Download The Carboniferous Limestones of the Lake District

The Lake District Sinks
Beneath the Waves
After the Caledonian mountains had been worn down by erosion, in the
Carboniferous period about 350 million years ago, northern England was
flooded by a warm tropical sea.
This shallow sea was rich in life, including corals, sea lilies, the early
ancestors of squid, and shellfish superficially similar to cockles and
mussels, together with early fish and even sharks. With no high land nearby
to provide other sediment, limestone accumulated in shallow water from
material secreted by algae and from shell fragments, in much the same
way as it does on the Bahamas Banks today. Many millions of years later
in the Carboniferous period, the seas began to retreat and rivers brought in
sediment to build up deltas on top of which lush forests grew in swamplands.
The thick vegetation was buried and compacted to form coal, which was
mined for many years in the Whitehaven area.
Although the Carboniferous
limestones do not occur in
the central Lake District, they
are widespread around the
flanks of the region and were
originally deposited across the
entire region. Uplift of the heart
of the Lake District meant that
they have now been removed
by erosion from above the
rocks that we see out of the
window today.
Limestone is extensively
quarried around Cumbria for
use in cement and aggregates,
and we have found that some
limestones ring well and can
be used in instruments. If you
look at the polished surfaces
of some of the keys you will be
able to see fossils of the corals
that lived in that long past
tropical sea. Near Barrow-inFurness, some limestone beds
became replaced by iron oxides
after they had been buried, and
it was mining of this ore for iron
that led to the development
of steel and related industries
around Barrow.
Limestones almost always develop where there is warm, clear water with little sand or mud being brought
in, as this would swamp the supply of calcium carbonate from organisms. Shallow seas are also important
because of the greater biological productivity near the surface.
Image courtesy of Ove Hoegh-Guldberg, Centre for Marine Studies, University of Queensland
Just as today, the tropical seas in which the
Carboniferous limestones were laid down were
home to a wide variety of species, including many
that produced shells.
Image courtesy of Ove Hoegh-Guldberg, Centre for Marine Studies,
University of Queensland
Modern day mangrove swamps give an excellent
impression of how northern England would have
appeared later in the Carboniferous when coal beds
began to form. In detail the plants are quite different,
but the thick, tangled vegetation and matted
root systems sometimes invaded by the sea are
probably very similar.
Image courtesy of Rob Mackay-Wood, Centre for Marine Studies,
University of Queensland
Funded by:
Ruskin Rocks Team and School of Earth and Environment, University of Leeds
A collaborative project led by the University of Leeds
Further information at www.ruskinrocks.org.uk