
Sedimentary Rock Types
Other structures: (not on exam)
• Fossil Burrows: <up>, <environment>

43. • Water escape: <up>
Sedimentary Rock Types
Other structures: (not on exam)
• Water escape: <up>

44. • load casts: <up>
Sedimentary Rock Types
Other structures: (not on exam)
• load casts: <up>
bottom side of sandstone over mud

45. • load casts: <up>
Sedimentary Rock Types
Other structures: (not on exam)
• load casts: <up>
bottom side of sandstone over mud

46. • sole marks: <up>, <flow>
Sedimentary Rock Types
Other structures: (not on exam)
• sole marks: <up>, <flow>
bottom side of sandstone over mud

47. • sole marks: <up>, <flow>
Sedimentary Rock Types
Other structures: (not on exam)
• sole marks: <up>, <flow>
bottom side of sandstone over mud

48. McKinney Geology Museum
Sedimentary Rock Types
Visit the
McKinney Geology Museum