Hostname: page-component-78c5997874-g7gxr Total loading time: 0 Render date: 2024-11-10T13:54:09.226Z Has data issue: false hasContentIssue false
  • English
  • Français

How reliable is the K-Ar glauconite chronometer? A case study of Eocene sediments from the Isle of Wight

Published online by Cambridge University Press:  09 July 2018

N. Clauer ,
J. M. Huggett  and
S. Hillier
N. Clauer*
Affiliation:
Centre de Géochimie de la Surface (CNRS/ULP), 1 rue Blessig , 67084 Strasbourg, France
J. M. Huggett
Affiliation:
Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK
S. Hillier
Affiliation:
Macaulay Institute, Craigiebuckler, Aberdeen AB15 8QH, UK
*
*E-mail: nclauer@illite.u-strasbg.fr
Get access Rights & Permissions [Opens in a new window]

Abstract

K-Ar ages of Eocene glauconite pellets from the Isle of Wight are related to quantified amounts of older glauconite pellets and to occurrences of detrital mica/illite particles that might have been added to synsedimentary pellets during reworking processes. Addition of older glauconite did not significantly bias the K-Ar dates, as the results most often provide the expected stratigraphic reference ages or even significantly lower ages. Alternatively, K-Ar dates significantly greater than those suggested by the stratigraphy appear to result from non-glauconized detrital mica in the pellets which is not always removable, even by high-gradient magnetic separation.

Unexpected ‘old’ K-Ar glauconite ages do not result from misapplication of the method, but from inability to systematically identify and remove the `contaminant' particles from glauconite splits. Analysis of highly evolved glauconite separates is definitely appropriate for reliable isotopic age determinations, but it might not be enough for the final selection, as long-lasting diagenesis might have taken over the synsedimentary process. Much if not all depends on the separation and characterization of the separates, but also on the completion of the glauconitization process which effects cannot always be anticipated.

Keywords

glauconitesedimentary reworkingK-Ar datingEoceneIsle of WightUK
Type
Research Article
Information
Clay Minerals , Volume 40 , Issue 2 , June 2005 , pp. 167 - 176
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2005

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

Bonhomme, M., Thuizat, R., Pinault, Y., Clauer, N., Wendling, A. & Winkler, R. (1975) Méthode de dotation potassium-argon. Appareillage et technique. Note Technique, Institut de Géologie, Université de Strasbourg, 3, France.Google Scholar
Clauer, N. & Chaudhuri, S. (1995) Clays in Crustal Environments. Isotopic Dating and Tracing. Springer Verlag, Heidelberg, Berlin, New York.Google Scholar
Clauer, N., Keppens, E. & Stille, P. (1992a) Sr isotopic constraints on the process of glauconitization. Geology, 20, 133–136.Google Scholar
Clauer, N., Stille, P., Keppens, E. & O'Neil, J.R. (1992b) Le mécanisme de la glauconitisation: Apports de la géochimie isotopique du strontium, du néodyme et de l'oxygène de glauconies récentes. Comptes Rendus de I'Académie des Sciences, Paris, 315, II, 321-327.Google Scholar
Gale, A.S., Jeffery, P.A., Huggett, J.M. & Connolly, P. (1999) Eocene inversion history of the Sandown Pericline, Isle of Wight, southern England. Journal of the Geological Society of London, 156, 327–339.CrossRefGoogle Scholar
Hillier, S. & Hodson, M.E. (1997) High gradient magnetic separation applied to sand-size particles: an example of feldspar separation from mafic minerals. Journal of Sedimentary Research, 67, 975–989.Google Scholar
Huggett, J.M. & Gale, A.S. (1997) Petrology and palaeoenvironmental significance of glaucony in the Eocene succession at Whitecliff Bay, Hampshire Basin, U.K. Journal of the Geological Society of London, 154, 897–912.Google Scholar
Hurley, P.M., Cormier, R.F., Hower, J., Fairbairn, H.W. & Pinson, W.H. (1960) Reliability of glauconite for age measurements by K-Ar and Rb-Sr methods. American Association of Petroleum Geologists’ Bulletin, 44, 1793–1808.Google Scholar
McRae, S.G. (1972) Glauconite. Earth-Science Reviews, 8, 397–440.CrossRefGoogle Scholar
Odin, G.S. (1982) Numerical Dating in Stratigraphy. J. Wiley & Sons, Chichester, UK.Google Scholar
Odin, G.S. (1988) Green Marine Clays. Developments in Sedimentology, 45. Elsevier Science Publishers, Amsterdam.Google Scholar
Odin, G.S. & Dodson, M.H. (1982) Zero isotopic age of glauconies. Pp. 277–305 in: Numerical Dating in Stratigraph. (G.S. Odin, editor). J. Wiley & Sons, Chichester, UK.Google Scholar
Odin, G.S. & Hunziker, J.C. (1974) Etude isotopique de l'altération naturelle d'une formation a glauconie (méthode a l'argon). Contributions to Mineralogy and Petrology, 48, 9–22.Google Scholar
Odin, G.S. & Matter, A. (1981) De glauconarium origine. Sedimentology, 28, 611–641.CrossRefGoogle Scholar
Smith, P.E., Evensen, N.M. & York, D. (1993) First successful 40Ar-39Ar dating of glauconies: Argon recoil in single grains of cryptocrystalline material. Geology, 21, 41–44.Google Scholar
Steiger, R.H. & Jager, E. (1977) Subcommission on Geochronology: Convention on the use of decay constants in geo- and cosmochronology. Earth and Planetary Science Letters, 36, 359–362.Google Scholar
Stille, P. & Clauer, N. (1994) The process of glauconitization. Chemical and isotopic evidence. Contributions to Mineralogy and Petrology, 117, 253–262 Google Scholar