Comment on bg-2021-186

Abstract

The Ullafelsen at 1869 m a.s.l. in the Tyrolean Stubai Alps next to Innsbruck is an important (geo-)archaeological reference site for the Mesolithic period. Buried fireplaces on the Ullafelsen plateau were dated at 10.9–9.5 cal. kyrs BP and demonstrate together with thousands of flint stone artifacts the presence of hunter-gatherers during the Early Holocene. Most recently, we demonstrated the great potential of n-alkane and black carbon biomarkers for contributing to a better understanding of pedogenesis and landscape evolution. In order to study the importance of human and/or animals for occupation of this relevant geoarchaeological site, we carried out steroid and bile acid analyses on two modern faeces samples from cattle and sheep and on 37 soil samples from seven soil profiles at the Ullafelsen. The modern animal faeces show a dominance of 5β-stigmastanol and deoxycholic acid for ruminants (cattle and sheep), which is in agreement with literature data. The OAh horizons, which have accumulated and developed since the Mesolithic, revealed high contents of steroids and bile acids; the E (LL) horizon coinciding with the Mesolithic living floor is characterized by medium contents of steroids and bile acids. By contrast, the subsoil horizons Bh, Bs and BvCv contain low contents of faecal biomarkers indicating that leaching of steroids and bile acids into the podsolic subsoils is not an important factor. Deoxycholic acid is the most abundant bile acid in all soil samples and gives evidence for strong faeces input of ruminants. The steroid and bile acid patterns and ratios indicate a negligible input of human faeces on the Ullafelsen. β-Sitosterol as plant-derived steroid has also a strong influence on the faecal biomarker pattern in our soils. Root input into the subsoils is likely reflected by β-sitosterol contents. In conclusion, our results reflect a strong faecal input by livestock, rather than by humans as found for other Anthrosols such as Amazonian Dark Earths. Further studies need to focus on the question of the exact timing of faeces deposition.