Information Board
OUTLINE OF THE GEOLOGY OF THE YOUR DALES ROCKS PROJECT
AREA
The Yorkshire Dales National Park and Nidderdale Area
of Outstanding Natural Beauty have a unique character, but have you
ever thought why?
It actually results from the rocks beneath your feet, the effects
of the ice ages and the way man has influenced the land since the ice
melted. Millions of years of earth history have culminated with the
landscape,
plants, animals, land use and buildings that make the area such a
pleasant
place in which to live, work and visit.
Outline Geology
(Click to enlarge)
© BGS (NERC)
ANCIENT ROOTS (Ordovician and Silurian Periods)
Nearly half a billion years old, the ancient roots of the Dales
are seen in the quarries and waterfalls of the River Doe upstream
from Ingleton. Further east around Helwith Bridge, and NW in
the Howgill Fells, rocks a little younger (420 - 450 million
years old) are present. These grey slates and sandstones began
life as muddy and sandy submarine flows in a deep ocean basin.
There they were buried under layers and layers of sediment, uplifted
into mountains, squashed, folded and changed for almost 80 million
years. Weathering and erosion then wore the rocks flat before
they were swamped by the tropical seas of the Carboniferous period.
TROPICAL SEAS (Carboniferous Period)
The warm seas deposited beds of Carboniferous Limestone onto the eroded,
steeply dipping older rocks producing a spectacular unconformity.
Shelly limestones packed with fossils and coral reefs prove that
around 350 to 335 million years ago the area was a reef-edged lagoon
in a tropical sea.
SWAMPS AND DELTAS
The tropical paradise did not last. By 330 million years ago mud
and sand periodically washed into the tropical sea from river
deltas. A cyclic repetition of events gave limestones, mudstones,
sandstones and coals. Called the Yoredale cycle by geologists,
it lends its name to “Your Dales Rocks”! As time
progressed, the influence of the river delta systems became greater
and thick sandstones and mudstones were laid down. Preserved
now as the gritstone moors, these rocks occur mainly to the east
in Nidderdale AONB. The youngest of these rocks is around 311
million years old. The rocks that remain have been faulted, folded
and injected with mineral veins. Many deposits have been eroded
away, taking with them clues to the events that formed them -
most of 300 million years of rock history is now missing.
BURIED IN ICE (Quaternary Period)
Taking a giant leap forward in time, to between 478,000 and 423,000
years ago, saw the whole area buried in ice. Massive erosion
occurred and much of the present day landscape was shaped beneath
ice-sheets and glaciers; this sculpting continued during another,
more recent, ice age (30,000 to 12,000 years ago). This ice also
moulded the gravelly clays of the valley bottoms into trains
of rounded hills called drumlins. The ice transported rocks from
far away and when it melted left behind exotic rocks called erratics
perched on different rocks.
