Sedimentary Structures
Sedimentary Structures • Features that form within sediment during accumulation and before it is lithified.
Sedimentary Structures
Uses of Sedimentary Structures Sedimentary Structures & Environments Uses of Sedimentary Structures 1. Paleoenvironmental indicators: many features only form under certain physical conditions.
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
Sedimentary Structures & Environments From Shrock 1948
Modern Raindrop Imprints on Clay Sedimentary Structures & Environments Modern Raindrop Imprints on Clay From Shrock 1948
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
“Michigan River Delta” Illinois Late Paleozoic “Michigan River Delta” NE flow directions Indiana SW
“Michigan River Delta” Illinois Late Paleozoic “Michigan River Delta” flow directions Indiana
Uses of Sedimentary Structures Sedimentary Structures & Environments Uses of Sedimentary Structures 3. Stratigraphic “up” direction: • indicates original orientation in tectonically deformed beds ?
Examples of Sedimentary Structures Sedimentary Structures & Environments Examples of Sedimentary Structures 1. Bedding = stratification: • Change or break in deposition causes a marked plane.
Examples of Sedimentary Structures Sedimentary Structures & Environments Examples of Sedimentary Structures 1a. Massive bedding: • thick uniform bedding • constant conditions during deposition • relatively quite water
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
Examples of Sedimentary Structures Sedimentary Structures & Environments Examples of Sedimentary Structures 1b. Cross bedding:
Cross bedding Sedimentary Structures & Environments http://www.ndsu.nodak.edu/instruct/ashworth/webpages/g304/reportphotos2003/cross-bedding.jpg
flow erosion deposition Sedimentary Structures & Environments http://www.ndsu.nodak.edu/instruct/ashworth/webpages/g304/reportphotos2003/cross-bedding.jpg
flow erosion deposition Sedimentary Structures & Environments http://www.ndsu.nodak.edu/instruct/ashworth/webpages/g304/reportphotos2003/cross-bedding.jpg
flow up Sedimentary Structures & Environments http://www.ndsu.nodak.edu/instruct/ashworth/webpages/g304/reportphotos2003/cross-bedding.jpg
• forset in flow direction Sedimentary Structures & Environments • truncated side = up, • forset in flow direction
up flow • truncated side = up, • forset in flow direction Sedimentary Structures & Environments • truncated side = up, • forset in flow direction up flow
Sedimentary Structures & Environments
Sedimentary Structures & Environments ?
two directions = beach/tides Sedimentary Structures & Environments two directions = beach/tides
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
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
Sedimentary Rock Types
Environmental significance of sandstones Sedimentary Rock Types Environmental significance of sandstones Graded beds of graywacke
Sedimentary Rock Types 2. Ripples and dunes: two kinds
2a. Asymmetrical ripples: Sedimentary Rock Types 2a. Asymmetrical ripples:
2a. Asymmetrical ripples: Sedimentary Rock Types 2a. Asymmetrical ripples: • long face and short face • short face points down current/wind
2a. Asymmetrical ripples: Sedimentary Rock Types 2a. Asymmetrical ripples: map view Flow Direction? http://www3.interscience.wiley.com:8100/legacy/college/levin/0470000201/chap_tutorial/ch03/images/le03_20.gif
2a. Asymmetrical ripples: Sedimentary Rock Types 2a. Asymmetrical ripples: map view Flow Direction? http://www3.interscience.wiley.com:8100/legacy/college/levin/0470000201/chap_tutorial/ch03/images/le03_20.gif
2b. Symmetrical ripples: Sedimentary Rock Types 2b. Symmetrical ripples:
2b. Symmetrical ripples: Sedimentary Rock Types 2b. Symmetrical ripples: • back and forth, wave motion • pointed crests rounded troughs • directional indicator, crest UP
2b. Symmetrical ripples: Sedimentary Rock Types 2b. Symmetrical ripples: map view Flow Direction? http://course1.winona.edu/csumma/images/sedstrux/rip300.jpg
2b. Symmetrical ripples: Sedimentary Rock Types 2b. Symmetrical ripples: map view Flow Direction? http://course1.winona.edu/csumma/images/sedstrux/rip300.jpg
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
Sedimentary Rock Types 3. Mud cracks: • directional indicator, curl UP
• 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>
• Raindrop imprints: <up>, <environment> Sedimentary Rock Types Other structures: (not on exam) • Raindrop imprints: <up>, <environment>
• Fossil Burrows: <up>, <environment> Sedimentary Rock Types Other structures: (not on exam) • Fossil Burrows: <up>, <environment>
• Water escape: <up> Sedimentary Rock Types Other structures: (not on exam) • Water escape: <up>
• load casts: <up> Sedimentary Rock Types Other structures: (not on exam) • load casts: <up> bottom side of sandstone over mud
• load casts: <up> Sedimentary Rock Types Other structures: (not on exam) • load casts: <up> bottom side of sandstone over mud
• sole marks: <up>, <flow> Sedimentary Rock Types Other structures: (not on exam) • sole marks: <up>, <flow> bottom side of sandstone over mud
• sole marks: <up>, <flow> Sedimentary Rock Types Other structures: (not on exam) • sole marks: <up>, <flow> bottom side of sandstone over mud
McKinney Geology Museum Sedimentary Rock Types Visit the McKinney Geology Museum