Antidunes
Antidunes are the sediment bedforms created by fast, shallow flows of water with a Froude number greater than 0.8. Antidunes form beneath standing waves of water that periodically steepen, migrate, and then break upstream. The antidune bedform is characterized by shallow foresets, which dip upstream at an angle of about ten degrees that can be up to five meters in length. They can be identified by their low angle foresets. For the most part, antidunes bedforms are destroyed during decreased flow, and therefore cross bedding formed by antidunes will not be preserved.
Read more about this topic: Sedimentary Structures