New Villafranchian finds from the Lower Valdarno (Tuscany, Central Italy)

Abstract

The deposits of the Elsa river Graben and its northwestern extension - namely the basin between Montealbano, to the East, and the Pisani Mountains, to the West - are cut through by the Arno river, which sharply separates a southern domain prevailingly characterized by Plio-Pleistocene marine sediments, from a northern one, mostly characterized by continental deposits. During recent field surveys of the continental sequences, (Middle?) Late Villafranchian (from about 2.5 to about 1 Ma) terrestrial mammal remains were found, which yielded substantial stratigraphical information on the study area. Fan delta conglomerates, disconformably overlying the deposits of the Middle Pliocene cycle (dated to about 2.5 Ma on the basis of paleomagnetic evidence) in the area near the small town of Vinci, provided remains of Sus cf. strozzii, of a large-sized Equus stenonis cf. vireti and hyenid's coprolites. In the area between Lamporecchio and Stabbia, the conglomerates are overlain by sediments that yielded several Viviparus cf. ampullaceus specimens and a tooth of Castor plicidens. Coeval to the latter sediments are the deposits underlying Mid-Pleistocene gravels along the southern and southeastern cliffs of the Cerbaie Hills. Geological and paleontological observations have shown that these sediments do not belong to the Pliocene marine sequences as previously believed, but are prevailingly continental deposits which are likely to be referred to the Upper Villafranchian (about 1.7 / 1.0 Ma). If confirmed by further evidence, the fossil mammals from Vinci are particularly significant because they sugges the presence of Middle Villafranchian deposits (about 2.5 -2.2 Ma) which may well fill in the hiatus that is believed to separate the end of the Pliocene cycle - marked by the renowned continental mammals from Montopoli - from the new tectonic phase responsible for the formation of the new continental basin. Eventually, the occurrence of Hippopotamus cf. tiberinus at San Regolo, on the left side of the Arno river, would indicate the presence of Late Villafranchian or Galerian deposits (about 1.0 / 0.5 Ma) which had never been reported up to now.