Megafans on the southern side of the Alps are known to respond to climatically-driven fluctuations of the sedimentary input from the Alpine range, especially in relation to major environmental changes related to Quaternary glaciations (Fontana et al., 2014). Aggradation/incision trends of these alluvial systems mirror the development and downwasting of valley glaciers, thus providing reliable proxy information on upland areas, which may be often scant, disjoined and difficult to date (Rossato and Mozzi, 2016; Rossato et al., 2018). In our investigation, we could integrate OSL and radiocarbon dating in the juxtaposed megafans of the Brenta and Piave rivers, through morpho-stratigraphic correlation and sediment provenance analysis. The catchments of these rivers include the highest portion of the Dolomites mountains, with main peaks exceeding 3000 m asl and extensive plateaus above 2500 m asl. We correlated the piedmont megafan sector of the Montebelluna Piave megafan (MPM) with the terminal moraines of the LGM Piave glacier ('Quero amphitheater') and the lower Alpine valley sector. Results show that the proximal sector of the MPM and related Piave valley alluvial fill were continuously aggrading in the 37-27 ka BP time-frame, well before the outermost positioning of the LGM glacier fronts at around 26 ka cal BP. This was accompanied by increased sediment production and fan aggradation in the unglaciated Prealpine tributary catchments, similarly to what observed in alluvial fans located to the east in the Friulian piedmont plain (Monegato et al., 2010). MPM alluvial succession shows no significant variation in lithofacies characteristics and assemblage, nor the presence of major unconformities, at the transition between MIS 3 and 2. Only sand petrography highlights a change in the drainage system just before 27 ka cal BP: a major tributary of the Piave River, the Cismon River, moved towards the Brenta catchment, probably due to the constant growth of the Piave glacier at the junction between these two systems. We conclude that valley glaciers in the upper Piave and Cismon catchments probably started to develop in the late MIS 3. Such environmental change could be related to the climatic deterioration recognized in the pollen sequence of nearby Fimon Lake around 38.7±0.5 ka (Pini et al., 2010) and correlated with Heinrich Event 4. References Fontana et al., 2014, Sediment. Geol. 301, 150-171. Monegato et al., 2010, J. Quaternary Sci. 25, 617-632. Pini et al., 2010, Quat. Sci. Rev. 29, 3115-3137. Rossato and Mozzi, 2016, Quat. Sci. Rev. 148, 115-127. Rossato et al., 2018, Earth Surf. Dynam. 6, 809-828.
Evidence of late MIS 3 onset of the last glaciation in the southern Eastern Alps
Sandro Rossato;Giovanni Monegato;
2019
Abstract
Megafans on the southern side of the Alps are known to respond to climatically-driven fluctuations of the sedimentary input from the Alpine range, especially in relation to major environmental changes related to Quaternary glaciations (Fontana et al., 2014). Aggradation/incision trends of these alluvial systems mirror the development and downwasting of valley glaciers, thus providing reliable proxy information on upland areas, which may be often scant, disjoined and difficult to date (Rossato and Mozzi, 2016; Rossato et al., 2018). In our investigation, we could integrate OSL and radiocarbon dating in the juxtaposed megafans of the Brenta and Piave rivers, through morpho-stratigraphic correlation and sediment provenance analysis. The catchments of these rivers include the highest portion of the Dolomites mountains, with main peaks exceeding 3000 m asl and extensive plateaus above 2500 m asl. We correlated the piedmont megafan sector of the Montebelluna Piave megafan (MPM) with the terminal moraines of the LGM Piave glacier ('Quero amphitheater') and the lower Alpine valley sector. Results show that the proximal sector of the MPM and related Piave valley alluvial fill were continuously aggrading in the 37-27 ka BP time-frame, well before the outermost positioning of the LGM glacier fronts at around 26 ka cal BP. This was accompanied by increased sediment production and fan aggradation in the unglaciated Prealpine tributary catchments, similarly to what observed in alluvial fans located to the east in the Friulian piedmont plain (Monegato et al., 2010). MPM alluvial succession shows no significant variation in lithofacies characteristics and assemblage, nor the presence of major unconformities, at the transition between MIS 3 and 2. Only sand petrography highlights a change in the drainage system just before 27 ka cal BP: a major tributary of the Piave River, the Cismon River, moved towards the Brenta catchment, probably due to the constant growth of the Piave glacier at the junction between these two systems. We conclude that valley glaciers in the upper Piave and Cismon catchments probably started to develop in the late MIS 3. Such environmental change could be related to the climatic deterioration recognized in the pollen sequence of nearby Fimon Lake around 38.7±0.5 ka (Pini et al., 2010) and correlated with Heinrich Event 4. References Fontana et al., 2014, Sediment. Geol. 301, 150-171. Monegato et al., 2010, J. Quaternary Sci. 25, 617-632. Pini et al., 2010, Quat. Sci. Rev. 29, 3115-3137. Rossato and Mozzi, 2016, Quat. Sci. Rev. 148, 115-127. Rossato et al., 2018, Earth Surf. Dynam. 6, 809-828.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
