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
||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.