Waterloo Bay, Larne - Northern Irelandís Jurassic Park

The Late Triassic seismite in Northern Ireland, southwest England and south Wales

The base of the seismite at Waterloo Bay, Larne, Northern Ireland. The dark grey rocks in the lower part of the picture are mudstones which were fairly consolidated at the time of the earthquake and so were not deformed. The alternating mudstones (dark) and fine sandstones (paler) above were still soft and unconsolidated when the earthquake struck and so were intensely crumpled and deformed by the shock. Middle part of the seismite at Larne, Northern Ireland, showing how the deformation varies. Below the hammer the beds are barely disturbed. A little higher, to the left of the hammer, the layers are tightly folded, as are the darker rocks near the top of the picture where the folded layers have been weathered out. The pale grey rocks just above the hammer were so disturbed by the earthquake shock that nearly all trace of the original layering was destroyed.
Manor Farm Quarry, near the old Severn Bridge north of Bristol, southwest England. The lower quarry face exposes dark grey pyritic mudstones and sandstones of the Westbury Formation, which are undisturbed except near the top. The pale rocks above are mudstones and siltstones of the Cotham Member of the Lilstock Formation, which were intensely deformed by the earthquake shock. The paler band about halfway up the Cotham Member is a secondary limestone in which deformed layering is particularly conspicuous. Detail of the limestone band in the Cotham Member at Manor Farm Quarry, showing intensely deformed laminations. This limestone is not an original feature that was deformed by the earthquake, but was formed by carbonate cementation of calcareous silts after the earthquake shock had deformed them. The surrounding, much softer, siltstones and mudstones also are intensely deformed but usually this is difficult to see because of the effects of weathering.
St. Mary's Well Bay, near Cardiff, south Wales. The grey rocks in the lower half of the cliff are the upper part of the Lilstock Formation, which is overlain by pale brown limestones and grey mudstones of the Lias Group at the base of the Jurassic. The Cotham Member seismite is the pale band exposed near the base of the cliff. The Cotham Member seismite at St. Mary's Well Bay. Deformed laminations are clearly visible in the pale bed to the left of the hammer but were truncated by erosion at some time after the earthquake shock, producing the flat top to this bed. This erosion removed the upper part of the seismite, and the tsunamite which must once have lain above it. More sandstones and mudstones were then deposited on top of this erosion surface some time later but, being deposited after the earthquake, they are undisturbed.
Cookie Policy :: © National Museums Northern Ireland, 2007