The potential of plant biomarker evidence derived from rock hyrax middens as an indicator of palaeoenvironmental change

Hyrax middens are unique environmental archives with the potential to provide unprecedented high-resolution palaeoenvironmental records, particularly in the arid regions of southern Africa. This study provides the first detailed characterisation of the organic matter composition of hyraceum and aims to identify biomarker evidence capable of providing new or supplementary palaeoenvironmental data from these novel archives. Pyrolysis gas chromatography mass spectrometry reveals hyraceum to be dominated by nitrogen-containing aromatic compounds, notably benzamide. This is almost certainly derived directly from the hyrax urine and is probably the main source of nitrogen as measured in bulk δ15N measurements. Solvent-extractable lipids comprise homologous suites of long-chain n-alkanes (C24–C34) and n-alkanols (C16–C26), characteristic of higher plant leaf waxes, along with an abundance of animal-derived sterols, higher plant sterols and terpenoids; as well as the ubiquitous benzamide. ne distributions and compound specific δ13C clearly differentiate samples from the C3 vegetation dominated Cape Floristic Region, and the more arid, C4 grass-rich savannas of central Namibia (Klein Spitzkoppe). Distinct changes in n-alkane distribution and δ13C are observed within the Spitzkoppe midden; most notably the mid to late Holocene period (c. 6000–2000 cal yr BP), which records a progressive reduction in grass-derived organic matter inputs. Based on the animalʹs feeding behaviour and contemporary site ecology, a phase of increasing aridity is inferred, which is consistent with other proxy data from this site (e.g. bulk δ15N). The excellent preservation of plant and animal biomarkers suggests that there is significant potential for midden-derived biomarkers to provide long-term palaeoenvironmental proxies.