Hostname: page-component-848d4c4894-nr4z6 Total loading time: 0 Render date: 2024-06-01T10:32:28.727Z Has data issue: false hasContentIssue false
  • English
  • Français

The Ordovician graptoloid Didymograptus murchisoni in South Wales and its use in three-dimensional absolute strain analysis

Published online by Cambridge University Press:  03 November 2011

C. J. Jenkins
C. J. Jenkins
Affiliation:
Ocean Sciences Institute, University of Sydney, NSW 2006, Australia.
Get access Rights & Permissions [Opens in a new window]

Abstract

The dimensional statistics and proximal development characters of the Llanvirnian pendent didymograptid D. murchisoni are defined using the type material from near Builth Wells (Powys) and other collections from Abereiddi Bay (Dyfed). Population variability (as expressed by variation coefficients) in the undeformed faunas amounts to about 10% for the sicula lengths and thecal spacings, but is over 20% (up to 200%) for stipe lengths and divergences. Characters with low variability have greater species-diagnostic value. Proximal development in the species involves a dicalycal th 11 and a low origin for that theca from the sicula. The taxa Didymograptus amplus, D. nanus, D. geminus, D. geminus latus and D. acutus are varieties within populations of D. murchisoni and are therefore junior synonyms.

The resulting rationalised taxonomy allows advances to be made in the use of the species in stratigraphy and tectonics. For example, an occurrence of undeformed (pyritised) D. murchisoni in full relief at Abereiddi in the same beds as flattened and deformed faunas, allows a calculation of the absolute three-dimensional strains to be made for the slates there. The strains are strongly flattening (K < 0 · 3) and involve volume changes of about −56%. The high dilatation values imply that stylolite and grain-boundary pressure solution operated during the deformations to take the changes in volume beyond what is possible with simple compaction (i.e. porosity reduction).

Keywords

graptolitesslatevolume change
Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 78 , Issue 2 , 1987 , pp. 105 - 114
Copyright
Copyright © Royal Society of Edinburgh 1987

