Sedimentary Structures

Sedimentary Structures

1. Laminations

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

2. Beds

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

3. Graded-bedding

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

4. Cross-bedding

   • 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 

5. Ripple Marks

   • Symmetrical
     • Wave-formed ripple marks, generally with a sharp crest and broad troughs  Formed by oscillating currents
   • Assymetrical
     • Current ripple marks Result from deposition by water or air currents flowing in one direction 

6. Mud Cracks

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

7. Trace Fossils

   • Indications of organic activity. Intense activity results in bioturbation involving disruption of sediment 
   • Tracks
   • Trails
   • Tubes
   • Burrows