Sedimentary structures are features found in the rock that were created at the time of deposition. Sedimentary structures exclude fossils and diagenetic changes to the rock. These structures often help evaluate the environment of deposition.
This web site page contains images of various sedimentary structures and an explanation of what they are and how they formed.
These two images of Salt Casts are from the Triassic Moenkopi Formation of northern Arizona. The salt casts represent periods of aridity during the time of the deposition of this silty sandstone. Drying of the sediments is an indication of very arid conditions allowing the development of the salt crystals. The salt crystals were later dissolved away and the voids were then filled with sand to produce the casts.
RIPPLE MARKS are a very common type of sedimentary structure. This on is also from the Triassic Moenkopi Formation of northern Arizona. These symmetrical ripple marks simply indicate that a current was present - in this case a back and forth current from the top of the picture to the bottom. Symmetrical ripple marks indicate one of two possible current direction and are associated with deeper, calmer waters.