LIMESTONE PAVEMENT EarthCache

Thanks to the John Muir Trust and the Scottish Access Code for permission for this Earthcache.

Formation

The formation of limestone pavements in the UK and Ireland began with the scouring of the limestone by kilometre thick glaciers during the last ice age. The weight of the ice removed the soil that lay over the limestone, and also fractured the limestone along existing horizontal surfaces of weakness known as bedding planes. Fractured rocks were stripped away leaving level platforms of limestone on which a thick layer of boulder clay (glacial till) was deposited as the glaciers retreated. Windblown material was then deposited on top of the boulder clay..

This external material is particularly important for soil formation, as limestone does not weather down into soil which would mean if there had been no glacial deposits, there would have been no soil development. From the flat limestone surfaces, the characteristic features of limestone pavement have been formed by water in the glacially deposited soil exploiting cracks and fissures in the rock such as bedding planes and joints (lines of weakness in the rock generally running at 90o to bedding planes).

Legal protection in the UK

Under the Wildlife and Countryside Act (1981) limestone pavement is subject to protection measures known as Limestone Pavement Orders. Areas of limestone pavement can be notified to the local authority (for example Cumbria County Council or the Yorkshire Dales National Park), who may then make a Limestone Pavement Order (LPO) to protect the pavement. Once an LPO is in place, removal of rock becomes a criminal offence under the Wildlife and Countryside Act and anyone taking pavement from a designated site can be prosecuted and fined, even if the rock they remove is loose or lying in a field.

The limestone pavement is situated near Loch an Daimh on the Schiehallion road is Dalradian Limestone which is 600 million years old and has passed through the Caledonian orogeny. The Dalradian is a sedimentary limestone which has been indurated. The pavement has deep channels called Grykes which have been worn by acid water flowing over and dissolving the calcium carbonate of the rocks. The ridges between Grykes are called Clints. The principal mineral in the rock is calcite but there are bands of mica, muscovite and biotite.

The CaCO3 that limestone is composed of and the way that it has formed controls the way that it erodes and the landforms that are created. The layers in limestone are separated by horizontal weaknesses called bedding planes and these are split by vertical cracks called joints that formed when the limestone dried. Water can flow down and along these weaknesses and this results in erosion along them. Limestone is a very hard rock but it is readily dissolved by weak acids in water by a process called carbonation or solution.

Rainwater combines with carbon dioxide in the atmosphere to form the weak acid, carbonic acid, and this converts the calcium carbonate in the limestone to calcium bicarbonate which is washed away down faults and bedding planes.

The limestone makes the soil calcium rich and provides a suitable habitat for certain lime-loving plants such as Rock Rose, Thyme, Wild Strawberry and Bottle Sedge. Rarer lime loving plants are Astragalus and Northern Felwort. The deep grykes are shelter for woodland plants where they are protected not only from the weather but also from grazing by sheep and deer. The whole area was at one time covered by the original Caledonian Pine Forest and the woodland plants are a remnant of this era. Dog's Mercury, Herb Bennet, Herb Robert, Ivy, Wood Anemone and Wood Sorrel are to be found in the Grykes.

Also deposited on the limestone platforms were Erratic rocks, ranging in size from pebbles to huge boulders. These Erratics, often rocks of a different type to the limestone, are one of the most visible indicators of glaciation on limestone pavements..

Karst scenery..

Limestone pavement is a type of karst landform. Karst is the word for an area of soluble rock in which the landforms are of a solutional nature (i.e. they are caused by water dissolving the rock ) where drainage is usually underground through rock fissures rather than in surface streams. Karst, a term originating from a limestone region in the former Yugoslavia, is derived from the Slovenian word kras, meaning a bleak, waterless place. It is used to describe a landscape containing erosional features such as bare pavements, subterranean water systems, dry valleys, dolines which are small to medium sized closed depressions with no surface outlet for water (hundreds of metres in diameter and tens of metres deep); and poljes which are large depressions with diameters of 1km upwards and depths of over 50m or so.

TASKS.

Your Earthcaching tasks are as follows:

Q1. Given that the Dalradian Limestone in the area of Schehallion is different in its makeup make up to that of the Carboniferous Limestone of Malham; what are the millions of things that are missing from Dalradion Limestone. A bonus point for answering why those millions of THINGS are missing.

Q 2. Along with “Clints” and “Grykes” there are other features that form within the pavement, describe one of them. Bonus points for naming 2/3.

Q3. Another geological formation can be observed on this pavement, please describe this feature and say how it got here. Observe the honeycomb weathering and give the explanation for this.

4.OPTIONAL TASK We all like to prove the integrity of our claim and authenticate it by including a photo of:

a. You at the site

b. Your GPS’r clearly showing the screen detail

c. Your GPS’r on one of the features

Your photos, whilst in no way obligatory, would be most welcome, as would your logged observations of this magnificent, geological feature.

Reference: Geology of Rannoch limestone-pavements.org.uk/geology