Il Pliocene e il Quaternario della Media Valle del Tevere (Appennino centrale)

Abstract

New data on Pliocene-Quaternary stratigraphy and on the geological evolution of the Middle Valley of the Tiber River (M.V.T.) are here presented. It is also presented the Geological Map of the Middle Valley of the Tiber River (two sheets), at scale 1:40,000. Two main tectono-sedimentary phases are recognised: the first one, Middle Pliocene-Early Pleistocene in age, was dominated by subsidence; the second, spanning from Early Pleistocene to Holocene, was dominated by the Apennine Chain’s uplift and volcanism. Two 3rd order sedimentary cycles characterise the first phase. The 1st cycle corresponds to the Tenaglie-Fosso San Martino Unit (Piacentian-early Gelasian) and is composed of coastal and marine shelf deposits. The 2nd cycle is composed of: the shallow marine and transitional Chiani-Tevere Formation (Late Gelasian-Santernian); the laterally continuous Poggio Mirteto Formation, of the fluvial-deltaic environment; the regressive, fluvial-lacustrine Giove in Teverina Formation. Fourth order progradational-transgressive cycles are recorded within the Chiani-Tevere Formation. The second phase comprises the products of the Mt Cimino Volcanic Complex (late Early Pleistocene) and the terraced fluvial deposits of the Civita Castellana Unit (late Early Pleistocene-Middle Pleistocene), Graffignano Unit (Middle Pleistocene), Rio Fratta Unit (late Middle Pleistocene), Sipicciano Unit (Late Pleistocene) and of the modern Tiber River plain. The fluvial units are covered by volcanics from the Vulsini Mts, Vico and Sabatini Mts Districts (Middle-Late Pleistocene), by the travertines of the Grotte Santo Stefano Unit (Middle Pleistocene), Fiano Unit (Late Pleistocene) and “Travertini recenti” (Holocene). The palaeogeography during the first phase was characterised by the transverse drainage of prograding fluvial- deltaic systems, which flowed from ENE to the centre of the M.V.T. basin. During the second phase the modern Tiber river developed with axial drainage. Type sections for the Chiani-Tevere and Poggio Mirteto Formations and for the Civita Castellana, Graffignano, Grotte Santo Stefano, Rio Fratta and Sipicciano Units are proposed.