By John Counts and Emma Morris.
Europe has a wide variety of interesting sites for geologists, including areas with scientifically interesting formations, amazing scenery, and classic outcrops, many of which are recognized for their international geological significance and are designated as UNESCO Global Geoparks. Rarely, however, do all of these factors come together in such a spectacular way as they do in County Clare, western Ireland. The Cliffs of Moher, the barren karst hills of The Burren, and the spectacularly exposed deepwater to deltaic succession of Carboniferous-aged sediments on the Atlantic coast can all be found within a few kilometers of one another in County Clare. As such, the area makes for an amazing geological destination, and is also the subject of active research by University College Dublin sedimentologists Emma Morris and Peter Haughton. Emma and I talked recently about the rocks of County Clare, what it’s like to do fieldwork on the Wild Atlantic Way, and what makes the region so special.
Geological Significance and History of Investigations
County Clare is most famous (in a geological sense) for “the Burren”, an extensive area of almost-bare limestone hills that form a geomorphologically unique landscape. These rocks were initially deposited as tropical limestones during the Visean (Mississippian; 331-347 Ma), but the area is recognized today as one of the best known examples of the combined effects of karstification and Quaternary glacial activity. Karstification processes continue today, resulting in a limestone pavement that hosts a highly diverse community of flora and fauna unlike anywhere else in Ireland. The Burren forms the focal point of the Burren National Park, and is a major part of the Burren-Cliffs of Moher Geopark. Whilst the Burren forms a worthwhile geological destination in itself, it is only one part of the geological richness of the region.
In Lisdoonvarna, the 6-cm thick St. Brendan’s Well Phosphate Bed (a matrix supported conglomerate with cm-sized clasts of rounded phosphate, some of which contain shark teeth), marks the boundary between the shallow-water limestones of the Burren and the overlying clastic fill of the Clare Basin. The Clare Basin, a Carboniferous-aged intracratonic basin that formed over the Iapetus suture, is filled by a deepwater to shallow-marine succession, encompassing the initial sand-starved Clare Shale, the basin floor fan system of the Ross Formation, the muddy slope of the Gull Island Formation and five delta cycles of the Central Clare Group; the lower two delta cycles of which form part of the iconic Cliffs of Moher.
Shortly after deposition, the Clare Basin was subjected to deformation during Variscan orogeny; this resulted in low-amplitude folding and tilting of the deposits, which can be observed in the obliquely exposed outcrops seen today along the western Irish coastline. The present day geomorphology of the region corresponds well to ancient Clare Basin paleoenvironments; the deepest point of the former basin lies overlies the Iapetus Suture within Shannon Estuary.
These sediments have been the subject of detailed geological study since the 1950’s, when geologist Mike Hodson began examining the glacially driven cyclic stratigraphy of the Clare Basin in detail. During the 1960s, Gillian Lewarne examined the condensed sections that formed during the highstands, noting that each contained a distinctive ammonoid assemblage that permitted accurate dating and regional correlation throughout the basin. Gillian’s pioneering detailed research on the biostratigraphy of the Clare Basin is still used today by researchers working there. Following completion of her PhD, Gillian Lewarne (later Sheehan) became the first female geology lecturer in Ireland, at Trinity College Dublin.
Current Research in the Basin
University College Dublin researcher and EGU SSP division member Emma Morris and is currently reexamining the deepwater sediments of the Clare Basin from a new perspective, looking at levee and overbank deposits associated with basin-floor channels. “Thin-beds in levees record more depositional events than the channel floor,” says Emma, “allowing us to reconstruct the processes forming these types of turbidite fans to a level of detail not possible in many other places” While the beautiful outcrops in County Clare make her work possible, there are also other factors that make the area a prime location for sedimentological research. “Between 2009-2011, Equinor and UCD initiated a behind-outcrop drilling program that drilled 12 cores, amounting to more than a kilometer of core for research and training purposes. These cores were drilled tens of meters from the outcrops and provide new insight on the deposits, highlighting the amount and variety of thin-bedded deposits within the Ross Formation, and locally aids with reconstructing the 3D geometry of depositional elements” says Emma. This core-to-outcrop correlation, combined with additional biostratigraphic control, the ease of access, and the relatively complete sedimentary record of a basin floor fan to slope to deltaic system, makes the region an attractive destination for student and professional field trips from across Ireland, Europe and beyond. “Conducting field work here is amazing” Emma notes “but the weather is unpredictable, the waves can get quite big, and the rocks are slippery and covered at high tide. Luckily the locals watch out for me! The UCD School of Earth Sciences has a great relationship with the people in the area — we run workshops in the local schools, lead geology walks several times a year and are developing art-science workshops on geology and ceramics. This is a rural area without a lot of infrastructure, and engagement is very important here, so we want to be ambassadors for science and make sure we give back to the community as much as we can.”
What’s in store for the future?
The area is already a UNESCO geopark, and is therefore the subject of significant geo-tourism. UCD research on Ross Formation will continue for the near and mid-term future, as there are still numerous sedimentological questions that need to be answered. In the long term, there are tentative plans to relocate one half of the slabbed behind-outcrop core to a dedicated facility in west Clare (the site is already in place) to serve as a destination for geology trips and training. A geo-tourism centre in Kilkee is also in the works, this will explain local geology to both scientists and the public. “There is going to be a lot of interest in the area and in these rocks specifically for years to come” Emma predicts.
About the authors:
Dr. Emma Morris (firstname.lastname@example.org) is a postdoctoral researcher at University College Dublin and is currently researching deepwater sediments in the Clare Basin. Dr. John Counts (email@example.com) – also a postdoc at UCD, is looking at modern systems as analogs for stratigraphic traps in the subsurface.
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