Summary of site:
The exposure at Bovevagh Old Church is a ‘window’ in the west bank of the Bovevagh River 21m long and 4m deep. It exposes glacial sediments, fossiliferous in part. Carbon-14 and amino acid ratios show the fossils to be older than the limits of these dating techniques. This site is 12km inland at a height of 95m above sea level.
The sediments are flat lying unfossiliferous gravels and sands, with beds of mixed grain sizes from mud to gravel. The section also exhibits thick deposits of mud which contain the fossils. The beds finger into each other in such a way that indicates they were all deposited at the same time. The most common fossils are tall-spired sea snails, microscopic foraminifera and ostracods. All are marine. The foraminifera include some that live today in waters off western Norway, while others indicate an environment distinctly similar to sea beds near ice caps.
Interpretation of the sediments suggests that they were deposited at a point where a stream transporting glacial debris of all grain sizes formed a delta as it entered a shallow sea margin. Taken with the fossil evidence, it is believed that the sediments date from the onset of the last glacial phase in Ireland, the Midlandian.
The obvious problem posed by this section is how sediments formed in a glacial sea are found almost 8 miles inland at a height of 95 m. Two models have been proposed:
- During glaciations, under ice loading by massively thick continental ice sheets, land masses settle further into the deep, more plastic, rocks of the Earth’s interior. In post-glacial times following melting, the land rises to reach a new equilibrium in its unloaded state. The suggestion here is that the glacial delta formed at a time of heavy ice loading and, following the melt, the deposits rose as the land gradually achieved its present elevation.
- Advancing glaciers gouged into a sea floor and carried massive slabs of sediment with their fossil content on to the adjacent landmass. As the glacier melted the sediments were released and washed by melt water streams into a shallow lake which eventually drained stranding them at the 95m contour.
The first model requires thick ice-caps at the start of the Midlandian for which there is little supporting evidence at present. The second explains the mixing of different climatic faunas more easily, but assumes ice transport without pulverising the fossils. Research continues.