Burren and Cliffs of Moher UNESCO Global Geopark - Geology

Fossil Wind
Ancient ripples formed by wind waves on a
shallow coast 315 million years ago.
There are three main rock types; Igneous rocks
which are formed from molten magma from the
Earth’s interior that has cooled, Sedimentary rocks
which are formed from particles (sediments); bits
and pieces of rocks and fossils and Metamorphic
rocks which are any rock that has been deformed
by deep burial and the forces of plate tectonics.
The rocks of the Burren are sedimentary rocks.
At the Cliffs of Moher, the layers are made of
particles of sand and mud and occasionally bits of
fossils. These particles were transported by rivers
from long-gone distant mountains and finally
deposited into the sea. After they were buried by
more and more sediment they were eventually
turned into rock. So, while the sand and mud
and bits of land plants often ended up in the sea,
they were transported considerable distances
from where they were originally eroded on land.
As these bits of eroded land entered the sea, they
were sometimes buried beside sea creatures that
were living in the sea at that time. So, we often find
land and sea creatures preserved together there.
The limestone of the Burren is also a sedimentary
rock, but limestone is a bit different. The particles
that make up limestone are often dominated by
fossils or fragments of fossils. They haven’t been
transported by rivers and are usually turned
into rock close to where they lived. All the
fossils in the Burren limestone are sea creatures
and lived and died in a shallow tropical sea.
Here the process of turning into rock is quicker
as the tropical seas are very rich in calcium
carbonate which crystalizes out to form the
cement that holds all the bits of fossils together.
This can happen very shortly after the creatures
died and they don’t need to be buried deeply.
The processes that act on the particles of sand,
mud or fossils while they are on the seafloor can
tell us a lot about where exactly they were, and
this is one way we get to understand what was
happening over 300 million years ago. One of
those processes is wave action produced by wind.
When wind blows across a body of water it can
generate a circular motion in the water, these
circular cells of water decrease in size the deeper
you go in the water until at a certain depth they
disappear. If the water is shallow enough, those
circular cells will impact the sea floor creating a
back-and-forth motion that can move the loose
sand on the seafloor. This back-and-forth motion
creates wave ripples. If these are buried by another
layer of sand, they may be preserved as fossil
ripples. They are, in effect, fossilized wind energy.
These ripples, which can be seen along the
walls of the path along the Cliffs of Moher have
been quarried locally. We know how important
waves are to local surfing and energy generation
now, they have been important to whoever
was living here for over 300 million years.
Article written by Dr. Eamon Doyle, Geologist for
Burren and Cliffs of Moher UNESCO Global Geopark, Clare County Council.
www.burrengeopark.ie