Unconformity

An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous.

The local record for that time interval is missing and geologists must use other clues to discover that part of the geologic history of that area.

A disconformity is an unconformity between parallel layers of sedimentary rocks which represents a period of erosion or non-deposition.

[7][8] Angular unconformities can occur in ash fall layers of pyroclastic rock deposited by volcanoes during explosive eruptions.

[12] A blended unconformity is a type of disconformity or nonconformity with no distinct separation plane or contact, sometimes consisting of soils, paleosols, or beds of pebbles derived from the underlying rock.