Fossil Wind

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.

Dr. Eamon Doyle, geologist for the Burren and Cliffs of Moher UNESCO Global Geopark.