Sedimentary Structures

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• Layers less than 1 cm thick Form mostly as particles settled from suspension

Annotations:

• Layers more than 1 cm thick  Form as particles settle from suspension and from moving sediment as sand in a stream channel

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• Individual layers with an upward decrease in grain size Deposition by turbidity currents or during waning stages of floods

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• Layers deposited at an angle to the surface in which they accumulated Deposition of a sloping surface at the downwind side of a sand dune 

1. Symmetrical

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   • Wave-formed ripple marks, generally with a sharp crest and broad troughs  Formed by oscillating currents
2. Assymetrical

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   • Current ripple marks Result from deposition by water or air currents flowing in one direction 

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• Intersecting cracks in clay-rich soils Drying and shrinkage of mud along a lakeshore, a floodplain, or on tidal flats 

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• Indications of organic activity. Intense activity results in bioturbation involving disruption of sediment 

1. Tracks
2. Trails
3. Tubes
4. Burrows