Utilisation of XRF core scanning on peat and other highly organic sediments

Abstract

XRF core scanning (XRF-CS) is a valuable tool, which allows for the rapid, non-destructive geochemical analysis of sediment cores at extremely high (sub-millimetre) resolution. Peat sediments, due to their near-worldwide distribution, high organic content allowing for reliable radiocarbon chronology development, and typically autochthonous nature, have long been used for palaeoenvironmental reconstructions. However, XRF-CS methods have been utilised on peat sediments relatively rarely. This is due in part to analytical uncertainty relating to high water content, uneven sediment surfaces and high organic matter contents negatively impacting the ability of the approach to reliably reproduce elemental compositions. Here we provide evidence from Mohos peat bog record in central Romania, and, by comparing to ICP measurements, indicate the ability of XRF-CS to consistently investigate the elemental geochemistry of peat sediments for major elements such as Fe and Ti. However, trace element (Cu, Ni and Sc) measurements appear to be unreliable, due in part to measurements approaching detection limits, and the diluting nature of the peat. Further, we investigate the usefulness of the Incoherent/Coherent (inc/coh) scattering ratio as a proxy for organic matter content, concluding that within high-organic sediment such as peat, the ratio does not pick up small shifts (<5%) in organic content. Finally, we present a review of approaches applied to investigating peat sediments via XRF-CS to date, with a number of suggestions for future avenues of research.