Abstract
This research focuses on the effects of the last eruption occurred at Ustica, which formed the Falconiera tuff-cone at around 130 ka BP in the north-eastern tip of the island. This eruption was mainly explosive and phreatomagmatic, with the emplacement of a series of pyroclastic-surge beds that determined the formation of an asymmetric tuff cone. This is the most easily recognizable Ustica volcanic edifice, although its north-eastern sector has been partially dismantled by the erosion. A section of the feeding conduit is exposed northward, showing the solidified lavas that fed the latest stages of the eruption. These were characterized by the formation of an intracrateric lava lake and a Strombolian scoria-fallout deposit. The eruption occurred during the Upper Pleistocene Marine Isotopic Substage 5.5, a warm period characterized by a high sea-level stand (6±3 m above the present sea level in stable areas) and the diffusion in the Mediterranean sea of subtropical flora and fauna. This eruption slightly modified the Ustica morphology, but impacted on both marine and terrestrial environments, burying beach deposits rich of mollusk shells (i.e. Strombus bubonius, Conus testudinarius, Brachidontes puniceus) , colonies of corals ( Cladocora caespitosa ) and subaerial plants ( Chamaerops humilis ). These organisms, found in some cases in their vital position, along with other lines of evidence, give information on the palaeogeography of this sector of the island at the time of the eruption, and on the local impact of this event on the environment.
Highlights
The island of Ustica is the top of a vast submerged volcanic complex that rises more than 2,000 m from the bottom of the Tyrrhenian Sea on thinned continental crust [15-20 km; Giese and Morelli, 1973]
The origin of Ustica volcanism has been related to the activation of left-transtensional deep faults, linked to the deformational events that accompanied the and reaches a maximum elevation of 248 m asl It is anticlockwise rotation of the Italian peninsula and the mainly composed of volcanic rocks, and subordinately opening of the Tyrrhenian basin, in the course of the SANDRO DE VITA AND FRANCO FORESTA MARTIN
The Falconiera tuff-cone succession shows a quasi-regular alternation of fine-grained, plane-parallel and cross-stratified base surge deposits, and massive to crudely stratified, coarse-ash surge and scoria fallout deposits. This kind of succession can be interpreted as the product of a pulsating energy during the eruption, in which water gained periodic access to the volcanic conduit. This generated a series of closely-timed repetitive explosions that emplaced base surge deposits, that dispersed radially away from the vent, up to a distances
Summary
The island of Ustica is the top of a vast submerged volcanic complex that rises more than 2,000 m from the bottom of the Tyrrhenian Sea on thinned continental crust [15-20 km; Giese and Morelli, 1973]. It is situated 60 km north of the Sicily coast, west of the Aeolian arc, and a few km east of the E-W trending Anchise seamount (Figure 1). Ustica basalts are characterized by incompatible elements and Sr-isotope ratios that are intermediate between intraplate basalts from Pantelleria and calc-alkaline mafic rocks from Aeolian islands [Cinque et al, 1988]. The origin of Ustica volcanism has been related to the activation of left-transtensional deep faults, linked to the deformational events that accompanied the and reaches a maximum elevation of 248 m asl It is anticlockwise rotation of the Italian peninsula and the mainly composed of volcanic rocks, and subordinately opening of the Tyrrhenian basin, in the course of the
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