Sedimentary Structures

Anotações:

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

Anotações:

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

Anotações:

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

Anotações:

• 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

   Anotações:

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

   Anotações:

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

Anotações:

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

Anotações:

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

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