PLANT LEAF WAXES: MOLECULAR AND ISOTOPIC INDICATORS OF PALEOENVIRONMENTS (Invited Presentation)

Fossil leaves provide key records of terrestrial paleoclimate and past ecosystems. Plant biomarkers are molecular fossils that can be preserved in sediments over geologic time and are commonly observed where there is no intact leaf material or cuticle. Stable hydrogen (D/H) and carbon (¹³C/¹²C) isotope compositions of plant-derived molecular biomarkers can record the isotopic composition of leaf water at the time of plant growth, atmospheric δ¹³C_CO2, mechanisms of carbon fixation (i.e. C3 versus C4 C-fixation) or a measure of water utilization and water stress. Although stable isotopes of plant-derived biomarkers are increasingly utilized in the reconstruction of past hydrology or landscape elevation, the magnitude of apparent hydrogen or carbon isotope fractionation can vary due to soil- or leaf-water evaporation or differing water-use strategies between different plants. Sedimentary biomarker records integrate molecules from across an ecosystem over the timescale of soil formation. As a result, there are clear ecosystem-level differences in the magnitude of apparent carbon and hydrogen isotope fractionation that impacts application of plant-biomarker isotopes for paleoenvironmental reconstruction.This study examines differences in C and H isotope discrimination in modern and ancient plant materials and soils that span a range of environmental conditions in order to elucidate the impact of ecosystem-level differences on C and H isotope discrimination. These relationships are applied to Cenozoic biomarker isotope records from western North America to provide more detailed constraints on climatic and tectonic change in this region.