3). The facies Ac at the bottom of the cores SG27 and SG28 testifies to the existence of a river delta channel present before the lagoon ingression in this area (i.e. before 784 BC). The dating of a peat sample at 7.37 m below m.s.l. in SG28 gives the age as 2809 BC (Eneolithic Period) and supports this hypothesis. The river delta channel probably belonged to the Brenta river, because it flowed within the geographical area of the Brenta megafan reconstructed in Bondesan et al. (2008) and RG7204 Fontana et al. (2008). The facies P in SG28, instead, is proof of the abandonment of this path by the river and testifies a phase of an emerged delta plain in the area, near the lagoon

margin. The abundant vegetal remains found within this sedimentary layer consist of continental, palustrine and lagoonal vegetation. Probably, between 2809 BC and 784 BC, the river channel moved from the SG28 core position, occupied before 2809 BC, to the position of the SG27 core. The river channel is possibly the same alluvial channel that crossed the Venice subsoil found through passive and controlled source seismic surveys by Zezza (2008) and Boaga et al. (2010). The facies BMS-387032 order Lcs and Lcl in SG25, SG27 and SG28 belong to a more recent tidal channel. This tidal channel occupied the river path as a result of the lagoon ingression in this area (784 BC). The river channel became gradually

influenced by lagoonal brackish water evolving into a tidal channel.

The tidal channel is clearly visible in the southern part of profile 2 (Fig. 2b) and 3 (Fig. 2c) and in the full fantofarone profile 4. The inclined reflectors in profile 2 and 3 correspond to the palaeochannel point bar migration northward by 20–30 m. The stratigraphic record of core SG25 (Fig. 2c) presents sandy sediments (facies Lcs) from 6.60 m to 5.2 m below m.s.l. and mainly clayey-silty sediments (facies Lcl) between 5.2 and 1.2 m. The 14C dating on a mollusk shell at 5.2 m below m.s.l. between the two sedimentary facies dates back to 352 AD, showing that the channel was already active during Roman Times. It is possible to distinguish two different phases in the channel evolution: the first phase being a higher energetic regime with sand deposition and channel migration; the second phase having a finer filling with apparently no migration. The deterioration of the climatic conditions during the first Medieval Cold Period starting from the 4th century AD (Veggiani, 1994, Frisia et al., 2005 and Ljungqvist, 2010) possibly explains this change in the channel hydrology. In the same period, an increase in sea level caused the abandonment of many human settlements in the lagoon area (Canal, 2002). Only in the 6th–7th century, a more permanent phase of settlements took place in the lagoon of Venice. The palaeochannel was still active in 828 AD, i.e.