Was Ireland shaken by a giant meteorite impact

200 million years ago?

Evidence that the Earth may have been struck by a giant meteorite 200 million years ago has been found in rocks exposed around the shores of Co. Antrim, by Dr. Mike Simms, Curator of Palaeontology at the Ulster Museum. The results of this research have just been published in the journal Geology. (Read abstract of article)

The impact may have been several hundred km to the west of Ireland, but the earthquake it caused affected a vast area. Its effects are recorded in the rocks at Larne and at many other places around the UK.

Rocks exposed on the shore at Larne, Co. Antrim, show that the area was shaken violently by an earthquake 200 million years ago. Soft sand and mud on this ancient sea floor was deformed by the shock, with chunks then ripped up by a tsunami ("tidal wave") that swept across soon after, triggered by the earthquake.

Earthquake-shaken sediments like these, in which the originally horizontal layers have been bent and deformed, are known as seismites, and sediments deposited by tsunamis are called tsunamites. Part of the seismite and tsunamite on the shore at Larne can be seen in this photograph. (Click image for more detailed information and larger image) It is probably one of the best examples anywhere in Britain or Ireland.

The seismite seen at Larne is unique in that it can be traced across more than 250,000 km2 of the United Kingdom, from Magilligan in Co. Derry, eastwards to near Whitby, Yorkshire, and southwards across the Midlands and Bristol Channel to Dorset. No other seismite is known to cover such a vast area of the UK.

Larne is one of 3 sites that were examined in particular detail, with another near Bristol and a third near Cardiff. But the seismite has been found in quarries, cliffs and boreholes at more than 30 locations, indicated by each of the dots on this map.
(More detail....)

Earthquakes normally are caused by faults and volcanoes, but these are just not powerful enough to have affected the vast area covered by this 200 million year old seismite. At present the only thing that geologists believe could cause such a massive earthquake is an impact from a meteorite perhaps 4-5 km across.

Geologists have yet to find a giant impact crater of the right age but a thin layer enriched in Iridium, an indicator of meteorite impacts, has been found in rocks of the same age in the eastern USA. [Olsen, P.E. et al., 2002: Ascent of dinosaurs linked to an Iridium anomaly at the Triassic-Jurassic boundary. Science, vol. 296, pp. 1305-1307].

There was a global mass extinction 200 million years ago, at the end of the Triassic Period, which killed off many different types of animals and plants, both on land and in the sea. Could this mass extinction have been caused by the effects of a giant meteorite impact? Was the catastrophic earthquake recorded in the rocks at Larne and across the UK caused by this giant impact? Much more work needs to be done before we can be sure, but whatever caused the earthquake it was certainly a unique event in the history of Britain and Northern Ireland.