Giuliano Ruggieri, 1965. "A Contribution to the Stratigraphy of the Marine Lower Quaternary Sequence in Italy", International Studies on the Quaternary: Papers Prepared on the Occasion of the VII Congress of the International Association for Quaternary Research Boulder, Colorado, 1965, H. E. Wright, Jr., David G. Frey
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Progress in the knowledge of the Italian Quaternary sequence has been retarded by some preconceived ideas and by objective difficulties in the dating of series of terraces or even of isolated terraces.
Among the first ones is the correlation between the Calabrian and the Villafranchian. Such a correlation is generally admitted despite some evidence to the contrary, for instance, the finding of the remains of Villafranchian vertebrates in a Pliocene marine deposit in Tuscany, indicating that the beginning of the Villafranchian preceded that of the Calabrian.
The boundary between the Pliocene and the Pleistocene has been proposed by different researchers through different means, often on the basis of the occurrence of “northern guests,” which determined the beginning of the Calabrian. Artica islandica (L.) gives an older limit than that obtained by using Hyalinea balthica (Schr.).
The difficulty in distinguishing the Sicilian from the Calabrian through paleontology can be overcome by considering the gastropod Natica tigrina Defr. Very common from the Pliocene to the Calabrian, it evolved so rapidly during the interval from the Calabrian to the Sicilian that by the Sicilian it had differentiated into a new species, N. millepuntata Lamck. The use of these fossils makes possible corrections in a number of datings; two examples of these are given.
A phenomenon that until now has not been properly understood is the reappearance during the Sicilian of species that had appeared to die out during the Calabrian or even in the Pliocene. If these are properly understood, we can avoid placing formations in the Calabrian or Pliocene when in reality they belong in the Sicilian.