Presenza di depositi medio-pleistocenici intensamente deformati in Val Cerrina (Monferrato settentrionale)

Presence of intensely deformed middle Pleistocene deposits in Val Cerrina (Northern Monferrato area)

Abstract

A succession of gravel, sand and silt continental terraces resting on a Messinian clayey-marl substrate has been observed in a quarry near the village of Castagnone, near Pontestura (province of Alessandria). The oldest of the five cover complexes contained fragments of fossils, including a broken upper molar of Dicerorhinus hemitoechus, and a complete, left mandibular molar of Megaceros cf. verticornis. This association is typical of the repopulation of Europe on the part of new vertebrate forms that replaced the Villafranchian fauna. The earliest phases of this changeover go back to 0.69 to 1 m. y. Poorly preserved fossils of Limnaea and Planorbis and Bithinia opercula were also found. The more recent complexes could not be dated. They are, however, terraced and their surface is at the same height as other terraced surfaces in Val Cerrina. The series displays marked evidence of tectonic activity. A roughly northward overthrust of Messinian marly clays over the earlier Quaternary gravelly sands can be recognized. The structure exposed over some 60 ÷ 70 metres is displaced by direct faults in at least three places.