Helium-Uranium Ratios for Pleistocene and Tertiary Fossil Aragonites

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Abstract
Uranium: helium ages are compared with Th230: U234 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, Ra226: Th230, or U234: U238 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.