Corrib sandstone.
Using laser analysis techniques never
previously applied to sandstone, researchers at University College Dublin
have discovered that sand grains in drill cores from the Corrib gas
field originated from Greenland and Canada, not from Ireland as previously
thought.
According to the findings published
in Geology, a leading scientific journal published by the Geological
Society of America, the sand grains were transported there by ancient
rivers, up to 1,000 km long, which drained a now-vanished super-continent
some 230 million years ago.
“With this new geological discovery,
we can highlight other areas off the western Irish seaboard where similar
sandstones to those from the Corrib gas field are likely to have been
laid down by these newly-discovered ancient rivers,” says lead researcher
Dr Shane Tyrrell from the UCD School of Geological Sciences. “And
because these sandstones are proven to act as good reservoirs for hydrocarbons,
this will help narrow the search for potential oil and gas accumulations
off the west coast of Ireland.”
The new technique applied by the UCD
geologists involves sampling individual grains using a laser. The laser
drills a small hole into the sand grains and a stream of gas carries
particles into a mass spectrometer which is used to measure the different
isotopes of lead (Pb). “By sampling with a laser we were able to measure
Pb isotopes in individual grains of the mineral K-feldspar, a common
component in sandstones” explains Dr Tyrrell.
“Rocks from different regions on
Earth can have distinct abundances of Pb isotopes so we could tell that
K-feldspar sand grains from the Corrib gas field could only have originated
from Greenland and Canada” says Dr Tyrrell. “Greenland and North
America were, of course, much closer to Ireland 230 million years ago,
as the Atlantic Ocean had not yet formed.”
