The volcanic ash, representing the principal component of the deposit, is composed of shards and pumices of phonolithic composition with millimetre-sized phenocrysts of sanidine. The non-volcanic component consists of quartz clasts and, to a much lesser extent, feldspars and fragments of metamorphic rocks.
Thermal (TL) and optical stimulated luminescence (OSL) techniques were used to date the potassium feldspar crystals of volcanic origin and the quartz crystals from the non-volcanic component. The stratum contains sediments of different origins. The feldspar fraction was subjected to high temperatures at the moment of volcanic emission, zeroing the internal luminescence clock. The quartz fraction was exposed to light probably only at the moment of sedimentation, with the possibility of only partial bleaching of luminescence signal. OSL ages are chronologically undistinguishable between the quartz and feldspar fractions. The quartz and feldspar fraction ages obtained by OSL are, respectively, 28±3 ka and 27±2 ka. TL measurements reveal an age of 41±3 ka for the quartz fraction and 33±3 ka for the feldspar fraction. The age and chemical and mineralogical composition of the volcanic fraction indicate the source for the large explosive eruptions occurred in the Campanian area (Ischia-Flegrei, southern Italy) between 42 and 25 ka.