Neolithic to Bronze Age Somma-Vesuvius activity improved by distal tephrostratigraphy

Mt Somma-Vesuvius (SV) volcano is one of the most dangerous volcanoes in the world. Many stratigraphic studies allowed reconstructing its eruptive history (e.g. Santacroce et al., 2008), which was characterised by few large explosive eruptions, and minor explosive and effusive events. The periods between large explosive eruptions were characterised by different behaviours, with the frequency of the minor eruptive events that increases with the decreasing age. As an example, very few explosive events are recorded into the proximal stratigraphy of the Mercato-Avellino interplinian period (between 8890±90 and 4365±40 cal yr BP). However, several phonolitic-trachytic tephra layers recognised in the Sulmona paleo-lake and dated between ca 7600 and 4800 cal yr BP (Giaccio et al., 2009) have been interpreted as products of the SV activity. This correlation contradicts the proximal data, and points out the need of further study in order to better constrain the eruptive history of the SV. Further material to this discussion is supplied by the tephrochronologic study of the marine core MD90-918 from Ionian sea (ca. 400 km S-E of SV). The core chronology and stratigraphy is supported by 14C AMS dating and isotopic δ18O. Geochemical investigations on the recognised tephra layers, indicate for the first time the existence of 5 distinct Vesuvian tephra layers in the Mercato-Avellino period, which encompass the Neolithic-Bronze Age transition. All the tephra layers are geochemically fully comparable to the phonolitic products of the Mercato and Avellino eruptions. It is noteworthy that they are geochemically different from the Sulmona basin’s tephra layers. The first and older tephra layer in core MD90-918 occurs during the Sapropel S1a, and can be easily correlated to the Mercato eruption. It is followed by a rhyolitic tephra layer which can be correlated to the Gabellotto-FiumeBianco eruption from Lipari island (Siani et al., 2004). The remaining 4 tephra layers have an astonishing similar composition with the Mercato products, suggesting that they were erupted from the same magma chamber. This finding evidences as distal archives can preserve more efficiently the traces of the past volcanic activity with respect to the proximal ones, and points out how the eruptive history of one of the most hazardous and studied volcanoes in the world is not yet completely resolved. Giaccio, B., et al., Tephra layers from Holocene lake sediments of the Sulmona basin, central Italy: implications for volcanic activity in Peninsular Italy and tephrostratigraphy in the central Mediterranean area, QSR (2009). Santacroce R., et al., Age and whole rock-glass compositions of proximal pyroclastics from the major explosive eruptions of Somma-Vesuvius: a review as a tool for distal tephrostratigraphy. JVGR (2008). Siani G., et al., Tephrostratigraphy study for the last 18,000 14C years in a deep-sea sediment sequence for the South Adriatic. QSR (2004) 23 : 2485-2500.