I molluschi pleistocenici della Rocca del Campione (Cherasco, CN) nel quadro dell’evoluzione geologica e paleoambientale del Fiume Tanaro

ABSTRACT – [The Pleistocene molluscs of Rocca del Campione (Cherasco, NW Italy) in the frame of the geological and palaeoenvironmental evolution of the Tanaro River] In the quaternary outcrop of Rocca del Campione located in the municipality of Cherasco, province of Cuneo, NW Italy, sandy-gravelly continental deposits in sub-horizontal layers occur, unconformably overlying a marly Messinian succession. The deposit is about 10 m thick and lays ca. 40 m above the water level of the Tanaro River, which abundantly eroded this deposit, so that a limited remain of the deposit was left behind. The palaeontological remains (mainly molluscs) have been studied with the purpose of reconstructing the plaeoenvironmental evolution during the Pleistocene, also using the information of foregoing works. Some components of the malacofauna, such Discus perspectivus (von Mühlfeldt) or Helicodonta angigyra (Rossmässler) can be attributed to a warm temperate and humid climate, yet they are found with minor frequency than those species which are less thermophilic, such as Succinea oblonga Draparnaud or Galba truncatula (Müller). Among aquatic molluscs we report species adapted to still-water or wetland condition, such as the bivalve Pisidium pseudosphaerium Schlesch. There are also species of open environment, such as Vallonia pulchella (Müller), but in definitely lower frequency. Also Charophyta occur, only in the older layers, including Lichnothamnus barbatus (Meyen), characteristic of shallow and cool water. The abundance of the aquatic species decreases from older to younger layers, whereas the one of terrestrial species is increasing, so that in the succession we can point out the transition from an environment covered by shallow water to another with a nearly dry soil. The deposit yielded remains with a definite biochronological indication, such as a M2 tooth of Arvicolidae and a few shell of the gastropod Belgrandia cf. B. latina (Settepassi), which point to a late quaternary age (late Pleistocene?). In consideration of the geographic and palaeogeographic context we believe that the deposit can result from the deposition in an ancient bed of the Tanaro River, which was going to be abandoned. This possibly occurred during a stadial/interstadial climatic oscillation, corresponding to a pause of the intense erosional activity which led to the formation of the deeply incised present Tanaro valley. Judging from the results obtained we can hypothesize that the deposit corresponds to one of the cool oscillations after the last interglacial (MIS5).