Exposed Units: Aymestry Limestone
Conservation Status: Site of Special Scientific Interest (and others)
The quarries found on the Croft Castle Estate sit within Fishpool Valley. Both of the quarries display fine examples of the Aymestry Limestone Formation. The quarries are large, with the northern quarry being long and narrow at 40m long and 8m deep, with 3-4m high rock faces. The southern quarry is 30m wide, 40m deep and has rock face that reaches 5-6m.
Both quarries display bedded nodular clay-rich limestones and calcareous (calcium carbonate rich) siltstones that are typical of Aymestry Limestone Formation exposures. The nodules are more pronounced in the northern quarry, where weathering has eroded away much of the lime cement, which allows for the shapes of the nodules to be seen more clearly. Both quarries also contain thin layers (4-6cm thick) of calcareous siltstones. These thin siltstones are separated by approximately 2m of the nodular limestones. Due to their soft compositions they have weathered preferentially in comparison to the harder limestones and therefore can be easily identified.
The beds in the northern quarry are dipping (tilting) approximately 6˚ to the south-east. This dip is attributed to the fact that the rocks in this area are sitting on the southern limb of large anticlinal fold. This structure is known as the Ludlow Anticline, formed during a period of mountain building in the mid-Devonian Period (391Ma).
This site is part of the Community Earth Heritage Champions Project.
Terminology
Fold – A curved or angular shape of an originally planer geological structure.
Anticlinal fold – A fold closing in any direction in which the older rocks occupy the core.
Photos
Nodular limestone beds in the Aymestry Limestone at Croft Castle Quarry 1.
Back wall of Aymestry Limestone at Croft Castle Quarry 2.
Nodular limestone beds in the Aymestry Limestone at Croft Castle Quarry 2.
Community coral fossils at Croft Castle Quarry 1.
Solitary coral fossils as Croft Castle Quarry 1.
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.
British Geological Society. 2000. Ludlow, England and Wales Series Sheet 181 (Provisional Series). Solid and Drift.
Cross, P. 1966. The Glacial Geomorphology of the Wigmore and Presteigne basins and some adjacent areas. Thesis, MSc, Univ London. 89pp.
Holland, C.H. & Lawson, J.D. 1963. Facies patterns in the Ludlovian of Wales and the Welsh Borderland. Liverpool Manchester Geological Journal, 3 (2), pp269-288.
Lawson, J.D. & Straw, S.H. 1956. The Ludlovian rocks of the Welsh Borderland. Advanced Science. 12 pp563-570.
Lawson, J.D. 1960. The succession of shelly faunas in the British Ludlovian. Report on the International Geological Congress, Norden (XXI session), (7), pp114-125.
Lawson, J.D. 1973. Facies and faunal changes in the Ludlovian rocks of Aymestrey, Herefordshire. Geology Journal. 8 (2), pp247-278.
Lawson, J.D. 1999. Watkins’ benthic associations in the Ludlow series of the Welsh Borderland. in BOUCOT, AI and LAWSON, JD (EDS), Palaeocommunities: a case study from the Silurian and lower Devonian. Cambridge: Cambridge Univ Press; World and regional geology series. 11 (29), pp388-394.
Newell, G. 1966. A faunal and sedimentary study of the Aymestry Limestone and adjacent beds in parts of Herefordshire and Shropshire. Ph.D thesis, Univ. Manchester.
Siveter, D.J. et al. 1989. The Ludlow anticline and contiguous areas: a shelf marine to non-marine transition. in Siveter, D.J, Owens, R.M. and Thomas, A.T., Silurian field excursions: a geotraverse across Wales and the Welsh Borderland. National Museum of Wales, Geological Ser. 10, pp37-70.
Watkins, R. 1979. Benthic community organization in the Ludlow Series of the Welsh Borderland. Bulletin British Museum Natural History (Geology). 31, pp175–280.
Woodcock, N. and Strachan, R. 2000. Geological History of Britain and Ireland. Blackwell Scientific Publications.
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