Caratterizzazione petrologico-tessiturale di una successione piroclastica in prossimità di Monte Salto del Cane (versante meridionale dell'Etna): implicazioni sui processi di alterazione e di pedogenesi

Within the frame of investigations on the processes of volcanic soil formation at Mount Etna, a tephra section was cored to a depth of 130 cm, on the southern flank of the volcano (1372 m a.s.l.), near to the Monte Salto del Cane adventive cone. Eight levels were distinguished (on the grounds of soil science criteria; Dazzi, pers. comm.), in the core, samples of which were distributed among several research units. Field and laboratory data suggest that the various levels of the sampled sequence belong to distinct eruptive episodes, the differences among them being chiefly due to their petrological features and emplacement conditions. The primary chemistry commonly appears less changed in the coarse fraction (>2 mm) than in the the finer-grained one, where elements like Si, Mg, Ca, and alkalies are preferentially extracted by weathering and hydration processes, leading Al, Fe, and Ti to be passively enriched there. Integrated field, textural and pétrographie data give some information on the succession and type of the various eruptive episodes. The whole sequence was divided into two intervals, due to the presence of an interlayered paleosol level: the lower interval is composed of four monocomponent levels (Walker, 1971). The three lowest ones are given by fall-out deposits (juvenile lapilli and ash), whereas the fourth one, composed of lithic fragments, is probably related to phreatic explosive episodes. At the top of the lower interval a deeply weathered level probably marks an eruption, followed by a quiescent stage long enough to allow the paleosol to be formed. The upper sequence is made up of three levels, the lowest and thickest of which might be referred to the plinian» 122 b.C. eruption deposit.