Geology of Portland Park

The unique Magnesian Limestone found at the park supports many rare plant species, creating an area of fascinating natural history. What's the story of what lies beneath?

Ancient Rocks

The solid geology of Nottinghamshire occurs as a series of north-south trending outcrops with the youngest in the east and the oldest in the west of the county. Indeed to the west of Portland Park in the Erewash Valley lie the oldest rocks in Nottinghamshire.

These rocks belong to the Upper Carboniferous Period (354-290 million years old) and form the Upper Carboniferous Coal Measures.The mudstones, coals and sandstones of these Coal Measures were overlain by the Magnesian Limestone formed in the succeeding Permian Period (290-248 million years old).

Magnesian Limestone is so named because the rock contains the magnesium rich mineral 'dolomite' and is now commonly referred to as 'dolomitic limestone'. This also gives it it's distinctive colour.

The magnesium-rich limestone was deposited on the edge of a shallow marine sea that once covered this part of Europe. As a consequence the rock is composed from the shells of the millions of sea-creatures and corals from the time.
Magnesian Limestone outcrop at Portland Park

Magnesian Limestone outcrop at Portland Park - formed over 250 million years ago

A Unique Environment

Portland Park is located on this unique band of Magnesian Limestone, part of a thin, broken strip between west Nottinghamshire and County Durham which is no more than five miles wide. Indeed the site is so rare this shallow escarpment only outcrops in two areas of the world; Portland Park and a similar section in Poland!

The limestone supports important 'calcareous' vegetation that is also both rare in Nottinghamshire and uncommon in Britain generally.This enables many rare plant species to grow, creating an area which is abundant with fascinating natural history and making it a Site of Special Scientific Interest (SSSI).
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Common Spotted orchid

Common Spotted Orchids flourish in the unique calcareous environment of Portland Park.

Magnesian Limestone Section

Magnesian Limestone
A section of the unique Magnesian Limestone found in Portland Park - now commonly referred to as Dolomitic Limestone because of its high dolomite content compared to usual limestones. The best place to see this is behind the Visitor Centre, the site of a now disused old rifle range.

Geological Map of Portland Park

The Geology of Portland Park

What is Magnesian Limestone?

Magnesian Limestone is so named because the rock contains the magnesium rich mineral 'dolomite' i.e. calcium magnesium carbonate. This important rock has many uses including aggregate for road building and construction and the production of agricultural lime. Historically the site was quarried and traces of this past can be seen particularly the 'Humps and Hollows'.
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Where is it?
The best place to see examples of magnesian limestone in the park is behind the Visitor Centre in the now disused old rifle range (see map above).
Magnesian Limestone outcrop in the old rifle range
Further information and resources
Related links
Flora of Portland Park
Birds - Chaffinch
Birds of Portland Park
Fauna - Grass Snake
Fauna of Portland Park
Geology - Dolomitic Limestone
Geology of Portland Park
Walks - Bottom path, Portland Park
Walks of Portland Park
History - Bess of Hardwick
History of Portland Park