Abstract
Abstract. Archaeological research in high mountain regions has gotten a lot more attention since the discovery of the copper age mummy called “Ötzi” in the Ötztaler Alps in 1991. In the Tyrolean Stubai Alps, the Mesolithic site Ullafelsen at 1869 m a.s.l. (above sea level) close to the recent upper timberline in the Fotsch Valley represents, on the one hand, a very important archaeological reference site and offers, on the other hand, intriguing research questions related to, amongst others, pedogenesis. Given that no biomarkers and stable isotopes have been hitherto investigated, we aimed at contributing with respective analyses and additional radiocarbon dating to a better understanding of the landscape evolution and pedogenesis on and around the Ullafelsen. Our results for modern vegetation suggest that leaf-wax-derived n-alkanes allow us to chemotaxonomically distinguish between subalpine deciduous trees (nC27 predominance) versus (sub)alpine grasses, herbs and dwarf shrubs (nC29, nC31 and/or nC33 predominance). Except for Juniperus, conifers produce no or extremely low n-alkane contents. Although no clear vegetation changes could be inferred from the n-alkane patterns of the investigated soil profiles, the total n-alkane content (TAC) was developed for the first time as an unambiguous proxy for distinguishing between buried (= fossil) topsoils (2Ahb horizons) and humus-enriched subsoils such as Bh horizons of podzols. Based on this leaf wax proxy, we can rule out that the 2Ahb?/Bh? horizons under question on the Ullafelsen are buried topsoils as suggested previously. Dating of the H2O2-pretreated soil samples yielded 14C ages for the podzol Bh horizons ranging from 6.7 to 5.4 cal kyr BP. This is clearly younger than the overlying Mesolithic living floor (LL) (10.9 to 9.5 cal kyr BP) but pre-dates the assumed intensification of alpine pasturing from the Bronze Age onwards. Both the LL and the directly overlying OAh3 horizon yielded black carbon maxima and benzene polycarboxylic acid patterns reflecting fire-induced human impact during the Mesolithic. The discrepancy between the Mesolithic charcoal 14C ages (ages of ≥ 9.5 cal kyr BP) versus the 14C ages obtained for bulk n-alkanes ranging from 8.2 to 4.9 cal kyr BP suggests that non-alkane-producing conifers predominated the vegetation on and around the Ullafelsen after the Mesolithic occupation. Only with the anthropo-zoological lowering of the timberline associated with alpine pasturing since the Neolithic and especially the Bronze Age has an n-alkane-producing vegetation cover (grasses, herbs or dwarf shrubs) started to predominate.
Highlights
Archaeological research in high mountain regions has gotten a lot of attention since the discovery of the copper age mummy called “Ötzi” in the Ötztaler Alps in 1991
Based on stratigraphical features and related soil analyses, Geitner et al (2011, 2014) suggested that the living floor (LL) developed by aeolian dust deposition during the Younger Dryas (YD) and that it overlies a late glacial buried topsoil (2Ahb) that developed during the favourable climatic conditions of the Bølling–Allerød period
Geitner et al (2011, 2014) suggested that the LL developed by aeolian dust deposition during and after the Younger Dryas (YD) and that it overlies a late glacial buried topsoil (2Ahb) that developed during the favourable climatic conditions of the Bølling–Allerød period
Summary
Archaeological research in high mountain regions has gotten a lot of attention since the discovery of the copper age mummy called “Ötzi” in the Ötztaler Alps in 1991. Other molecular lipid biomarkers allow us to infer, for instance, dietary information in geoarchaeological studies (Grillo et al, 2020), and the stable nitrogen isotopic composition (δ15N) of soils allows us to infer the human-induced opening of the N cycle (Zech et al, 2011a). The overall aim of this geoarchaeological follow-up study was, to contribute with biomarker and stable isotope analyses, as well as with radiocarbon dating, for a better understanding of the pedogenesis, the human impact and the landscape evolution on and around the Mesolithic site Ullafelsen. We addressed the following questions. (i) Is the humus-enriched subsoil horizon on the Ullafelsen a buried topsoil (2Ahb horizon) or humus-enriched by podzolisation (Bh horizon)? (ii) Do biomarker and stable isotope results validate the LL as the Mesolithic living floor and/or eluvial albic horizon? (iii) Do n-alkane biomarkers allow us to chemotaxonomically distinguish the dominant vegetation types around the Ullafelsen and is there any evidence for late glacial and Holocene vegetation changes from n-alkanes on the Ullafelsen? (iv) Is there evidence for human impact from black carbon on the Ullafelsen? (v) Can we gain new insights from merging existing knowledge with new biomarker-based findings?
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