On Saturday June the 16th members of CGA met at Whiting Bay near Ardmore, Co. Waterford for the annual end of year fieldtrip. Dr. Ed Jarvis was our leader.
From the carpark at Whiting Bay we walked South past cliffs of Quarternary deposits to our left, which have collapsed in several places due to undermining of the cliff base. The material in these cliffs has a high clay content and contains Ailsa Craig granite transported from Scotland during the last ice age.
We walked along the northern limb of the anticline of which the lowest beds belong to the Crows Point formation. These are Sedimentary Rocks of the Lower Carboniferous Period. Approaching the top of the anticline there is a “marker bed”- a quartz pebble conglomerate- containing nicely rounded quartz pebbles. This is a distinct bedding indicating a very different environment. The formation of this conglomerate is associated with a transgression event where rising sea levels transported a deposit of off-shore pebbles ashore.The youngest rocks are at the centre of the anticline and weathering and erosion has exposed the older rocks almost symmetrically on either side.
There was a ‘wow’ reaction at our next stop which were the ‘megaripples’ of the lower carboniferous period. Ed referred to these as the best examples in Europe. These ripples were formed under the sea by a high energy event – probably a tsunami which may have occurred as a result of early activity of the Variscan Orogeny. The length of each ripple was approx 50 cm. and each had a double peak due to the work of large scale eddies during this event.
Goat Island was our final stop where we investigated an excellent example of ‘monoclinal folding’. This type of folding has high dip sandstone cliffs at the back of the beach and low dip limestone towards the shore. There are some excellent examples of normal faulting in the sandstone cliff which because of the near horizontal bedding are easy to observe.
Finally on close examination of the younger limestone we found micro fossils of crinoids and brachiopods. The limestone showed evidence of solution weathering. Ed pointed out layers of chert within the limestone. Chert forms as a mass of cryptocrystalline silica from skeletons of micro fossils. Chert is much harder than limestone and so we could see an excellent example of differential erosion.
We completed our trip at 4.p.m. and all agreed we had seen many excellent examples of geological importance from our megaripples to monoclinal folding to micro fossils. A great trip. Thanks to Ed and the CGA committee.
