Burren and Cliffs of Moher UNESCO Global Geopark - Geology

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Stress Release in The Burren One of the most striking features of the Burren are the vertical cracks or fissures in the limestone. They are known as ‘grikes’ although I prefer the local term ‘Scealps’. For most people they are just the things you have to step over, however they initially formed as fractures almost 300 million years ago. At that time, we were down near the equator and the tectonic plates on Earth were colliding to form one supercontinent called Pangea. This slow collision built up huge stresses in the rocks which eventually fractured, releasing the stress. This is the same process by which Africa is colliding with Europe right now and causing Earthquakes throughout southern Europe, most recently in Croatia. This is all part of the journey of the tectonic plates that make up the Earth’s crust as they move around on their merry slow dance through geological time. This fracturing in the Burren limestone opened millions of thin vertical gaps (mostly oriented nearly North -South) which were then filled by fluids which had been trapped at depth under enormous pressure. These fluids crystallized in the gaps forming thin mineral veins, mostly of calcite, which effectively sealed the fractures. These fractures remained buried and sealed until the rock was brought to the surface and exposed to the potent force of rain, which slowly dissolves the veins and limestone, particularly under acidic soils. A second set of fractures (mostly oriented East- West) formed much later as the rocks that buried the limestone were removed by erosion on our long journey from the equator to here. We know that at least a couple of kilometres of rock have been eroded over the last 300 million years. Removing that huge weight also released further stresses which caused the rocks to fracture. Finally, a third stress was caused by the weight of thick ice sheets on the limestone surface during the ice age. This weight pressed down on the rock surface building up new stresses which were released after the ice melted, forming new fractures which are mostly horizontal. So the fractured surface of the Burren is all about stress release. Next time you are there, just relax. Article written by Dr. Eamon Doyle, Geologist for Burren and Cliffs of Moher UNESCO Global Geopark, Clare County Council. www.burrengeopark.ie
The patterns on Moher Flags are ancient geological footprints. Geological footprints leave elegant patterns Justifiably famous for their elegant patterns, Moher flags have been quarried along the west coast of Clare for centuries. The thin, rigid slabs were ideal for roofing in times past but more recently they are primarily used for paving stones and decorative walls. The quarrying methods have hardly changed, and the family-owned quarries still extract the slabs manually, using techniques handed down through the generations. To a geologist, the Moher flags (short for flagstones) are sandstones. That means they are sedimentary rocks composed of grains of sand between 0.06 and 2mm in diameter. The grains of sand are mostly the mineral quartz with some calcite as well as more exotic minerals such as feldspar, biotite and chlorite. These sand grains were eroded from long-gone mountains and transported by extinct rivers into a sea that disappeared over 300 million years ago. Dr. Shane Tyrell of NUIG and his student Martin Nauton- Fourteu have been studying the ancient transport patterns (provenance) of these grains in similar rocks along the coast of Clare and have shown they were carried here from the south/ southwest. As fascinating as that is, the internal composition of the sandstone is overshadowed by the beautiful, complex patterns on the surface. These patterns are called ‘trace fossils’; that is, they are the marks left by living creatures but not the creatures themselves. They are geological footprints. The patterns are actually burrows, made by an organism as it burrowed horizontally, just below the surface on a sandy coast. The creature was ‘mining’ the sand for organic matter, taking it in at one end, extracting the food and packing the processed sand behind itself at the other end - this is why the burrows were able to be preserved. The trace fossils are very abundant, so we know the creature was ideally suited to the environment, however, the lack of other fossils or trace fossils indicates difficult living conditions, so this creature must have had some advantage to have been able to thrive. If you look closely at the burrows you will see a central ridge. This was likely produced by a siphon of some kind sticking up from the creature as it burrowed, most likely connecting it to the overlying seawater, perhaps giving it access to more oxygen, just like a snorkel. We have never seen any hardshell fossils in these burrows, and it is tempting to say that the creature did not have a shell. However, calcite shells can dissolve very quickly once buried if the groundwater is slightly acidic and the chance of shells being preserved as fossils is low. The trace fossils of the Moher flags are an active area of research for us right now, so watch this space for further updates. Why not get a look at the Moher Flag Stones in person by paying a visit to the Cliffs of Moher. Article written by Dr. Eamon Doyle, Geologist for Burren and Cliffs of Moher UNESCO Global Geopark, Clare County Council. www.burrengeopark.ie
Page 1: Managed By Supported By
Page 5 and 6: History in water flowing through th
Page 7 and 8: Our Fossil Roots In sandstone rocks
Page 9 and 10: Biokarst coastline, near Doolin. In
Page 11 and 12: Lough Garrig on top of Sleive Elva
Page 13 and 14: A clay layer between two layers of
Page 15 and 16: Big Brachiopods Large brachiopods a
Page 17 and 18: Our Geological Connection with Ukra
Page 19 and 20: The corals of the Burren National P
Page 21 and 22: Conodonts: bizarre fossils in the B
Page 23 and 24: Sedimentary layers: reading the pag
Page 25 and 26: Oh poop... We have quite a wide var

Burren and Cliffs of Moher UNESCO Global Geopark - Geology

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