Abstract
DR. K. M. CHEER'S attempt1 to superimpose the palaeomagnetically derived polar wandering paths of the various continents is a promising new method which may eventually help to solve the problem of the former continental configurations. At present, however, many of the palaeomagnetic results are still too doubtful, as Van Hilten2 pointed out, to eliminate the guess-work in the construction of the paths of polar wanderings. Van Hilten's acceptance of Creer's paths of polar wanderings for Africa and South America makes it desirable to point out some of the uncertainties and discrepancies contained in Creer's data:
(1) The Silurian pole. Neither the Silurian age of the Urucum beds nor that of the Table Mountain Series has been proved by fossils. The Silurian pole, as derived from the Urucum beds, seems to lie too far from the thick glacial deposits of the Silurian Zapla beds3 to fit the geological evidence.
(2) The Devonian pole. The reconstruction shows the Devonian pole situated on northern Africa. Such a position is contradicted by the extensive development of Devonian coral reefs in West Africa4. The only well-documented Palaeozoic glacial deposit in northern Africa is of Ordovician age5. This discrepancy between the geological facts and the palaeomagnetic measurements casts doubt on the age of the magnetization of the South American Devonian red-beds as used by Creer. The fact that Devonian glacial deposits have been reported from Argentina6 and from Brazil7,8, though the evidence is perhaps not completely conclusive, strengthens this suspicion. No evidence for a Devonian pole has as yet been derived from African rocks.
(3) The Pennsylvanian pole. The pole position used for the reconstruction of the polar wandering path would harmonize with the geological observations, but the palaeomagnetic data cannot be regarded as reliable according to Irving's list of palaeomagnetic pole positions9.
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References
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Lohmann, H., Geol. Rundsch., 54, 161 (1964).
Haughton, S. H., Stratigraphic History of Africa South of the Sahara (Oliver and Boyd, London, 1963).
Sougy, J., and Lecorche, J. P., Laboratoire de Géol. de la Faculté de Sci. de l'Univ. de Dakar. Raport No. 2 (1963).
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Irving, E., Paleomagnetism (John Wiley and Sons, New York, 1964).
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MARTIN, H. Ancient Continental Configurations. Nature 211, 398 (1966). https://doi.org/10.1038/211398b0
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DOI: https://doi.org/10.1038/211398b0
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