structures and processes
Restored quarries are ideal for demonstrating different types
of geological structures and processes. These include features
such as cross-bedding and ripple marks that originated
during the deposition of the rock, along with tectonic structures
such as folds and faults that formed later as the result
of stress on the rocks. Small structures within quarries often
reflect the orientation of larger, unexposed, structures in
the surrounding area so detailed measurements in quarries can
help us understand the overall structural geology of an area.
Quarries are excellent for demonstrating major gaps or unconformities in
the geological sequence when there are major differences in
the beds below and above the break in sedimentation.
The various types of cross-bedding provide good indications
of the environment under which the sediment was deposited.
Cross-sets dipping consistently in one direction, indicating
deposition in a river system.
Cross-sets dipping in opposite directions, indicating deposition
in a marine environment.
These are formed in very shallow marine environments as the
water moves in and out – present day examples can be
seen on sandy beaches. If the ripples are asymmetrical it signifies
that they have been deposited in flowing fresh water.
Folds and faults
Folds and faults are produced when rocks are subjected to pressure
and have either deformed (folded) or fractured (faulted). Faults
and folds may occur on all scales, from the microscopic to
instances where the beds have been displaced many kilometres.
Small-scale faults and folds within quarries may reflect the
presence of nearby larger faults and folds with similar trends.
Fold structures where the youngest beds are preserved in the
centre (‘core’) of the fold are known as ‘synclines’.
Fold structures in which the oldest beds are preserved in the
core of the fold are known as ‘anticlines’.
Exposed in a quarry, this high-angle, ‘normal’ fault
shows displacement of bedding.
An unconformity is the name given to a major gap in the geological
sequence where there are big differences in the beds below
and above the break in sedimentation. Unconformity exposed
in a quarry in Somerset. The grey coloured Carboniferous-age
limestone below the unconformity was deeply-buried, folded
(tilted), re-exposed and eroded by the sea before the overlying
yellow-coloured flat-lying, Jurassic-age limestones were deposited.
of an unconformity exposed in a quarry in Somerset.