Isotope compositions (C, O, Sr, Nd) of vertebrate fossils from the Middle Eocene oil shale of Messel, Germany: Implications for their taphonomy and palaeoenvironment

摘要

The Middle Eocene oil shale deposits of Messel are famous for their exceptionally well-preserved, articulated 47-Myr-old vertebrate fossils that often still display soft tissue preservation. The isotopic compositions (O, C, Sr, Nd) were analysed from skeletal remains of Messel's terrestrial and aquatic vertebrates to determine the condition of geochemical preservation. Authigenic phosphate minerals and siderite were also analysed to characterise the isotope compositions of diagenelic phases. In Messel, diagenetic end member values of the volcanically-influenced and (due to methanogenesis) C-12-depleted anoxic bottom water of the meromictic Eocene maar lake are isotopically very distinct from in vivo bioapatite values of terrestrial vertebrates. This unique taphonomic setting allows the assessment of the geochemical preservation of the vertebrate fossils. A combined multi-isotope approach demonstrates that enamel of fossil vertebrates from Messel is geochemically exceptionally well-preserved and still contains near-in vivo C, O, Sr and possibly even Nd isotope compositions while bone and dentine are diagenetically altered.