Final answer:
A sediment deposit with unlayered and randomly sorted material at the bottom and layered, well-sorted material at the top can be explained by graded bedding. It occurs when the coarse particles settle first, forming the bottom layer, and the finer particles settle later, forming the top layer.
Step-by-step explanation:
A sediment deposit that contains unlayered and randomly sorted material at the bottom and layered, well-sorted material at the top can be explained by the process of graded bedding. Graded bedding is a sedimentary structure where a change in grain size can be observed within a single sedimentary bed. In this case, the coarse particles settle out first and form the unlayered and randomly sorted material at the bottom, while the finer particles settle later and form the layered, well-sorted material at the top. This can happen when the transport energy decreases over time, like in a river where the water velocity changes, or during rapid depositional events such as turbidity currents.