THE LATEST CONTINENTAL FILLING OF VALLE UMBRA (TIBER BASIN, CENTRAL ITALY) DATED TO ONE MILLION YEARS AGO BY MAGNETOSTRATIGRAPHY

Abstract

Bizzarri R., Albianelli A., Argenti P., Baldanza A., Colacicchi R. & Napoleone G., The latest continental filling of Valle Umbra (Tiber Basin, central Italy) dated to one million years ago by magnetostratigraphy. Paleogeography of central Italy during Pliocene and Pleistocene is characterized by the on-setting of continental basins, oriented almost parallel to the uplifting Apennine mountain chain and marked by the valleys of main rivers Arno, Chiana, Tevere, together with minor intermountain basins (e.g.: Colfiorito). The internal range, with its complex of intermountain basins, was bounded by coastal marine deposits of the Tyrrhenian and Adriatic seas. Due to a decidedly established palaeoenvironmental and magnetostatigraphic scenery for Valdarno, Valtiberina and Colfiorito Basins, the short section at Arquata in the Valle Umbra Basin, here presented, may be constrained much more closely to the evolutionary pattern of the former ones by means of a similar magnetostratigraphic characterization. In particular, detailed magnetostratigraphy led to date the earliest deposits in the Valdarno Basin at 3.3 Ma, whereas in Valtiberina the oldest analyzed deposits, which don’t reach the substratum yet, postdate 2.8 Ma. Upward, the two above mentioned main sedimentary profiles reach 2.0 Ma and 2.1 Ma, respectively, and in the shorter section of Colfiorito only the youngest dates are attained, until 0.78 Ma. The same younger date was detected in the Valdarno, where also the Olduvai chron (1.95-1.77 Ma) is recorded, followed by the Jaramillo chron (1.05-0.97 Ma) after a long sedimentary hiatus. The Valle Umbra profile exposed near Bevagna is dated across the Jaramillo chron, the duration of its deposition extending approximately 300 ky. Both results are very close to the previously mentioned final fillings of Valdarno and Colfiorito. Valle Umbra