An unconformity represents: a gap in the geological record, an intrusive igneous structure, an epeirogenic change, a location that was once covered by water

An unconformity represents a gap in the geological record. The correct option among all the options that are given in the question is the first option. This is basically the time when deposition had stopped or erosion had taken place. I hope that the answer has come to your help.

The correct answer is:   [b]:   "physical systems" .