Sedimentary

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Sedimentary Rocks II
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Sedimentary Structures

• Strata or beds
• Distinct layers having variations in texture,
  color or physical properties
• Formations
• Large scale stratification
• Contain numerous individual strata

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• Surface impressions
• Indicate the top of a sedimentary bed
• Preserve features indicating past environment
• Ripple marks
• Mud cracks

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Sedimentary Structures

• Cross-bedding
• Individual layers are inclined in reference to
  the top or bottom of the larger bed
• Formed by movement of sand waves or dunes
• Inclination shows flow direction and right-side-up

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Cross-bed Formation
-good paleo-current indicator -direction and
velocity -useful way up indicator
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TOP
BOTTOM
Cross-bedding formed by dune/ripple migration.
Flow direction and top of bed indicated.
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• Graded bedding
• Progressive change in grain size upward
• Fining upward
• Commonly formed by turbidites
• Subaqueous sediment flows
• Coarsest particles settle first

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• Fossils
• Fossil remains or trace fossils
• Indicate paleo-environment
• Detailed study may provide
• Depth of water
• Temperature and salinity
• Relative age of rock

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Sedimentary Systems

• Systems include
• Weathering
• Transportation
• Deposition
• Lithification
• Sedimentary rock records processes that produced
  it

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Idealized diagram of major sedimentary systems.
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• Advance and retreat of shallow seas
• Common example of a stratigraphic sequence
• Cycle consists of
• Sandstone-shale-limestone-shale-sandstone

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Transgression and regression of shallow sea
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Transgressive Sequence in Outcrop
Shale shallow water
Limestone deepwater
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What the heck is a Facies? Sounds like a
drinking game to me.
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Sequence Stratigraphy

• Sedimentary rock formations classified by rock
  type
• Sequences of formations may be grouped together
• Sequences separated by unconformity
• Relate global scale events
• e.g., Change in sea level

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Changes in sea level throughout geologic history
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• Plate tectonics plays a major role
• Sediment deposition geographic distribution
• Sediment source areas
• Formation of sequences

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