Download The Geology How old are the rocks?

www.lancashire-geologists.co.uk
The Geologists’ Association (GA) was formed in 1858,
and actively promotes the study of geology to all
who are interested in Earth Sciences. The Lancashire
Group is a local branch of the GA which meets monthly
in Clitheroe. It is an informal, friendly and inclusive
organisation and welcomes members and guests
regardless of their level of geological knowledge. It
organises a programme of winter lectures and summer
field excursions which are open to all. The group
has very close ties with GeoLancashire and the two
organisations have worked together on a number of
projects in recent years.
The Ribble Way provides a ready-made excursion into many of the
geological landscapes of Lancashire and the Yorkshire Dales. These
short geotrails provide a way of exploring them. A geological guide
to the whole route is planned for the future.
River
Douglas
Ribble Way
Longton
Preston
Walk No1
River
Ribble
Lytham
St Anne’s
Brockholes
Walk No2
Preston
Ribchester
Walk No3
Blackpool
Dinckley
Walk No4
Longridge
Fell
Clitheroe
Clitheroe
Walk No5
River
Hodder
Fleetwood
Gisburn
Easington
Fell
Stainforth
Ordovician-Silurian
Settle
(See timeline below)
The Geologists’ Association (LGGA)
Gisburn
Clitheroe
Ribchester
POCKET GUIDE
POCKET GUIDE
POCKET GUIDE
Walk 2 Brockholes
Walk 3 Ribchester
Walk 4 Dinckley Gorge
Walk 5 Clitheroe
ARNSBERGIAN
CHOKERIAN
370 Million years
590
4500
DINANTIAN
(Carboniferous
Limestone)
515
445
415
370
280
235
135
195
NAMURIAN
(Millstone Grit)
Westphalian
(Coal Measures)
280 Million Years
Stephanian
2.5
PENDLEIAN
ORIGIN OF EARTH
Ribble alley
POCKET GUIDE
Walk 1 Preston
CAMBRIAN
5
POCKET GUIDE
ORDOVICIAN
POCKET GUIDE
SILURIAN
4
Ribble alley
DEVONIAN
POCKET GUIDE
CARBONIFEROUS
3
Ribble alley
The youngest solid rocks are of Permian
and Triassic age (290-205 Ma). These are
also sandstones but mostly reddish in
colour; they form the coastal plain of West
Lancashire and the Fylde.
PERMIAN
POCKET GUIDE
Overlying the limestone are Carboniferous
sandstones, gritstones and finer-grained
sediments of Namurian 'Millstone Grit'
age (326–312 Ma). Erosion over millions
of years has removed much of this rock
to form the dark moorland landscapes of
Bowland, Pendle Hill and Longridge Fell.
JURASSIC
Ribble alley
Walk 4 Dinckley Gorge
CARBONIFEROUS STAGES
The Ribble Way
Ribble alley
POCKET GUIDE
Walk 4 Dinckley Gorge
Ribble alley
Age/Million Years (Ma)
Whernside
Ribble alley
QUATERNARY
GeoLancashire
Ribble alley
PERIOD or SYSTEM
Ingleborough
Ribblehead
Ribble alley
POCKET GUIDE
CRETACEOUS
Horton in
Ribblesdale
Ribble alley
Ribble alley
65
Stainforth
Ribble alley
ROCKS occurring in the study area
Preston
TERTIARY
Settle
Geolancashire is a voluntary organisation founded in
1991 to protect and raise public appreciation of the
geology and landscapes of Lancashire. It has produced
a number of geotrail guides and other publications for
several sites across the county, details of which may be
found on the website.
Ribble alley
Rocks of Carboniferous age (360-290
Ma) covered the older rocks and now
dominate the landscape of the Ribble
valley. The river rises in an area of
the oldest Carboniferous rocks, the
Craven limestones, which have given
the Yorkshire Dales National Park its
characteristic landscapes. The sink holes,
caves and limestone pavements around
Ingleborough, Whernside and Pen-y-ghent
are produced by solution weathering of
these limestones.
