Exceptional preservation through phosphatization is primarily controlled by a reduction in pH, favoring the precipitation of apatite over that of calcite. Laboratory experiments have suggested that phosphatization results from anoxic decay. Here we report results of the fine-scale mineralogical characterization of Cretaceous phosphatized fossils of teleost fishes and crustaceans from the Jebel oum Tkout Lagerstätte (Morocco). Data collected using complementary laboratory and synchrotron-based X-ray techniques reveal that oxidative conditions were established at a certain step of decay. Supporting these conclusions are the presence, covering and embedded in the phosphatized tissues, of Fe(III)-rich mineral phases, the precipitation of which was likely biologically induced during decay. The present study highlights that the establishment of oxidative conditions during decay can be compatible with exceptional preservation of fossils through phosphatization.

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