An unconformity may indicate that the beds below it have at some time been raised above the sea and have been eroded.
They are separable into a lower and upper division with an unconformity often occurring between them.
At Llandovery they rest unconformably upon Ordovician rocks (Bala), but in many other places no unconformity is traceable.
An unconformity thus records movements of the crust and a consequent break in the deposition of the strata.
Either of these events would have produced an unconformity; the two make it more pronounced.
Such an erosion surface, called an “unconformity,” marks a gap in the geological record of the district where it occurs.
If beds of rock may be regarded as leaves in the volume of geologic history, an unconformity marks a gap in the record.
And if the unconformity be widespread, the lost interval is correspondingly great.
A surface between successive strata representing a missing interval in the geologic record of time, produced either by an interruption in deposition or by the erosion of depositionally continuous strata followed by renewed deposition. An unconformity is a type of discontinuity.