Linton Quarry

Exposed Units: Much Wenlock Limestone, Upper Ludlow Shales, Downton Castle Sandstone

Conservation Status: Local Geological Site, SSSI

Access: Private Land

An interesting site that shows the relationship between the Wenlock, Ludlow and Pridoli units.

Starting at the bottom of the quarry and working upwards:

The Much Wenlock Limestone Formation (known locally as the Gorsely Limestone) is approximately 6m thick throughout the quarry. It is a thickly bedded limestone with a nodular appearance containing some irregular bands of silty material. Many fossils can be seen; brachiopods, corals and crinoid ossicles. At the top of this bed there is an unconformity represented by an irregular eroded surface. The unconformity represents a period of approximately 2 million years of missing rock units, in this case the Lower Ludlow Shales Group and Aymestry Limestone Formation.

The Upper Ludlow Shales is a much finer grained, bluish-grey limestone unit and is approximately 3.5m thick. The unit at this site is subdivided into the Lower and Upper Siltstones, which are separated from each other by the Lower and Upper Phosphatised Pebble Beds. The Lower Siltstones (approximately 1.4m thick) contain mainly shelly fauna in which brachiopods can be found.  Graptolite fossils have also been recorded at the site.  The Lower Phosphatised Pebble Bed is very thin (approximately 2-13mm thick) and consists of small brownish pebbles of siltstone and mudstone. The Upper Siltstones (approximately 2.1m thick) shows cross lamination and there are many fossiliferous layers which have weathered to a yellow-brown decalcified ‘rottenstone’. Fossils include brachiopods as well as acritarchs. The Upper Phosphatised Pebble Bed (approximately 2-7mm thick) contains rounded phosphatised siltstone and mudstone pebbles. This phosphatised bed is the equivalent of the Ludlow Bone Bed, found elsewhere on the Midland Platform.

The Downton Castle Sandstone Formation can be best seen on the western terrace. It is approximately 8m in thickness and consists of a lower shaley siltstone (approximately 1.4m thick) which shows fine laminations and cross bedding. Fossils found in the bed include brachiopods and plant remains. The Upper Sandstone (approximately 4.6m thick) is pale orange with darker spots and cross beds (ripples). The lower beds are thought to be marine, transgressing into the terrestrial sandstone.

This site is part of the Community Earth Heritage Champions Project.

Terminology

Unconformity – A boundary separating two or more rocks of markedly different ages, indicating a gap in geological time.

Acritarchs – Fossils of micro-organisms that are similar to phytoplankton and zooplankton.

Photos

General view of the quarry, facing East.

Bedding and fine laminations in the Upper Ludlow Shales at Linton Quarry

Unconformity between the Gorsley Limestone and Upper Ludlow Shales (facing SE) shown by the dashed yellow line.

Cross-bedding in the Downton Castle Sandstone.

References

Aldridge, R et al. 2000, British Silurian Stratigraphy. Geological Conservation Review Series Volume 19. Joint Nature Conservation Committee.

Brenchley, P.J. and Rawson, P.F. 2006, The Geology of England and Wales. The Geological Society. The Geological Society Publishing House, Bath.

Cherns, L. 1980, Hardgrounds in the Lower Leintwardine Beds (Silurian) of the Welsh Borderland. Geological Magazine, Vol.117, no.4, pp. 311-408.

Lawson, J.D. 1954. The Silurian Succession at Gorsley (Herefordshire), Geology, Vol. 91, pp. 227-237.

Lawson, J.D., Curtis, M.L.K., Squirrell, H.C., Tucker. E.V. and Walmsley, V.G., 1982, The Silurian Inliers of the South-Eastern Welsh Borderland. Geologists’ Associations Guide No.5. The Geologists’ Association, London.

Squirrell, H.C. and Tucker, E.V., 1982, ‘Woolhope and Gorsley’, in Lawson, J.D., Curtis, M.L.K., Squirrel, H.C., Tucker. E.V. and Walmsley, V.G. (eds.), The Silurian Inliers of the south-eastern Welsh Borderland’, Geologists’ Association Guide No. 5, The Geoogists’ Association, London.

Woodcock, N. and Strachan, R. 2000, Geological History of Britain and Ireland. Blackwell Scientific Publications.

Worrsam, B.C. et al. 1989, Geology of the country around Tewkesbury. British Geological Survey Memoir.

March 2011