Each layer of sediment is squeezed together by the weight above is this is called compaction! Cementation and compaction are very similar! Imagine this : A rock has weathered and eroded. The sediment is deposited in a river delta. Everyday, more and more sediment is deposited on the top for the first batch of sediment and the air and the water pushing lots of the sediment and this is the process of compaction.
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