Uranium isotope compositions of biogenic carbonates - Implications for U uptake in shells and the application of the paleo-ocean oxygenation proxy

Radioactive fossils: The uranium anomaly and its paleobiological implications

In this study, several natural radionuclides (⁴⁰K, ²³⁸U, ²³⁵U, ²²⁸Ac) and their decay product were investigated in various invertebrate and vertebrate fossils. In the high radioactivity group of fossils, ²³⁸U and ²³⁵U concentrations increased from 141 to 3621 Bq/kg and from 5.4 to 167 Bq/kg, respectively. In the low radioactivity group of fossils, concentrations of both U isotopes increased from 4.6 to 51 Bq/kg and from 0.18 to 2.3 Bq/kg, respectively. High radioactivity has been linked to the phosphatization process that affected the uranium sorption. Scanning of electron microscope images and X-ray fluorescence analysis were used to confirm the mode of preservation of studied fossils and the presence of a correlation between the phosphorus content and uranium elements in fossil specimens.