Redating the moraines in the Kromer Valley (Silvretta Mountains) – New evidence for an early Holocene glacier advance

Abstract

Among the many well-preserved moraine systems that are found throughout the Austrian Silvretta Mountains, a set of prominent moraines in the upper Kromer Valley located in front of the ‘Little Ice Age’ positions are of particular interest as they have been allocated to contrasting time periods in the past. Initial assumptions associated them with the transition period from the Younger Dryas to the early Holocene, but first exposure dating results published in 2006 suggested a relation to the ‘8200-year event’. However, since then, the lack of comparable evidence elsewhere in the Alps prompted a re-evaluation of the moraines at this site based on the recalculation of the original ages with the recently available lower 10Be production rate (‘Northeast North America’) and by dating additional boulders in the Kromer Valley and in the neighbouring Kloster Valley. The newly sampled boulders ( n = 9) show, depending on interpretation, moraine stabilization around 10,000 years. These ages implicate that glacier termination occurred considerably earlier than during the previously suggested 8200-year cooling event, but also clearly after the climatic cold period of the Younger Dryas (>11,700 years) and the Preboreal Oscillation (~11,400 years). Consequently, our results suggest that the Kromer Valley moraines represent a marked glacier advance during the Boreal period before the final recession to mid- and late Holocene glacier size.