Conclusions. The thermal waters hosted in the Mesozoic carbonatic platform of the Friuli
Venezia Giulia coastal area have the nature of ancient, diagenetically modified seawater. Srisotopes
indicate that the deep saline reservoir might represent remnants of seawater entrapped
in the Cretaceous carbonate strata during the late Oligocene - Miocene sea transgression
which followed the uplift of some portions of the carbonatic units during upper Eocene. The
carbonatic aquifer has a complex geometry, is confined and interested by important fault
systems which allow the development of hydrothermal cells and some local mixing with the
shallower freshwater aquifers. The data indicate that the waters outflowing at Monfalcone
and sampled by the deep wells of Grado-1 and Lignano likely fed by the same regional saline
reservoir, which underwent interactions with more superficial aquifers at different extent in
the different sites.
