unconformity

A stratum of amnesia in the geologic record, where overlying rock, significantly younger than what lies below, represents some break in an otherwise continuous story of formation. Often, the original strata have been established, then lifted, tilted, folded, or severely eroded before being topped with new deposits by vulcanism or sedimentation. This unconformity represents the place in deposition when time passed without leaving a local record. As the rings in a tree indicate a steady counting of seasons from the pith of origin to the living cambium of the present moment, the lithic record in bedrock may show an unbroken stratigraphic succession of events, materials, and processes. The unconformity in this succession represents a time when the recorded sequence of geologic progress was broken before the next stage in development began to leave a new record.

Kim Stafford