New sedimentological and coastal and marine geological data on the Quaternary marine deposits of the Ischia island (Gulf of Naples, Southern Tyrrhenian sea, Italy)

Quaternary marine deposits of the Ischia island have been analyzed based on marine geological survey and sedimentological data. The Ischia island represents the emerged part of a large volcanic field, extending from the Procida island to the submerged volcanoes of the western Ischia offshore. The volcanic field develops over an area of about 42 km2, E-W trending, composed of calderas, such as the Ischia caldera, linked to the great explosive eruptions, plinian and ignimbritic ("Sintema del Rifugio di S. Nicola"). The grain-size analyses of sea bottom samples have evidenced the occurrence of gravelly sands, sands, silty sands, muddy sands, sandy silts and silts. The comparison of the obtained results with previous sedimentological data collected in the Ischia offshore, coupled with the construction of marine geological maps at the 1:10.000 scale has shown that the sands seem to prevail in the eastern Ischia offshore, while the gravelly sands, mainly bioclastic are located at the top of relict volcanic edifices, such as the Forio Bank (western Ischia offshore) and the Ischia Bank (south-eastern Ischia offshore). Moreover, the obtained data have evidenced the occurrence of rhodolith beds on the relict volcanic edifice of the Ischia Bank and the on the related parasitic vent and in the Ischia Channel, a morphological saddle located between the Ischia and Procida islands.