A small group had an excellent visit to this limestone quarry, now a Nature Reserve in Lancashire close to RSPB Leighton Moss. The quarry was worked from 1857 for approximately 100 years and was close to the railway line, and produced tarmac. Some of the last buildings were removed in the 1970s.
Diagrammatic representation of the Geology of the Quarry.
Prior to quarrying there was a hill with a steep, scarp side to the east and a slope to the west. Here the horizontal limestone beds formed in the early Carboniferous times had been tilted to the east by the collision of tectonic plates forming the super continent Pangea, locally it is known as the Silverdale Disturbance extending from Storth in the north to Trowbarrow.
Visually this means the layers of rock have been turned just over 90 degrees and are now vertical, thus one layer of very useful limestone, the Upper Urswick formation was available for quarrying, but has also meant there is considerable visible geology.
Colonial coral and “stick” trace fossils
Fossils in some of the later rocks represent colonial coral, indicating warm shallow seas, and trace fossils known here as “stick” fossils, which represent the filled in trails of early creatures.
Trowbarrow Quarry vertical walls and floor
Fluting, current day weathering at the top of the face
The most obvious sight in the quarry is the large vertical walls of remaining rock often used as climbing walls.
Here more fossils can be seen but also evidence of current weathering, fluting, where water with dissolved carbon dioxide making it slightly acidic has grooved the rock face.
The ancient land surface with soil remnants
The Red Wall
At the north end of the quarry is an ancient land surface looking almost like the limestone pavement we are used to seeing, the reddening is from the iron in the soil and is known as a Paleokarst, a fossil limestone pavement.
Round on the west side is an even larger red wall, again an ancient land surface with large depressions possible representing ancient tree roots. These surfaces indicate the warm sea level rose and fell at times leaving the surface exposed to warmer drier climates.
Contrasting limestones, rubbly right and vertical blocky on the left
Looking at the various exposed limestones there is considerable difference in their appearance, some being broken rubble others being large and massive blocks. These reflect the different depths of deposition and wether the conditions were stable, but also the effect of later pressures on the differing rocks
Standing in the Trough, the absent Woodbine Shale
The trow of Trowborough comes from the presence of The Trough which also extends from Storth to Trowbarrow and is formed by the weathering away of a shale layer, Woodbine Shale, mudstone formed by a change in the environment and the deposition from deeper muddy water drained from land in the north. On either side of this weak rock much harder limestone was deposited and the differential weathering has left the Trough. Once again climate and sea level changes perhaps due to changes in glaciation at the South Pole have been rendered visible.
The floor of the quarry was a further delight with many of our familiar limestone flowers, even the buds of Bee Orchids. Yes, there were some rock climbers enjoying the area too. Lunch was taken under the large “shelter rock” just as the quarry men used to do.
An excellent day out.
Leader Josephine Drake
Information available
https://www.arnsidesilverdaleaonb.org.uk/uploads/2016/04/guide_to_trowbarrow.pdf
Words and pictures by Josephine D
Content loaded by Keith P
