On the origin and post-depositional history of widespread massive ash deposits: the case of Intermediate Brown Tuffs (IBT) of Lipari (Aeolian Islands, Italy)

We analysed a widespread, massive ash unit outcropping on the island of Lipari, which belongs to the IntermediateBrown Tuffs (IBT) succession of the Aeolian Islands, Italy.The use of amultidisciplinary approach that integrates textural, petrological and pedologicalmethods, allows usto discriminate between syn-eruptive and post-depositional features. The deposits are dominated byuncrystallised blocky glass fragments of homogeneous shoshonitic composition, confirming a provenance fromhydromagmatic eruptions on the island of Vulcano.Many glass fragments are surrounded by a coating separatedby a thin void of syn-eruptive origin due to alteration by aggressive acid gases in the eruptive cloud. The lack ofthis coating in the northern part of Lipari can be explained as a progressive dispersion of the gases far from thevent and/or to post-depositional processes. The degree of soil development significantly increases from south(soil profiles P1 and P2 at Valle Muria) to north (P3 and P4, at Madoro and Chiesa Vecchia sites, respectively)as a response to a decrease in slope steepness, which has brought about a progressive deepening of the pedogeneticfront on gentler landforms and conversely its rejuvenation on steep slopes. The relatively poor tomoderatedegree of pedogenic evolution of the studied IBT unit is consistent with its emplacement during part of the lastglacial period.