Normal and chaotic messinian successions at the North-eastern margin of the Langhe domain, Tertiary Piedmont Basin

Geological mapping and stratigraphic analysis of the upper Miocene sediments of the north-eastern sector of the Langhe basin have allowed both to distinguish, within the Gessososolfifera Formation, a «normal» succession and a «chaotic» interval of sediments and to define their stratigraphic relationships. The former was deposited during the evaporitic stage, even if the almost complete absence of primary evaporite deposits and the lack of any proof of subaerial exposure indicate that the effects of the sea level drop related to the Messinian salinity crisis were more subdued in the studied area that never experienced a complete prolonged desiccation. The chaotic sediments are quite similar to the chaotic complexes already recognized in other sectors of the Tertiary Piedmont basin. The observed stratigraphic relationships suggest that the chaotic interval was deposited at the beginning of the post-evaporitic stage. Intra-Messinian tectonic deformation probably played a fundamental role in the genesis of mass-wasting processes, that affected large portion of the Messinian succession. These data confirm that remarkable heterogeneities exist between Messinian deposits of the different areas of the Tertiary Piedmont basin and that good similarities can be drawn with the Messinian succession of the Apennine foredeep.