Following on from my blog post about the Geo-SEW-ence of Scotland back in September, I have been busy stitching the rest of the British Isles. After working south through North England, I turned my attention to the Island of Ireland. It has taken me a good few months, but I finally completed it this month, and decided to capture some of its fantastic geology, and the highs and lows of cross stitching it, in this months blog.
"For a relatively small area, 70,000 sqkm, Ireland has a diverse geological history spanning 1.8 billion years" Geological Survey Ireland
I started in Northern Ireland, where the youngest rocks are found and form the Antrim-Derry plateau (pink). They are extrusive igneous rocks (or lavas) that erupted from volcanoes and fissures 60 million years ago as the Atlantic Ocean began to open. Before this, the UK was joined to Canada in the super continent of Laurasia. But plate tectonic forces led to the opening of the Atlantic Ocean and a long rift of volcanos that spewed lava across NW Britain. The most famous place to see this lava is at Giant’s Causeway, on the North coast of NI. Here, an ancient lake of molten rock slowly cooled to form beautiful columnar jointing. It’s well worth a visit. Read more about the Giant's Causeway in my blog article 'Geo-holiday in Northern Ireland'!
The rest of Northern Ireland tells a similar story to the geological history of Scotland, and I love that you can follow the geology from Scotland across to Ireland. The metamorphosed remnants of the Caledonian Mountain Range seen in Donegal (light pink, green) correlate to the Scottish Highlands. And the deformed Iapetus Ocean deposits, that separated north and south Britain 600 million years ago (purples) can be clearly traced from the southern uplands of Scotland across to County Down.
The rocks that are the same age in the Republic of Ireland tell a very different story. The purples in the south east or Ireland, south or Dublin) represent the other side of the ancient Iapetus ocean: fossil-filled shales, greywackes and sands (now metamorphosed into quartzites).This ocean separated the ancient continents of Laurentia in the north, and Avalonia in the south (orange in the very SE at Carnsore Point). As the Iapetus closed, the ocean’s crust was pushed below the continents, causing the ocean crust to melt forming granite (red), and volcanoes that erupted lava (light pink, green) across the region.
The Iapetus ocean closed, and once the continents were joined and Ireland sat close to the equator. Hot, and arid, Ireland was covered but a hot desert expanse of sand dunes around 415 million years ago. Occasional flash floods deposited conglomerates between layers of the classic cross-bedded Old Red Sandstones of the Devonian period, best seen in the very southwest of Ireland (brown). By the Carboniferous, the sea had returned, flooding Ireland with by a warm shallow sea full of corals, crinoids and brachiopods. Limestones formed across much of Ireland’s interior (blue) as a result. I used SO MUCH blue thread to complete Ireland - I started to hate this rock! But, it has now, under the action of rain and water, eroded in to a karst landscape, forming limestone pavement- one of my favorite landscapes!
The late Carboniferous (360 million years ago) saw the deposition of a now world-class geological outcrop: the County Clare basin infill clastics (yellow). Deep water, slope and delta deposits are exposed along high sea cliffs, allowing geologists to view the deposits at the scale they would find them in the subsurface. It is one of the best places in the world to view deep water fans, channels and soft sediment deformation, and has been an important site to test the concepts of sequence stratigraphy.
Annoyingly, I ran out of my Devonian brown and Carboniferous blue thread with only a handful of stitches to finish the SW of Ireland, but the wait to completed it was worth it - I love how the map has come together. I've thoroughly enjoyed getting to know the geology of this amazing country, and SW Ireland is now top of my geo-holiday bucket list. I was scheduled to attend a conference there this summer (to present my Indonesian research), but understandably given the current pandemic situation, this has been postponed until 2021. So expect a geo-holiday blog post next year! In the meantime, its onwards to cross-stitching Wales!
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