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Barr, M. & Coward, M. P. 1974. A method for the measurement of volume change. GEOL MAG 111, 293–6.CrossRefGoogle Scholar
Bell, T. H. & Duncan, A. C. 1978. A rationalized and unified shorthand terminology for lineations and fold axes in tectonites. TECTONOPHYSICS 47, T1–T5.CrossRefGoogle Scholar
Berry, W. B. N. 1962. Didymograptus bifidus (J. Hall)—its lectotype, description and occurrence. J PALEONTOL 36, 294–9.Google Scholar
Berry, W. B. N. 1964. The Middle Ordovician of the Oslo Region, Norway No. 16. Graptolites of the Ogygiocaris Series. NOR GEOL TIDSSKR 44:1, 61–170.Google Scholar
Braithwaite, L. F. 1976. Graptolites of the Lower Ordovician Pogonip Group of western Utah. SPEC PAP GEOL SOC AM 166.Google Scholar
Cooper, R. A. 1973. Taxonomy and evolution of Isograptus Moberg of Australasia. PALAEONTOLOGY 16, 45–115.Google Scholar
Cooper, R. A. 1979. Ordovician geology and graptolite faunas of the Aorangi Mine area, north-west Nelson, New Zealand. PALAEONTOL BULL N Z GEOL SURV 47, 1–127.Google Scholar
Cooper, R. A. & Fortey, R. A. 1982. The Ordovician graptolites of Spitsbergen. BULL BR MUS NAT HIST (GEOL) 36, 157–302.Google Scholar
Ekström, G. 1973. Upper Didymograptus Shale in Scania. SVER GEOL UNDERS AFH (SER C) 403, 1–53.Google Scholar
Elles, G. L. & Wood, E. M. R. 1901–1918. A Monograph of the British Graptolites. PALAEONTOGR SOC (MONOGR).Google Scholar
Fortey, R. A. & Cocks, L. R. M. 1986. Fossils and tectonics. J GEOL SOC 143, 149–150.CrossRefGoogle Scholar
Goodarzi, F. & Norford, B. S. 1985. Graptolites as indicators of the temperature histories of rocks. J GEOL SOC 142, 1089–99.CrossRefGoogle Scholar
Hede, J. E. 1951. Boring through Middle Ordovician-Upper Cambrian strata in the Fågels˚ang district, Scania (Sweden). ACTA UNIV LUND (NEW SER) 2:46:7, 1–84.Google Scholar
Hisinger, W. 1840. Lethaia Suecica, seu Petrificata Suecicae, suppl., 1–29.Google Scholar
Hopkinson, J. & Lapworth, C. 1875. Descriptions of the graptolites of Arenig and Llandeilo rocks of St David's. Q J GEOL SOC LONDON 31, 631–73.CrossRefGoogle Scholar
Hughes, C. P., Jenkins, C. J. & Rickards, R. B. 1982. Abereiddi and the adjacent coast. In Bassett, M. G. (ed.) Geological Excursions in Dyfed, South-west Wales, 51–63. Cardiff: National Museum of Wales.Google Scholar
Jaanusson, V. 1960. Graptoloids from the Ontikan and Viruan (Ordovician) limestones of Estonia and Sweden. BULL GEOL INST UNIV UPPSALA 38, 289–366.Google Scholar
Jenkins, C. J. 1979 (unpubl.) Stratigraphy and graptolite biostratigraphy of the Llanvirn Series' type area, St Davids, Dyfed, Wales. Ph.D. Thesis, University of Cambridge, U.K.Google Scholar
Jenkins, C. J. 1983. Ordovician graptolites from the Great Paxton Borehole, Cambridgeshire. PALAEONTOLOGY 26, 641–53.Google Scholar
Sir Murchison, R. I. 1839. The Silurian System founded on geological researches in the counties of Salop etc. London.Google Scholar
Packham, G. H. 1962. Some diplograptids from the British Lower Silurian. PALAEONTOLOGY 5, 498–526.Google Scholar
Ramsay, J. G. 1967. Folding and fracturing of rocks. New York: McGraw-Hill.Google Scholar
Ramsay, J. G. & Huber, M. I. 1983. The techniques of modern structural geology. Vol. I: Strain analysis. London: Academic Press.Google Scholar
Ramsay, J. G. & Wood, D. S. 1973. The geometric effects of volume change during deformation processes. TECTONOPHYSICS 16, 263–77.CrossRefGoogle Scholar
Rickards, R. B. 1973. The structure at Abereiddy Bay, Pembrokeshire. GEOL MAG 110, 185–7.CrossRefGoogle Scholar
Simpson, G. L., Roe, A. & Lewontin, R. C. 1960. Quantitative Zoology. New York: Harcourt, Brace & Co.Google Scholar
Skevington, D. 1965. Graptolites from the Ontikan limestones (Ordovician) of Öland, Sweden. II: Graptoloidea and Graptovermida. BULL GEOL INST UNIV UPPSALA 43, 1–74.Google Scholar
Skevington, D. 1970. A Lower Llanvirn graptolite fauna from the Skiddaw Slates, Westmorland. PROC YORKSHIRE GEOL SOC 37, 395–444.CrossRefGoogle Scholar
Skwarko, S. K. 1974. Some Ordovician graptolites from the Canning Basin, Western Australia, 2. Graptolites from the Goldwyer No. 1 Well. BULL BUR MINER RES GEOL GEOPHYS AUST 150, 43–54.Google Scholar
Strachan, I. 1986. The Ordovician graptolites of the Shelve District, Shropshire. BULL BR MUS NAT HIST (GEOL) 40.Google Scholar
Strachan, I. & Khashogji, M. S. 1984. The type specimen of Didymograptus murchisoni. LETHAIA 17, 223–31.CrossRefGoogle Scholar
Tullberg, S. A. 1882. On the graptolites described by Hisinger and the older Swedish authors. BIH K SVEN VETENSK ACAD HANDL 6:13, 3–23.Google Scholar
Wright, T. O. & Platt, L. B. 1982. Pressure dissolution and cleavage in Martinsburg Shale. AM J SCI 282, 122–35.CrossRefGoogle Scholar