PLANT WAX BIOMARKERS IN LATE NEOGENE PALEOSOLS AS ARCHIVES OF GREAT PLAINS VEGETATION

Stable isotope-based vegetation records from ancient terrestrial ecosystems have become an essential tool for studying ecosystem change and attendant effects on fauna through time. The majority of carbon isotope records from terrestrial sediments come from paleosol carbonate or bulk soil organic matter. Plant-wax biomarkers in paleosols and other terrestrial sediments are an emerging tool for reconstructing vegetation, particularly in paleosols that lack pedogenic carbonate or have low or inherited organic carbon. Modern plants and sediments demonstrate that carbon isotopes and molecular distributions of long-chain n-alkyl lipids provide information about vegetation. However, there is very little data on plant wax preservation and their isotopic fidelity in paleosols.

Here we explore plant wax biomarkers from late Neogene sediments of the Meade Basin in southwest Kansas as a tool for reconstructing vegetation in the Great Plains over the last ca.10 million years. Critical steps for generating reliable data for paleoecological reconstructions include establishing sampling protocols that prevent potential contamination from modern plant waxes and assessing biomarker preservation prior to isotopic analysis. Plant wax molecular distributions from Meade Basin sediments indicate excellent biomarker preservation and concentrations sufficient for compound specific isotope analysis in nearly all samples. Carbon isotope data indicate a wide range of environments from C₃‑dominated (>75% C₃ vegetation) to C₄‑dominated landscapes with an overall trend towards more C4 vegetation from the late Miocene to present. Plant wax isotope data from the C₃₁ n‑alkane show the best agreement with co-existing carbon isotope data from carbonate samples taken from the same stratigraphic horizon. Plant wax isotope data from terrestrial sediments in the Meade Basin illustrate the potential for biomarkers in reconstructing local vegetation from terrestrial sediments, particularly from paleosols where pedogenic carbonates are absent.