*3.2. Structural and Lithostratigraphic Setting*

The lithostratigraphic setting of the plain comprises sediments of the Plio-Pleistocene and Holocene ages. East of the study area, this sequence is underlain by marls. Marly limestone and marls have been found in some wells NE of Aspropyrgos City at depths between 63–71 and 96–170 m from the ground surface, respectively [36,37]. Cretaceous limestone and Triassic carbonate occur at the depths of 20–40 and 80–100 m from the ground surface, respectively, N of Eleusis City. Arkoses, greywackes, and shales of the Palaeozoic age have been found NE and SE of the study area in alternations with phyllites.

The Thriassion Plain was influenced by tectonic factors during the Neogene-Quaternary [34,35,38–40]. The Triassic carbonate is massive in a large extent, and, in some places, it is karstified, depending on the extent to which it has been affected by karstification and/or tectonism. During Pliocene and Pleistocene, intense tectonic actions created horsts and grabens (Figure 4). Geophysical research carried out in the area by [38] showed that the Mesozoic basement is not found to the depth of 320–450 m at the central part of the plain. The study area has been influenced by Pleistocene sea level changes, as well [41–44].

**Figure 4.** Geological-Hydrogeological cross-section of the N-S direction.
