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HRS 914 Porth Wen faulted arch and sea

HRS 914 Porth Wen brickworks, Faulted arch
Graig Wen & Porth Wen SH 40259470 & SH 40009466
This site provides rare exposure of the unconformity between the Precambrian Gwna Group schists and quartzites (Greenly, 1919) and the Ordovician (Arenig) conglomerates of the Porth Cynfor Formation and the sandstones of the Torllwyn Formation above (Bates, 1972). The Ordovician conglomerates are spectacularly exposed on the west shore of Porth Wen (SH40259470), whilst the unconformity between the quartzites of the Gwna Group and the Ordovician conglomerates is well seen on the Graig Wen ridge to the west at SH 40009466. This unconformity is important in understanding the palaeogeography of this area in late Precambrian to early Ordovician times, a time span of around 100 million years. It demonstrates that the sedimentary rocks of the Precambrian must have been involved in uplift and erosion during a tectonic event prior to the area being transgressed by the sea and new sediments being deposited at the onset of the Ordovician Period. Since no intervening Cambrian rocks are to be found in this area, this limits the duration of this tectonic event." Source & acknowledgement www.geomon.co.uk
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Keywords:anglesey, cymru, faulting, faults, geology, geopark, wales, ynys mon

HRS 914 Porth Wen faulted arch and sea