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

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Presentation on theme: "Sedimentary Structures. Sedimentary Structures: Features that form within sediment during accumulation and before it is lithified. Sedimentary Structures."— Presentation transcript:

1 Sedimentary Structures

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

3 Sedimentary Structures: Sedimentary Structures

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

5 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

6 Sedimentary Structures & Environments From Shrock 1948

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

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

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

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

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

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

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

14 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

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

16 Sedimentary Structures & Environments Cross bedding

17 Sedimentary Structures & Environments flow erosion deposition

18 Sedimentary Structures & Environments flow erosion deposition

19 Sedimentary Structures & Environments flow up

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

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

22 Sedimentary Structures & Environments

23 ?

24 two directions = beach/tides

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

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

27 Sedimentary Rock Types

28 Graded beds of graywacke Environmental significance of sandstones

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

30 Sedimentary Rock Types 2a. Asymmetrical ripples:

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

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

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

34 Sedimentary Rock Types 2b. Symmetrical ripples:

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

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

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

38 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 Sedimentary Rock Types Summary: massive beds: cross bed:,, graded beds:, asymmetrical ripple: symmetrical ripple: mud cracks:,

41 Sedimentary Rock Types Other structures: (not on exam) Raindrop imprints:,

42 Sedimentary Rock Types Other structures: (not on exam) Fossil Burrows:,

43 Sedimentary Rock Types Other structures: (not on exam) Water escape:

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

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

46 Sedimentary Rock Types Other structures: (not on exam) sole marks:, bottom side of sandstone over mud

47 Sedimentary Rock Types Other structures: (not on exam) sole marks:, bottom side of sandstone over mud

48 Sedimentary Rock Types Visit the McKinney Geology Museum


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