Integrated geological and petrographic study supporting the interpretation of ancient artefacts: the case history of Palagonia area (SE Sicily)

A little area located in the northern margin of the HybleanPlateau (SE Sicily), close to the little town of Palagonia (administrativeterritory of Catania), in the archaeological area of Caltagirone,was studied by means of geological and petrographic integrated surveys.The starting point for the study was the occasional discovery ofan uninterpreted ancient artefact, whose manufacture was oursubject of interest.The geological-geomorphological study consists of detailed fieldmapping at 1:10.000 scale and of the reconstruction of the stratigraphyand of the hydrogeological setting of the site.The area is characterized by a succession of interbedded volcanicand sedimentary litotypes ranging in time from the latePliocene to Holocene affected by tectonic episodes causing theformation of a graben-horst setting.In detail, the find is located close to a graben whose floor wasoccupied by a lake (now disappeared) in the Holocene time, representinga superficial aquifer system. Furthermore, the detailedreconstruction of the stratigraphic succession, represented by athick horizon of vulcanoclastites (late Pliocene-early Pleistocene)overlapped by a thin level of calcarenites (early Pleistocene) wascoupled with petrographic investigations, that emphasized thedegree of alteration of the volcanoclastic sequence, as testified bythe widespread occurrence of secondary authigenic minerals suchas clayey material that substitute volcanic glass and primary mineralsand, at the same time, fills in the open vesicles; this processdetermines an increase in impermeability of the site’s substratumcompared to the overlying calcarenite. Thus, the geological and petrographicdata suggest the presence during the recent past, of ashallow unconfined aquifer.The collected data, that testify a probable high availability ofwater, are in agreement with the direct observation of the ancientartefact, mainly represented by a system of circular and squaredchambers linked by narrow trenches, of which we also estimatedpotential the water amount that could be stored in.