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Phengite spherules from the Dalradian Bonahaven Formation, Islay, Scotland: glauconitized microfossils?

Published online by Cambridge University Press:  01 May 2009

I. J. Fairchild
I. J. Fairchild
Affiliation:
Department of Geology, Sedgwick Museum, Downing Street, Cambridge CB2 3EQ, England
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Summary

Abundant spherules of phengite, 50—150 μm in diameter and with a radial texture, occur in mudstones at the top of the lowest member of the Bonahaven Formation. They have smooth, sharp boundaries, show flattening next to desiccation cracks and exhibit a restricted, bi-or tri-modal size distribution. It is inferred that the spherules represent infilled voids in a sediment which was deposited entirely from suspension. Accordingly, it is considered likely that the spherules are microfossils, although characteristic morphological features are lacking. They were probably infihled by glauconite, which was transformed to phengite during diagenesis and low-grade metamorphism.

Type
Articles
Information
Geological Magazine , Volume 114 , Issue 5 , September 1977 , pp. 355 - 364
Copyright
Copyright © Cambridge University Press 1977

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References

Berner, R. A. 1971. Principles of chemical sedimentology, 240 pp. New York: McGraw-Hill, Inc.Google Scholar
Bjerkli, K. & Östmo-Saeter, J. S. 1973. Formation of glauconite in foraminiferal shells on the continental shelf off Norway. Mar. Geol. 14, 169–78.CrossRefGoogle Scholar
Burst, J. F. 1958. ‘Glauconite’ pellets: their mineral nature and application to stratigraphic interpretation. Bull. Am. Ass. Petrol. Geol. 42, 310–27.Google Scholar
Cloud, P. E. 1955. Physical limits to glauconite formation. Bull. Am. Ass. Petrol. Geol. 39, 484–93.Google Scholar
Cloud, P. E. 1960. Gas as a sedimentary and diagenetic agent. Am. J. Sci. 258A, 35–45.Google Scholar
Curtis, C. D. & Spears, D. A. 1968. The formation of sedimentary iron minerals. Econ. Geol. 63, 257–70.CrossRefGoogle Scholar
Dapples, E. C. 1967. Diagenesis of sandstones. InDiagenesis in Sediments (ed. Larsen, G. and Chilingar, G.V.). Amsterdam: Elsevier.Google Scholar
Downie, C., Lister, T. R., Harris, A. L. & Fettes, D. J. 1971. A palynological investigation of the Dalradian rocks of Scotland. Inst. geol. Sci. Rep. No. 71/9. 30 pp.Google Scholar
Elliston, J. 1968. Retextured sediments. XXIII Int. geol. Cong. 8, 85–104.Google Scholar
Fairbridge, R. W. 1967. Phases of diagenesis and authigenesis. In Diagenesis in Sediments (ed. Larsen, G. and Chilingar, G. V.), pp. 19–89. Amsterdam: Elsevier.CrossRefGoogle Scholar
Harris, A. L. & Pitcher, W. S. 1975. The Dalradian Super-group. In: A correlation of Precambrian rocks of the British Isles, pp. 52–75. Spec. Rept. geol. Soc. Lond. 6, 136 pp.Google Scholar
Hendricks, S. B. & Ross, C. S. 1941. Chemical composition and genesis of glauconite and celadonite. Am. Miner. 26, 683–708.Google Scholar
Hennig, A. & Elias, H. 1971. A rapid method for the visual determination of size distribution of spheres from the size distribution of their sections. J. Microsc. 93, 101–7.CrossRefGoogle ScholarPubMed
Holland, H. D. 1972. The geologic history of sea-water — an attempt to solve the problem. Geochim. cosmochim. Acta 36, 637–51.CrossRefGoogle Scholar
Hower, J. 1961 Some factors concerning the nature and origin of glauconite. Am. Miner. 46, 313–34.Google Scholar
Klein, G. de V. 1970. Tidal origin of a Precambrian quartzite: the Lower Fine-grained Quartzite (Middle Dalradian) of Islay, Scotland. J. sedim. Petrol. 40, 973–85.Google Scholar
Leone, M., Alaimo, R. & Calderone, S. 1975. Genesis of chlorite pellets from Mesozoic bedded cherts of Sicily. J. sedim. Petrol. 45, 618–28.Google Scholar
McRae, S. G. 1972. Glauconite. Earth-Sci. Rev. 8, 397–440.CrossRefGoogle Scholar
Millot, G. 1970. Geology of clays (English edition). New York: Springer-Verlag.CrossRefGoogle Scholar
Peach, B. N. & Horne, J. 1930. Chapters on the geology of Scotland. London: Oxford University Press.Google Scholar
Pokorny, V. 1963. Principles of zoological micro-palaeontology, English ed., vol. 1. London: Pergamon Press.Google Scholar
Rogers, A. 1974. Statistical analysis of the spatial dispersion. The quadrat method. London: Pion.Google Scholar
Rohrlich, V., Price, N. B. & Calvert, S. E. 1969. Chamosite in the Recent sediments of Loch Etive, Scotland. J. sedim. Petrol. 39, 624–31.Google Scholar
Sarjeant, W. A. S. 1974. Fossil and living Dinoflagellates. London: Academic Press.CrossRefGoogle Scholar
Schoen, R. 1964. Clay minerals of the Silurian Clinton Ironstones, New York State. J. sedim. Petrol. 34,855–63.Google Scholar
Spencer, A. M. & Spencer, M. O. 1972. The Late Precambrian/Lower Cambrian Bonahaven Dolomite of Islay and its stromatolites. Scott. J. Geol. 8, 269–82.CrossRefGoogle Scholar
Takahashi, J. I. & Yagi, T. 1929. Peculiar mud grains and their relation to the origin of glauconite. Econ. Geol. 24, 838–54.CrossRefGoogle Scholar
Triplehorn, D. M. 1966. Morphology, internal structure, and origin of glauconite pellets. Sedimentology,6, 247–66.CrossRefGoogle Scholar
Velde, B. 1967. Si+4 content of natural phengites. Contr. Miner. Petrol. 14, 250–8.CrossRefGoogle Scholar
Wilkinson, S. B. 1907. The geology of Islay. Mem. geol. surv. U.K.Google Scholar
Zumpe, H. H. 1971. Microstructure in Cenomanian glauconite from the Isle of Wight, England. Mineralog. Mag. 38, 215–24.CrossRefGoogle Scholar