Question

If a layer was deposited but does not appear in the rock record, what has occured

Answer 1

Erosion. Erosion is the action and movement of a surface process (e.g. water or wind) that removes and transports a material layer from one location to another. Once eroded, the deposited layer will not appear in the rock record. 

Answer 2

I think you forgot to give the choices along with the question. I am answering the question based on my research and knowledge. If a layer was deposited but does not appear in the rock record, the thing that happened is erosion. I hope that this is the ans wer that has actually come to your desired help.