Drill Hole SM-3 data in the vicinity of Porto Marghera also showed that
DZNep sediments deeper than 11 m, deposited before the formation of Venice Lagoon, are characterized by rapidly decreasing chloride concentrations (Fig. 6A). The much older estimated ages of the sediments below ~ 11 m depth, i.e., well over 10–12 thousand years (Gieskes et al., 2011b), attest to the pre-Lagoonal classification of these deeper sediments. Sediments below 11 m are part of a section characterized by a plethora of aquifers (Teatini et al., 1995 and Teatini et al., 2011), with Hole SM3 representing the upper section of shallow aquifers. In many previous investigations an aquitard has been reported at a depth of ~ 10 m. A chloride gradient into the Lagoonal section of the sediments suggests minor
diffusion of chloride into the deeper sediments, but in some locations sediments are affected by SGD (Rapaglia et al., 2010a). Chloride concentrations in the upper 5 m of SM3 are similar to those of nearby Site C (Fig. 6B). The upper 5 m of SM3 are characterized by elevated trace metal contents of the sediments (Gieskes et al., 2011b), which indicate a young age for this section, probably related to re-deposition of dredged sediments from the nearby canal.
