Landscape
The rocks of the Burren
Information
Sheet No
How rocks are formed
5
B3
section Module
How the rocks of North Clare
were formed
All of the rocks in North Clare are
SEDIMENTARY ROCKS. They underwent
four major stages to produce the rock
formations we see on the surface today.
The Earth is a dynamic planet. Its surface, and
its interior, are constantly changing. One of the
effects of this is the formation of new rock.
Rocks are formed in three ways:
1. Through the laying down of sediment
particles and the remains of plants and
animals (PRODUCES SEDIMENTARY
ROCKS, e.g. limestone, mudstone,
sandstone)
2. Through the melting of existing rocks deep
underground and from volcanic activity
(PRODUCES IGNEOUS ROCKS, e.g.
granite, basalt)
3. Through the distortion of existing
rocks deep underground (PRODUCES
METAMORPHIC ROCKS, e.g. slate)
Step 1. Sediment particles such as silt, clay and
parts of plants and animals were deposited on
the sea floor. These sediments would have been
quite soft and pliable.
Step 2. The sediments were buried as more
sediment was laid down on top. The sediments
were compacted, the particles were pushed
closer together and water was squeezed out.
The particles became cemented together as salts
formed in between them. At this point, the
sediments had been turned into rock.
Step 3. The rocks of North Clare were gradually
uplifted (pushed upwards) by tectonic forces.
Weathering of
Rocks at Surface
Step 4. The rocks of North Clare were exposed
at the Earth’s surface and were eroded and
weathered by wind, rain and temperature
changes. This is why there are no siltstones,
sandstones or shales in the north part of the
Burren. They have been eroded away exposing
the older, underlying limestones.
Erosion &
Sediment
Transport
Deposition
of Sediment
Burial &
Compaction
Igneous Rock
Uplift
Sedimentary Rock
Metamorphic Rock
Crystallisation
of Magma
Deformation &
Metamorphism
Melting
Metamorphic Rock
million years ago
350
300
250
200
150
100
50
0
Burial
400
Laid down
on the
sea floor
Uplifted by
tectonic
forces
Exposed at
the Earth’s
surface
B3
section Module
Landscape
The rocks of the Burren
Information
Sheet No
How the limestones of North Clare
were formed
6
During the Carboniferous Period, in Earth’s
history (between 359 and 299 Ma*), the land
that would become Ireland was located 10ºS of
the equator (Ref: Module A1 Information Sheet
No. 4).
The Carboniferous limestones of the Burren
(and Ireland), were formed in a warm, shallow,
tropical sea. This sea was similar to the Bahamas
or Persian Gulf today.
The sea was full of marine life such as corals and
shellfish.
When these marine animals and plants
completed their natural life cycle and died, their
remains floated down to the sea floor. Their soft
body parts rotted away over time, leaving the
hard skeletons.
At the same time particles of calcium carbonate,
deposited out of the sea water, were also
building up in layers on the sea floor. The
hard skeletons of the marine plants and animals
became embedded in the layers of calcium
carbonate. Over a long time these layers
compacted to form limestone and the skeletons
of the organisms became fossilised within those
rocks.
Around 326 Ma, the sea deepened very rapidly.
The formation of the limestone ended abruptly,
as it can only be formed in shallow seas, where
the light reaches the sea floor.
Only about 500m of the Burren limestone is
visible on the surface. We have to go down
another 300m before we reach the base. It
took approximately 20 million years for all this
limestone to form.
Limestones are grey coloured
rocks made up mostly of calcium
carbonate (lime). They can be
dissolved slowly by rainwater.
* Mega Annum, or millions of years
B3
section Module
LANDSCAPE
The rocks of the Burren
Information
Sheet No
How the shales, sandstones and
siltstones of North Clare were formed
7
About 318 million years ago large volumes of
silt, fine sand and clay were quickly washed in
on top of the shales from large rivers that flowed
from the continent to the south west. These
sediments formed a massive river delta, similar
to the Mississippi today.
Direction of delta movement from ancient
continental land mass during late Carboniferous
Between 326 and 318 million years ago, the sea
that covered North Clare was deep, dark and
quiet; no animals lived there as there was very
little oxygen. There was an ancient continent
100–200 km to the south-west (off today’s coast).
Area covered
by the
ancient delta,
316million
years ago
This delta covered an area of several hundred
square kilometres, and stretched all the way
from north Clare (at Doolin) to Limerick and
Kerry.
As time passed, small amounts of very fine clay
particles, originating from rivers located on
that far away continent, were carried into the
deep sea basin by coastal currents. These clay
The Clare Shales are fineparticles settled on the seabed
grained, black coloured rock
on top of the limestones. They
s
that can easily be broken into
eventually became compacted
distinct layers. They lie on top into black shale rocks (known to
of the limestone in the south
geologists as the Clare Shales).
Burren and can be seen at
Poulacapple, Slieve Elva and
the Fisherstreet cliffs at Doo
lin.
e mouth
is formed at th
A river delta
sea. The
e it enters the
of a river wher
breaks
in by the river
water carried
angular
tri
reams, in a
up into little st
of an
the appearance
shape, giving
rry clay,
The streams ca
uprooted tree.
and
out with them
gravel and sand
reams
st
e
th
of water in
as the current
e
ar
ese sediments
slows down, th
twards.
ing the delta ou
dropped build
Ireland 330 million years ago