Barnt Green Road Quarry

Exposed Units: Lickey Quartzite, Barnt Green Volcanics

Conservation Status: Local Geological Site

Access: Open to public

Barnt Green Road Quarry is located next to the Barnt Green Road at the eastern edge of the Lickey Hills Country Park and exposes the lowest part (but not the base) of the Lickey Quartzite Formation.

The quartzite in Barnt Green Road Quarry is pale grey to purple in colour and interbedded with thin shale/mudstone layers which could possibly be volcanic tuffs. The quartzites are immature to submature and forms flaggy beds 3-6cm in thickness that are separated by layers of sandy shale. Some of the quartzite bands are soft in texture and are composed of quartz and volcanic or tuffaceous material. The shaley layers are predominantly purple in colour and micaceous. The top most beds of the quarry face are sharply bent over from the south-east to the north-west in small recumbent folds. These overturned folds are well presented in Lapworth’s 1882 paper.

In the south-east corner of the quarry, to the left of a small normal fault, it is has been proposed that the boundary between the Lickey Hill Quartzite Formation and the Barnt Green Volcanics Formation can be found (Lapworth, 1882). The amount of volcanic material seems to increase towards the fault; this implies the boundary with the Barnt Green Volcanic Formation is close by. However, from studying the geological map, the Barnt Green Volcanic Formation is found much further to the south. The only way to determine whether the boundary is there is through excavation work.

The age of the formation has been the topic of much discussion, with many early authors like Lapworth, Boulton and Humphries placing the formation in the Cambrian. However since the use of radiometric dating to date rocks the formation has been placed in the Ordovician period, 510 – 439Ma. The Lickey Quartzite Formation itself was not dated as it contains no components used for radiometric dating; however the Barnt Green Volcanic Formation, believed to underlie the Lickey Quartzite Formation has been dated to the Tremadoc, 510Ma, thus giving a rough date for the Lickey Quartzite Formation.

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

Terminology

Volcanic Tuff – Consolidated volcanic ash.

Micaceous – A rock composed of a high percentage of the mineral mica (silicates of aluminium and potassium, and with magnesium and iron in the dark varieties).

Fold – A curved or angular shape of an originally planer geological structure.

Axial surface – The imaginary surface within a fold passing through and comprising all the hinges of the folded bedding surfaces.

Radiometric dating – A technique used to accurately date rocks using naturally occurring radioactive elements, such as Uranium.

Photos

Lickey Hills Lower Quarry.

Diagram showing relationships between hinge line, limbs and axial surface of a recumbent fold. In a recumbent fold, the hinge line and axial surface are both horizontal i.e. the structure is ‘lying down’.

Quarry face at Lickey Hills Lower Quarry.

Diagram showing the relationships between the limbs and axial surface of an overturned fold. In an overturned fold, axial surface and both fold limbs dip (tilt) in the same direction.

Picture taken in the late 19th century (possibly taken by Lapworth) of the overfolding of the quartzite. Courtesy of the Lapworth Museum.

References

Boulton, W.S. 1928. The geology of the northern part of the Lickey Hills, near Birmingham. Geology Magazine, 65, 255-266.

British Geological Society (1996) Geology of the country around Birmingham. Sheet 168 (England and Wales), 1:50,000.

Eastwood, T. et al. 1925. The geology of the country around Birmingham. British Geological Survey Memoir.

Hardie, W.G. 1971. Lickey Hills, in Hardie, W.G. et al. Geology of the area around Birmingham (2^nd Edition). Geologists Association Guide. (1) 12-15.

Hardie, W.G. 1991. A guide to the rocks and scenery of the Lickey Hills. B’ham: Lickey Hills Society. 27pp.

Humphries, J. 1897. Geology of the Lickey Hills. Transactions of the Worcestershire Naturalists Club, for 1897-9. 50-52.

Humphreys, J. 1922. The Lickey Hills. Transactions of the Worcestershire Naturalists Club, for 1918-1922. 370-373.

Lapworth, C. 1882. On the discovery of Cambrian rocks in the neighbourhood of Birmingham. Geology Magazine, 563-566

Old, R.A. et al. 1991. Geology of the country around Redditch. British Geological Survey Memoir.

Richardson, L. 1906. The geology of the Lickey Hills, near Birmingham. Cotswolds Naturalists Field Club, 7pp.

Tucker, M.E. 1991. Sedimentology Petrology (2^nd Edition). Blackwell Scientific Publications.

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

March 2011