Tephrochronological dating of varved interglacial lake deposits from Piànico‐Sèllere (Southern Alps, Italy) to around 400 ka

Abstract

2006. Tephrochronological dating of varved interglacial lake deposits from Piànico-Sèllere (Southern Alps, Italy) to around 400 ka.ABSTRACT: The sediment record from the Piànico palaeolake in the southern Alps is continuously varved, spans more than 15 500 years, and represents a key archive for interglacial climate variability at seasonal resolution. The stratigraphic position of the Piànico Interglacial has been controversial in the past. The identification of two volcanic ash layers and their microscopic analysis provides distinct marker layers for tephrochronological dating of these interglacial deposits. In addition to micro-facies analyses reconstructing depositional processes of both tephra layers within the lake environment, their mineralogical and geochemical composition has been determined through major-element electron probe micro-analysis on glass shards. Comparison with published tephra data traced the volcanic source regions of the Piànico tephras to the Campanian volcanic complex of Roccamonfina (Italy) and probably the Puy de Sancy volcano in the French Massif Central. Available dating of near-vent deposits from the Roccamonfina volcano provides a robust tephrochronological anchor point at around 400 ka for the Piànico Interglacial. These deposits correlate with marine oxygen isotope stage (MIS) 11 and thus are younger than Early to Middle Pleistocene previously suggested by K/Ar dating and older than the last interglacial as inferred from macrofloral remains and the geological setting.

Centennial-scale oscillations in oxygen and carbon isotopes of endogenic calcite from a 15,500 varve year record of the Piànico interglacial

“…A 0.7 mm thick volcanic ash layer has been geochemically and mineralogically correlated with the Roccamonfina Brown Leucitic Tuff (Brauer et al, 2007b) dated from near-vent deposits at 393±12 ka. Using the estimated length of the MLP (8500 years) and the varve count from the BVC unit (15,500 years), the studied interval comprised the time span between about 415.1±12 ka (bottom of the BVC unit) and 391.1±12 ka (top of the studied sequence), with the BVC/MLP boundary at 399.6±12 ka.…”

“…On the basis of the tephrochronological match of the distal volcanic ash layer with the Roccamonfina Brown Leucitic Tuff (BLT; Brauer et al, 2007b), the stratigraphic position of the Piànico interglacial is assumed to correspond to MIS 11. This calls for a tentative correlation with marine and ice records from this time interval (Fig.…”

Tephrochronology and its application: A review

“…The compositions of plagioclase crystals, or pyroxene, amphibole, and olivine crystals, obtained by EPMA, frequently allow source volcanoes to be readily identified (Lowe, 1988a(Lowe, , 1988bSmith and Leeman, 1982;Preece et al, 2000;Brauer et al, 2006;Westgate et al, 2008). In New Zealand, for example, clinopyroxene and hornblende in late Quaternary Egmont-derived andesitic tephras are typically more calcic than those from Tongariro, and hornblende from these two andesitic sources is more pargasitic than that from the rhyolitic centres .…”

Combined µ-XRF and Microfacies Techniques for Lake Sediment Analyses

“…12.1b) that formed under interglacial conditions. The age of these deposits has been determined by tephrochronology at ca 400 ka BP thus coinciding with Marine Isotope Stage (MIS) 11 (Brauer et al 2007b). Although this age has been questioned (Pinti et al 2007) it still appears to be the most realistic estimate (Brauer et al 2007c).…”

“…The mean varve thickness varies between 0.2 and 0.8 mm. Four detrital layer facies, intercalated in the varve succession, have been described: 0.03 mm-6 cm thick detrital layers composed of Triassic dolomite, ma- (Mangili et al 2005) consisting of medium to coarse silt-sized detrital grains embedded in a matrix of fine-grained isomorphic calcite, clay layers and a tephra layer rich in volcanic glass (Brauer et al 2007b). Detrital layers are interpreted as triggered by extreme rainfall events (Mangili et al 2005).…”