TRIASSIC
Morecambe
Bay
www.geolancashire.org.uk
Ribble alley
2
Horton
Carboniferous
Limestone (Dinantian)
THE GEOLOGICAL TIMESCALE
Pendle Hill
1
Permo-Triassic
Millstone Grit (Namurian)
POCKET GUIDE
4
Ribble alley
Ribble alley
The Ribble valley's oldest rocks are
sandstones and limestones which were
laid down 410-510 million years (Ma) ago
in the Ordovician and Silurian periods.
They have been affected by folding and
faulting during their long history. Around
Horton-in-Ribblesdale and Stainforth
these processes uplifted the older rocks to
the surface, where today they are quarried
for roadstone at Horton and Ingleton.
Ribblehead
Age of Rocks
Ribble alley
This Ribble Valley Geotrail
Pocket Guide is just one of
5 pocket guides currently
available or in preparation
POCKET GUIDE
The Geology How old are the rocks?
Ribble alley
Millstone Grit (Gritstone), Rossendale
CAINOZOIC
ERA
MESOZOIC
THE GEOLOGICAL TIMELINE
ORDOVICIAN
Million Years Ago 515
w w w. g e o l a n c a s h i r e . o r g . u k
445
DEVONIAN
415
DINANTIAN
370
The most recent deposits are less than
25,000 years old. Thick layers of glacial till
(boulder clay) can be found especially on
the lower ground, while sands and gravels
CARBONIFEROUS
characterise the hill margins. Post-glacial
NAMURIAN
WESTPHALIAN
STEPHANIAN
PERMIAN
TRIASSIC
deposition includes alluvium on the river
PENDLEIAN
ARNSBERGIAN
280
235
195
floodplain, mud and sand in the estuary
Warley
Pendle
Sabden Shales
Wise
and blanket peat over the higher hilltops.
Grit
Grit
Limestone Pavement
Gordale Scar
Copster Green Sandstone
THE GEOLOGICAL TIMELINE
CARBONIFEROUS
GeoLancashire
RIGS Group
This is a Quick Response (QR) code. When
scanned with a smartphone (see below) it can
link you directly to a page on the GeoLancashire
website to provide you with more information
about this walk. To scan a QR code you will
need a smartphone or tablet with a camera
and an ‘app’ to read the code. You will also need access to the
internet on your device. There are many free QR scanner apps
available. You can download them from sites like www.qrstuff.
com and www.qrdroid.com
SILURIAN
PALAEOZOIC
Details of these may be found on our website. We plan to
produce a further five Ribble Valley geotrail guides for the
section from Clitheroe to Horton-in-Ribblesdale and details will
be available on the website as they are published.
PRECAMBRIAN
GeoLancashire
RIGS Group
GeoLancashire
RIGS Group
GeoLancashire
RIGS Group
GeoLancashire
RIGS Group
RIGS Group
GeoLancashire
TRIASSIC
205
PERMIAN
250
Million Years Ago
STEPHANIAN
290
WESTPHALIAN
307
NAMURIAN
DINANTIAN
312
ARNSBERGIAN
Sabden Shales
326
DEVONIAN
360
410
SILURIAN
ORDOVICIAN
440
510
PENDLEIAN
Warley
Wise
Grit
Pendle
Grit
Copster Green Sandstone
Maps used in this leaflet contain Ordnance Survey data © Crown copyright and database right 2012
Dinckley Leaflet A3 version 3.indd 1
10/01/2013 19:56
Ribble alley
RIGS Group
GeoLancashire
4
granite cobble
Walk 4
Dinckley Gorge
1
Walk 4 Dinckley Gorge ROUTE
The footpath leads to a hard rocky outcrop
of Warley Wise Grit at the bottom of the gorge
where the river is narrowest. This restriction
contrasts with the wide basin immediately
downstream known as the Sales Wheel which
has been cut in the softer Sabden Shales.
The rocks are
youngest to
the west and
they get older
upstream. The
rocks in this
little crag are
made of coarse
Slickensides
sand grains
and quartz pebbles stuck together. They were
deposited in a shallow, fast-flowing river channel
which was part of a large delta straddling the
equator. Also, look for ‘slickensides’ (see photo)
- polished surfaces with parallel scratches where
faulted rocks have slid past each other.
