An 18m thick volcaniclastic interval in Pantelleria Trough, Sicily Channel, deposited from a large gravitative flow during the Green Tuff eruption

A 30-m long piston core from the floor of Pantelleria Trough penetrated an 18 m thick volcaniclastic interval under- and overlain by hemipelagic sediments. The distribution and thickness of the interval is mapped in 3.5 kHz profiles across the trough. Core sediments have been analysed for grain size, carbonate content, detrital petrology, and physical properties such as bulk density and magnetic susceptibility. Chemical analyses of tephra and included minerals have been made by electron microprobe. The volcaniclastic interval is correlated with the youngest large explosive eruption on Pantelleria, the 50 ka Green Tuff ignimbrite eruption, on the basis of the sedimentation rate of overlying sediment, calcareous nannofossil and foraminiferal biostratigraphy, a calibrated radiocarbon age of 43-47 ± 02 ka (possibly infinite) in the underlying marls, and many similarities in tephra and mineral chemistry and abundance. The lower 8 m of the volcaniclastic interval consists of poorly sorted massive units of lapilli tuff, interpreted as resulting from the direct flow of a pyroclastic flow into the sea, with the energetic hyperconcentrated flows crossing the length of Pantelleria Trough and eventually freezing on the low gradients. The overlying 10 m thick turbidite probably developed from the dilute turbulent pyroclastic flow of the co-ignimbrite cloud and the resulting turbulent subaqueous flow eroded bioclastic material from the shelf and deposited a well-graded bed from sand through silt to mud. The poorer sorting of the volcaniclastic interval compared with the Green Tuff ignimbrite on land supports the concept that ignimbrite deposits are sorted by aggrading bed processes.