1. References

Frosterley Marble is a dark grey to black limestone which has been used as an ornamental stone locally and internationally in churches and buildings such as Durham Cathedral.

Frosterley Marble is not a true marble as it is not a metamorphic rock (true marble is limestone which has recrystallised during thermal or regional metamorphism). Stonemasons use the term marble for some limestones which can take a high polish.

Much of the Frosterley Marble has been worked from quarries around Frosterly, in Weardale, County Durham. Frosterley Marble was formed during the Lower Carboniferous Period (325 million years ago) when the northern Pennines area was closer to the equator. The area alternated between a deltaic and tropical marine depositional environment. The Great Limestone Member was deposited in a marine environment and is in places, 22m thick. The Frosterley Marble forms a fossil rich band in this rock.

Frosterly Marble containing numerous fossil corals.
Image: Carole Rushall.

This photograph shows a boulder of the marble which contains abundant fossil specimens of the coral Dibunophyllum bipartitum. Unlike many corals which live as colonies, Dibunophyllum bipartitum was a solitary coral (it is now extinct). The solitary coral organism had a curved cone shaped calcareous skeleton in which lived a soft-bodied polyp whose tentacles captured organic matter from the sea water. When the organism died, the skeleton settled into the limy ooze on the sea floor which eventually formed limestone.

You can download an illustrated leaflet about Frosterley Marble produced by the North Pennines AONB Partnership by clicking here…

References

Stone, P., Millward, D., Young, B., Merritt, J.W., Clarke, S.M., McCormac, M. & Lawrence, D.J.D. (2010). British Regional Geology: Northern England (Fifth edition). Keyworth, Nottingham: British Geological Survey.

Scrutton, C. (ed) (2004). Northumbrian Rocks and Landscape : A Field Guide. (Second edition). Yorkshire Geological Society.

Our thanks go to Carole Rushall for providing this month’s article.

PLEASE NOTE: Tees Valley RIGS Group cannot be held responsible for the content of external websites.

©2011 Tees Valley RIGS Group.

Trilobite of the species Paradoxides.

They are one of the earliest creatures to have evolved hard-parts, presumably to protect against predators and, as such, are well-represented in the fossil record. The oldest rocks in the Tees Valley, the Carboniferous and Permian strata, may hold fossilised examples of these remarkable creatures. Trilobites have three parts to their bodies: the head or cephalon, body or thorax and tail or pygidium. They were marine animals which lived on the sea floor at a variety of depths.

Trilobites are so named for the three longitudinal lobes: 1 – left pleural lobe; 2 – axial lobe; 3 – right pleural lobe. The trilobite body can also be divided into three major sections (tagmata): 4 – cephalon; 5 – thorax; 6 – pygidium.

Trilobites survived until the end of the Palaeozoic Era, marked by the Permo-Triassic Mass Extinction which occurred around 250 million years ago.

This trilobite is Walliserops trifrucatus from Djebrl Oufaten in Morocco.

TVRIGS Group cannot be responsible for the content of external sites.

Sylvinite - This specimen from Russia.
Image courtesy of shakko.

These rocks form an economically important group of minerals. Sylvinite (a mixture of potassium chloride, sodium chloride and clay minerals) and halite (rock salt) are extracted by Cleveland Potash Ltd. from their mine at Boulby, near Staithes. The sylvinite lies within Permian strata over a kilometer below the surface. It is a little under 290 million years old and was laid down when a shallow ancient sea, dubbed the Zechstein – and which occupied an area between Northern England, through the North Sea Basin, to Poland – underwent several cycles of evaporation and transgression. Sea water comprises ~3.5% dissolved salts of which the bulk is sodium chloride or common salt. Evaporation yields successively limestone, anhydrite (calcium sulphate), halite and finally potassium and magnesium salts. Anhydrite was formerly mined and processed at Billingham on Teesside.

Cleveland Potash Mine, Boulby, Cleveland. UK

Evaporite deposits can flow under pressure producing salt-domes which disturb the strata through which the pass and internally exhibit complex folding. They also retain heat and may be a target for future geothermal energy projects.

Anhydrite - Once mined at Billingham on Teesside, UK.
Credit: Commons Wikimedia

1. Site Description
2. Site Map
3. Site Assessment
4. Surveyors

Grid Reference NZ 471 371
BGS Sheet 27
OS Sheet 93
Forwarded as RIGS 30/09/2003

Site Description

Site Status SNCI
Description of Geodiversity Deep gorge environment revealing exposures of Magnesian limestone. The gorge forms steep sides consisting of face of Magnesian limestone in a fluvial environment. Glacial erratics can be found in the stream bed.
Literature References The Geology of the Country Between Durham and West Hartlepool – Denis Smith 1967

Site Map

Site Assessment

Surveyors

Andrew Carter, John Waring

1. Site Description
2. Site Map
3. Site Assessment
4. Surveyors

Grid Reference NZ 524 344
BGS Sheet 27
OS Sheet 93
Forwarded as RIGS 30/09/2003

Site Description

Site Status SNCI
Description of Geodiversity Wave washed platform of Magnesian limestone. The exposure reveals examples of stack an pillar coastal features.
Literature References The Geology of the Country Between Durham and West Hartlepool – Denis Smith 1967

Site Map

Site Assessment

Surveyors

Andrew Carter