“While we stand holding hands
I’m living in the Ice age” – Joy Division
Dublin recently hosted INQUA 2019, allegedly the largest-ever gathering of geoscientists in Ireland. As I shuttled between parallel sessions for 6 days trying to absorb knowledge about Quaternary geology (an exhausting effort), I found myself thinking “this is all well and good, but what does it mean for the structural framework and geomanifestations” – because everyone working on the GeoConnect³d project is now conditioned to process every geological thought in those terms!
INQUA is the International Union for Quaternary Research and it meets for a mega-conference every four years to discuss all geoscience within the Quaternary Period. As the conference website said, “The Quaternary Period witnessed the evolution of modern humans against a back-drop of recurrent advance and retreat of glaciers and continental ice sheets, major oscillations in global sea level, abrupt reorganizations of global meteorological and oceanographic circulation patterns, and a range of other physical and biological adjustments to climate change.”
Quaternary geology in Ireland, at least to this neophyte, is largely about Pleistocene glaciations and Holocene bogs (peatlands). It’s not immediately obvious how that can be related to the bedrock geology of the structural framework. In other countries, the Quaternary includes volcanism and tectonics. But even in Ireland, it is the Quaternary Period and its processes that govern how the structural framework and geomanifestations are revealed to us.
Dispersal of glacially eroded sediment is a major landscape-modifying process of the Quaternary. In Geological Survey Ireland (GSI), we have been finding, more and more, when using our Tellus airborne radiometric data to map tills of contrasting lithology, that tills are transported surprisingly short distances from their bedrock source – a kilometre or two at most. Glacio-fluvial sediment, of course, can travel further, so it is important to understand the Quaternary geology when using soil or subsoil geochemistry to explore for a bedrock mineral occurrence, for example – one of our main types of geomanifestation.
Karstification of the glacially exposed Carboniferous limestones is another process operating through the Holocene, alongside growth of the peatlands, and probably also during the Pleistocene at deeper levels in the limestone basins. Karstification is very much a process guided by the fracture template in the rocks – the structural framework. Shallow karst systems influence both the supply and the vulnerability of our groundwater, and are a cause of flooding when excessive rainfall raises the water table. GSI is studying and monitoring our karst groundwater systems to ensure plentiful, safe drinking water and mitigate the flood hazard. Springs, turloughs and other karst features are important geomanifestations for us to relate to our structural framework. Deep karst systems are the target of current efforts in the GeoERA Hotlime project, seeking karstic fluid flow pathways in the otherwise ‘tight’ limestone for district heating schemes (and possibly electricity generation in other countries).
Concentration of radon is another hazard controlled by karst, particularly where it overlies buried granite. The magnetic data of our Tellus airborne survey are finding or delimiting these buried granites. It isn’t clear yet how unconformity surfaces or intrusive contacts will be handled in the structural framework, but we need it to be able to relate a karst system to an underlying contact with a radon-generating granite. There was some debate at the GeoConnect³d geomanifestations meeting in Warsaw back in June about treating anomalous sample values in, for example, a geochemical survey as geomanifestations. Why is a high value a geomanifestation but a low value isn’t? The anomaly needs to be related back to the occurrence or phenomenon, in these cases via a karstified fracture or a glacial sediment pathway – that is, through Quaternary geology.
GSI is planning a major new project in our cut-away peatlands that are too degraded for re-wetting, mapping their glacial sediments and bedrock mineral occurrences, karst systems and geothermal potential, as a contribution to the “Just Transition” – providing employment in other geological resources for communities affected by the switch to clean renewable energy. Perhaps I’ll get to talk about that in a future blog.
The Anthropocene got surprisingly little look-in at the conference. A few speakers using geochemical signals (=pollution) as proxies for time referred to it, but there was no debate, as far as could be gleaned from the programme, about designation as an Epoch. For all of us working in the GeoERA Energy theme, the aim is that the pollution signals displayed in the wiggle diagrams beloved by Quaternary climate-change geologists will become mere spikes as we transition to clean energy in the future.
Brian McConnell
GSI, Geological Survey Ireland
To view and download detailed geological mapping, go to https://dcenr.maps.arcgis.com/apps/webappviewer/index.html?id=de7012a99d2748ea9106e7ee1b6ab8d5&scale=0
The INQUA 2019 Dublin programme and abstracts are currently still available at http://www.inqua2019.org/online-programme/
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