Preservation of lipid hydrogen isotopes 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-logged sediments from the Miocene (15 to 20 Ma) Clarkia lacustrine deposit in northern Idaho, 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 support the high degree of lipid preservation as previously reported. Three lines of evidence strongly suggest that original hydrogen isotope ratios of lipids are preserved after 15 to 20 million years of burial in the water-logged lacustrine sediment: (1) dD values of individual lipids show large variations (up to 120? between sediments and fossils, and up to 81? between different fossil genera); (2) hydrogen isotope values of fossil lipids differ by more than 122? from the associated sediment water; (3) hydrogen isotope offsets between the fossil lipids and the sediment water are similar in range to those between the lipids of modern plant counterparts and environmental water. These data are consistent with minimum isotope exchange between lipid bound hydrogen and sediment water hydrogen. Our results validate the use of lipid hydrogen isotope ratios for paleoecological studies over an extended geological time scale.