Whitman’s Hill Quarry

Exposed Units: Much Wenlock Limestone Formation, Coalbrookdale Formation

Conservation Status: Local Geological Site

Whitman’s Hill Quarry is located within a complex of faulted Silurian rocks just north of the Malvern Hills.

There are two rock formations present in the quarry: 12m of the Coalbrookdale Formation which forms the basal units, and 25m of the Much Wenlock Limestone Formation which sits above. The boundary between the two units represents a rapid decrease in sea levels in the area

The Coalbrookdale is characterised by olive grey to dark blue-grey silty mudstones with some calcareous siltstones and contain calcareous nodules and impersistent nodular calcareous beds. These beds are highly fossiliferous and contain a wide range of marine fauna, including brachiopods, trilobites, corals, calcareous algae, bivalves, orthocone nautiloids, crinoids and bryozoa. IN the eastern rock face at the bottom of the quarry are examples of spheroidal (‘onion skin’) weathering in the siltstones of the Coalbrookdale Formation. This weathering process has a produced ball-like structures ranging in size from 100mm to just over 2m.

The overlying Much Wenlock Formation is characterised by pale grey nodular to thinly bedded limestones. Some of the more nodular beds are known locally as the ‘Storridge Porridge’. The Much Wenlock Formation also contains small reef structures known as bioherms and one of these structures is found in the centre of the northern rock face

Within these two formations nine bentonite layers can be identified. These 2-3cm layers of fine clay are volcanic ash layers, formed when a volcano erupts and the ash is deposited on the surface of the sea. The ash sinks through the water column, killing much of the sea life. These soft bentonite layers are easily identified within the rock face as they have weathered preferentially in comparison to the harder limestones. Radiometric dating of uranium and lead in the bentonites yielded ages of around 425 million years for the deposition of these ash layers and demonstrates that the Coalbrookdale and Much Wenlock Formations were deposited around this time.

The nodular Much Wenlock Limestone (425 million years) was primarily quarried for aggregates and for the use in Lime Kilns. Eventually the underlying silty Coalbrookdale Formation (427 million years) was reached and quarry operations ceased, as the Coalbrookdale Formation is not a good aggregate material.

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

Whitman’s Hill Geodiversity Discovery Site – Earth Heritage Trust

and the Whitman’s Hill Geodiversity Discovery Venture.

Terminology

Fault: A line of weakness within the Earth’s crust along which movement and displacement occurs

Photos

Much Wenlock Limestone Formation overlying the Coalbrookdale Formation (Facing SE).

Bioherm (reef mass) in Much Wenlock Limestone Formation on east face of the quarry.

South East corner of the quarry. From top of picture: Wenlock Limestone Formation with bentonite layer, then bentonite layer, then the base of the Much Wenlock Limestone Formation (with bentonite layers) above Coalbrookdale.

Ball of spheroidal weathering (Onion-skin) in Colbrookdale Formation unit.

Quarrying at Whitman’s Hill during Summer 1977

References

Barclay, W.J., Ambrose, K., Chadwick, R.A., and Pharaoh, T.C., (1997), Geology of the country around Worcester, Memoirs of the British Geological Survey; HMSO, London

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

Fleischer, M. and Altschuler, Z.S., 1986, The lanthanides and yttrium in minerals of the apatite group – an analysis of the available data. Neues Jahrbuch Mineralogische Monatschefte, vol. 10, pp. 467-480.

Jackson, J., 1997, Glossary of Geology, Fourth Edition. American Geological Institute.

Penn, J.S.W., 1969, ‘The Silurian rocks to the west of the Malvern Hills from Clencher’s Mill to Knightsford Bridge’. Thesis, PhD, University of London, pp. 145.

Penn, J.S.W., 1971, ‘Bioherms in the Wenlock Limestone of the Malvern area (Herefordshire, England)’. Mémoires du Bureau de Recherche Géologique et Minières, vol. 73, pp. 129-137.

Reeve, F.A.E., 1953, ‘The structure of the Silurian rocks of the Malvern and Abberley Hills, Worcestershire’. Thesis, PhD, University of Birmingham, pp. 286.

Rosenbaum, M., 2009, Balls in the Bank, Earth Matters, vo. 6, pp10.

White, D.E., 1991, ‘Additional palaeontological and biostratigraphical contributions to the 1:50000 sheet 199 (Worcester) memoir’. Report of the British Geological Survey, WH/91/147R, pp. 4.

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

March 2011