Event Report: Cumbrian Limestone Pavements

Cumbrian Limestone Pavements – Helleborines to Kamenitzas by Peter Standing

Annual Joint Meeting of the Cumberland Geological Society and Carlisle Natural History Society
At Tullie House Museum, Carlisle, January 24th 2018.

Peter first explained his lifelong interest in limestones which progressed from schoolboy caving to a busy five years with the University of Bristol Spelaeological Society exploring new caves in the Mendips, South Wales and County Clare. At the time Bristol had one of the leading karst research centres in the world. He also managed to fit in a medical degree but, after retirement from general practice at 60, he returned to limestones by studying geography at Lancaster University followed by a Masters on Cumbrian landscapes with dissertations on pavements. His lecture built on the joint attraction of these unique landscapes to geologists and natural historians.

Outcrops of Carboniferous limestone encircle most of the Lake District with spectacular pavements at Great Asby Scar, Holme Park, Hutton Roof, Beetham and Gait Barrows (just over the Lancashire border). All of these pavements are formed on beds of Asbian Limestone formed during glacio-eustatic cycles between 335 to 331 million years ago. These formations have many different local names but around Morecambe Bay they are called Urswick Limestone, following the 1941 classification of Rose and Dunham.
At Holme Park Quarry we saw ancient palaeokarst pavement with pits formed around the roots of early Carboniferous trees. At Trowbarrow Quarry similar palaeo-pavements have been turned from horizontal to vertical as part of a Variscan monocline with palaeopits still recognizably preserved.
The formation of the pavements we see today in Cumbria depends on four things – durable beds of limestone like the Urswick, glacial scour by late Devensian ice sheets, structural weaknesses presented by joints and a generous rainfall for dissolution both under soil cover and sub-aerially.
Karren is the name for small scale dissolution features on pavements of which the best known are clints (solid platforms), grikes (vertical fissures around clints), runnels (surface drainage channels) and kamenitzas (depressions or pans). Karren features formed by subaerial erosion tend to be rough whereas those which have developed beneath soil have smooth surfaces.

The microclimates of grikes vary with orientation which affects brief duration of exposure to sunlight and the mean depth of flora. Shade tolerant ferns and mosses flourish. Botanists Stephen Ward and David Evans carried out a 3 year survey for the Nature Conservancy of 537 UK pavements and in 1976 published the classic paper ‘Conservation assessment of British limestone pavements based on floristic criteria’. Gait Barrows came first in the country in their floristic index league table but nearby Cumbrian pavements at Hutton Roof, Lancelot Clark Storth and Whitbarrow featured in the top ten.
After questions, Peter Standing was warmly thanked for his fascinating and beautifully illustrated talk.