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Reconnaissance potassium–argon geochronology of the Suregei–Asille district, northern Kenya

Published online by Cambridge University Press:  01 May 2009

F. J. Fitch ,
P. J. Hooker ,
J. A. Miller ,
J. G. Mitchell  and
R. T. Watkins
F. J. Fitch
Affiliation:
Department of Geology, Birkbeck College, University of London, 7/15 Gresse St, London WIP 1PA
P. J. Hooker
Affiliation:
Bullard Laboratories, Department of Earth Sciences, University of Cambridge, Madingley Rise, Madingley Road, Cambridge, CB3 0EZ
J. A. Miller
Affiliation:
Bullard Laboratories, Department of Earth Sciences, University of Cambridge, Madingley Rise, Madingley Road, Cambridge, CB3 0EZ
J. G. Mitchell
Affiliation:
School of Physics, The University, Newcastle-upon-Tyne, NE1 7RU
R. T. Watkins
Affiliation:
Department of Geology, University of St Andrews, College Gate, St Andrews, Fife, KY16 9ST
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Abstract

Potassium–argon dating of 44 samples of basalt lavas and pantelleritic ignimbrites provides a provisional chronology for the 1900-metre thick Cenozoic succession of the Suregei–Asille district, northeast of Lake Turkana. Volcanic rocks of the Asille Group range in age from late Oligocene (Chattian) to late Miocene (Tortonian). Data obtained from conventional K–Ar total-rock analysis of basalt samples are appraised statistically to indicate the presence of three periods of enhanced volcanism centred around 27, 17 and 11.5 Ma. Equivalent ages obtained from the pyroclastic pantellerites by conventional K–Ar total-rock analysis and 40Ar/39Ar analysis of sanidine concentrates indicate that basic and acid eruptions were closely spaced in time. Continental tholeiite flood lavas belonging to the Gombe Group are of Pliocene age, but are difficult to date precisely because of their young ages and relatively high atmospheric contamination occurring as a result of the secondary alteration in the ubiquitous glass mesostasis. Those ages involving least atmospheric correction are considered most reliable, and are closely similar for the Chen Alia and Harr formations at around 4.85 Ma, although later flood eruptions may have occurred to the south and west of the Suregei–Asille district at about 3.85 Ma.

Type
Articles
Information
Geological Magazine , Volume 122 , Issue 6 , November 1985 , pp. 609 - 622
Copyright
Copyright © Cambridge University Press 1985

