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Hardgrounds in the Lower Leintwardine Beds (Silurian) of the Welsh Borderland

Published online by Cambridge University Press:  01 May 2009

Lesley Cherns
Lesley Cherns
Affiliation:
Department of Palaeobiology, Uppsala University, Box 564, S-751 22 Uppsala, Sweden
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Summary

The base of the Lower Leintwardine Beds (Silurian-Ludlow Series) in the shelf sequences of the Welsh Borderland is marked by a widespread development of shelly conglomeratic limestone beds. Borings into some intraclasts indicate that they were hardgrounds. The early lithification, sometimes in situ, of both sand-grade and mud-grade carbonates is demonstrated by the conglomerates. Some compound intraclasts (‘hiatus concretions’) indicate a complex history of deposition, scouring and lithification. Boring of clasts which have not been further eroded is inferred to have taken place locally. The borings are of the narrow, single entrance form referable to Trypanites. The distribution of the conglomerates relates closely to Leintwardinian palaeogeography. Repeated hardground formation in sequences of inner shelf areas reflects episodic deposition alternating with periods of omission and erosion. There is evidence throughout the shelf of a break in sedimentation with hardground formation at the end of Bringewoodian times. The nature of the conglomerates suggests that they formed in shallow water conditions; there is no lithological indication of sub-aerial exposure. The absence of the Aymestry Limestone in the SE shelf is more probably due to its non-deposition or lateral lithological change to muddier beds with a different faunal assemblage than to its subsequent removal by erosion.

Type
Articles
Information
Geological Magazine , Volume 117 , Issue 4 , July 1980 , pp. 311 - 326
Copyright
Copyright © Cambridge University Press 1980

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References

Bathurst, R. G. C. 1971. Carbonate Sediments and Their Diagenesis. Developments in Sedimentology, no. 12. Amsterdam, Oxford, New York: Elsevier.Google Scholar
Berdan, J. 1968. Possible palaeoecological significance of leperditiid ostracodes. Geol. Soc. Am. Prog. A. Mtg. North-eastern Sect. Washington D.C. 17 (Abstr.).Google Scholar
Bromley, R. G. 1972. On some ichnotaxa in hard substrates with a redefinition of Trypanites Mägdefrau. Paläont. Z. 46, 93–8.CrossRefGoogle Scholar
Bromley, R. G. 1975. Trace fossils at omission surfaces. In The Study of Trace Fossils (ed. Frey, R. W.), pp. 399–428. New York: Springer-Verlag.CrossRefGoogle Scholar
Cave, R. & White, D. E. 1968. (Log of Brookend borehole). Inst. Geol. Sciences Ann. Rep. for 1967, 75–6.Google Scholar
Cave, R. & White, D. E. 1971. The exposures of Ludlow rocks and associated beds at Tites Point and near Newnham, Gloucestershire. Geol. J. 7, 239–54.CrossRefGoogle Scholar
Cave, R. & White, D. E. 1978. (Stratigraphy of Brookend borehole.) Ludlow Research Group Bull. 25, 44–5.Google Scholar
Cocks, L. R. M., Holland, C. H., Rickards, R. B. & Strachan, I. 1971. A correlation of Silurian rocks in the British Isles. Jl geol. Soc. Lond. 127, 103–136. (Also as Geol. Soc. Lond., Special Report no. 1).CrossRefGoogle Scholar
Coppack, B. C. & White, D. E. 1974. (Log of Dean borehole.) Inst. Geol. Sciences Rep. 74/7, 6.Google Scholar
Goldring, R. & Kazmierczak, J. 1974. Ecological succession in intraformational hardground formation. Palaeontology 17, 949–62.Google Scholar
Hecker, R. T. 1970. Palaeoichnological research in the Palaeontological Institute of the Academy of Sciences of the U.S.S.R.. In Trace fossils (ed. Crimes, T. P. and Harper, J. C.). Geol. J. Spec. Issue 3, 215–226.Google Scholar
Holland, C. H. & Lawson, J. D. 1963. Facies patterns in the Ludlovian of Wales and the Welsh Borderlands. Lpool Mnchr geol. J. 3, 269–88.CrossRefGoogle Scholar
Holland, C. H., Lawson, J. D. & Walmsley, V. G. 1959. A revised classification of the Ludlovian succession at Ludlow. Nature, Lond. 184, 1037–9.CrossRefGoogle Scholar
Holland, C. H., Lawson, J. D. & Walmsley, V. G. 1963. The Silurian rocks of the Ludlow district, Shropshire. Bull. Br. Mus. nat. Hist. (Geol.) 8, 93–171.Google Scholar
Jaanusson, V. 1961. Discontinuity surfaces in limestones. Bull. geol. Instn Univ. Upps. 40, 221–41.Google Scholar
Kennedy, W. J. 1975. Trace fossils in carbonate rocks. In The Study of Trace Fossils (ed. Frey, R. W.), pp. 377–98. New York: Springer-Verlag.CrossRefGoogle Scholar
Lawson, J. D. 1954. The Silurian succession at Gorsley (Herefordshire). Geol. Mag. 91, 227–37.CrossRefGoogle Scholar
Lawson, J. D. 1955. The geology of the May Hill inlier. Q. J. geol. Soc. Lond. 111, 85–116.CrossRefGoogle Scholar
Lawson, J. D. 1960. The succession of shelly faunas in the British Ludlovian. Rep. XXIst Int. Geol. Congr., Norden, 1960, 7, 114–125.Google Scholar
Lawson, J. D. 1973. Facies and faunal changes in the Ludlovian rocks of Aymestrey, Herefordshire. Geol. J. 8, 247–78.CrossRefGoogle Scholar
Lindström, M. 1963. Sedimentary folds and the development of limestone in an early Ordovician sea. Sedimentology 2, 243–92.CrossRefGoogle Scholar
Palmer, T. J. & Palmer, D. D. 1977. Faunal distribution and colonization strategy in a Middle Ordovician hardground community. Lethaia 10, 179–99.CrossRefGoogle Scholar
Seilacher, A. 1969. Palaeoecology of boring barnacles. Am. Zool. 9, 705–19.CrossRefGoogle Scholar
Shergold, J. H. & Shirley, J. 1968. The faunal stratigraphy of the Ludlovian rocks between Craven Arms and Bourton, near Much Wenlock, Shropshire. Geol. J. 6 (1), 119–38.CrossRefGoogle Scholar
Shinn, E. A. 1969. Submarine lithification of Holocene carbonate sediments in the Persian Gulf. Sedimentology 12, 109–44.CrossRefGoogle Scholar
Squirrell, H. C. & Tucker, E. V. 1960. The geology of the Woolhope inlier, Herefordshire. Q. Jl geol. Soc. Lond. 116, 139–85.CrossRefGoogle Scholar
Voigt, E. 1968. Über Hiatus-Konkretionen (dargestellt an Beispielen aus dem Lias). Geol. Rdsch. 58, 281–96.CrossRefGoogle Scholar
Walmsley, B. G. 1959. The geology of the Usk inlier (Mon.). Q. Jl geol. Soc. Lond. 114, 483–521.CrossRefGoogle Scholar
Warme, J. E. 1975. Borings as trace fossils and the processes of marine bioerosion. In The Study of Trace Fossils, pp. 181–227. (ed. Frey, R. W.). New York: Springer-Verlag.CrossRefGoogle Scholar
Whitaker, J. H. McD. 1962. The geology of the area around Leintwardine. Q. Jl geol. Soc. Lond. 118, 319–51.CrossRefGoogle Scholar