New constraints on the occurrence of Y-3 Upper Pleistocene tephra marker layer in the Tyrrhenian Sea.

A widespread tephra layer, other than the well known Y-5, has been identified in the Upper Pleistocene marine succession in the Tyrrhenian Sea. Two investigated gravity cores showed, in fact, the presence of two companion pyroclastic tephra layers, separated by a varying thickness of pelagic sediments. The pyroclastic layers are mainly made up of pumice fragments and glass shards together with few K-feldspars and clino-pyroxene crystals. Both layers are alcali-trachytic in composition, even though a sharp difference emerges in the K/Na ratio that characterizes the two glasses. 14C dating of foraminiferous shells embedded in the clay layers directly underlying the most recent tephra gave an age of about 26 ka. An accurate review of literature regarding tephrostratigraphy in the Mediterranean area made it possible to correlate the older one to the Y-5 marker layer, joined to the Campanian Ignimbrite eruption, a paroxystic event in the Campi Flegrei area. The younger layer has been correlated with the Y-3 marker layer and probably represents another huge pyroclastic flow event from the Campanian area, whose products have not yet been distinguished in the field from those of typical Campanian Ignimbrite. This work clearly identifies the layer Y-3, firstly recorded by Keller et al. (1978), as the result of a specific volcanic event different from the Campanian Ignimbrite (marker layer Y-5), defines its mineralogical and chemical composition together with its relative age offering an useful support for paleoclimatic and paleoenvinromental reconstruction of the sedimentation in the Tyrrhenian area.