Sedimentary structures

Sedimentary structures is associated with sedimentary rocks, nearly all sedimentary rock will contain sedimentary structures. These are developed right at the time of deposition or shortly after deposition. These are important features that tells us the history of deposition and sediments transportation.

Bedding or stratification

The most common sedimentary structure is the bedding or stratification, layers that develops during the deposition. Sediments deposits at a level surface so thus applies the law of horizontality that states as all sediments deposit as horizontal layers.

Cross bedding

Cross bedding consists of small layers that are deposited at an angle to the main beds. These are developed in the transportation of sediments by wind or water. The sediments as transported by wind, these moves down slope and is thus at an angle to the main beds. Same is the case with the water where water moving down slope deposits sediments at an angle to the main bed. Cross bedding is common in sands deposited by wind, streams, ocean currents and wind on beaches. 

Ripple marks

Ripple marks are the small ridges which are developed by the wind or water. These contains of crest and trough just like sand waves or dunes but are at a small scale. These gives the movement direction of the water or wind. If the movement is in a single direction then the ripple marks are asymmetrical and when the movement is to and fro like a pendulum then the marks will be symmetrical.

Graded bedding

Graded bedding is formed as the larger grains which is of-course the heavier settles down at the bottom and the finer and smaller grains settle later which will give a fining upward succession. Graded bedding is commonly formed at a flood plain or when both grains mixes in water.

Mud cracks

Mud cracks develop when mud shrinks as it dries up. This indicates that water was accumulated with it being in a shallow marine and then dries periodically. 
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