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References

Baker, B. H., Mohr, P. A. & Williams, L. A. J. 1972. Geology of the Eastern Rift System of Africa. Geological Society of America Special Paper no. 136.CrossRefGoogle Scholar
Baker, B. H., Williams, L. A. J., Miller, J. A. & Fitch, F. J. 1971. Sequence and Geochronology of the Kenya Rift Volcanics. Tectonophysics 11. 191–215.CrossRefGoogle Scholar
Brereton, R. N. 1972. A reappraisal of the 40Ar/39Ar stepwise degassing technique. Geophysical Journal of the Royal Astronomical Society 27, 449–78.CrossRefGoogle Scholar
Dalrymple, G. B. & Lanphere, M. A. 1969. Potassium-argon Dating. San Francisco: W. H. Freeman & Company. 258 pp.Google Scholar
Fitch, F. J. 1972. Selection of suitable material for dating and the assessment of geological error in potassium–argon age determination. In Calibration of Homonid Evolution (ed. Cole, S.), pp. 77–911. New York: Wenner-Gren.Google Scholar
Fitch, F. J. & Miller, J. A. 1973. Dating granites by the potassium–argon method. In Symposium on Granites, Gneisses and Related Rocks (ed. Lister, L. A.), pp. 219–25. Geological Society of South Africa Special Publication no. 3.Google Scholar
Fitch, F. J. & Miller, J. A. 1976. Conventional potassium–argon and argon-40/argon-39 dating of volcanic rocks from East Rudolf. In Earliest Man and Environments in the Lake Rudolf Basin (ed. Coppens, Y.), pp. 123–47. Chicago, London: University of Chicago Press.Google Scholar
Fitch, F. J. & Miller, J. A. (1985) Dating Karoo Igneous Rocks by the Conventional K–Ar and Argon-40/Argon-39 Age Spectrum Methods. Geological Society of South Africa Special Publication (in press).Google Scholar
Fitch, F. J., Forster, S. C. & Miller, J. A. 1974. Geological time scale. Report on Progress in Physics 37, 1433–96.CrossRefGoogle Scholar
Fitch, F. J., Hooker, P. J. & Miller, J. A. 1978. Geochronological problems and radioisotopic dating in the Gregory Rift Valley. In Geological Background to Fossil Man (ed. Bishop, W. W.), pp. 441–61. Geological Society of London Special Volume.Google Scholar
Fitch, F. J., Miller, J. A. & Hooker, P. J. 1976. Single whole-rock K–Ar isochrons. Geological Magazine 113, 1–10.Google Scholar
Fitch, F. J., Miller, J. A. & Mitchell, J. G. 1969. A new approach to isotopic dating in orogenic belts. In Time and Place in Orogeny (ed. Kent, P. E.), pp. 157–96. Geological Society of London Special Volume.Google Scholar
Fitch, F. J., Watkins, R. T. & Miller, J. A. 1975. Age of a new carbonatite locality in northern Kenya. Nature 254, 581.Google Scholar
Fitch, F. J., Findlater, I. C., Watkins, R. T. & Miller, J. A. 1974. Dating of the rock succession containing fossil hominids at East Rudolf, Kenya. Nature 251, 213–15.CrossRefGoogle Scholar
Grasty, R. L. & Miller, J. A. 1965. The omegatron, a useful tool for argon isotope studies. Nature 207, 1146–48.Google Scholar
Harland, W. B., Cox, A. V., Llewellyn, P. G., Pickton, C. A. G., Smith, A. G. & Walters, R. 1982. A Geologic Time Scale, Cambridge University Press. 131 pp.Google Scholar
Harris, J. M. & Watkins, R. T. 1974. New early Miocene vertebrate locality near Lake Rudolf, Kenya. Nature 252, 576–7.CrossRefGoogle Scholar
Hooker, P. J. & Watkins, R. T. 1980. The nature and age of the youngest basalts of the Suregei-Asille district. Proceedings of the 8th Pan African Congress of Prehistory and Quaternary Studies, Nairobi pp. 100–2.Google Scholar
Hurford, A. J., Fitch, F. J. & Clarke, A. 1984. Resolution of the age structure of the detrital zircon populations of two Lower Cretaceous sandstones from the Weald of England by fission track dating. Geological Magazine 121, 269–77.CrossRefGoogle Scholar
McDougall, I. Watkins, N. D. & Kristjansson, L. 1976. Geochronology and palaeomagnetism of a Miocene–Pliocene lava sequence at Bessastadaa, Eastern Iceland. American Journal of Science 276, 1078–95.CrossRefGoogle Scholar
Miller, J. A. & Brown, P. E. 1964. How old is Scotland? Advancement of Science 20, 527–39.Google Scholar
Mitchell, J. G. 1968. The argon-40/argon-39 method of potassium–argon age determination. Geochimica et Cosmochimica Acta 32 781–90.CrossRefGoogle Scholar
Steiger, R. H. & Jäger, E. 1977. Subcommission on Geochronology: convention on the use of decay constants in geo- and cosmochronology. Earth and Planetary Science Letters 36, 359–62.Google Scholar
Watkins, R. T. (in press). Volcano-tectonic control on sedimentation in the Koobi Fora basin, Lake Turkana. In Sedimentation in the African Rift System (ed. Frostick, L. E. and Renaut, R.). Geological Society of London Special Volume.Google Scholar
Watkins, R. T. & Williamson, P. J. 1980. The Warata Formation, northern Kenya: its character and palaeo-environmental significance. Proceedings of the 8th Pan-African Congress of Prehistory and Quaternary Studies, Nairobi, pp. 107–8.Google Scholar