2 Walking upstream, two beds of mudstone can be
3
by the reddish, medium to coarse Copster Green
Sandstone which marks a return to deltaic deposition
in shallow water. Its generally uniform texture makes
it a good building stone and it has been used in many
of the cottages in Copster Green and Ribchester. St
Leonard’s Chapel in Old Langho is a good example.
Line
of Ge
4
ologic
al Se
ction
2
3 The shingle bank adjacent to the bridge contains
many different rock types. These include pebbles of
black chert sandwiched between grey limestone, various
sandstones, blue/green volcanic rocks and an occasional
granite cobble. All these stones have been transported
by the river but some – like the granite – were originally
brought here by ice from the Lake District and Yorkshire
Dales. They are known as ‘glacial erratics’.
1
1 kilometre
0
4 The rock beneath the pebble bank is Pendle Grit
Start: Car park east of Salesbury Hall at SD676357 Route: A footpath leads from the back of the car park
down to the river bank alongside a gully containing a
small stream. From Location 1, follow the footpath
upstream along the river bank crossing a number
of small streams. This section can be very muddy. At
the end of the woods a gate gives access to the field
beyond. Keep to the waymarked track through the
field to the suspension bridge. At this point you
can either retrace your route back to the car park or
follow the extension.
Distance: From car park to location 4 and return
is approximately 3.5km (2 miles) Entire circuit is
approximately 7.5km (4.7 miles)
sandstone and it provides sound foundations for the
bridge. Many of Preston’s best buildings such as the
Harris Museum are made of this stone which was quarried
extensively around Longridge and Waddington Fell.
Millstone Grit
All the rocks around Dinckley belong to the
Millstone Grit group and are about 230 million years
old. The coarse-grained gritstones were deposited
rapidly in a huge shallow water delta. They alternate
with thinner beds of finer-grained muds and shales
laid down slowly in deeper water.
250m
500m
750m
1km
Maps: OS Explorer 1:25K Sheet 287; OS Landranger
1:50K Sheet 103
Extension: Cross the bridge and follow the path
towards Trough House farm. Immediately before the
farm, watch out for the footpath marked with the
Ribble Way logo on the left. Follow the Ribble Way
through three fields; cross Starling Brook then take
the right hand path at the edge of the wood up to
above Hey Hurst. Cross the road to the house then
fork left downhill looking for a fingerpost in the field.
Cross the low ridge beyond then bear over to the
right to Haugh Wood and down to the river bank.
Follow this for half a mile to Dewhurst House. The
access road on the left leads to de Tabley bridge and,
turning left, the road back to the car park.
seen in small exposures on the river bank, separated
At the first location you will notice that the
prominent flat surfaces of the rocks are
dipping about 40 degrees downstream.
Dips & folds: the flexible rocks
Ribble alley
Since the sands which make up the rocks were
laid down on the horizontal surface of the sea
floor, the rocks must have been crumpled up later
into a series of huge folds, of which this section
is just a tiny exposure. You can get some idea
how big this fold is from the 2km cross-section.
The Warley Wise gritstone bed which you are
standing on dips to a low point north of the river
and emerges back on the surface in the north face
of Longridge Fell 12 miles to the North West.
NORTH WEST
NORTH WEST
Sabden Shales
bedding planes:
dipping about 40 degrees
POCKET GUIDE
Dinckley Leaflet A3 version 3.indd 2
Sabden Shales
Pendle Grit
(mudstone)
Warley
Wise Grit
Pendle Grit
(mudstone)
Warley
Wise Grit
SOUTH EAST
Pendle Grit
(mudstone)
Copster Green
(sandstone)
Pendle Grit
River
Ribble
(mudstone)
Copster Green
(sandstone)
River
Ribble
Pendle Grit
(sandstone)
Pendle Grit
(sandstone)
Bowland Shale
Group SOUTH
EAST
Bowland Shale
Group
2km Geological Section
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