Early Pleistocene distal pyroclastic-fallout material in continental and marine deposits of western Umbria (Italy): chemical composition, provenance and correlation potential

Abstract

Bizzarri R. et al., Early Pleistocene distal pyroclastic-fallout material in continental and marine deposits of western Umbria
(Italy): chemical composition, provenance and correlation potential. (IT ISSN 0394-3356, 2010).
Distal pyroclastic fallout material has been recently documented in the Orvieto area (Umbria, central Italy), within Early Pleistocene
continental and marine deposits. Due to the age constrains, the association with Middle Pleistocene “Paleobolsena” Volcanic events
can be excluded. In order to individuate a possible provenance, the Laser Ablation – Inductively Coupled Plasma – Mass
Spectrometry (LA-ICP-MS) analytical procedure has been carried out. The procedure has been tested on pumice lapilli (2-5 mm) and
glass inclusions contained in idiomorphic clinopyroxene crystals, both coming from the Early Pleistocene conglomerate of the Il Caio
section. The study is still in progress: some preliminary results are here proposed. Data on melt inclusions seem to be more reliable
than data on pumice fragments for the purpose of recognising pristine magmatic compositions of pyroclastic material and to achieve
information on the provenance of volcanic clasts. Nevertheless, both data suggest the affinity with the Roman Comagmatic Provence.
Since crystal fragments with melt inclusions are common in many distal fallout deposits, the LA-ICP-MS protocol presented here can
be of general application to tephrochronology and volcanological studies. Together with the biostratigraphic record, indeed, the procedure looks promising as a tool for stratigraphic correlations and geodynamic reconstructions.