An unconformity is essentially a buried
surface of erosion and/or non-deposition
that represents a significant break in the
rock record.
TYPES OF
UNCONFORMITIES
Block diagrams illustrate
three major types of
unconformities that occur
in the geologic record. In
each type there is a
marked discordance
between the rocks below
and the rocks above the
contact plane (buried
surface of erosion). The
process of forming an
unconformity involves the
following steps:
(1) Formation of older
rocks;
(2) Uplift, possible
deformation and formation
of an erosion surface;
(3) Removal of some older
rocks by erosion;
(4) Subsidence (burial)
and deposition of younger
sediments on the erosion
surface.
(Examples of each type are
illustrated below)