Exposed Units: Post-Anglian Deposits (Worcester Member)

Conservation Status: Active quarry complexes – no public access

Two quarries operated by Tarmac Ltd. expose good sections of the post-Anglian Worcester Member, a sand and gravel terrace deposited by and around the ancient River Severn.

The terrace deposits at both sites are dominated by sand, with lesser amounts of gravel, silt and clay. Sand and gravel typically occur as well-bedded sequences, but gravel tends to be more common towards the base of the unit and is seen lying directly on the Triassic bedrock in places. The gravel beds are seen to truncate underlying sedimentary layers, suggesting that these layers have an erosive base. Imbrication and cross bedding is apparent in places, also indicating deposition in moving water. Individual beds also tend to get finer grained moving vertically upwards and may also be separated by a fine layer of silt or clay.

The features seen at these quarries suggest that the Worcester Member represents both river channel fill and sand/gravel bars that were laid down by a braided river system at the end of the Last Ice Age (the Devensian).

Terminology

Well-bedded – A rock unit that contains prominent sedimentary bedding (layering).

Imbrication – vertical stacking of clasts in a sedimentary rock formed by currents.

Photos

General view of one of the Tarmac quarries.

General view of extraction at one of the Tarmac quarries.

Active quarry face displaying alternating layers of sand and gravel.

Layers of sand and gravel containing a marked horizon of black peat, indicating that the sediments had been exposed at the surface long enough for vegetation to become established.

Sedimentary layering in a sand and clay succession within the sand and gravel unit.

Detail of the sedimentary layering in a sand and clay succession. The dark grey layer represents a band of organic material.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

References

Dawson, M.R. 1989, ‘The Severn Valley north of Bridgnorth’, In: Keen, D.H. (eds), The Pleistocene of the West Midlands Field Guide; Quaternary Research Association, Cambridge, pp. 78-100.

Maddy, D. & Lewis, S.G., 2005, ‘The Lower Severn Valley’, In: Lewis, C.A. and Richards, A.E. (eds), The glaciations of Wales and adjacent areas, 6, Logaston Press, Almeley, pp. 73-84.

Wills, L.J., 1938, ‘The Pleistocene development of the Severn from Bridgnorth to the sea‘,y Journal of the Geological Society, vol. 94, pp. 161-242.

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, London, pp. 156.

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