Revisiting the subalpine Mesolithic site Ullafelsen in the Fotsch Valley, Stubai Alps, Austria – new insights into pedogenesis and landscape evolution from leaf-wax-derived n-alkanes, black carbon and radiocarbon dating

Zech, Michael; Lerch, Marcel; Bliedtner, Marcel; Bromm, Tobias; Seemann, Fabian; Szidat, Sönke; Salazar, Gary; Zech, Roland; Glaser, Bruno; Haas, Jean Nicolas; Schäfer, Dieter; Geitner, Clemens

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.

page172Our results for modern vegetation suggest that leaf-wax-derived inline-formulan-alkanes allow us to chemotaxonomically distinguish between subalpine deciduous trees (inline-formulanCinline-formula27 predominance) versus (sub)alpine grasses, herbs and dwarf shrubs (inline-formulanCinline-formula29, inline-formulanCinline-formula31 and/or inline-formulanCinline-formula33 predominance). Except for Juniperus, conifers produce no or extremely low inline-formulan-alkane contents. Although no clear vegetation changes could be inferred from the inline-formulan-alkane patterns of the investigated soil profiles, the total inline-formulan-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 Hinline-formula2Oinline-formula2-pretreated soil samples yielded inline-formula14C 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 inline-formula14C ages (ages of inline-formula≥ 9.5 cal kyr BP) versus the inline-formula14C ages obtained for bulk inline-formulan-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 inline-formulan-alkane-producing vegetation cover (grasses, herbs or dwarf shrubs) started to predominate.

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Zech, Michael / Lerch, Marcel / Bliedtner, Marcel / et al: Revisiting the subalpine Mesolithic site Ullafelsen in the Fotsch Valley, Stubai Alps, Austria – new insights into pedogenesis and landscape evolution from leaf-wax-derived n-alkanes, black carbon and radiocarbon dating. 2021. Copernicus Publications.

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