Preservation of lipid hydrogen isotope ratios in Miocene lacustrine sediments and plant fossils at Clarkia, northern Idaho, USA

We measured D/H ratios of individual lipids isolated from plant fossils and water-lain sediments from the Miocene Clarkia lacustrine deposit (15–20 Ma) in northern Idaho, USA, in order to assess the preservation potential of lipid hydrogen isotope ratios. Distinct n-alkyl lipid profiles in plant fossils (Platanus, Quercus, Salix) and the sedimentary matrix demonstrate the high degree of lipid preservation, as previously reported. Our data suggest that original hydrogen isotope ratios of carbon-bound hydrogen in lipids may have been preserved after 15–20 million years of burial in the water-lain lacustrine sediment, because δD values of individual lipids show large variations between different fossil genera and between fossils and sediments, and hydrogen isotope values of fossil lipids differ by more than 123‰ from the associated sediment water. These data are consistent with minimal isotopic exchange between carbon-bound hydrogen in lipids and sediment water hydrogen. Our results validate the use of lipid hydrogen isotope ratios for paleoecological studies over an extended geological time period.