Exposed Units: Post-Anglian Deposits
Conservation Status: Local Geological Site
The Post-Anglian Deposits exposed here have been classified as the Sutton Walls Member (which corresponds to the 4th terrace of the Lugg Valley Formation). This is the oldest and highest of the river terraces in the Lugg Valley. Most of the gravels have been removed by quarrying but some can still be seen on either side of the trackway into the hill fort and under the ancient earthworks.
The unit comprises fine, well-bedded gravels and sands, with the coarser material typified by well-rounded to sub-rounded gravels (fragments less than 5cm diameter). The gravels are interbedded with sands that exhibit common permanganate staining and calcite precipitation. Cross bedding is evident within the unit and indicates deposition by water current flowing SE and SW. The lithologies are dominantly derived from north of the site and include Silurian sandstones and siltstones, Old Red Sandstone limestones and sandstones, Lower Palaeozoic greywackes, rare coal clasts and Longmyndian (late Precambrian) igneous pebbles.
Terminology
Greywacke – A type of sedimentary rock characterised by sand and gravel particles contained within a clay matrix and its formation is commonly associated with gravity flows, such as turbidity currents. Note: Greywackes are not equivalent to conglomerates or breccias as the processes of formation are different.
Photos
General view of overgrown outcrop of Post Anglian sand and gravel at Sutton Walls Hill Fort.
Detail of the exposure at Sutton Walls.
References
Brandon, A., 1989, ‘Geology of the country between Hereford and Leominster’. Memoir Geological Survey Great Britain, Sheet 198, 62pp.
Brandon, A., 1982, Quaternary deposits of sheet SO 54 (Hereford NE); explanation of 1:10000 sheets SO 54 NW, NE, SW and SE with special emphasis on potential resources of sand and gravel, British Geological Survey, (WA/VG/82/4), 40pp.
Luckman, B.H., 1970, ‘The Hereford Basin’, in Lewis, C.A. (ed), The glaciations of Wales and adjoining regions, Longman Press, London, pp. 175-196.
Richards, A.E., 1998, ‘Re-evaluation of the middle Pleistocene stratigraphy of Herefordshire, UK’, Journal of Quaternary Science, vol. 13, 2, pp. 115-136.
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