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Helium-Uranium Ratios for Pleistocene and Tertiary Fossil Aragonites

F. P. Fanale and O. A. Schaeffer
Science
New Series, Vol. 149, No. 3681 (Jul. 16, 1965), pp. 312-317
Stable URL: http://www.jstor.org/stable/1715972
Page Count: 6
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Helium-Uranium Ratios for Pleistocene and Tertiary Fossil Aragonites
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Abstract

Uranium:helium ages are compared with Th$^{230}$:U$^{234}$ ages and stratigraphic ages for selected Pleistocene and Tertiary shells and corals. Agreement is good except for those fossils for which independent criteria (for example, aragonite: calcite, Ra$^{226}$:Th$^{230}$m ir Y$^{234}$:U$^{238}$ ratios) indicate a chemically open system. Certain of the Tertiary samples yield erroneously low ages which probably result from secondary addition of uranium. The helium geochronometer appears to yield reliable minimum ages and may be applicable to direct dating of aragonitic fossils-especially those of Pleistocene age-when used in conjunction with other isotopic and geologic information.

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