Late glacial explosive activity on Mount Etna: Implications for proximal–distal tephra correlations and the synchronisation of Mediterranean archives

Abstract

Plinian and Ignimbrite deposits represent explosive activity (ca. 17–19calka) within the predominantly effusive and mildly explosive (Strombolian) volcanic history of Mount Etna (Italy). Proximal glasses from the Biancavilla Ignimbrites and Unit D Plinian fall deposits are characterised. Fall deposits recorded at Acireale (D1b and D2b) and Giarre (D1a and D2a) are geochemically distinct confirming they relate to different eruptions. The Acireale Plinian fall (D1b and D2b) deposits compositionally overlap with the Biancavilla Ignimbrite deposits. These explosive eruptions from Etna are considered responsible for widespread ash dispersals throughout the central Mediterranean region, producing the marker tephra layers (Y-1/Et-1) recorded in marine and lacustrine sedimentary archives. Stratigraphically these distal tephras occur at or close to the onset of the last deglaciation (Termination 1) within their respective palaeoenvironmental records, therefore making them potentially crucial tephrostratigraphic markers. This study investigates distal tephra deposits thought to be from Etna recorded in the Ionian Sea (Y-1), Lago Grande di Monticchio (LGdM, Italy; tephras TM-11 and TM-12-1), Lago di Mezzano (Italy) and the Haua Fteah cave (Libya). The glass chemistry of Y-1 tephras recorded in the Ionian Sea and at Haua Fteah is consistent with the Biancavilla Ignimbrites (16,965–17,670calyrs BP) and the upper Acireale Plinian fall (D2b). The LGdM record indicates that explosive activity on Etna associated with Unit D spans a minimum of 1540±80 varve years. TM-12-1 (19,200–19,804calyrs BP) in LGdM appears to represent the oldest distal counterpart of Etna Unit D explosive activity and is associated with the lower Acireale (D1b) Plinian eruption. The proximally undefined TM-11 (17,640–18,324calyrs BP) and distal correlatives are geochemically distinct from the Ionian Sea Y-1 tephra. Such significant compositional differences seen between distal tephra layers are not observed within individual proximal units and are likely to indicate that the distal tephras relate to separate eruptive phases. Until proximal relationships can be established, the TM-11 type Y-1 equivalents should be termed TM-11. Great care should be exercised when using these distal ash layers to synchronise sedimentary records during a crucial period of environmental change.