II
ABSTRACT
Prior to the definition of a geotechnical model of Castagneto Carducci plain, a geological survey, supported by detailed photo-interpretation studies, was needed in order to produce a geological map of the plain (1:20.000). The map would be used as the basis for addictional geotechnical investigation. These studies showed that the plain of Castagneto Carducci, belonging to the Neogenic basin of Castiglioncello - St.Vincenzo, is characterized by both continental and marine deposits belonging to the “Neoautoctono Toscano” complex.
These deposits have been subdivided into:
- Lacustrine and lagoonal - evaporitic Miocenic Deposits
“Argille, sabbie e marne sabbiose lacustri con Bithynia” (Clay, sand and marlstones lacustrine deposits with Bithynia)
“Conglomerato di Montebamboli” (Conglomerate of Montebamboli)
- Marine Pliocenic deposits
“Conglomerati della trasgressione pliocenica” (Conglomerates of the Pliocenic transgression) “Argille Azzurre” (Sky-Blue shales)
- Marine and continental deposits of Middle\lower Pleistocene
“Calcareniti sabbiose, sabbie e conglomerati di Bibbona” (sandstones, sands and conglomerates of Bibbona)
“Conglomerati di Bolgheri” (Conglomerates of Bolgheri) “Sabbie di Val di Gori” (Sands of Val di Gori)
- Marine and continental deposits of Late Pleistocene “Calcareniti di Biserno” (sandstones of Biserno) “Sabbie di Donoratico” (Sands of Donoratico)
“Ghiaie e sqabbie di Quadrelle” (Gravels and sands of Quadrelle)
In addition to the mentioned neogenic deposits, Holocenic deposits are widely represented: recent floods, coastal dunes, lacustrine and lagoonal marsh, clay and silt.
The correlation between the surface geology and logs from mechanical surveys yielded geological sections that helped build the subsurface model.
Surface investigations and the geological sections showed that continental deposits, linked to at least three fluvial cycles, are detected in the plain in addition to coastal marine deposits such as “Calcareniti sabbiose, sabbie e conglomerati di Bibbona” and “Calcareniti di Biserno”.
These deposits were terraced afterwards. Three terrace systems can be pointed out:
1) The oldest terrace (Middle Pleistocene), which lies in unconformity (toplap) with Pliocene and Miocene sediments, and sometimes on pre-neogenic geological formations.
2) A more recent terrace characterized by Neogene formations of the last cycle (Upper Pleistocene) onlapping against the upper terrace.
3) The last terrace, where the Holocene deposits lie on the Neogene formations of the last cycle. The results confirm the stratigraphic and tectonic schemes previously proposed bay many authors for the study area. The authors recognized a recent upflit that involved either continental and marine deposits belonging to Middle\Upper Plestocene formations.
