Prove palinologiche dell’età pleistocenica inferiore di depositi « villafranchiani» in Piemonte

Palinological evidence of lower Pleistocene age of «Villafranchian» deposits in Piedmont

Abstract

This paper deals with the palinological and sedimentological studies of continental sediments usually indicated as « Villafranchian » on account of their facies and stratigraphic position, and assigned to the Pliocene. The outcrops in question lie in the pre-Apine area between the points where the Stura di Lanzo and Orco streams debouch into the plain, or, more precisely, along the incision of the Rio di Ca’ Viettone, in the municipality of Levone Canavese (Province of Turin). Samples for sedimentological and palinological analysis were taken from an approximately 40 m thick and an approximately 7 m thick section, consisting of a series of sands locally alternating with pebble layers with subordinate pelitic horizons, that can be regarded as the distal deposits of large conoids. The pelite facies, in particular, appears to reflect sedimentary episodes within small, ephemeral sheets of water, i. e. the ideal environment for the accumulation of plant remains and pollens, topped from time to time by coarser deposits in the form of fluvial overbanks. The series displayed a qualitatively poor association of Tertiary pollens, though some typical plants, such as Taxodium, Cedrus, Tsuga and Carya were still present. Taxodium/Sequoia was entirely absent in the top part only; enabling this to be classed as lower (or middle) Pleistocene and the remaining levels as the end of the Pliocene. These findings suggest that « Villafranchian » sediments are, almost in part, lower (or middle) Pleistocene rather than only Pliocene. It also seems likely that the boundary between the initially marine and subsequently continental lower sedimentary cycle, marked by primarily fine deposits and not subjected to terracing during its sedimentation, and the upper, solely continental and typically terraced cycle, with its generally coarse deposits, does not correspond to the Plio-Pleistocene boundary, but lies within the lower (or middle) Pleistocene. It thus represents a sudden, intense geodynamic event rather than a climatic change.