Widespread syn-eruptive volcaniclastic deposits in the Pleistocenic basins of south-western Calabria

Since late Tortonian, depositional sequences developed along the Southern Calabrian forearc, inside the halfgrabendepressions of the Mesima-Gioia Tauro and Reggio Calabria basins. In these basins volcaniclasticsedimentation took place during lower to middle Pleistocene. Volcaniclastic deposits consist of isolatedpumice swarms, ash layers and thick successions of lapilli and ash.In this paper we describe and discuss the depositional characteristics of these volcanogenic sediments andthe morphology, mineralogy and chemistry of pumices, shards, lithics and crystal fragments. These depositsall have the characteristics of a proximal tephra fall deposit from a Plinian plume, which has been reworkedin a shore environment. In the Mesima basin the deposits reach 6 m in thickness and in the Gioia Tauro plain21 m of pumiceous sediments have been cored in a drill hole. The compositional homogeneity of fragmentsand the absence of non-volcanic detritus as well as of soil or organic matter suggest that the deposits werequickly reworked after their primary emplacements. All the tephra deposits exhibit calc-alkaline affinity anddacitic to rhyolitic composition. The mineralogical assemblage, including orthopyroxene as phenocryst,indicates provenance from magmatic-arc volcanism. ICP-MS and LA-ICP-MS analyses of crystals and glasspoint to a common origin, probably from a single eruption. This makes these volcaniclastic layers a veryuseful tool for stratighaphic reconstructions at a regional scale.The geological setting of the deposits, their petrological and geochemical signature and the occurrence oflarge-size clasts suggest a provenance from explosive eruptions preceding the emplacement of the 50 kadacitic lava dome of the island of Panarea (Aeolian Archipelago). However a provenance from a different calcalkalinevolcanic system cannot be excluded. These deposits can therefore represent the only evidence of alarge explosive eruption in the Southern Tyrrhenian Sea whose very proximal equivalent is not preserved.