On the stratigraphic integrity of leaf-wax biomarkers in loess paleosols

[摘要] Paleoenvironmental and paleoclimate reconstructions based on molecularproxies, such as those derived from leaf-wax biomarkers, in loess-paleosolsequences represent a promising line of investigation in Quaternary research.The main premise of such reconstructions is the synsedimentary deposition ofbiomarkers and dust, which has become a debated subject in recent years. Thisstudy uses two independent approaches to test the stratigraphic integrity ofleaf-wax biomarkers: (i) long-chain n-alkanes and fatty acids arequantified in two sediment-depth profiles in glacial till on the SwissPlateau, consisting of a Holocene topsoil and the underlying B and Chorizons. Since glacial sediments are initially very poor in organic matter,significant amounts of leaf-wax biomarkers in the B and C horizons of thoseprofiles would reflect postsedimentary root-derived or microbialcontributions. (ii) Compound-specific radiocarbon measurements are conductedon n-alkanes and n-alkanoic (fatty) acids from several depth intervals inthe loess section "Crvenka", Serbia, and the results are compared toindependent estimates of sediment age.

We find extremely low concentrationsof plant-wax n-alkanes and fatty acids in the B and C horizons below thetopsoils in the sediment profiles. Moreover, compound-specific radiocarbonanalysis yields plant-wax ¹⁴C ages that agree well with publishedluminescence ages and stratigraphy of the Serbian loess deposit. Bothapproaches confirm that postsedimentary, root-derived or microbialcontributions are negligible in the two investigated systems. The goodagreement between the ages of odd and even homologues also indicates thatreworking and incorporation of fossil leaf waxes is not particularly relevanteither.

[学科分类] 地球化学与岩石