Palaeomagnetic record in Late Pleistocene and Holocene dry lake deposits at Tlapacoya, Mexico |
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| Authors: | J C Liddicoat R S Coe P W Lambert† S Valastro Jr |
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| Institution: | US Geological survey, 345 Middlefield Road, Menlo Park, California 94025, USA;Earth Sciences Board of Studies, University of California, Santa Cruz 95064, USA;Institute Nacional de Antropología e Historia, Mexico, D.F., Mexico;Radiocarbon Laboratory, The University of Texas at Austin, Austin, Texas 78757, USA |
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| Abstract: | Summary. A palaeomagnetic investigation of Carbon-14-dated marsh and near-shore lacustrine sediments deposited between about 25000–5000 yr bp at Tlapacoya, Mexico, reveals normal polarity of the geomagnetic field in all samples measured. At one site, anomalous palaeomagnetic directions in a mud unit dated about 14500 yr bp raised the possibility of a geomagnetic excursion, but subsequent work at six additional sites in the unit revealed no abnormal directions. Thus the anomalous directions are most likely not a true reflection of geomagnetic field behaviour, although no specific alternative explanation is entirely convincing. The preliminary Tlapacoya data of anomalous directions have been cited by others as positive evidence for an excursion. We strongly recommend it no longer be considered as such. |
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