Final answer:
Graded bedding is a sedimentary structure where grain size changes within a single bed.
Step-by-step explanation:
Graded bedding is a common sedimentary structure where a change in grain size can be observed within a single sedimentary bed.
At the bottom of the bed are mainly coarse particles which get progressively smaller as you move vertically up the bed. This occurs because smaller sand grains are transported as suspended sediment while larger grains are transported as bedload. The process of graded bedding represents depositional environments where transport energy decreases over time, such as in a river.
Turbidity currents can also cause graded bedding by depositing sediment in which the finest particles settle at the top and the coarser particles settle at the bottom.